03 - Load Flow and Panel

ETAP 5.0 Load Flow Analysis

Copyright 2003 Operation Technology, Inc.

System Concepts

Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 2

Power in Balanced 3-Phase Systems S = V I 1φ

S

3φ

=

*

LN

= 3× S

3 ×V

LL

1φ

I

*

= P + jQ Inductive loads have lagging Power Factors. Capacitive loads have leading Power Factors. Lagging Power Factor

Leading Power Factor


Current and Voltage

Slide 3

Leading & Lagging Power Factors PowerStation displays lagging Power Factors as positive and leading Power Factors as negative. The Power Factor is displayed in percent.

+

Q j

P

−

Q j

P


+

Q j

Lagging Power Factor

P

Leading Power Factor

Slide 4

3-Phase Per Unit System kVA B IB = 3kVB (kVB ) 2 ZB = MVA B

S = 3VI    V = 3ZI SB   = I B 3VB     2 V Z = B   B SB 

I actual I pu = IB

Vactual Vpu = VB

Zactual Z pu = ZB

Sactual Spu = SB


If you have two bases: Then you may calculate the other two by using the relationships enclosed in brackets. The different bases are: •IB (Base Current) •ZB (Base Impedance) •VB (Base Voltage) •SB (Base Power) PowerStation selects for LF: •100 MVA for SB which is fixed for the entire system. •The kV rating of reference point is used along with the transformer turn ratios are applied to determine the base voltage for different parts of the system.

Slide 5

Example 1: The diagram shows a simple radial system. PowerStation converts the branch impedance values to the correct base for Load Flow calculations. The LF reports show the branch impedance values in percent. The transformer turn ratio (N1/N2) is 3.31 and the X/R = 12.14 Transformer Turn Ratio: The transformer turn ratio is used by PowerStation to determine the base voltage for different parts of the system. Different turn ratios are applied starting from the utility kV rating.

kVB1

To determine base voltage use:

N1 kV = kVB2 N2 1 B

kVB2

Transformer T7: The following equations are used to find the impedance of transformer T7 in 100 MVA base.

X pu


X Z pu ×   R  = 2 X   1+   R 

R pu

x pu = X  R  Slide 6

X pu =

0.065(12.14) 1 + (12.14) 2

= 0.06478

R pu =

0.06478 = 0.005336 12.14

The transformer impedance must be converted to 100 MVA base and therefore the following relation must be used, where “n” stands for new and “o” stands for old. o n o  VB  Zpu = Zpu  n   VB 

2

2

 SnB   13.8   100   o  = (5.33×10−3 + j0.06478)  = (0.1115+ j1.3538)   13.5   5   SB 

% Z = 100 × Z pu = 11.15 + j135.38 Impedance Z1: The base voltage is determined by using the transformer turn ratio. The base impedance for Z1 is determined using the base voltage at Bus5 and the MVA base.

kVutility 13.5 = = 4.0695 VB =  N1  3.31  N2  Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

VB2 (4.0695) 2 = = 0.165608 ZB = MVA 100

Slide 7

The per-unit value of the impedance may be determined as soon as the base impedance is known. The per-unit value is multiplied by one hundred to obtain the percent impedance. This value will be the value displayed on the LF report.

Zactual (0.1 + j1) Zpu = = = (0.6038+ j6.0382) ZB 0.1656 % Z = 100 × Z pu = 60.38 + j603.8 The LF report generated by PowerStation displays the following percent impedance values in 100 MVA base


Slide 8

Load Flow Analysis


Slide 9

Load Flow Problem • Given – Load Power Consumption at all buses – Configuration – Power Production at each generator

• Basic Requirement – Power Flow in each line and transformer – Voltage Magnitude and Phase Angle at each bus


