Design Criteria Electrical

TATA STEEL LIMITED Joda East Iron Mine RAW MATERIAL HANDLING SYSTEM (PACKAGE – 2 & 3)

DESIGN CRITERIA & SIZING METHODOLOGY - ELECTRICAL DOCUMENT NO: M5006-E670-001

A REV. NO

05-09-2008 DATE

ISSUED FOR APPROVAL REVISION

RS PREP BY

RS PROC ENG

PROJ ENG

FUNC MNGR

PROJ MNGR

CLIENT

Page: 2 of 38 REV: A Date: 05-09-2008

RAW MATERIAL HANDLING SYSTEM DOCUMENT NO: M5006-E670-001 ITEM: DESIGN CRITERIA – ELECTRICAL

CONTENTS

1.0

SCOPE

2.0

STANDARDS AND CODES

3.0

SYSTEM PARAMETERS

4.0

DISTRIBUTION SYSTEM DESIGN

5.0

SUBSTATIONS

6.0

CONTROL PHILOSOPHY

7.0

SAFETY

8.0

MV SWITCHGEAR

9.0

POWER FACTOR CORRECTION AND HARMONIC FILTERING

10.0

POWER TRANSFORMERS

11.0

MOTOR CONTROL CENTRES

12.0

LV BUS DUCTS

13.0

SMALL POWER PLUG/SOCKETS & WELDING

14.0

CABLING

15.0

EARTHING

16.0

LIGHTNING PROTECTION

17.0

ILLUMINATION

18.0

BATTERY & CHARGER SYSTEM

19.0

VVVF DRIVES


1.0

SCOPE 1.1

This narrative covers the design criteria and philosophy for the electrical scope of work for the Material Handling package for Joda Mines expansion project of TISCO.

1.2

Included • • • • • • • • • • • • • •

1.3

Primary distribution in the Plant Main Substation to the various Process Units. Secondary distribution in the plant substations to the process areas. MV Switchgear Motor control center Transformer & NGR selection criteria Motors selection criteria Cable selection and typical voltage drop calculations Selection criteria for Earthing and lightning protection. LT Bus duct selection criteria AC Drive selection criteria PF improvement requirement based on final load list Selection criteria for Outdoor and indoor lighting and small power. DC system selection criteria Cable trays selection criteria

Battery Limits • •

2.0

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Incoming terminals of the Plant Main 3.3kV Switchboard at Bateman built substation room. NBC-3/3A drives at RLS.

STANDARDS & CODES 2.1

Statutory Requirements • • •

2.2

Indian Electricity Rules State CEIG Rules TISCO & Bateman statutory requirements

Standards •

All the relevant Indian Standards and codes of practice applicable to the equipment and installation for the scope of work defined above. The reference to the specific IS is taken under the respective chapter.

•

IEC standards and codes of practice applicable to the equipment and installation for the scope of work defined above. The reference to the specific IEC is taken under the respective chapter.

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3.0

SYSTEM PARAMETERS 3.1

System Voltages Primary distribution Secondary distribution (Normal & small drives) Secondary distribution (large VFDs) Lighting and small power sockets Emergency Lighting (DC) Control Voltages (AC) Control Voltage (DC) UPS Supply Panel Lighting & Panel/Motor space Htr. Welding socket outlets

3.2

: 25kA for 1 sec : 25kA for 1 sec : 50kA for 1 sec : 50kA for transformer fed MCCs / DBs : 10kA for LDBs, UPS DBs etc.

System Frequency System Frequency

3.5

: Resistance grounding : Resistance grounding : Solidly earthed : Solidly earthed : Solidly earthed

Design Fault Levels 11kV systems (Upstream) 3300V systems 690V systems 415V systems 230V Lighting and small power

3.4

: 690V, 50Hz, 3ph, 3 wire : 230V, 50Hz, 1ph, 2 wire : 110VDC, +/-15% : 110VAC, 50Hz, +10/-15% : 110VDC, +/-15% : 230V, 50Hz, 1ph : 230VAC, 50Hz, 1ph : 415V, 50Hz, +/-10%

System Earthing 11kV systems (Upstream) 3300V systems 690V systems for VFDs 415/230V systems 110V control power

3.3

: 3.3kV, 50Hz, +10/-15% : 415V, 50Hz, +/-10%, 3ph, 4 wire

: 50Hz, +/-5%

Site Conditions Design Ambient temperature Relative humidity Altitude Seismic data Soil Resistivity

: 45 deg.C max & 0 deg.C min. : 89% : > 1000 mtrs from MSL : Seismic zone-II (Stable zone) as per IS-1893 : 400 ohm-meter avg.(based on soil resistivity report)


4.0

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DISTRIBUTION SYSTEM DESIGN

4.1

Primary Distribution Cable feeders from the existing 3.3kV switchboard at existing RLS substation will feed power supply to the new 3.3kV switchboard new Plant Main Substation. For this purpose, 2 nos of spare feeders at the existing substation will be used for feeding the new board.

4.2

Secondary Distribution The Main Plant Substation will be located close to the new RLS-1 & 2 and TP-2. Therefore, the transformers, MCCs, VFDs and process control system hardware for this area will be installed in the same building. The power will be fed to various loads and the new RLS from this main substation through cables laid on the trays.

4.3

Voltage Variation The variation in voltage of TSL is controlled by automatic tap changers, and hence will be limited to +3/-5%. However the equipment will be designed to the voltage variations of +10/-15%. Cables will be selected on the basis of maximum voltage drop from nominal at motor and other power user terminals of 3% for running and 15% for starting, except that the latter will be 20% for motors with fluid coupling. This will be reduced as necessary for specific cases of high inertia loads. The voltage drop for welding outlets will be limited to 5%.

4.4

Power Factor Correction & Harmonic Filtering The design calculations for Capacitors, with harmonic filters if necessary, will be carried out and the suggestions will be provided for maintaining the overall power factor at 0.94. (This latter figure is assumed for the study, but will have to be reviewed when the tariff structure to be adopted is known so as to arrive at the economically optimum level.)

4.5

Emergency Power Generation The requirement of emergency power generator is not envisaged as of now.

5.0

SUBSTATIONS 5.1

General Design 5.1.1

There will be only one building for housing MV switchgear and related equipment, LV Switchgear, distribution, converter and lighting transformers, Lighting DBs, battery charger, UPS etc. Control systems, remote I/O, control desk will be installed in the control rooms which will be above the switchgear room. The control room will be air conditioned and VFDs will also be installed in this control room with a separation.

5.1.2

Switchrooms and MCC rooms will generally be constructed of brick or block with concrete floors and concrete or sheeted roofs, the latter with thermal insulation and ceilings.

5.1.3

Cable will be laid in suitably designed trenches.


6.0

7.0

8.0

Page: 6 of 38 REV: A Date: 05-09-2008

5.1.4

Floors and trench bottoms will be maintained in order to avoid water ingress and accumulation.

5.1.5

Transformers will be placed in the switchgear room with proper separation.

5.1.6

Equipment access doors will be installed for each room. These doors will also serve as the emergency exits from the rooms and be fitted with the appropriate hardware. A personnel access door for each room will also be provided.

CONTROL PHILOSOPHY 6.1.1

MV circuit breakers will be electrically operated, generally from the switchgear panel itself. LV circuit breakers will also be electrically operated from the panel.

6.1.2

The feeders from the 3.3kV Intake Substation to the Plant Main Substation will normally be operated in parallel. The interlocking is therefore required between the buscoupler and the incomers in such a way that both the incomers are ON only when bus coupler is OFF.

6.1.3

As both the 3.3kV incomer circuit breakers will normally be closed, an alarm will be activated with a signal to the Main Control Room on the opening of any one of them, whether due to a fault or switching. This will be achieved through a hard wire connection between MV switchgear and the RIO at the MCC which in-turn will transfer the signal to the main PLC.

6.1.4

Fault trips resulting from relay operation will be hand reset on the relays. A common signal from each feeder for faults will be taken to the main control room via MCC RIO panel.

6.1.5

Transformer temperature alarms will be a common input to the control system and will also trip the MV switchgear breaker.

6.1.6

Direct on line Motors will be controlled by semi-intelligent control systems. Control of each starter will be directly by the control system, via the hard wired signals between the RIO and the feeder and this inturn will be controlled via communications bus from the remote I/O to be installed in MCC with the main control system.

6.1.7

VFD driven motors will be controlled from the main plant PLC via a communication bus.

6.1.8

All the motors will have both manual (LPB) and auto mode of operations.

SAFETY 7.1

Each drive will have a local mushroom head emergency stop pushbutton.

