electric motor 9

Engi ngine nee erin ring g Ency ncyclo clope pedia dia Saudi Sa udi A ramco DeskTop Standards

Selecting Se lecting Me Mediu diu m Voltage Moto Moto r Starters Starters

Note: The source of the technical material in this volume is the Professional Engineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, sold, given, or disclosed to third parties, or otherwise used in whole, or in part, without the written permission of the Vice President, Engineering Services, Saudi Aramco.

Chapter : El Electrical File Reference: EEX21609

For additional information on this subject, contact W.A. Roussel on 874-1320

Engineering Encyclopedia

Electrical Selecting Medium Voltage Motor Starters

C O NT E NT S

P AG E

SELECTING CLASS E2 COMBINATION MOTOR STARTERS (CONTROLLERS) (CONTROLLERS) ...................................................................................................1 Characteristics Characteristics of Class E2 Combination Combination Motor Starters (Controllers) (Controllers)......1 ......1 Starter Components.........................................................................2 Electrical Electrical Ratings Ratings ............................................................................4 Motor Data .................................................................................................7 Full-Load Amperes .........................................................................7 Voltage............................................................................................7 Horsepower.....................................................................................7 Power Factor...................................................................................8 Service Factor .................................................................................8 Fault Duties ................................................................................................8 Symmetrical Current.......................................................................9 Asymmetrical Asymmetrical Current..................................................................... 9 SELECTING SELECTING POWER CIRCUIT BREAKER BREAKER STARTERS ................................10 Breaker Components ................................................................................10 Circuit Breaker Compartments Compartments .....................................................10 Control Circuit ..............................................................................15 Protection Components.................................................................16 Electrical Electrical Ratings......................................................................................20 Nominal Ratings ...........................................................................20 Maximum Voltage (Column 4).....................................................20 Voltage Range Factor (K) (Column 5)..........................................21 Maximum Voltage Divided Divided by K (Column 6) 6) ..............................22 Continuous Current (Column 7) ...................................................22 Permissible Permissible Tripping Delay (Column (Column 8) .......................................22 Short Circuit Current Current At Maximum kV (Column 9) .....................23 Symmetrical Interrupting Interrupting Capability Capability (Column 10) .......................23

Saudi Aramco DeskTop Standards



C O NT E NT S

P AG E

SELECTING CLASS E2 COMBINATION MOTOR STARTERS (CONTROLLERS) (CONTROLLERS) ...................................................................................................1 Characteristics Characteristics of Class E2 Combination Combination Motor Starters (Controllers) (Controllers)......1 ......1 Starter Components.........................................................................2 Electrical Electrical Ratings Ratings ............................................................................4 Motor Data .................................................................................................7 Full-Load Amperes .........................................................................7 Voltage............................................................................................7 Horsepower.....................................................................................7 Power Factor...................................................................................8 Service Factor .................................................................................8 Fault Duties ................................................................................................8 Symmetrical Current.......................................................................9 Asymmetrical Asymmetrical Current..................................................................... 9 SELECTING SELECTING POWER CIRCUIT BREAKER BREAKER STARTERS ................................10 Breaker Components ................................................................................10 Circuit Breaker Compartments Compartments .....................................................10 Control Circuit ..............................................................................15 Protection Components.................................................................16 Electrical Electrical Ratings......................................................................................20 Nominal Ratings ...........................................................................20 Maximum Voltage (Column 4).....................................................20 Voltage Range Factor (K) (Column 5)..........................................21 Maximum Voltage Divided Divided by K (Column 6) 6) ..............................22 Continuous Current (Column 7) ...................................................22 Permissible Permissible Tripping Delay (Column (Column 8) .......................................22 Short Circuit Current Current At Maximum kV (Column 9) .....................23 Symmetrical Interrupting Interrupting Capability Capability (Column 10) .......................23




Closing and Latching Latching Capability (Column (Column 12) .............................23 SELECTING SELECTING PROTECTIVE PROTECTIVE RELAYS...............................................................25 Voltage and Horsepower Horsepower Ratings Ratings .............................................................25 4 kV or Greater, Less Than 10,000 hp..........................................25 4 kV or Greater, 10,000 10,000 hp or Greater ..........................................25 Types of Protective Devices.....................................................................26 Class E2 Combination Combination Controller Controller .................................................26 Power Circuit Circuit Breakers Breakers .................................................................27 SAES-P-114 (25 APR 94)........................................................................29 Induction Motors, 600 V or Greater, Less than 5,000 hp .............29 Induction Motors, 600 600 V or Greater, 5,000 hp or Greater ............29 WORK AID 1: RESOURCES USED TO SELECT A CLASS E2 COMBINATION COMBINATION MOTOR STARTER (CONTROLLER) ..................................30 Work Aid 1A: 16-SAMSS-506 16-SAMSS-506 ................................................................30 Work Aid 1B: Vendor’s Literature, Literature, Westinghouse DB-8850, AMPGARD Medium Voltage Starters..........................................................................30 Work Aid 1C: NEMA ICS 2-324, Table 2-324-1 and and Table 2-324-2B ...30 Work Aid 1D: Applicable Selection Selection Procedures... ...................................33 WORK AID 2: RESOURCES USED TO SELECT A POWER CIRCUIT BREAKER MOTOR STARTER........................................................34 STARTER........................................................34 Work Aid 2A: ANSI/IEEE Standard Standard C37.06-1987 ..................................34 Work Aid 2B: SAES-P-114, SAES-P-114, Chapter 6 ....................................................35 Work Aid 2C: Vendor’s Vendor’s Literature, Westinghouse Westinghouse SA-11671, SA-11671, Medium Voltage VacClad-W Metal-Clad Metal-Clad Switchgear Switchgear .........................................................35 Work Aid 2D: Applicable Selection Selection Procedures... ...................................35 WORK AID 3: RESOURCES USED TO SELECT PROTECTIVE RELAYS ..............................................................................................................37 Work Aid 3A: ANSI/IEEE Standard Standard C37.96-1988 ..................................37 Work Aid 3B: 16-SAMSS-506 ................................................................43