Slide 10

Load Flow Studies • Determine Steady State Operating Conditions – Voltage Profile – Power Flows – Current Flows – Power Factors – Transformer LTC Settings – Voltage Drops – Generator’s Mvar Demand (Qmax & Qmin) – Total Generation & Power Demand – Steady State Stability Limits – MW & Mvar Losses Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 11

Size & Determine System Equipment & Parameters • Cable / Feeder Capacity • Capacitor Size • Transformer MVA & kV Ratings (Turn Ratios) • Transformer Impedance & Tap Setting • Current Limiting Reactor Rating & Imp. • MCC & Switchgear Current Ratings • Generator Operating Mode (Isochronous / Droop) • Generator’s Mvar Demand • Transmission, Distribution & Utilization kV Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 12

Optimize Operating Conditions • Bus Voltages are Within Acceptable Limits • Voltages are Within Rated Insulation Limits of Equipment • Power & Current Flows Do Not Exceed the Maximum Ratings • System MW & Mvar Losses are Determined • Circulating Mvar Flows are Eliminated Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 13

Calculation Process • Non-Linear System • Calculated Iteratively – Assume the Load Voltage (Initial Conditions) – Calculate the Current I – Based on the Current, Calculate Voltage Drop Vd

Assume VR Calc: I = Sload / VR Calc: Vd = I * Z Re-Calc VR = Vs - Vd

– Re-Calculate Load Voltage VR – Re-use Load Voltage as initial condition until the results are within the specified precision. Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 14

Load Flow Calculation Methods 1.

Accelerated Gauss-Seidel Method •

2.

Low Requirements on initial values, but slow in speed.

3.

Fast-Decoupled Method •

Two sets of iteration equations: real power – voltage angle, reactive power – voltage magnitude.

Newton-Raphson Method •

Fast in speed, but high requirement on initial values.

•

Fast in speed, but low in solution precision.

•

First order derivative is used to speed up calculation.

•

Better for radial systems and systems with long lines.


Slide 15

Load Nameplate Data

kWRated HP × 0.7457 kVARated = = PF × Eff PF × Eff kVARated FLA3φ = 3 × kV kVARated FLA1φ = kV Where PF and Efficiency are taken at 100 % loading conditions


kVA = (kW ) 2 + (kVar ) 2 PF =

kW kVA

kVA ( 3 × kV) kVA I1φ = 1000 × kV

I3φ = 1000 ×

Slide 16

Constant Power Loads


•

In Load Flow calculations induction, synchronous and lump loads are treated as constant power loads.

•

The power output remains constant even if the input voltage changes (constant kVA).

•

The lump load power output behaves like a constant power load for the specified % motor load.

Slide 17

Constant Impedance Loads • In Load Flow calculations Static Loads, Lump Loads (% static), Capacitors and Harmonic Filters and Motor Operated Valves are treated as Constant Impedance Loads. • The Input Power increases proportionally to the square of the Input Voltage. • In Load Flow Harmonic Filters may be used as capacitive loads for Power Factor Correction. • MOVs are modeled as constant impedance loads because of their operating characteristics.

Constant Current Loads • The current remains constant even if the voltage changes. • DC Constant current loads are used to test Battery discharge capacity. • AC constant current loads may be used to test UPS systems performance. • DC Constant Current Loads may be defined in PowerStation by defining Load Duty Cycles used for Battery Sizing & Discharge purposes.


Slide 19

Constant Current Loads


Slide 20

Generic Loads

Exponential Load Polynomial Load Comprehensive Load


Slide 21

Generator Operation Modes

Feedback Voltage •AVR: Automatic Voltage Regulation •Fixed: Fixed Excitation (no AVR action)


Slide 22

Governor Operating Modes • Isochronous: This governor setting allows the generator’s power output to be adjusted based on the system demand. • Droop: This governor setting allows the generator to be Base Loaded, meaning that the MW output is fixed.