7.2

Conveyors will, in addition to the emergency stop push-button at the head end, have hard-wired pull-wire switches along accessible sides.

7.3

Transformers will have emergency push buttons near to the equipment.

7.4

Positive isolation will be provided on all switching points in MCC and necessary locking arrangements will be provided.

MV SWITCHGEAR

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8.1

Indoor, draw-out, metalclad switchgear will be included for the New RMHS Substation.

8.2

Circuit breakers will be electrically operated, i.e. electrical closing spring charging, trip release and closing release.

8.3

Protection and metering will be integral with the switchgear assemblies.

8.4

Voltage transformers will be bus connected.

8.5

The board shall be of IP-4X and outer paint shade shall be RAL-7032 (Siemens grey).

8.6

Will permit extension on both the sides.

8.7

Lockout provisions with breakers racked out will be included.

8.8

Electrical interlocks between the two incomers and the bus coupler will be included such that only one incomer with bus coupler can be switched on and the other incomer will be off. Alternatively both the incomers can be switched on only when the bus coupler is off. Mechanical interlock will also be provided by means of castle key.

8.9

The breakers will be VCBs of type VD4 or equivalent. The incomers and bus coupler breakers will be of 1250A rating and all the other feeders shall be of 630A rating.

8.10

The main bus will be rated for 1250A and the size will be calculated based on the following factors: a. Short Circuit Rating of bus bar i.e. 26.2kA for 1 sec b. Continuous Rating of bus bar The short circuit rating of the bus bar will be calculated based on the following method:

A = (Ish X √t) / K Where, A = Cross sectional area in Sq.mm. Ish = Fault current in kA t = Fault clearing time in seconds K = Constant kA / sq.mm. (K = 0.0799 for Aluminum)

I continuous

=

I table X K1 X K2 X K3 X K4

Where, I table = Current carrying capacity at 50ºC amb. & 90ºC end temp. (Ref. ABB swgr manual) K1

= Correction factor for load variations relating to conductivity = 0.99 for conductivity of 35 m/(Ω.mm2) for Aluminum. (Ref. ABB switchgear manual)

K2

= Correction factor for the deviation in ambient temperature and/or bus bar temperature = 1.15 for amb. Temp. of 50ºC & bus bar temp. 90ºC (Ref. ABB switchgear manual)

K3

= Correction factor for the thermal load variation due to difference in layout = 1.0 (Ref. ABB switchgear manual)


8.11

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K4

= Correction factor for the electrical load variation due to difference in layout = 1.0 (Ref. ABB switchgear manual)

K5

= Correction factor for influences specific to location = 1.0 (Ref. ABB switchgear manual)

Protection 8.11.1 Incomers: Numerical Overcurrent, IDMT and instantaneous, and earth fault relay SPAJ140C or equivalent 8.11.2 Transformer Feeders: Numerical Overcurrent, IDMT and instantaneous, and earth fault relay SPAJ140C or equivalent Temperature trip and alarm. Restricted earth fault 8.11.3 Feeders: Numerical Overcurrent, IDMT and instantaneous, and earth fault relay SPAJ140C or equivalent 8.11.4 Bus Coupler: Numerical Overcurrent, IDMT and instantaneous, and earth fault relay SPAJ140C or equivalent 8.11.5 General: Trip circuit supervision for all.

8.12

Normal control supplies Voltage for spring charging motor mechanism

230V AC, 50Hz

Control voltage for closing, tripping, indication, interlocking, annunciation circuits etc.

110V DC

Auxiliary power supply for relays, transducers etc.

110V DC

Panel Space Heaters, Cubicle illumination lamp, Plug Socket

230V AC, 50Hz

Circuits of all panels and motor space heaters etc.

230V AC control supplies will be derived from lighting supply source. This will be terminated at Incomer1 of the switchgear.

9.0

POWER FACTOR CORRECTION AND HARMONIC FILTERING Design Methodology The following factors will be considered for designing the capacitor bank size: 1.

The total continuous load on the transformer [A]

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2.

The total intermittent load on the transformer [B]

3.

The total standby load on the transformer [C]

4.

Co incident factor for intermittent loads [k1 = 0.5 considered]

5.

Co incident factor for standby loads (which generally used during shut down / maintenance etc.) [k2 = 0]

6.

Power factor of various loads [based on available data sheets of motors]

7.

10% margin for additional capacity

8.

Rounding off the calculated kVAr to the nearest standard size available.

The capacitor bank size will be calculated based on the following calculation: Basic KW / KVA

[L] = (A) + (k1 x B) + (k2 x C)

PF1

= KW / KVA

PF2

= 0.94

tan Φ1

=

cos

–1

(PF1)

tan Φ2

=

cos

–1

(PF2)

Required Reactive Compensation

[N] = KW ( tan Φ1 - tan Φ2 )

Calculated size with 10% additional capacity

[M] = L x 1.10

For the purpose of calculating the load current / KVA, the power factor and efficiency of the motors will be derived from the data sheets of the motors and in case of non availability of the same, the standard technical data of ABB/Siemens make motors will be considered for the purpose of this sizing calculations. The power factor and efficiency in the case of power feeders will be derived and approximated from the same data for the largest motor within that load. Detuned filter will be provided where % VFD load is more than 10%. The harmonic spectrum of the drives will be considered while designing detuned filters, by the drive manufacturer.

10.0

DISTRIBUTION & CONVERTER DUTY TRANSFORMERS 10.1

The transformers will be AN cooled, dry type, Cast resin, vacuum encapsulated type with manual off circuit links on primary side for voltage variations for +/-7.5% with steps of 2.5%.

10.2

The transformers will be housed in a suitable enclosure of at least IP-20 and the windings shall have class-F insulation.

10.3

Transformers will have winding temperature detector / scanner with indication, alarm and trip functions.

10.4

A lockable push button will be provided on the transformer enclosure for emergency stop.

10.5

Primary side shall have provision for cable connections and the secondary will have a provision for bus duct for transformers of rating 1600kVA and above. The transformers below 1600kVA will have cables on the secondary side.

10.6

The impedance will be decided by the fault level, but a minimum impedance of 5.5% (with tolerance as per IS) will be maintained.

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10.7

The distribution transformers shall be of Dyn11 vector group and the neutral shall be earthed through NGR of 10A rated continuously.

10.8

There will be 2 nos of transformers feeding each of the incomer of PMCC. The rating of the transformer will be decided in such a way that in case of stoppage of one of the transformers, the other is loaded upto a maximum of 90%. The kVA rating of the transformers will be the sum of the total kVA of the continuous load on PMCC and the total kVA of intermittent load on PMCC. The following factors considered for designing the transformer size: ♦ The total continuous load on the transformer [A]. The kVA of a motor is calculated by the

formula: kVA = motor kW / (motor efficiency x power factor) ♦ The total intermittent load (such as power supplies, cranes, hoists, heaters etc) on the transformer [B] ♦ The total standby load on the transformer [C]. (loads which are generally used during failure of running motors, shut down / maintenance etc.) ♦ The load capacity factor (is the calculated motor mechanical absorbed power divided by the motor rated power) of 0.90 and diversity factor of 0.90 is considered (total factor – 0.90 x 0.90 = 0.81) for the continuous loads. [k1 = 0.81] ♦ Co incident factor for intermittent loads [k2 = 0.5 considered] ♦ Co incident factor for standby loads [k3 = 0] ♦ Power factor of various loads [based on available data] ♦ 20% margin for spare / additional capacity ♦ Rounding off the calculated kVA to the nearest standard size available with the manufacturer.

The transformer size will be calculated based on the following calculation:

Basic size in KVA

[L] = (k1 x A) + (k2 x B) + (k3 x C)


[M] = L x 1.20

For the purpose of calculating the load current / KVA, the power factor and efficiency of the motors will be derived from the inputs given by the suppliers and in case of non availability of the same, the standard technical data of ABB make motors will be considered for the purpose of this sizing calculations.

The power factor and efficiency in the case of power feeders will be derived and approximated from the same data for the largest motor within that load.

The adequacy of the transformer rating will be further checked for the maximum demand required and the voltage drop at the time of starting of the largest direct-on-line motor connected with the PMCC. This will be calculated with the assumption that the motor will draw 6 times of the load current.

The converter transformer will be designed to take care of the following:


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•

Prevention of electrostatic transfer of higher surge voltages to the converters.

•

Mitigation of stray losses due to harmonics.

•

A metallic shield with an earthing terminal is provided between the primary and the secondary, in such a way to protect the thyristor from over voltage surges due to the network.