Work Aid 3C: SAES-P-114, SAES-P-114, Chapter 6 ....................................................43 Work Aid 3D: Applicable Selection Selection Procedures... ...................................43 GLOSSARY ........................................................................................................44

TABLE TABLE OF FI GURES Figure 1. Class E2 Ampgard Controller................................................................1 Controller................................................................1 Figure 2. Typical Control Circuit Schematic ........................................................3 Figure 3. 3. Class E2 Controller Controller Ratings...................................................................4 Ratings...................................................................4 Figure 4. Class E2 Controller Voltage And Interrupting Interrupting Ratings .........................5 Figure 5. Class E2 Horsepower Ratings................................................................6 Ratings................................................................6 Figure 6. Fault Profiles .........................................................................................9 Figure 7. 7. Vacuum Breaker Breaker Compartments..........................................................11 Compartments..........................................................11 Figure 8. Air-Magnetic Breaker Compartments..................................................12 Compartments..................................................12 Figure 9. Breaker With Open Shutters................................................................14 Figure 10. Power Circuit Breaker Control Circuit ..............................................15 Figure 11. Protection Components......................................................................16 Figure 12. Bar-Type Ct .......................................................................................17 Figure 13. Voltage Transformer..........................................................................18 Figure 14. Breaker Capability Curves.................................................................21 Figure 15. Breaker Operating Times...................................................................22 Figure 16. Medium Voltage Voltage Circuit Breaker Ratings .........................................24 Figure 17. Class E2 Controller Controller Protection Protection (1500 Hp Or Less)............................26 Figure 18. Power Circuit Circuit Breaker Protection (Less Than 10,000 Hp) ................27 Figure 19. Additional Protection (Greater Than 5000 Hp) .................................28 Figure 20. Backup Electromechanical Electromechanical Protection...............................................28 Protection ...............................................28 Figure 25. Class E2 Controller Controller Motor Current Current Ratings.......................................31 Ratings.......................................31 Figure 26. Class E2 Controller Controller Voltage And Interrupting Interrupting Ratings .....................32 Figure 27. Power Circuit Breaker Ratings ..........................................................34 Figure 28. C37.96 Mv Motor Class Class E2 Controller Controller Protection Protection Scheme...............37 Figure 29. 29. C37.96 Class Class E2 Controller Controller Protective Relays ..................................38 Saudi Aramco DeskTop Standards



Figure 30. C37.96 Small Mv Motor Protection Protection Scheme.....................................39 Figure 31. C37.96 Large Mv Motor Protection Protection Scheme.....................................40 Figure 32a. C37.96 Power Circuit Breaker Breaker Ratings Ratings And Relay Types ...............41 Figure 32b. C37.96 Power Circuit Breaker Breaker Relay Types (Cont’d) (Cont’d) .....................42




SELECTI NG CLASS E2 COM BINATION MOTO R STARTERS (CONTROL LERS) Char acteristics of Class E2 Combination M otor Star ters (Contr oller s) A Class E2 combination starter (controller) consists of the following components: Note: Starter and controller are used interchangeably throughout this Information Sheet; both terms are correct. •

contactor (fixed or drawout)

•

isolation device, feature, or mechanism

•

current limiting fuses (NEMA Type R)

•

control circuit

•

protective relays

Figure 1 describes a Cutler-Hammer/Westinghouse Ampgard motor starter that uses a switch as the isolation device and a drawout type contactor.

Figure 1. Class E2 Ampgard C ontr oller


1



Starter Components Contactor - Class E2 controllers use the contactor as the device that actually starts and stops

the motor. The contactor may or may not be a drawout device. The incoming power is supplied through the fuses to the contactor. The contactor shown in Figure 1 is designed to be a drawout device that allows for easy servicing and maintenance. Interlocks are available to prevent the removal or installation of the contactor when it is closed. Isolation Switch - The purpose of the isolation switch shown in Figure 1 is to allow the user to

isolate the contactor from the main power. On some controller designs isolation is accomplished by withdrawal of the contactor. The isolation switch is interlocked to the door to prevent access to the contactor or other energized devices while the switch is closed. If the user has access to the contactor while the contactor is energized, a hazardous condition exists. The isolation switch has the capability of allowing the switch to be locked out when the switch is in the open position. Current Limiting Fuses are used to interrupt short circuits or faults exceeding the contactor’s

rating. Control Circuit - A control power transformer (CPT) supplies control power to the control

circuit. Figure 2 shows the Ampgard motor starter control circuit diagram. Note: The control circuit is a vendor specified function . The control circuit for a medium voltage motor starter is similar to the control circuit of a larger low voltage combination starter. Two main differences do exist. •

On a medium voltage starter, the primary of the CPT is protected by small current limiting fuses.

•

There is the capability to use an external source of control power for testing and maintenance purposes. An external source of control power must be used when the isolation switch is open. There is no test position for the drawout contactor as there is for a circuit breaker.