Slide 23

Isochronous Mode


Slide 24

Droop Mode


Slide 25

Droop Mode


Slide 26

Droop Mode


Slide 27

Adjusting Steam Flow


Slide 28

Adjusting Excitation


Slide 29

In PowerStation Generators and Power Grids have four operating modes that are used in Load Flow calculations. Swing Mode •Governor is operating in Isochronous mode •Automatic Voltage Regulator Voltage Control •Governor is operating in Droop Mode •Automatic Voltage Regulator Mvar Control •Governor is operating in Droop Mode •Fixed Field Excitation (no AVR action) PF Control •Governor is operating in Droop Mode •AVR Adjusts to Power Factor Setting Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 30

• In the Swing Mode, the voltage is kept fixed. P & Q can vary based on the Power Demand • In the Voltage Control Mode, P & V are kept fixed while Q & θ are varied • In the Mvar Control Mode, P and Q are kept fixed while V & θ are varied

• If in Voltage Control Mode, the limits of P & Q are reached, the model is changed to a Load Model (P & Q are kept fixed)


Slide 31

Generator Capability Curve


Slide 32



Slide 33



Slide 34

Maximum & Minimum Reactive Power Machine Rating (Power Factor Point) Field Winding Heating Limit

Steady State Stability Curve Armature Winding Heating Limit


Slide 35

Generator Capability Curve Field Winding Heating Limit

Machine Rating (Power Factor Point)

Steady State Stability Curve


Slide 36

Generation Categories Generator/Power Grid Rating Page Load Flow Loading Page

10 Different Generation Categories for Every Generator or Power Grid in the System


Slide 37

Power Flow V1 = V1 ∠δ 1    V 2 = V2 ∠δ 2  S = V* I = P + jQ V *V = 1 2 *SIN (δ 1 − δ 2 ) + X

2  V1*V 2 V2  j *COS (δ 1 − δ 2 ) −  X   X

V1*V 2 P= *SIN (δ 1 − δ 2 ) X 2 V1*V 2 V2 Q= *COS( δ 1 − δ 2 ) − X X Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 38

Example: Two voltage sources designated as V1 and V2 are connected as shown. If V1= 100 /0° , V2 = 100 /30° and X = 0 +j5 determine the power flow in the system.

V1 − V 2 100 + j0 − (86.6 + j50) = X j5 I = −10 − j2.68 I=

I

V1I* = 100(−10 + j2.68) = −1000 + j268 V2 I* = (86.6 + j50)(−10 + j2.68) = −1000 − j268 | I |2 X = 10.352 × 5 = 536 var


Slide 39

The following graph shows the power flow from Machine M2. This machine behaves as a generator supplying real power and absorbing reactive power from machine M1. 1

( V ⋅E) X ( V ⋅E) X

( ) ( )

1

S

0

⋅sin δ ∆

⋅cos δ ∆ −

Power Flow

2

V

X 1

−2 2

0

Real Power Flow Reactive Power Flow


δ∆

π

Slide 40

Bus Voltage PowerStation displays bus voltage values in two ways •kV value •Percent of Nominal Bus kV

For Bus4:

kVCalculated = 13.5 kVNo min al = 13.8 kVCalculated × 100 = 97.83% V% = kVNo min al For Bus5:

kVCalculated = 4.03 V% =


kVNo min al = 4.16

kVCalculated × 100 = 96.85% kVNo min al Slide 41


Slide 42

Lump Load Negative Loading


Slide 43

Load Flow Adjustments • Transformer Impedance – Adjust transformer impedance based on possible length variation tolerance

• Reactor Impedance – Adjust reactor impedance based on specified tolerance

• Overload Heater – Adjust Overload Heater resistance based on specified tolerance

• Transmission Line Length – Adjust Transmission Line Impedance based on possible length variation tolerance

• Cable Length – Adjust Cable Impedance based on possible length variation tolerance Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 44