•

The transformers shall be designed to suppress harmonic voltages specially the 3rd and 5th so as to eliminate distortion in wave form and the possibility of circulating currents between the neutrals of different transformer stations. The Total Harmonic Distortion (%THD) of the voltage waveform because of harmonics developed due to the drives will be taken care by the supplier while designing the transformer.

The paint shade of the transformer will be 631 as per IS-5 (dark grey).

11.0

MOTOR CONTROL CENTRES 11.1

MCC construction will be indoor duty, free-standing, metal-enclosed, IP42, back-to-back, form 4 to IEC439 (each starter in a separate compartment with segregated bus compartment and wireways for external cable entry). The PMCC shall be of single front and non-draw out type.

11.2

The board will be designed for a fault level of 50kA / 1 second.

11.3

Spare space equivalent to approximately 20% of starter and feeder space will be included to cater for changes and possible future additions.

11.4

The contactors used for the motor starters will be of AC-3 duty.

11.5

Type-2 co-ordination will be generally used for the selection of the components.

11.6

Control supply shall be 110V AC from a common double wound transformer per MCC.

11.7

Both the incomers and the bus couplers shall be equally rated and will be capable of carrying the total load of both the sections of MCC.

11.8

Normally the bus coupler will be off and the load on each section will be catered by the respective transformer. In case of one transformer out of service, the bus coupler will be switched on and the total load will be catered by one transformer.

11.9

A suitable electrical interlock as well as castle interlock will be provided between both the incomers and the bus couplers.

11.10

Feeders Each Incoming feeder will comprise of the following: 2 no. -

415V,suitably rated, ACB with O/C, S/C and E/F releases

1 no. -

Trip circuit healthy PB

1 no. -

Breaker control switch close-neutral-trip (lockable)

1 no. -

Control supply failure check relay

1 no. -

Panel space heater with MCB &Thermostat


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1 no. -

DP switch fuse for DC supply

1 no. -

Trip ckt. healthy check indication

1 no. -

Digital Multifunction Meter with interface feature for Remote display of Current, Voltage, Frequency, Active (KW), Reactive (KVAR) and Energy (KWH)

1 set -

Phase indicating lamps

1 no. -

Ammeter with selector switch

1 no. -

Voltmeter with selector switch & Fuse

1 set -

CTs of suitable ratio for metering and protection

Each Direct On-Line (DOL) starter feeder will comprise of following: 1 no. - TPN Switch Fuse unit 1 no. - Power contactor 1 no. - Electronic over load relay (EOCR) 1 no. - MCB for space heater (for motors above 30 kW) 1 no. - Auxiliary Relay

Each power feeder will comprise of the following: 1 no. - TPN Switch Fuse unit

Each Reversible Direct On-Line (RDOL) starter feeder will comprise of following: 1 no. - TPN Switch Fuse unit 2 nos. - Power contactor 1 no. - Electronic over load relay (EOCR) 1 no. - MCB for space heater (for motors above 30 kW) 1 no. - Auxiliary Relay Since the PMCC panels are required to be of Semi-intelligent type, the PMCC line-up shall have a Remote I/O panel for marshalling of signals to and from the PLC.

11.11

Sizing calculations Generally the following sizing calculations will be carried out: • • •

Calculation of bus bar and incomer current rating Sizing of main bus bars for short circuit and thermal rating Voltage drop for bus bars

Current Rating: The rating of the PMCC main bus bars and the incomer breaker will be the sum of the total current of the continuous load on PMCC and the total current of intermittent load on PMCC. The following factors considered for designing the transformer size:

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♦ The total continuous load on the PMCC main bus [A]. The current of a motor is calculated by

the formula: A = motor kW / (motor efficiency x power factor x kV) ♦ The total intermittent load (such as power supplies, cranes, hoists, heaters etc) on the PMCC [B] ♦ The total standby load on the PMCC [C]. (loads which are generally used during failure of running motors, shut down / maintenance etc.) ♦ The load capacity factor (is the calculated motor mechanical absorbed power divided by the motor rated power) of 0.90 and diversity factor of 0.90 is considered (total factor – 0.90 x 0.90 = 0.81) for the continuous loads. [k1 = 0.81] ♦ Co incident factor for intermittent loads [k2 = 0.5 considered] ♦ Co incident factor for standby loads [k3 = 0] ♦ Power factor of various loads [based on available data] ♦ 10% margin for spare / additional capacity

The incomer and main bus ampere rating will be calculated based on the following calculation:

Basic size in Amp

[L] = (k1 x A) + (k2 x B) + (k3 x C)


[M] = L x 1.10

For the purpose of calculating the load current, the power factor and efficiency of the motors will be derived from the inputs given by the suppliers and in case of non availability of the same, the standard technical data of ABB make motors will be considered for the purpose of this sizing calculations. The power factor and efficiency in the case of power feeders will be derived and approximated from the same data for the largest motor within that load. Bus bar Sizing: Short Circuit sizing: Minimum cross sectional area of aluminum bus bar required during 50kA for 1 sec short circuit is given by formula: (I/A) x √ t = 0.0775 for aluminum Where, I = Short circuit current in kA t = Duration of short circuit, 1Sec. A = Cross section of bus bars in sq.mm Or,

A = (I / 0.0775) x √ t A = (50/0.0775) x √ 1 (putting the value) A = 645.16 sq.mm

Hence, a minimum value of 750 sq mm is suitable for the bus bars from short circuit point of view. Thermal Rating: The thermal rating of the bus bars is calculated based on the values given in Indal chart. 1. Derating due to ambient Temperature Factor (K1):


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It will be observed from the tables supplied by the manufacturer that the values for the bus bar system are given at ambient of 35°C for a temperature rise of 50°C. But present ambient is 50°C, limiting temperature rise to 35°C (bus bar temperature is 85°C). Hence, suitable deration factor is applied to arrive at correct ampere capacity of the bar Derating factor = (T2 / T1) 0.588 Where T2 = Temperature rise at ambient of 50°C T1 = Temperature rise at ambient of 35°C There fore derating factor = (35 / 50) 0.588 = 0.81 2. Derating due to Enclosure Factor (K2): K2 is considered as 0.9. 3. Proximity factor (K3): K3 is taken as 1.0, since the current carrying capacities of the bus bars are obtained from the Indal chart (Annex-A) for calculation. The de-ration of the bus bars for various combinations is already taken care of for the proximity effect in the chart. 4. Enclosure material factor (K4): K4 is not considered for currents < 3200 A. Hence K4 = 1.0 5. The Final Capacity of the Bus Bars: I = I1 x K1 x K2 x K3 x K4 I1 = I0 Indal chart √ {(width X thickness )actual /(width X thickness )Indal chart } For example: If the current rating of a bus bar of size 76.2mm x 9.53mm is 2050A as per Indal chart and the bus bar available in the market is of 75mm x 10mm, then the current rating of 75 x 10mm bus bar will be: I0 = 2050√ (75x10 / 76.2x9.53)

= 2083 A Where K1, K2, K3, K4 are as defined above Hence, I = 2083 x 0.81 x 1.0 x 1.0 x 1.0 A = 1687 A Voltage drop The adequacy of the bus bars rating will be further checked for the maximum demand required and the voltage drop at the time of starting of the largest direct-on-line motor connected with the PMCC. This will be calculated with the assumption that the motor will draw 6 times of the load current. 12.0

LV BUSDUCTS The busducts shall be provided for the transformers of rating 1600kVA and above. The busduct shall be of non-segregated, self cooled type. The cooling medium inside the duct will be air. The Busbars shall be of aluminium with continuous rating as specified below. All buses and connections shall be able to withstand maximum short circuit current. Space heater shall be provided. All the three phases will be enclosed in a weather proof, dust tight MS CRCA enclosure of 2.00mm thick. Outdoor section will be rain proof. Minimum degree of protection of busduct enclosure will be IP 52 for Indoor and IPW 53 for outdoor section.


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The bus duct shall be designed for carrying the rated current, considering the derating due to temperature and the other effects. The LT bus duct shall be of phase non-segregated type with aluminum bus bars enclosed in sheet steel enclosure for rating up to 3200Amps and in aluminum enclosure for ratings above 3200Amps. Design of bus duct involves the following: 1.

Deration of the current carrying bus bars due to the correction factors.

2.

Temperature rise calculation

3.

Voltage drop calculation

4.