Protective Relays are used to provide thermal overload and locked rotor protection, phase and

ground fault protection, and other abnormal operating conditions (e.g. single-phasing) protection. Note: Work Aid 1 was developed to assist in the selection of the controller without protective relays. Work Aid 3 will describe procedures for selecting the relays.


2



Figur e 2. Typical Contr ol Cir cuit Schematic


3



Electrical Ratings Electrical ratings for Class E2 controllers are specified in NEMA Standard ICS 2-324. The specific ratings to be discussed in this Information Sheet are maximum voltage, maximum horsepower, contactor current rating, starter interrupting capacity and contactor interrupting capacity. Figure 3 lists the ratings of a typical medium voltage Class E2 controller.

Figur e 3. Class E2 Contr oller Ratings

Maximum Voltage ratings as listed in NEMA Standard ICS 2-324 are a motor utilization RMS

voltage at which the interrupting rating applies (See Figure 4). Starter Interrupting Capacity also is listed in Figure 4.

The starter’s interrupting capacity as listed is the interrupting rating of the NEMA R current limiting fuses. Note: The three-phase MVA rating equals 1.732 times the symmetrical amperes times the normal utilization voltage. For example: MVA = 1.732 X 50 kA X 4.6 kV 400 MVA.


4



Figure 4. Class E2 Contr oller Voltage and I nter r upting Ratings


5



Maximum Horsepower ratings as listed in NEMA Standard ICS 2-324 (Figure 5) are shown

only for reference. The vendor must state the maximum horsepower rating for their controllers. Although larger horsepower rated controllers are available, SAES-P-114 limits use of controllers to 1500 hp (1125 kW) or less. Contactor C urr ent Ratings are also as listed in Figure 5. Service limit values are 1.15 times the

continuous current ratings.

Figur e 5. Class E2 Hor sepower Rat ings

Contactor Interr upting Capacity is the rating where the contactor must be capable of making and

breaking the maximum current at which the overload relays alone cause interruption (crossover point). The cross-over point is determined from the characteristic curves of the overload relays and the total clearing time curves of the medium voltage motor circuit fuses. For the contactor that was described in Figure 3, the contactor’s interrupting capacity is 50 MVA or 7217 amperes at 4.0 kV (I = 50000/(1.732 X 4.0) = 7217A).


6



Motor Data The following listed motor data should be provided to the controller vendor in order to ensure both full utilization and proper protection of the motor. •

full-load amperes (FLA)

•

voltage (kV)

•

horsepower (hp)

•

power factor (p.f.)

•

service factor (S.F.)

Full-Load Amperes The controller’s continuous current rating as was listed in Figure 5 is based on the nameplate full-load amperes (FLA) of the motor. The service-limit current ratings (also listed in Figure 5) represent the maximum RMS current that the controller may be expected to carry for protracted periods in normal service. The ultimate trip rating of the overcurrent relays (Device 49) should not exceed the service-limit rating of the controller. Voltage The controller’s voltage rating is based on the motor’s nameplate voltage rating, which is a utilization voltage and not the system nominal voltage. As was discussed in EEX215.02, a 2.4 kV or 4.16 kV nominal system voltage would require 2.3 or 4.0 kV nameplate (utilization) rated motors respectively. Note: 16-SAMSS-506 requires a minimum 4.8 kV rating for Class E2 controllers. Horsepower The motor’s nameplate horsepower rating, but it is used for reference maximum horsepower rating for the the controller described in Figure 3 and 80 percent power factor.


rating is also compared to the controller’s horsepower purposes only. The vendor ultimately determines the specific controller at a maximum voltage. For example, had a maximum horsepower rating of 2500 hp at 5 kV

7



Power Factor Because this Module is restricted to selecting starters for induction motors, the power factor is assumed to be 80 percent. As was described in Figure 3, a synchronous motor having a power factor of 100 percent would increase the controller’s horsepower rating to 3000 hp versus 2500 hp for an 80 percent power factor motor. Service Factor The nameplate service factor of the motor ultimately determines the continuous current rating of the controller because the service factor determines the nameplate full-load amperes. Note: Saudi Aramco specifies only 1.0 S.F. motors . Fault Duties The Class E2 controller must be capable of interrupting the maximum available fault current at the line side terminals of controller. Per NEMA ICS 2-324, all controllers must be capable of interrupting 40 kA or 50 kA, which translates to 280 MVA or 350 MVA respectively at 4.0 kV, whereas 16-SAMSS-506 requires a minimum of 350 MVA at 4.8 kV. Figure 6 describes the voltage and current relationships under fault conditions.


8



Figur e 6. Fau lt Pr ofiles Symmetrical Cu r rent Virtually all electrical equipment manufactured in the United States is rated symmetrically; controllers are no exception. Asymmetrical Current Although most electrical equipment is rated symmetrically, it also has an implied asymmetrical rating as well. The controller’s asymmetrical rating is 1.6 times its symmetrical rating. Note: The interrupting rating of the controller is in fact the interrupting rating of the NEMA R fuses. The ratings listed in Figure 4 are in reality the ratings of NEMA R current limiting fuses as governed by ANSI/IEEE Standard C37.46.


9



SELECTING POWER CIRCUIT BREAKER STARTERS Power circuit breakers are typically used for controlling (starting and stopping) motors rated greater than 6.6 kV or greater than 8000 hp. Based on current technologies, manufacturing contactors greater than these ratings would be cost-prohibitive. Note: SAES-P-114 requires power circuit breaker motor starters for all motors greater than 4.0 kV and 1125 kW (1500 hp). Work Aid 2 has been developed to assist in the selection of power circuit breakers. Breaker Components Circuit Breaker Compar tments Medium voltage circuit breakers are actually sub-components of metal-clad switchgear, and they are constructed/manufactured in accordance with ANSI/IEEE Standard C37.06. The following conditions must exist for classification as switchgear: •

The interrupting or switching device (usually a circuit breaker) is removable, and it can be moved into a disconnected, connected test, or withdrawn positions.