Load Flow Study Case Adjustment Page Adjustments applied •Individual •Global

Temperature Correction • Cable Resistance • Transmission Line Resistance


Slide 45

Allowable Voltage Drop NEC and ANSI C84.1


Slide 46

Load Flow Example 1 Part 1

Transformers T1 = 30 MVA T2 = 15 MVA T3 = 5 MVA T4 = 3 MVA Select typical %Z & X/R Cable1 ICEA 15kV 3/C CU, 100% Size= 250 Length= 400 ft Cable2 KERITE 5kV 3/C CU, 100% Size= 500 Length= 300 ft

Power Grid 1000 MVAsc X/R = 22 Gen1 10 MW Voltage Control Design: %Pf = 85 MW = 5 Max Q = 4 Min Q = -1

Impedance Z1 13.8 kV 100MVA % Z = 0.01+j1

Load Flow Example 1 Part 2

Transformer T5 = 5 MVA Select typical %Z & X/R

Cable3 ICEA 5kV 3/C CU, 133% Size= 500 Length= 100 ft


Slide 48

Load Flow Alerts


Slide 49

Equipment Overload Alerts Bus Alerts

Monitor Continuous Amps

Cable


Reactor


Line

Monitor Line Ampacity

Transformer

Monitor Maximum MVA Output

DC Link

DC Link Loading Capability (Idc, Max. MVA)

Panel

Monitor Panel Continuous Amps

Generator

Monitor Generator Rated MW


Slide 50

Protective Device Alerts Protective Devices

Monitored parameters %

Condition reported

Low Voltage Circuit Breaker

Continuous rated Current

OverLoad

High Voltage Circuit Breaker


OverLoad

Fuses

Rated Current

OverLoad

Contactors


OverLoad

SPDT / SPST switches


OverLoad


Slide 51

If the Auto Display feature is active, the Alert View Window will appear as soon as the Load Flow calculation has finished.

Advanced LF Topics Load Flow Convergence Voltage Control Mvar Control


Slide 53

Load Flow Convergence • Negative Impedance • Zero or Very Small Impedance • Widely Different Branch Impedance Values • Long Radial System Configurations • Bad Bus Voltage Initial Values


Slide 54

Voltage Control • Under/Over Voltage Conditions must be fixed for proper equipment operation and insulation ratings be met. • Methods of Improving Voltage Conditions: – Transformer Replacement – Capacitor Addition – Transformer Tap Adjustment Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 55

Under-Voltage Example • Create Under Voltage Condition

• Method 2 - Shunt Capacitor

– Change Syn2 Quantity to 6. (Info Page, Quantity Field)

– Add Shunt Capacitor to Bus8

– Run LF

– Voltage is improved

– Bus8 Turns Magenta (Under Voltage Condition)

• Method 1 - Change Xfmr

– 300 kvar 3 Banks

• Method 3 - Change Tap – Place LTC on Primary of T6 – Select Bus8 for Control Bus

– Change T4 from 3 MVA to 8 MVA, will notice slight improvement on the Bus8 kV

– Select Update LTC in the Study Case

– Too Expensive and time consuming

– Bus Voltage Comes within specified limits


– Run LF

Slide 56

Mvar Control • Vars from Utility

• Method 2 – Add Capacitor

– Add Switch to CAP1

– Close Switch

– Open Switch

– Run Load Flow

– Run LF

– Var Contribution from the Utility reduces

• Method 1 – Generator – Change Generator from Voltage Control to Mvar Control – Set Mvar Design Setting to 5 Mvars


• Method 3 – Xfmr MVA – Change T1 Mva to 40 MVA – Will notice decrease in the contribution from the Utility

Slide 57

Panel Systems


Slide 58

Panel Boards • They are a collection of branch circuits feeding system loads • Panel System is used for representing power and lighting panels in electrical systems

Click to drop once on OLV Double-Click to drop multiple panels


Slide 59

Representation A panel branch circuit load can be modeled as an internal or external load Advantages: 1. Easier Data Entry 2. Concise System Representation