Calculation of short circuit withstand capability of the bus bars

Basic parameters considered during the sizing of the bus ducts: i)

Material of the bus bars shall be Aluminum

ii)

The design ambient is 50 Deg C.

iii)

Maximum allowable temperature of the bus bars over an ambient of 50 Deg. C shall be limited to 35 Deg.C.

iv)

The enclosure material shall be sheet steel for rating up to 3200Amps and Aluminum for rating above 3200Amps.

v)

The open air rating of the bus bar for 50 Deg. C rise over 35 Deg. C ambient is considered in Amps as = I0 (annexure-A)

vi)

The current carrying capacity of the bus bars is derived from the Indal chart (Annexure – A) depending on the number of bus bars used.

The current carrying capacity of bus bar sizes not mentioned in the Indal chart is calculated as: I1 = I0 √ {(width X thickness )actual /(width X thickness )Indal chart }

12.1

vii)

The calculated rated current carrying capacity of the bus bars = I1

viii)

The nominal/specified current carrying capacity of the bus bar = I2

Correction Factors The current carrying capacity of the bus bars depends upon various factors due to the temperature and enclosure. The main factors affecting the rating of a bus bar are: 1. Ambient temperature where the bus duct shall be installed 2. The size of the enclosure. 3. Sleeving and painting of the bus bars 4. Skin and proximity effects. 5. The material of the enclosure. The above factors are quantified as the correction factors in determining the rating of the bus bars. These correction factors are calculated as a)

K1: Temperature correction factor


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The temperature of the conductor is to be limited to a safe value, at which the metal does not deteriorate or change its properties. The safe temperature for an aluminum bus bar is 85-90 Deg. C. In this project we are limiting the end temperature of the bus bar as 85 Deg. C i.e. the allowable temperature rise of the bus bar over an ambient of 50 Deg. C is 35 Deg. C. The value of the correction factor considered is 0.815 as per Industrial power engg. And applications handbook (Annexure-B-1) b)

K2: Enclosure size correction factor

The enclosure of the bus duct provides the cooling surface for heat dissipation. The size of the enclosure has an effect over the temperature rise of the conductors and consequently the current carrying capacity of the conductor. The enclosure effect and the ventilation conditions of surroundings are to be considered while designing the bus duct system. The correction factor for the enclosure is based on the percentage ratio of the cross section area of conducting bus bar and the enclosure area cross section. ie (Cross Section Area of bus bar * 100)/Enclosure Cross section = % The derating factor corresponding to above calculated % is the enclosure correction factor K2 The derating factor is derived from the enclosed chart in Annexure-B.

c)

K3: Proximity effect

In ac systems the inductive effect caused by the induced electrical field causes skin and proximity effects. These effects play a complex role in determining the current distribution through the cross section of a conductor. The inductance of conductor varies with the depth of the conductor due to skin effect. In addition to this, the presence of other current carrying conductors in the vicinity of the conductor has the proximity effect on the conductor. These effects are to be considered while designing the bus bar system. The correction factor for the proximity effect is the ratio of the spacing between phases to the width of the conductor. K3 is considered as 1, as the current carrying capacities of the bus bars are obtained from the Indal chart (Annex-A) for calculation. The de-ration of the busbars for various combinations is already taken care of for the proximity effect in the chart.

d)

K4: Painting factor

The HT and LT bus bars are painted with non-metallic matt finish paint. As per the Indal aluminum bus bars, the current rating of the bus bar is increased because of the non-metallic matt finish paint. Hence there is an increase in the current carrying capacity of the bus bars. The up rating is approximately 20% more. (Reference :Indal Aluminum bus bars-Annexure A)

e)

K5: Enclosure material correction factor.

Depending upon the type of material of the enclosure this factor is decided. For aluminum enclosure (non magnetic) there is no correction required and hence the factor is 1. For mild steel enclosures (magnetic material) it is generally considered as 0.95 by all major leading bus duct manufactures. The total correction Factor is K is calculated as K= K1 * K2* K3 * K4 * K5 The net current carrying capacity of the bus bar is calculated as = (Total currents carrying capacity of the bus bars) * (Correction factor K)


Page: 17 of 38 REV: A Date: 05-09-2008

I1 = I’ * K 12.2

Temperature rise calculation Temperature rise is calculated as = (I1/ I2) = (T1 / T2) ^ 0.61 (Temperature rise calculation from Copper for Bus bars – Copper Development Association CDA) Where: I1 =Calculated rating in Amps. I2 =Specified/Nominal rating in Amps. T1 =Max. Temperature rise specified in Deg. C over the ambient T2 =Calculated temperature rise in Deg. C over the ambient. T2= T1/( I1/ I2) ^ 1.64 The calculated value of T2 should be within the design value of the temperature limits.

12.3

Voltage drop calculation The voltage drop is calculated as Vdrop = √3 *I2 *L *Z I2 = Load current in amps L = Length in meters Rdc = DC Resistance in micro hms per meter of conductor at 20 Deg. C(D50S-WP dc resistance) Rac = AC Resistance in micro ohms per meter of conductor at 85 Deg. C α20= Resistance- temperature co-efficient per Deg. C. =0.00363. (Indal Aluminum Book – see attached annex-F) Z= Impedance in micro ohms per meter of conductor θ1 = Temperature at which resistance is measured i.e. 20Deg. C θ2= Temperature at which bus bar is operating i.e. 85 Deg. C. 2 A = Cross section area in cm S= Centre spacing between the two phases in mm a= Space occupied by conductors of one phase in mm b=Width of the conductors in mm. Calculation of the impedance of the bus bar AC resistance Rdc at an operating temperature of 85 Deg. C .is taken from annexure –C (Indal Aluminum Book) =Rdc (1 +α20(θ2-θ1)) ohm/meter per conductor If there are ‘n’ number of runs then Rac = Rdc (1 +α20(θ2-θ1)) /n The value of Rac is calculated from the skin effect ratio n Rac/ Rdc.. The Rac is calculated as: 2 Area of cross section per phase =(n * a *b)= A in cm The value of ratio Rac = skin effect* Rdc, the skin effect r is derived from the annexure-D, 2 corresponding to A cm , on the b/a curve (by appx the interpolation). I.e. Rac / Rdc = r


Page: 18 of 38 REV: A Date: 05-09-2008

Rac = Rdc * r = 10-3 ohm/1000m per phase.

Reactance The reactance is calculated from the ratio of conductor spacing to semi perimeter. For a 3-phase system 1.26 multiplies the ratio. ie 1.26 * (S/(a+b)) = m The ratio of a/b gives the curve of reference on which the value m value gives the reactance in micro ohms/meter per phase.( Annexure-E) The impedance is calculated as Z=√( R2ac + X2) = =Z ohm/meter per phase Vdrop =(√3 *I2 *L *Z)/1000= V Volts The V volts are checked as a percentage of the rated voltage. If the drop is within the limits as specified in the contract specifications, the busbar size is acceptable. In the absence of specifications this shall be limited to 1-2% of the rated voltage. (Refer annex. B-2) 12.4

Calculation of the short circuit withstand capacity of bus bars The short circuit rating of the bus bar will be calculated based on the following method:

A = (Ish X √t) / K Where, A = Cross sectional area in Sq.mm. Ish = Fault current in kA t = Fault clearing time in seconds K = Constant kA / sq.mm. (K = 0.0799 for Aluminum) The LV bus ducts will be designed for the LV system fault level of 50kA for 1 second.

Page: 19 of 38 REV: A Date: 05-09-2008


13.0

SMALL POWER PLUG/SOCKETS & WELDING

Single phase switched socket outlets (SSOs) rated 230V, 15A will be provided in plant areas spaced apart such that all areas can be reached with a 50m extension lead. The overland conveyor will be provided with a 230V SSO every 100m for portable lighting and small tools or welding using 50m extension leads. At least 2 nos. of 230V SSOs will be provided in substation switchrooms and MCC rooms. Three phase welding sockets rated 415V, 63A will be installed for use with 100m extension leads. Socket outlets in plant areas and conveyors will be weatherproof. Those in substations will be surface mounted, and those in control rooms and offices will be installed in 3-way power skirting. Socket outlet circuits will be protected by MCCBs and MCBs for welding sockets and SSOs respectively, all with 30mA earth leakage protection. 14.0

CABLING 14.1

MV Cables Strip Armoured (GI), XLPE insulated, with stranded aluminum conductors and PVC bedding and inner / outer sheath. Voltage ratings:

3.6kV (UE)

Cable ratings, deratings and other data to be used are from cable manufacturer standard catalogues. 14.2

LV Power and Control Cables Armoured, 1100V PVC insulated, with stranded copper / aluminum conductors depending up on the size, and PVC bedding and PVC sheath. 2 Minimum size for power cables: 4 mm 2 Control cables size: 1,5mm Cables upto 4 sqmm will be of copper conductor and the rest of the sizes will be of aluminum conductors. Cable ratings, deratings and other data to be used are from cable manufacturer standard catalogues.