•

The primary bus conductors and connections are insulated.

•

Automatic shutters close off and prevent exposure of the primary circuit elements when the switching or interrupting device is removed from the operating position.

•

Both the secondary and primary contacts are self-aligning and self coupling.

•

Mechanical interlocks ensure safe and proper operation.

•

Grounded metal barriers enclose the major parts of the primary circuit. These parts include the buses, voltage transformers, control power transformers, and the switching and interrupting devices.

•

There are NO intentional spaces or openings between compartments. No openings help prevent a fire resulting from a switchgear failure or an electrical fault from entering other compartments or sections.


10



Air or Vacuum Compartments - Each vertical section is divided into four compartments by steel

barriers. Figure 7 shows the four compartments in a typical vertical section of vacuum switchgear. The breakers and the auxiliary equipment are mounted inside and at the front of the vertical section. Sometimes the breakers and auxiliary compartments are combined into one compartment as shown in Figure 7 (vacuum only).

Figur e 7. Vacuum Breaker Compart ments


11



At other times, they are located in two separate compartments with the auxiliary compartment above the breaker compartment as shown in Figure 8 (air breaker). Directly behind these two front compartments is the bus compartment. The compartment in the very back of each section is called the cable compartment.

Figure 8. Air -Magnetic Breaker Compar tments


12



- The auxiliary compartment contains many combinations of components. Typical items found in the auxiliary compartments are: Auxiliary

Compartments

•

control switches for breaker control

•

metering switches for voltmeter and ammeters

•

terminal blocks for control and metering

•

control power fuse blocks or control power circuit breakers

•

protective relays

•

auxiliary control relays

•

drawout voltage transformers (VTs)

•

control power transformers (CPTs)

Breaker Compartments - The breaker compartment encloses the switching or interrupting

device. The area where the circuit breaker is installed is called a cubicle, and the circuit breaker itself is called the element. Accessing the breaker compartment is through a hinged door. Figure 9 shows the interior of a typical breaker compartment with the circuit breaker removed. It also shows where the current transformers are mounted. The current transformers are wired to the auxiliary compartment, and they are connected to meters and protective relays. The main power studs or primary contacts connect the high voltage to the drawout circuit breaker. When the breaker is removed to the test position, the shutter automatically closes to prevent unintentional connection to the high voltage power studs. Figure 9 shows the shutter open to expose the current transformers and the main power studs. The racking or levering-in mechanism is a crank and screw mechanism that moves the breaker in and out of the cubicle and into the different positions. The secondary contact assembly is a self-aligning assembly that connects the control circuits between the drawout circuit breaker and the cubicle. The circuit breaker needs control power to operate the tripping and closing mechanism and coils. The circuit breaker also provides normally open and normally closed contacts from an auxiliary switch. These contacts are then used for indicating lights on the switchgear, or they may connect into other control circuits.


13



Figur e 9. Breaker With Open Shutter s


14



Contr ol Circuit Control circuits (logic) were discussed in detail in EEX216.03. Figure 10 is a typical control circuit for a medium voltage power circuit breaker, with a DC close coil, a DC trip coil, and a DC spring charging motor.

Figure 10. Power C ircuit Br eaker Contr ol Circuit


15



Pr otection C omponents The protection components consists of four sub-components (Figure 11): •

instrument transformers (CTs and VTs)

•

circuit breaker

•

DC station battery

•

relays

Failure of any of the components usually results in failure of the entire system.

Figure 11. Pr otection Components Cur rent Tr ansformers (CTs) connect in series with the line to transform the motor line current to

the standard five amperes that are suitable for a relay or meter. Many power system protection schemes fail, not because of fault relays, but because the relay engineer failed to take into account the effects of CT performance (saturation). CTs can be installed as shown in Figure 9, or a separate bar-type CT can be installed, as shown in Figure 12.


16



Figur e 12. Bar -Type CT


17



Voltage Transformers (VTs) are also used for protection and metering purposes. They are an

integral part of the switchgear. The VT compartment is designed so that when opened the transformers disconnect from the high voltage. Current limiting fuses electrically protect the VTs. Figure 13 shows a typical VT drawer in the withdrawn position.

Figur e 13. Voltage Tr ansfor mer DC Station Batteries when properly maintained offer the most reliable tripping source. They

require no auxiliary tripping devices, and they use single-contact relays that directly energize a single trip coil in the breaker. Power circuit voltage and current conditions during time of faults do not affect a battery-trip supply; therefore, battery trip is considered the best source for circuit breaker tripping. Saudi Aramco requires 125 VDC tripping power (batteries).


18



Relays are defined by IEEE Standard 100-1984 as devices whose function is to detect

defective lines or apparatus or other power system conditions of an abnormal or dangerous nature and to initiate appropriate control circuit action. Relays are classified as follows: •

Protective relays detect defective lines, defective apparatus, or other dangerous or intolerable conditions. These relays can either initiate or permit switching, or they can simply provide an alarm.

•

Monitoring relays verify conditions on the power system or in the protection system. These relays include fault detectors, alarm units, channel-monitoring relays, synchronism verification, and network phasing. Power system conditions that do not involve opening circuit breakers during faults can be monitored by verification relays.