Slide 60

Pin Assignment Pin 0 is the top pin of the panel ETAP allows up to 24 external load connections


Slide 61

Assumptions • Vrated (internal load) = Vrated (Panel Voltage) • Note that if a 1-Phase load is connected to a 3Phase panel circuit, the rated voltage of the panel circuit is (1/√3) times the rated panel voltage • The voltage of L1 or L2 phase in a 1-Phase 3-Wire panel is (1/2) times the rated voltage of the panel • There are no losses in the feeders connecting a load to the panel • Static loads are calculated based on their rated voltage Copyright 2004 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis

Slide 62

Line-Line Connections Load Connected Between Two Phases of a 3-Phase System A

A

B C

B C IB = IBC

IBC Load

IC = -IBC

LoadB

Angle by which load current IBC lags the load voltage = θ° Therefore, for load connected between phases B and C:

For load connected to phase B

SBC = VBC.IBC PBC = VBC.IBC.cos θ QBC = VBC.IBC.sin θ

SB = VB.IB PB = VB.IB.cos (θ - 30) QB = VB.IB.sin (θ - 30) And, for load connected to phase C SC = VC.IC PC = VC.IC.cos (θ + 30) QC = VC.IC.sin (θ + 30)


Slide 63

Info Page

NEC Selection A, B, C from top to bottom or left to right from the front of the panel Phase B shall be the highest voltage (LG) on a 3-phase, 4wire delta connected system (midpoint grounded)

3-Phase 4-Wire Panel 3-Phase 3-Wire Panel 1-Phase 3-Wire Panel 1-Phase 2-Wire Panel


Slide 64

Rating Page Intelligent kV Calculation If a 1-Phase panel is connected to a 3-Phase bus having a nominal voltage equal to 0.48 kV, the default rated kV of the panel is set to (0.48/1.732 =) 0.277 kV For IEC, Enclosure Type is Ingress Protection (IPxy), where IP00 means no protection or shielding on the panel

Select ANSI or IEC Breakers or Fuses from Main Device Library


Slide 65

Schedule Page

Circuit Numbers with Standard Layout

Circuit Numbers with Column Layout


Slide 66

Description Tab First 14 load items in the list are based on NEC 1999 Last 10 load types in the Panel Code Factor Table are user-defined Load Type is used to determine the Code Factors used in calculating the total panel load External loads are classified as motor load or static load according to the element type For External links the load status is determined from the connected load’s demand factor status


Slide 67

Rating Tab

Enter per phase VA, W, or Amperes for this load. For example, if total Watts for a 3-phase load are 1200, enter W as 400 (=1200/3)


Slide 68

Loading Tab For internal loads, enter the % loading for the selected loading category For both internal and external loads, Amp values are calculated based on terminal bus nominal kV


Slide 69

Protective Device Tab Library Quick Pick LV Circuit Breaker (Molded Case, with Thermal Magnetic Trip Device) or Library Quick Pick – Fuse will appear depending on the Type of protective device selected.


Slide 70

Feeder Tab


Slide 71

Action Buttons Copy the content of the selected row to clipboard. Circuit number, Phase, Pole, Load Name, Link and State are not copied.

Paste the entire content (of the copied row) in the selected row. This will work when the Link Type is other than space or unusable, and only for fields which are not blocked.

Blank out the contents of the entire selected row.


Slide 72

Summary Page Continuous Load – Per Phase and Total Non-Continuous Load – Per Phase and Total Connected Load – Per Phase and Total (Continuous + Non-Continuous Load)

Code Demand – Per Phase and Total


Slide 73

Output Report


Slide 74

Panel Code Factors The first fourteen have fixed formats per NEC 1999 Code demand load depends on Panel Code Factors Code demand load calculation for internal loads are done for each types of load separately and then summed up


Slide 75

03 - Load Flow and Panel

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