14.3

Recommended Practice for Cable Sizing The cables will be selected on the following basis: 1. Power cables: Based on the selection procedure described below. 2. Control cables: Based on customer specifications and general practices followed. 3. Lighting cables: Based on the current carrying requirements considering the voltage drop

Page: 20 of 38 REV: A Date: 05-09-2008


The power cable sizes are selected on the basis of the following: Current Carrying Capacity: The cable will carry the full load current of the circuit continuously under the specified ambient temperature and other conditions of installation. The current carrying capacity will be worked out on the basis of the following: Base current rating: The current ratings for cables shall be referred from the manufacturer’s cable data sheets. Correction factors for method of installation: The cables are mostly laid in metal ladder type GI cable trays in this project. The base current ratings of cables shall be de-rated for the following conditions: a) Variations in conditions of installation compared to the standard conditions mentioned above. b) Group running of cables. Correction factors for ambient air temperature: (Based on IS standards & manufacturers catalogue) The rating factor for variation in ground / air temperature should be taken into consideration. The o ambient to be design ambient considered shall be 50 C. Depth of Laying The rating factors for variation in depth of laying should be taken from IS/manufacturers catalogue. Normally standard depth of laying shall be adopted in which case the rating factor will be 1.0. In this project we are laying the cables above ground and hence will be considering the rating factor as 1.0. Group De-rating Factor The de-rating factor for group running of cables laid direct in ground and in ducts shall be taken from IS/ Manufacturer’s catalogue. The group de-rating factor for cables laid in air shall be as per IS/ Manufacturer’s catalogue. Overall Deration Factor considered based on the duration factors as per manufacturer’s catalogues: o

Deration factor considered for an ambient temperature of 50 C Deartion factor considered for depth of laying Deration factor considered for grouping of cables (laid touching each other)

– -

0.82 1.00

-

0.80

Overall derating factor considered (0.82 x 1.0 x 0.80 = 0.66)

-

0.66

Short circuit rating The cable, if protected by circuit breaker, shall be able to withstand the fault current of the circuit for the desired fault clearing time. For reliable tripping, the instantaneous tripping of breakers shall be


Page: 21 of 38 REV: A Date: 05-09-2008

provided within one cycle ie.0.2 sec. Hence for breaker controlled outgoing feeders, cables shall be capable of withstanding the system fault level for 0.2secs. The short circuit withstand capacity of cables shall be calculated as per following formula furnished in IS: A = ( Ish X √ t) / K Where, A Ish t K

= = = =

Cross sectional area in Sq.mm. Fault current in amps (rms) Fault clearing time in seconds 2 Constant amps / mm

The value of K for various combinations is as follows: For copper conductors insulated with PVC K=115 For copper conductors insulated with XLPE, / EPR, K=143 For Aluminum conductors insulated with PVC K=76 For Aluminum conductors insulated with XLPE / EPR, K=94 Fault current (Ish) = The maximum fault current of the system shall be taken. Fault clearing time (t) = The time ‘t’ shall be based on the maximum time taken by the breaker of the circuit to clear the fault on the operation of primary short circuit protection. The recommended value of ‘t’ for typical auxiliary system is as mentioned above. For the breaker controlled outgoing feeders on 3.3 kV side with system fault level of 26.3 kA, cleared by the breaker within 0.20 secs (from MRSS to incomers of Switchboards at new load center). Hence the cross section of the aluminum XLPE cables shall be a minimum of: A = (26.3*1000* √ 0.20/ 94) = 126 sq. mm. Hence a cable of 150 sqmm (minimum) is sufficient for the MV incomer cables.

For 415V system, the fault at 1.6 MVA (rating is tentative and for example only) transformer with a percentage impedance of 5.5% will be calculated as: 1.6 / (√3 x 0.415 x 0.055) = 40.5 kA For the breaker-operated incomers of PMCC on 415 V side with a fault level of ~ 40 kA, the fault clearing time shall be 0.2 Sec is considered for the selection of cables. Hence the cross section of the cables shall be a minimum of: A = (40*1000*√ 0.2 ) / 94 = 190 sq. mm. Hence a cable of 240 sqmm (minimum) is sufficient for the PMCC incomers.

Permissible voltage drop The voltage drop in the cable will be within permissible limits for satisfactory running and starting of the motor. The allowable voltage drop shall not exceed 3% of the nominal voltage for main distribution circuits, 5% of the nominal voltage at motor terminals during motor running and 15% of


Page: 22 of 38 REV: A Date: 05-09-2008

the nominal voltage during motor starting. In case of fluid coupling this shall be allowed upto a maximum of 20%. For welding receptacles the drop shall be limited to 5%. The total voltage drops considered will be within 5% between the transformer and the final consumer during normal running. The voltage drop is calculated from the following formula: Vdrop = IL x L x (t x R cosϕ + X sinϕ ) Where, IL = Load current in amps L = Length of cable run in metres (one conductor only) R = Resistance in ohms of one conductor only t = temperature correction factor X = Reactance of one conductor Cosϕ = Power factor (considered as 0.9) Sinϕ = √ (1-cosϕ2) =0.44 (as cosϕ = 0.9) 14.4

Cable Installation and cable trays Cables will be installed on vertical plane ladder trays where horizontal plane formation is precluded because of the possibility of dust, sand, etc. build-up reducing the heat dissipation and hence the effective current carrying capacity of cables mounted horizontally. Generally, all other cables will be installed on horizontal plane trays, except where it is more practical to mount trays in the vertical plane. The vertical cable trays will be filled by 80% of the area on the tray and 20% area on the tray will be kept spare for future use. In case of horizontal cables trays at sub station, the cables will be laid in two layers wherever required. Cable trays will be made of galvanized mild steel, supported on galvanized mild steel structural supports. The supports will be site fabricated and all the welded joints will be provided with zinc rich paint to avoid rusting. The trays shall be generally of 2.0mm thick sheet steel with side channels and 35x15mm wide rungs at a spacing of every 300mm. The tray width shall be of 150mm, 300mm, 450mm and 600mm and shall be supplied in standard lengths of 3 meters. Suitable bends shall be fabricated from the standard trays at site. Instrument cables will be installed on separate trays from power cables with a minimum spacing between parallel runs of 300mm. In case of vertical trays, the spacing between two trays will be 50mm. Cables will be tagged at each end only. The cables will be clamped with suitable nylon ties / aluminum clamps. In case of single core cables these will be laid in trefoil formation and suitable trefoil clamps will be provided. The cables will be laid in a maximum of two layers on horizontal trays. However on vertical trays the cable will be laid always in single layer only. Where ever there are very few no. of cables, these will be laid with angle iron support or through a suitable diameter MS/GI pipe.

15.0

EARTHING 15.1

Recommended practice for designing the grounding system


Page: 23 of 38 REV: A Date: 05-09-2008

15.1.1

The neutral point of 3.3/0.433KV distribution transformers shall be earthed through NGR on 433 V side.

15.1.2

The transformer neutral shall be earthed by two separate and distinct earth connections. In case of distribution transformers the two neutral earthing leads shall be taken to two separate earth electrodes. However finally all the earth pits including the neutral pits and lightning pits of the plant shall be interconnected rigidly through a buried earth conductor below the ground.

15.1.3

For plant building and indoor substations one main earthing ring shall be provided along the building periphery connected to required number of earth electrodes. The earthing ring shall be laid either suitably buried in the floor along building column/wall or laid along the steel structures in open execution. In case of buried conductor, it will be laid one meter away from the building.

15.1.4

Main earthing ring shall be further cross-connected so as to form a mesh depending on the layout and location of the equipment. The cross-connections shall generally run in cable cellars, cable tunnels, trenches, motor platform or embedded in concrete floor based on the layout. For buildings having a number of floors separate earthing rings shall be established in each floor where required. All non-current carrying metallic parts of various electrical equipment as well as cable armouring, metallic conduit/GI pipe system, cable racks, brackets, supporting structures etc shall be effectively earthed. Earthing of all equipment (except low voltage equipment) shall be done by means of two separate earth continuity conductors connected either directly to earth electrodes or to an earthing ring irrespective of use armored cable or metallic conduit/GI pipe. Low voltage equipment, 125V and above shall also have two earthing points. However equipment, 125V & below up to 24V may have single earthing. Building/technological steel structures, metallic utility pipes shall not be used as earth continuity conductor.