•

Programming relays establish or detect electrical sequences. relays are used for reclosing and synchronizing.

•

Regulating relays are activated when an operating parameter deviates from predetermined limits. Regulating relays function through supplementary equipment to restore the quantity to the prescribed limits.

•

Auxiliary relays operate in response to the opening or closing of the operating circuit to supplement another relay or device. These include timers, contactmultiplier relays, seal-in units, receiver relays, lock-out relays, closing relays, and trip relays.

Programming

Virtually all of the types of relays classified above are used to protect motors. The next Information Sheet will present procedures for selecting relays.


19



Electrical Ratings Ratings for both the air-magnetic and the vacuum circuit breakers are identical, therefore, the following information applies to both types of breakers. The best method to explain the ratings of medium voltage circuit breakers is to review a typical manufacturers’ rating chart (See Figure 16). Each of these columns has a specific rating for a selected breaker. Five rating limits never to be exceeded are: •

Rated Maximum Voltage (Column 4)

•

Rated Continuous Current (Column 7)

•

Rated Short Circuit Current (Column 9)

•

Maximum Symmetrical Interrupting Capability (Column 10)

•

Closing and Latching (Momentary) Capability (Column 11)

Nominal Ratings Voltage Class (Column 2) - This rating is the nominal voltage rating of the breaker. This voltage

should correspond to the voltage of the system to which the breaker is to be applied. Often, you will find a 4.16 kV breaker being used in a 2.4 kV system. This situation is often true in most new installations. Note: Even if used on a 2.4 kV system, Columns 7, 10 and 11 cannot be exceeded. MVA Class (Column 3) - This rating is the nominal MVA rating of the breaker, and it is used for

information purposes only. Maximum Voltage (Column 4) This rating is the highest rms voltage at the rated frequency for which the breaker is designed. The three standard maximum voltages are 4.76 kV, 8.25 kV and 15 kV.


20



Voltage Ran ge Factor (K) (Column 5) The K factor is the ratio of rated maximum voltage (Column 4) to the lower limit of the range of operating voltage (Column 6), where the required symmetrical and asymmetrical interrupting capabilities vary in inverse proportion to the operating voltage. The K factor is specified by ANSI C37.06 standards. Figure 14 shows typical capability curves for a 4160 volt, 250 MVA or a 13.8 kV, 500 MVA rated circuit breakers. Between the maximum voltage of 4.76 kV (15 kV) and 3.85 kV (11.5 kV), the rated interrupting current is inversely proportional to the operating voltage. As the operating voltage increases, the interrupting rating decreases. At 3.85 kV (11.5 kV), the interrupting rating is 36 kA (23 kA) (Column 10). At maximum kV, the interrupting rating is 29 kA (18 kA) (Column 9). To determine the symmetrical interrupting capability of a breaker at a voltage between the maximum and minimum voltage, use the following formula. Isym =[ISC max (Column 9) x kV max (Column 4)]/operating voltage

Figure 14. Breaker Ca pability Curves


21



Ma ximum Voltage Divided by K (Column 6) This rating is often misunderstood to be the minimum operating voltage of the breaker. The rating (number) is used to determine the maximum symmetrical interrupting capability of the breaker (Column 10). As stated earlier, 4.16 kV nominal rated breakers are used on 2.4 kV nominal systems because 2.4 kV rated breakers are no longer manufactured. Continuous Cur r ent (Column 7) The rated continuous current of a circuit breaker is the designated limit of rms current at rated frequency that it shall be required to carry continuously without exceeding the temperature O limitations based on a 40 C ambient temperature. The temperature limits on which the rating of circuit breakers are based are determined by the characteristics of the insulating materials used and the metals that are used in the current carrying components and springs. Standard continuous current ratings are 1200, 2000, and 3000 amps. Per missible Tr ipping Delay (Column 8) The rated permissible tripping delay is 2 seconds for all medium voltage circuit breakers. See Figure 15 for the IEEE Standard C37.010 breaker operating times.

Figure 15. Breaker Oper ating Times


22



Short Cir cuit Curr ent At Maximum kV (Column 9) This rating is the maximum rms current the circuit breaker will interrupt at rated maximum voltage (Column 4). Symmetr ical Inter r upting Cap ability (Column 10) This rating is the maximum rms current the circuit breaker will interrupt at the maximum voltage divided by K. This value equals K (Column 5) times rated short circuit current (Column 9). The short-time current rating specifies the maximum capability of a circuit breaker to withstand the effects of short circuit current flow for a standard period. For medium voltage breakers, it is usually three seconds. This rating allows time for downstream protective devices that are closer to the fault to operate and isolate the circuit. Closing and Latching Capability (Column 12) This rating indicates the breaker’s ability to close in and withstand the mechanical and thermal stresses of the maximum short circuit current of the first half-cycle. This value is very important because mechanical stresses are directly proportional to the square of the current. A medium voltage breaker is designed so that its momentary rating is 1.6 times the maximum interrupting rating (Column 10 x 1.6). If expressed in peak amperes, the momentary rating is 2.7 times the maximum interrupting rating (Column 10 x 2.7). Note: In AC medium voltage breakers, the predetermined X/R ratio is 15 (p.f. = 6.6%, which implies an A.F. (M m) equal to 1.52). It is often erroneously implied that these breakers have an asymmetrical rating of 1.6 times the symmetrical rating.