15.1.5

The earthing system shall be designed to ensure effective operation of protective gears in case of earth faults. The total earth resistance at any point of the earthing system shall not be more than one ohm.

15.1.6

For substations and plant buildings, number of electrodes to be provided for the earthing system shall be calculated based on the soil resistivity to achieve a final total grid resistance of 1 ohm. After installation, actual earth resistance shall be measured and if required, bentonite soil can be added to achieve the values indicated above. No earth ring shall have less than two earth electrodes.

15.1.7

Earth electrodes for earthing stations shall comprise GI pipes of 40mm nominal diameter and 3 meters length in accordance with IEEE-80. Bottom half of the pipe shall have holes drilled at intervals on its surface. Removable caps shall be provided at the top of pipe to facilitate pouring of water. Suitable clamps shall be provided with the electrodes for connecting earth conductors. The top of the electrodes shall be about 100mm below ground level while connection to the earth conductor shall be made at about 150mm below ground level. The top portion of electrodes shall be enclosed in 300 x 300 x 300mm M15 concrete housings and provided with concrete of top cover and marker. Provision shall be kept at each earth station for testing earth resistance. Each earth station shall be complete with alternate layer of coke and salt as per general practice.

15.1.8

Galvanised MS flats shall be used for transformer neutral earthing and station earth grid.Earth conductor shall comprise galvanised MS flat or stranded galvanised steel wire. Generally main earthing rings and earthing leads shall be directly buried in ground. Additional earthing rings wherever provided inside plant buildings / substations and earth continuity conductor shall be taken either exposed on cable racks, structures, walls, ceiling etc. or embedded in concrete depending on installation. Earth conductor directly buried in ground shall generally be taken at a depth of 600mm. Earth conductors laid on cable racks shall be placed in

Page: 24 of 38 REV: A Date: 05-09-2008


accessible location keeping adequate clearance to facilitate easy connection. Earth conductors laid along plant / equipment, structure, wall, ceiling etc. shall maintain symmetry with other installations and shall be uniformly spaced with cables / utility pipes running along the same route. MS galvanised saddles shall be used for clamping earth conductors on cable racks, structure, wall, ceiling etc. The saddles shall be clamped to MS galvanised flat spacers with tapped holes and supporting the earth conductors. Flats shall be supported at intervals not exceeding 1,500mm and standard wires at intervals of 750mm. Earthing leads from transformer neutral shall be so taken as to avoid contact with the transformer body. In case the contact cannot be avoided, the leads shall be suitably taped with insulation tapes. 15.1.9

As far as possible all earth terminations and connections shall be visible for inspection. Each earthing system shall be designed to permit testing of individual earth electrodes. Stub-ups shall be provided at convenient locations near the equipment as well as building columns for connecting earth continuity conductors leading to the equipment and structures.

15.1.10

Alternate columns of structural building shall be connected to earthing ring. Crane rails, transfer trolley tracks, railway tracks inside plant building, as well as rails for movable mechanism shall be earthed at an interval of 100mtrs. In no case the number of earth connections shall be less than two. Expansion joints of rails shall be bonded by means of loops of galvanised MS flat.

15.1.11

Earth connections to equipment subjected to movement, vibrations and shocks shall be made by stranded wires having enough loops. Connection of earthing leads to earth electrodes and termination of flat earth continuity conductors to equipment shall be made by means of bolting. Connection of stranded earth wire to flat earth conductor as well as to equipment shall be made through crimping type lugs and bolting. Jointing and tapping (`T Connection’) of flat earth conductors shall be done by means of welding. Termination of earthing flats to crane rail, building structures, etc. shall be done by means of welding.

15.1.12

Earth conductors from electrodes or earthing ring when entering basement, cable cellar, cable tunnel, concrete trench, cable pit etc. shall be generally taken embedded in concrete either directly or through pipes. Earth conductors crossing roads on rail tracks shall be taken through concrete pipe.

15.1.13

Cable screens and armours shall be bonded to earthing system. Also, metal pipes and conduits carrying cables shall be bonded and effectively earthed.

15.1.14

Earthing system shall be kept electrically separate from the metal work of surface by not connecting to pipes / machinery parts etc. for earth continuity.

15.2

Conductor Sizes: The various conductor sizes that will be generally used shall be as mentioned below: i)

Buried Earth Grid

:

40 mm dia MS rod

ii)

Earth Electrode/Pit

:

3 M long. 40mm dia. GI pipe

iii)

Conv. Gallery / Tunnel

:

50 x 6 mm GS Flat

iv)

Riser

:

50 x 6 mm GS Flat

v)

Exposed Main Grid

:

50 x 6 mm GS Flat

vi)

415V Switchgears cum MCC,

:

50 x 6 mm GS Flat

Transformers, MLDB, AC/DC DB viii)

Cable Tray

:

50 x 6 mm GS Flat

ix)

Motors Rated upto 5.5 KW

:

8 SWG GS Wire

Page: 25 of 38 REV: A Date: 05-09-2008


x)

Above 5.5 KW upto 30 KW

:

25 x 3 mm GS Flat

xi)

Above 30 KW upto 90 KW

:

35 x 6 mm GS Flat

xii)

Above 90 KW

:

50 x 6 mm GS Flat

xiii)

Push Button Stations, JBs etc. :

8 SWG GS Wire

xiv)

Control Panel, Lighting

:

25 x 3 mm GS Flat

Distribution Board, Starter Panel, Lighting Panel, I/O Rack Welding Receptacles

15.3

xv)

Lighting Fixtures

:

14 SWG GS Wire

xvi)

PLC Panels

:

Separate treated pits for Electronic Earthing

Sizing calculations

The following methodology will be followed:

The effective combined grid earth resistance required as per technical specifications is 1 (one) ohm.

Derive the size of earth conductor.

Derive the length and width of the grounding area of the control room. / load center / plant buildings etc. covering the total plant layout.

Derive the length of conductor buried in soil and number of electrodes.

Calculate the value of resistance of earth grid.

Calculate the value of resistance of earth electrodes.

Calculate the combined value of resistance of earth grid and electrodes.

Data Considered for the Calculations Soil resistivity

:

Average soil resistivity is considered as 400 ohm-metre for design purposes based on soil resistivity report

Size of Earth Electrode selected

:

40 mm dia. GI Pipe

Size of buried conductor

:

40 mm dia. MS Rod earth conductor

Fault level

:

Fault level as per specifications 26.3kA

Applicable Standard

:

IS-3043, IEEE 80 – 1986, IEC-364

Calculation for sizing of earth conductor Thermal sizing

Page: 26 of 38 REV: A Date: 05-09-2008


A = (If √ t ) / K Where, A Area of conductor in sq.mm. - Maximum earth fault current in amperes If t trip time - fault duration in secs. The factor K is determined from the formula ( Annex A –IEC –60364-5-54) o

K = √ [ {Qc (β+20 C) / ρ20} ln { 1+ [(θf – θi ) / (β+θi )] }] Where, Qc β

= =

ρ20 θi θf

= = =

o

o

Volumetric heat capacity of conductor material ( J / C mm3 ) at 20 C o Reciprocal of temp. coefficient of resistivity at 0 C for the conductor o (202 C - Table A.54.1 –IEC 60364-5-54 ) o Electrical resistivity of conductor material at 20 C ( Ω mm ) o Initial temperature of conductor (30 C) (table A.54.6) o Final temperature of conductor (200 C) (table A.54.6) o

The value of √ {Qc (β+20 C) / ρ20} is “78” for steel as per, Table A.54.1 of IEC 60364-5-54 Hence K = 78 √ ln { 1 +[(200 – 30) / (202 + 30)] } = 57.85 Therefore, the area of conductor for the maximum fault level of 50kA and considering the fault clearing time is < 0.5 sec. the conductor area is A = (50000 * √ 0.5) / 57.85 = 611 sq.mm. Hence the calculated minimum diameter of the MS Rod = √ {(611 * 4) / 3.14} = 27.89 mm Considering 10% corrosion allowance the diameter of the MS rod will be 31 mm. Hence MS rod of 31 mm diameter is sufficient. However we will select a standard size of 40mm MS rod for the main earth mat below ground as per project specifications. Resistance of earth conductor The resistance of earth grid can be calculated by using the formula given below: 2

Rg =[ (100 * ρ)/(2*π*L)] * Ln {(2 * L ) / (H * 2 * D)} - eq-1 Where ρ L H D

- resistivity of soil in ohm-mtr - length of earth conductor in cm. - depth of burial of conductor in cm. - diameter of earth conductor in cm (or half the width of strip in cm)