23



Figure 16. Medium Voltage Circuit Breaker Ratings


24



SELECTING PROTECTIVE RELAYS Voltage and Horsepower Ratings The required types of motor controllers, protection schemes, and relays for medium voltage induction motors were categorized by SAES-P-114 (01 Jul 91), Chapter 6. Note: Work Aid 3 has been developed to provide resources (standards and procedures) to select protective relays for medium voltage motor protection. 4 kV or G r eater, Less Than 10,000 hp SAES-P-114 (01 Jul 91), Section 6.2.4, required: •

Controller Types: (1) Combination, Class E2, with current limiting fuses (1500 hp or less) or (2) Power Circuit Breaker

•

Relay Protection: or

(1) Electromechanical Relay Set (2) Solid State MPP and Electromechanical Relay Set

4 kV or Gr eater, 10,000 hp or G r eater SAES-P-114 (01 Jul 91), Section 6.2.5, required: •

Controller Type:

(1)

Power Circuit Breaker

•

Relay Protection: or

(1) (2)

Electromechanical Relay Sets 1 and 2 Solid State MPP and Electromechanical Relay Set


25



Types of Pr otective Devices Class E2 Combination Controller SAES-P-114 (01 Jul 94), Section 6.2.4, and 16-SAMSS-506, Section 5, required motor protection (1500 hp or less) in accordance with Figure 17. Note: The detailed purpose of each device was described in EEX 216.02.

Figur e 17. Class E2 Contr oller Pr otection (1500 hp or L ess)


26



Power C ircuit Br eakers Electromechanical Pr otection - SAES-P-114 (01 Jul 94), Section 6.2.4, required induction motor

protection (less than 10,000 hp) in accordance with Figure 18. Note: The detailed purpose of each protective device was described in EEX 216.02.

Figur e 18. Power Cir cuit Br eaker Pr otection (Less Th an 10,000 hp)


27



SAES-P-114 (01 Jul 94), Section 6.2.4, also required additional protection for induction motors 5000 hp or greater in accordance with Figure 19.

Figure 19. Additional Protection (Gr eater Th an 5000 hp) Solid-State Protection - SAES-P-114 (01 Jul 94), Section 6.2.4, also permitted use of electronic

relays (motor protection packages-MPPs) instead of electromechanical relays. However, if motor protection packages were used, an electromechanical set of backup relays were also provided in accordance with Figure 20.

Figur e 20. Backup Electr omechanical Pr otection


28



SAES-P-114 (25 APR 94) The new SAES-P-114 now specifies solid-state motor protection packages (MPPs) for all categories of medium voltage motors. Note: Refer to EEX 216.02 for a review of MPPs . Ind uction M otors, 600 V or Gr eater, Less than 5,000 hp SAES-P-114 (25 APR 94), Section 6.2.4, now requires: •

Controller Types:

or

1) Combination, Class E2, with currentlimiting fuses (for 1,500 hp or less) 2)


•

Relay Protection:

1) Multifunction Motor Protection Package plus additional relays

•

Overtemperature:

See Para. 6.5 for Device 38B and 49T temperature monitor requirements

Ind uction M otors, 600 V or G r eater, 5,000 hp or G r eater SAES-P-114 (25 APR 94), Section 6.2.5, now requires: •

Controller Type:


•

Relay Protection:

Multifunction Motor Protection Package plus additional relays

•

Overtemperature:

See Para. 6.5 for Device 38B and 49T temperature monitor requirements

Note: For the specific relay functions specified under the new SAES-P-114, refer to Handout 4.


29



WORK AID 1:

RESOURCES USED TO SELECT A CLASS E2 COMBINATION MOTOR STARTER (CONTROLLER)

W or k Aid 1A:

16-SAM SS-506

For the content of 16-SAMSS-506, refer to Handout 5. Work Aid 1B:

Vendor’s Literatur e, Westinghouse DB-8850, AMPGARD Medium Voltage Star ters

For the content of Westinghouse DB-8850, refer to Handout 6. Work Aid 1C:

NEMA ICS 2-324, Table 2-324-1 and Table 2-324-2B

For the content of Table 2-324-1, refer to Figure 25. 2-324-2B, refer to Figure 26.


For the content of Table

30



Figure 25 lists the motor current ratings of Class E2 controllers.

Figure 25. Class E2 Contr oller M otor Cur r ent Ratings


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Figure 26 lists the voltage and interrupting ratings of Class E2 controllers.

Figure 26. Class E2 Contr oller Voltage and In terr upting Ratings


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Work Aid 1D:

Applicable Selection Procedures

1. Collect the following data from the motor nameplate: horsepower (hp) full-load amperes (FLA) voltage (kV) service factor (S.F.) Note: If motor nameplate data is not available (e.g. during the preliminary design stage), calculate the motor’s full-load amperes in accordance with the following formula:

FLA = [kVA/(1.732 x kV)] x S.F. where: kVA equals the design horsepower rating (1 kVA = 1 hp) kV equals nominal system line-to-line voltage S.F. = 1.0 for Saudi Aramco motors 2.

Collect the maximum available symmetrical short circuit current (SCA) from the system one-line diagram: Available short circuit current (SCA) -

3.

Calculate a required controller symmetrical interrupting rating 105 percent greater than the maximum SCA: Note: Saudi Aramco design practices require that all electrical equipment interrupting ratings be equal to 105 percent of SCA. controller interrupting rating in amperes - I int = 1.05 x SCA controller interrupting rating in MVA - M VA int = 1.732 x Iint x kV

4.

Select the next standard size contactor (catalog number) from pages 26 or 27 of Work Aid 1B (Handout 6) that equals or exceeds the FLA, kV, I int or MVAint from paragraphs 1, 2 and 3 above.

5.

Verify that the selected contactor meets 16-SAMSS-506 (Work Aid 1A, Handout 5) criteria.

6.

Verify that the selected contactor meets NEMA ICS 2-324 (Work Aid 1C) criteria.


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WORK AID 2:

RESOURCES USED TO SELECT A POWER CIRCUIT BREAKER MOTOR STARTER

Work Aid 2A:

ANSI/IEEE Standard C37.06-1987

Figure 27 lists the ratings of power circuit breakers.

Figure 27. Power Cir cuit Breaker Ra tings


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Work Aid 2B:

SAES-P-114, Chapter 6

For the content of SAES-P-114 (25 APR 94), Chapter 6, refer to Handout 4. Work Aid 2C: Vendor’s Liter atur e, Westinghouse SA-11671, Medium Voltage VacClad-W Metal-Clad Switchgear For the content of Westinghouse SA-11671, refer to Handout 7. Work Aid 2D:


1. Collect the following data from the motor nameplate: horsepower (hp) full-load amperes (FLA) voltage (kV) service factor (S.F.) Note: If motor nameplate data is not available (e.g. during the preliminary design stage), calculate the motor’s full-load amperes in accordance with the following formula:

FLA = [kVA/(1.732 x kV)] x S.F. where: kVA equals the design horsepower rating (1 kVA = 1 hp) kV equals nominal system line-to-line voltage S.F. = 1.0 for Saudi Aramco motors 2.

Collect the maximum available symmetrical short circuit current (SCA) from the system one-line diagram: Available short circuit current (SCA) -

3.

Calculate a required power circuit breaker symmetrical interrupting rating 105 percent greater than the maximum SCA: power circuit breaker interrupting rating in amperes - I int = 1.05 x SCA

4.

Calculate a required power circuit breaker closing and latching rating 2.7 times greater than the symmetrical interrupting rating (I int) from paragraph 3 above: closing and latching capability - I CL(peak) = 2.7 x Iint


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5.

If the breaker’s closing and latching capability is expressed in symmetrical amperes, calculate a required power circuit breaker closing and latching rating 1.6 times greater than the symmetrical interrupting rating (I int) from paragraph 3 above: closing and latching capability - I CL(sym) = 1.6 x Iint

6.

Select the next standard power circuit breaker from page 6 of Work Aid 2C (Handout 7) that exceeds the FLA, kV, I int and ICL(peak) or ICL(sym) from paragraphs 1 through 5 above.

7.

Verify that the selected power circuit breaker meets SAES-P-114, Chapter 6 (Work Aid 2B, Handout 4), criteria.

8.

Verify that the selected power circuit breaker meets ANSI/IEEE Standard C37.06-1987 (Work Aid 2A) criteria.


36



WORK AID 3:

RESOURCES USED TO SELECT PROTECTIVE RELAYS

Work Aid 3A:

ANSI/IEEE Standard C37.96-1988

Figure 28 describes the C37.96 relay protection scheme for medium voltage (MV) motors that are controlled by Class E2 controllers.

Figur e 28. C37.96 MV Motor C lass E2 Contr oller Pr otection Scheme


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Figure 29 lists the C37.96 ratings of and types of protective devices used with Class E controllers. Note: SAES-P-114 specifies use of Class E2 controllers only .

Figur e 29. C37.96 Class E2 Contr oller P r otective Relays


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Figure 30 describes the C37.96 protection scheme for small medium voltage (MV) motors that are controlled by power circuit breaker controllers.

Figur e 30. C37.96 Small MV Motor Pr otection Scheme


39



Figure 31 describes the C37.96 protection scheme for large medium voltage (MV) motors that are controlled by power circuit breaker controllers.

Figur e 31. C37.96 La r ge MV Motor Pr otection Scheme


40



Figures 32a and 32b lists the C37.96 ratings of relays and the relay types used with power circuit breaker controllers.

Figure 32a. C37.96 Power Circuit Br eaker R atings and Relay Types


41



Figur e 32b. C37.96 Power Cir cuit Br eaker R elay Types (Cont’d)


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W or k Aid 3B:

16-SAM SS-506

For the content of 16-SAMSS-506, refer to Handout 5. Work Aid 3C:

SAES-P-114, Chapter 6

For the content of SAES-P-114 (25 APR 94), Chapter 6, refer to Handout 4. Work Aid 3D: 1.


Collect the following data from the motor nameplate: horsepower (hp) voltage (kV) -

2.

Select the MPP relay functions and types from the charts and accompanying notes on pages 24 through 28 of SAES-P-114 (Handout 4).

3.

Verify that the selected (Work Aid 3A) criteria.

4.

Verify that the selected criteria.

5.

Using the relay symbols and device numbers sketch and label a motor protection scheme one-line diagram.


relays

meet

ANSI/IEEE

Standard

C37.96

relays meet 16-SAMSS-506 (Work Aid 3B, Handout 5)

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GLOSSARY air-magnetic br eaker

A type of medium voltage circuit breaker with its contacts in air. A powerful electromagnet built into the arc chutes aids in extinguishing the arc.