Resistance of earth electrode The resistance of earth electrode is given by Re (in ohms) = {(100*ρ) / (2 * π* l )} * ln (4*l/d) –Eq 2

–For Round electrodes / pipes

Page: 27 of 38 REV: A Date: 05-09-2008


Where ρ l d

- resistivity of soil in ohm-mtr - length of earth electrode rod/pipe in cm. - diameter of earth electrode rod/pipe in cm

Typical Design calculations (example) Main Substation Assumptions: Length of earth grid conductor (L) Depth of burial of conductor (H) Soil resistivity (ρ) Diameter of conductor (D) Length of earth electrode (l) Diameter of earth electrode (d)

: 100 mtrs = 10000 cm : 0.6 mtrs. = 60 cm : 400 Ohm meter : 40 mm = 4.0 cm : 3 mtr = 300 cm : 40 mm = 4.0 cm

The resistance of the earth grid with above data works out to Rg = 8.24 ohms (from eq-1). The resistance of the earth electrode with above data works out to Re = 12.72 Ohms (from eq-2) Similarly the earth resistance value for the other areas also will be calculated and all the earth grids will be connected rigidly below the ground. The no. of earth pits will be added in such a way that the total effective earth resistance will be maintained less than 1 ohm. The resistivity will be further improved by adding bentonite soil if required as suggested in IEEE-80 / technical specifications to maintain the value below 1 ohm. The earth pits will be 40mm galvanized pipe and the pits can be treated at regular interval by pouring the water. 16.0

LIGHTNING PROTECTION 16.1 Recommended practice for designing the grounding system 16.1.1

The minimum dimensions of the lightning protection conductors have been derived from the Table of ‘Minimum dimensions of Component parts’ as mentioned in the IS. The lightning protection system shall be integrated with the Plant earthing system.

16.1.2

Outdoor Equipment shall be protected against direct lightning stroke by means of overhead shielding wires or vertical air terminations (masts).The location and height of masts shall be so selected as to cover all major equipment within a cone of protection not exceeding 45 °.

16.1.3

Down conductors from shielding wires/Air terminations shall be as short as possible and shall follow the most direct path possible between the air termination and earth termination avoiding sharp bends, upturns and kinks. Joints shall be avoided in down conductors as far as possible. Each down conductor shall have an independent earth termination which shall be interconnected with the station earth mat.

16.1.4

All building having concrete roof shall be protected against lightning strike. Structures having roofing made of CGI sheets and metal chimneys/towers not exceeding 30 meters in height,

Page: 28 of 38 REV: A Date: 05-09-2008


shall not be provided with separate lightning protection system. However, such structures and installation shall be adequately earthed to ensure free conducting path for lightning stroke. 16.1.5

All buildings/structures irrespective of their type of construction when used for storing explosive, inflammable gases and fuel oils etc. shall be provided with lightning protection.

16.1.6

The lightning protection system shall comprise air terminations, in the form of horizontal conductors, down conductors and earth electrodes. Earthing system and lightning protection system shall be electrically interconnected except for building/structures used in storing, explosive, inflammable gases and fuel oils.

16.1.7

Unless otherwise specified air terminations shall be of horizontal conductor type. The horizontal air terminations shall be interconnected such that any part of the roof is not more than 10 meters away from the nearest horizontal conductor. For flat roof, horizontal conductors shall generally be provided along the outer periphery of the roof.

16.1.8

All metallic projections, chimneys, ducts, ventilation pipes, railing gutters etc. on or above the main surface of the roof shall be properly bonded to the air termination network. However, gas pipes shall in no case be bonded with this network.

16.1.9

The number of down conductors from air termination to the earth electrode shall be selected on the following basis: Area is <100sq mtrs

One down Conductor

Area is >100sq mtrs

One down conductor plus one for each additional 300sqmtrs, or one for each 30Mtr periphery of the Structure.

16.1.10 Conductors of lightning protection will not be connected with the conductors of safety earthing above ground level. However the pits meant for safety earthing and the lightning will be interconnected by a conductor below ground. Down conductors will be cleated on the outer side of the building wall at 1000mm interval or welded to the building columns at 1000mm interval. Test Link will be provide at 1000mm above ground level between down conductor and Rod electrode. 16.1.11 Lightning Conductors will not pass through or run in GI conduits. All metallic structures within a vicinity of 2000mm in air will be bonded to the conductors of lightning system. 16.1.12 The minimum size of horizontal conductor used as air termination shall be 25 x 3mm galvanised MS flat. Down conductor from air termination to earth shall also be 25 x 3mm galvanised MS flat. Vertical Air termination Rods will be of 20 mm Dia and 1000mm long GI Pipes. Rod electrode for earthing will be of 40mm Dia and 3000mm long GS Pipes.


Page: 29 of 38 REV: A Date: 05-09-2008

Calculation Methodology Air termination conductor: Specific criteria for provision of Air termination conductors. 1.Vertical conductors(VC): The zone of protection(ZP) is 45Deg

Vertical conductors shall be provided whenever two Levels of elevation exist on roofs. 2. Horizontal conductors(HC) –Along the Periphery of the roof building plus along the roof incase the distance between two parallel conductors exceeds 18 mtrs.

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Method of clamping horizontal air termination conductors on ridged type roofs. 3. Down conductors (DC) - Down conductors shall be used for connecting vertical air termination and horizontal conductors to the earth to discharge the lightning stroke. The number of down conductors is decided by empirical formula applicable for area of building exceeding 100 Sqmtr P/20 ( where P is perimeter of roof protected by lightning air termination conductors.) 4. Spike arrestors -These shall be preferable mounted on chimney of the highest elevation if required with extension of Vertical support for elevation. 17.0

ILLUMINATION Power for Normal A.C. lighting is derived through a 415/240 V dry type transformer connected to main lighting distribution board located in each substation.

Normal A.C.Lighting: a)

This is provided by A.C. lighting fixtures distributed throughout the plant and is ON as long as the A.C. supply is available.

b)

A.C. lighting fixtures is fed from respective area lighting panel, which in turn is connected to main lighting distribution board.

Emergency Lighting: Emergency lighting will be through DC emergency light fittings. The emergency lights will be provided at strategic locations and the entry / exit of the electrical rooms / control rooms. These will be standalone fittings and will be generally under charging when the mains power is available. The battery once fully charged can operate for 4 hours continuously.

Illumination Levels: The areas to be illuminated and their respective illumination level are furnished below:-

a)

Crusher House, Conv. Tunnel and Wagon tippler area, if any

:

200 Lux

Page: 31 of 38 REV: A Date: 05-09-2008


b)

Transfer Point, Pent House, Conv. Gallery

:

50 Lux

c)

Switchgear Rooms & Pump Houses

:

150 Lux

d)

Corridors, Walkways (Excluding Conv. Gallery),

:

70 Lux

Staircase & Cable Spreader Rooms

e)

Control Room

:

200 Lux

f)

Transformer Room

:

50 Lux

g)

Storage pile areas

:

50 Lux

h)

Outdoor yard area

:

20 Lux

Factors Considered: Quantities of lighting fixtures in various area are calculated on the basis of following design data:

a)

b)

Maintenance Factor : Control Room and

-

0.75

Switchgear room

-

0.65

Dusty Area

-

0.55

General Indoor Area

-

0.60

Utilisation Factor Dusty areas such as conveyor galleries, tunnels,

: 50% ceiling, 30% wall,10% floor

TPs, crusher house etc.

c)

Clean areas such as Switchgear & control room etc

: 70% ceiling, 50% wall,10% floor

Working Plane

: For Conveyors at walkway level For Buildings at Floor Level

Type of Fixtures :

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a)

Conveyor Gallery

:Industrial Well Glass Luminaire with 1 x 70 Watt SON Lamp.

b)

Transfer Points, Track hopper

:Industrial Well Glass Luminaire with 1 x 70 Watt SON Lamp. :Industrial Medium Bay Luminaire with 1 x 150 Watt SON Lamp :Industrial High Bay Luminaire with 1 x 150 Watt SON Lamp.

c)

Switchgear Room

:Industrial Type Luminaire with 2 x 40 Watt Fluorescent Lamps.

d)

Control Room

:Decorative Type Luminaire with 2 x 40 Watt SON Lamp.

e)

Transformer Room

:Industrial Medium Bay Luminaire with 1 x 150 Watt SON Lamp.

f)

Open yard

:Flood light Luminaire with 2 x 250 / 400 Watt SON Lamp

Methodology The requirement of number of light fittings and the type of the fittings is decided by the Lumen Method. This is a method for estimating luminaire quantities and spacing for layouts that is more accurate because the difference in photometric performance caused by room geometry and system depreciation are taken into account. Lamp utilization factor (COU) for Internal Lights for External lights Lumen out put of lamp (F) Illuminance or the Lux level (E) Maintenance factor (MF)

: 0.6 : 0.2 : From Mfr. Catalogue : As described above. : As described above.