American National for Standard s Institute (ANSI)

An organization whose members approve various standards

ar c chute

A structure affording a confined space or passage way, usually lined with arc-resisting material, into or through which an arc is directed to be extinguished.

asymmetrical (cur r ent)

The combination of the symmetrical component and the direct-current component of the current.

cir cuit br eaker

A mechanical switching device, capable of making, carrying, and breaking currents under normal and abnormal circuit conditions.

combinat ion star ter

A complete motor starter consisting of a disconnect device, a magnetic contactor, and protective devices for short circuit and overload. All devices are assembled in a single enclosure.

contactor

A magnetic device that has sufficient capability to start and stop a motor under normal and overload conditions.

current-limiting (fuse)

A fuse that, when it is melted by a current within its specified current-limiting range, abruptly introduces a high arc voltage to reduce the current magnitude and duration. Note : The values specified in standards for the threshold ratio, peak let2 through current, and I t characteristic are used as the measures of current-limiting ability.

fra me size

A term that denotes the maximum continuous current rating in amperes of a circuit breaker.

horsepower (shaft) (hp)

The mechanical output (shaft) rating of a motor. One (1) hp equals 746 watts. See kilowatt (shaft).

induction motor

An alternating-current motor in which a primary winding on one member (usually the stator) is connected to the power source, and a polyphase secondary winding or a squirrel-cage


use in American industries.

44



secondary winding on the other member (usually the rotor) carries induced current.


45



instantaneous (relay)

A qualifying term applied to a relay indicating that no delay is purposely introduced in its action.

Institu te of Electr ical and Electr onics Engineers (IEEE )

A worldwide society of electrical and electronics engineers.

kilowatt (sha ft) (kw)

The mechanical output (shaft) rating of a motor. horsepower (hp).

locked-rotor energized (rotating machinery)

The condition existing when the circuits of a motor are

locked-rotor current

The steady-state current taken from the line with the rotor locked and with rated voltage (and rated frequency in the case of alternating-current motors) being applied to the motor.

locked-rotor indicating code letter

Code letters marked on a motor nameplate to show motor kVA per hp under locked-rotor conditions.

manual starter

A starter that is operated by hand. Starting and stopping is performed by devices that are operated manually.

maximum design voltage

The highest voltage at which the device is designed to operate.

medium voltage

Voltage levels greater than or equal to 1000 volts and less than 100,000 volts.

momentar y curr ent

The current flowing in a device at the major peak of the maximum cycle as determined from the envelope of the current wave.

motor contr ol center (MCC)

A metal enclosure that contains several combination starters.

motor p r otection package (MPP )

A solid-state, self-contained motor protection relay such as the Multilin 269 Plus or the Westinghouse IQ-1000II.

National Electr ic Code (NEC)

An electrical safety code developed and approved every three years by the National Fire Protection Association (NFPA).


See

but when the rotor is not turning.

46



National Electr ical Manufacturers Association (NEMA) and

A nonprofit trade association of manufacturers of electrical apparatus and supplies, whose members are engaged in standardization to facilitate understanding between users manufacturers of electrical products.

negative sequence that curr ent components the unbalanced

Three balanced current phasors that are equal in magnitude 0

are displaced from each other by 120 in phase, and that have phase sequence opposite to that of the original set of phasors.

nomina l system voltage

A nominal value assigned to designate a system of a given voltage class.

oil circuit breaker

A type of circuit breaker that uses mineral oil as an insulating and arc interrupting medium.

overload r elay

A device that is used to sense an overload on a motor circuit. The most common type uses a heater that heats a bi-metallic strip that operates a set of contacts.

pilot d evice

Control and indicating devices used in motor control circuits. These devices include indicating lights, switches and pushbuttons.

positive sequence that curr ent components

Three balanced current phasors that are equal in magnitude

relay

An electrically controlled, usually two-state, device that opens and closes electrical contacts to affect the operation of other devices in the same or another electric circuit.

r eplica temperatu re proportional relay

A thermal relay whose internal temperature rise is

residual (current)

The sum of the three-phase currents on a three-phase circuit. The current that flows in the neutral return circuit of three wye-connected current transformers is residual current.

rotor (rotating machinery)

The rotating member of a machine, with shaft.


0

are displaced from each other by 120 in phase, and that have the same phase sequence as the original unbalanced phasors.

over a range of values and durations of overloads to that of the protected apparatus.

47



service factor

A multiplier that, when applied to the rated power, indicates a permissible power loading that may be carried under the conditions specified for the service factor.

short-time rating

A rating for low voltage power circuit breakers and medium voltage breakers that describes the breakers ability to withstand a fault current for a period of time. If a breaker does not have an instantaneous trip unit, it must have a shorttime rating.

single-phasing (motor )

An abnormal operation of a polyphase machine when its supply is effectively single-phase.

starter (motor)

An electric controller for accelerating a motor from rest to normal speed and for stopping the motor.

starting cur r ent (rotating machinery)

The current drawn by the motor during the starting period. This current is a function of speed or slip.

stator (rotating machinery)

The portion that includes and supports the stationary active parts. The stator includes the stationary rtions of the magnetic circuit and the associated winding and leads. It may, depending on the design, include a frame or shell, winding supports, ventilation circuits, coolers, and temperature A base, if provided, is not ordinarily considered to be part of the stator.

detectors.

sulphur-hexafluoride cir cuit br eaker (SF 6)

A type of circuit breaker that uses sulfur-hexafloride gas as an insulating and arc extinguishing medium.

vacuum cir cuit breaker

A specific type of medium voltage circuit breaker that is designed to interrupt the arc inside a container that is under a vacuum. This vacuum limits ionization of gases and makes the circuit breaker lighter and more compact.

symmetr ical (curr ent)

A periodic alternating current in which points one-half a period apart are equal and have opposite signs.

synchronous speed

The speed of the rotation of the magnetic flux, produced by or linking the winding.

tempera tur e rise (rotating machinery) specified refer

A test undertaken to determine the temperature rise above ambient of one or more parts of a machine under operating conditions. Note: The specified conditions may to current, load, etc.


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electric motor 9

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