The Coefficient of utilization factor(COU) is defined as ratio between flux received on working plane from luminarie to sum of nominal fluxes of all lamps in the luminaire. The COU is calculated based on room index (K) which is given by formula . K = (L * W) / [MH * (L + W)] Where Length of room is (L) Width of room (W) Mounting height (MH)


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The manufacturers generally specify the COU based on room index and room reflection factors for ceiling, wall and Floor separately. COU of 0.6 is considered for internal and COU of 0.2 is considered for external area lighting on average least value basis for the room indices for the purpose of calculations. (Detailed calculation sheet with reference to COU table shall be submitted with Detailed engineering for each building taking in to account of uniformity Factor) Maintenance factor is taken on the basis of room maintenance over the period of time. The factor mainly comprises 1. Lamp lumen Depreciation 2. Luminaire Dirt depreciation Based on general geometry, the Number of lamps (N) required is given by formula (DIN 5035) N = (1.25 e *A) / (F * COU * MF) Where 1.25e = E Specified lux level (The factor 1.25 is by which design value should be chosen to exceed nominal light intensity ‘e’.) MF-Maintenance Factor. A-Area of Building in sq mtr. F- Lamp luminance out put Typical Calculation for Sub-station building: Substation building tentative dimensions are (Assumed dimensions for example purpose only) 20mtrs. (L) x 16 mtrs.(W) X 6 mtrs.(H) 2 x 40W TL Fixtures (80W) are considered as per specifications. From manufactures catalogue (CGL) lumen output is 2450 lumens x 2 nos. MF = 0.65 (considered for sub-station room) Specified Lux level = 150 COU = 0.6 With substitution of values in above formula, we get, N= 32 Nos The similar calculation will be done to decide the no. of light fittings in all the similar type of buildings. Typical Calculation for Ridge type roofed buildings & conveyor galleries For transfer towers and Drive house buildings which shall have similar roof structures (Ridge type roofs with steel structure) the typical calculations will be as follows: The area of Building : 22 mtr x 12 mtr (the dimensions are for example only) As per Spec. we shall consider 1 x 150 W Sodium vapor Lamps


Page: 34 of 38 REV: A Date: 05-09-2008

From Manufactures Catalogue (CGL) Lumen out put per lamp is 13500 Lumens. MF=0.55 Lux level = 150 for Localized internal lighting COU= 0.6 Substituting above values in the formula, we get, N = 9 nos. The similar calculation will be done to decide the no. of light fittings in the other similar type of areas. Typical Calculation for Outside General Area Lighting: For typical calculations the area around TP is considered. Area of TP = 29 mtr (L) x 23 mtr (W) (Area assumed for calculation purpose only) Maintenance factor considered as 0.55 Lux level as specified in Lafarge specs. is 20 COU is taken as 0.2 For external lighting Lumen output of lamp for 2 x 250W HPSV lamp is 28000 Now substituting the above values in the formula, we get, N= 2 Nos These 2 Nos shall be suitably mounted on the structures to give effective Lighting for the area Covered. The similar calculation will be done to decide the no. of light fittings in the other similar type of outside general areas.

18.0

BATTERY & CHARGER SYSTEM General In this project all the DC loads shall be fed from 110V battery. The calculation for sizing of the battery and its charger are shown below. The battery is to supply the DC power requirements during the following conditions:

Load on dc system exceeds the maximum output of the battery charger.

Output of the battery charger is interrupted.

AC power is lost

The following factors will be considered while designing the battery system: Temperature derating factor: The operating temperature affects the available capacity of a cell. The standard temperature for stating cell capacity is 25 deg C. If the lowest expected electrolyte temperature is below standard a cell large enough to have the required capacity is selected. The capacity deration factor for the same is known as temperature factor.


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Design Margin: As a prudent design we are to provide a capacity margin to allow for unforeseen addition to the DC system. Aging Factor: The performance of a lead acid battery is relatively stable throughout most of its life, but begins to decline at the later stage of its life. To ensure that the battery is capable of meeting its design loads throughout its service life, the battery’s rated capacity should be at least 125% of the load expected at the end of its service life ie an ageing factor of 1.25 is considered. Design Considerations

The battery sizing is done for a duty cycle of 30 minutes.

The calculated battery size is to be corrected for design margin, aging compensation and minimum temperature.

The batteries considered are sealed, maintenance free lead acid type with a 10 hour discharge rate i.e. C10 batteries.

2Volt batteries with an end cell voltage of 1.75volts are considered.

K factors corresponding to 1.75 end cell voltage and temperature correction factor for the lowest ambient temperature are taken from Exide batteries ltd. (power stack series of VRLA batteries).

This calculation is done for battery nominal voltage of 110V D.C., which is the control supply voltage.

Design basis The loads on the battery are mainly pertaining to HT switchboard control supply only. It is required to be identified which all loads are instantaneous and which all loads are continuous. For example an 'on' lamp in a breaker feeder is a continuous load, while a tripping relay is an instantaneous load coming in at the time of a trip. A design margin of 5% may be allowed for unforeseen additions or future expansion as well as for below optimum operating conditions. Battery capacity is referred to at a nominal temperature of 20 deg.celcius. (The factors given by Exide are at 20deg C). A temperature correction factor for the lowest temperature is considered while determining the AH capacity of the battery. The voltage at the load terminals shall never be outside +10% and –15% of the nominal voltage. Load Details The individual loads supplied by battery during the duty cycle maybe classified as continuous or noncontinuous. Non-continuous loads lasting for 1 minute or less are designated as momentary loads. The loads, which are energized through out the duty cycle, are known as continuous loads. These loads are normally carried by the battery charger and are initiated at the inception of the duty cycle.


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Some of the continuous loads are: Indication lamps, (ON, TCH etc)., continuously energized coils , annunciator loads etc. Momentary loads are non continuous loads which can occur one or more times during the duty cycle but are of short duration i.e. less than 1 minute. Although the momentary loads may exist for only a fraction of second, it is common practice to consider that each load will last for one full minute because the battery voltage drop after several seconds. Some of the typical momentary loads are: switchgear coil operations (trip and close), etc. The AH capacity of the battery is calculated as: AH =AH1* K1 * K2 * K3 Where K1 = Ageing Factor K2 = Design Margin K3= Temperature correction factor (For the lowest temperature of 10deg C) AH1 = max of Σ (Ap – A (p-1) )*K Where p=1 to S (S is the section of the duty cycle being analyzed). K = Capacity rating Factor which is obtained from the Manufacturer for a given end cell voltage and discharge capacity.(annexure-A) The load cycle of the battery is as indicated below.


Page: 37 of 38 REV: A Date: 05-09-2008

We will consider for this project as, S1 = 1 minute, S2=28 minutes & S3=1 minute M1 = S1-0= S1 =1 minute, M2= S2-S1 = 28 minutes & M3=S3-S2 =1 minute Based on the above calculation methodology, the AH capacity of the battery will be selected. Float Charger Capacity ICC =Continuous DC load current which is the total continuous current requirement calculated for the loads A design margin of 5 % is considered for unforeseen continues loads. A trickle charging current ITC is as recommended by the manufacturer.(Usually 2%) ITC = ICC *0.02 The total required capacity of the float charger shall be = ICC *1.05 + ITC Based on the above calculation float charger capacity will be selected.


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Boost Charge capacity: The boost charger shall be equal to maximum allowable battery charging current (generally 14% of the battery ampereage or the float charger capacity, which ever is higher. 19.0

VVVF DRIVES: The following factors are considered for determining the drive rating: 1

The type of load (constant torque in case of conveyors, feeders etc)

2

Shaft power of the motor required by the mechanical load

3

Overloading capacity – will be considered as 120%

4

Overloading time and cycle – O/L for 60 seconds in every 600 seconds.

5

Overload type will be cyclic.

6

Speed range shall be 20% to 100%.

7

The drive will be sized for an ambient of 40 deg C.

All the drives selected for 690V motors (conveyors) shall be in the multidrive configuration, where the converter will be common and the inverters will be for individual motors. The drives for VF/belt feeders shall be single drives in this project. The sizing of the converter module and the inverter modules will be done based on the above parameters by using the sizing software generally provided by the manufacturers.

Design Criteria Electrical

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