loadflow panel

ETAP Workshop Notes © 1996-2010 ETAP/Operation Technology, Inc.

Load Flow Analysis

© 1996-2010 ETAP/Operation Technology, Inc. – Workshop Notes: Load Flow Analysis Slide 2

System ConceptsSystem Concepts


jQP

IV

SS

IVS

LL

LN

*

13

*1

3

3

Lagging Power Factor Leading Power Factor

Inductive loads have lagging Power Factors. Capacitive loads have leading Power Factors.

Current and Voltage

Power in Balanced 3-Phase Systems


Leading Power Factor

Lagging Power Factor

ETAP displays lagging Power Factors as positive and leading Power Factors as negative. The Power Factor is displayed in percent.

jQ P

Leading & Lagging Power Factors

P - jQ P + jQ


B

2B

B

B

BB

MVA

)kV(Z

kV3

kVAI

B

actualpu

B

actualpu

Z

ZZ

I

II

B

actualpu

B

actualpu

S

SS

V

VV

B

2B

B

B

BB

S

VZ

V3

SI

ZI3V

VI3S 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)

ETAP 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.

3-Phase Per Unit System


Example 1: The diagram shows a simple radial system. ETAP 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

2B

1B kV

2N

1NkV

Transformer Turn Ratio: The transformer turn ratio is used by ETAP to determine the base voltage for different parts of the system. Different turn ratios are applied starting from the utility kV rating.

To determine base voltage use:

2

pu

pu

RX

1

RX

ZX

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

RX

xR pu

pu

1BkV

2BkV


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.

06478.0)14.12(1

)14.12(065.0X

2pu

005336.014.12

06478.0R pu

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.

)3538.1j1115.0(5

100

5.13

8.13)06478.0j1033.5(

S

S

V

VZZ

23

oB

nB

2

nB

oBo

punpu

38.135j15.11Z100Z% pu

0695.431.3

5.13

2N1N

kVV utility

B

165608.0100

)0695.4(

MVA

VZ

22B

B


8.603j38.60Z100Z% pu

)0382.6j6038.0(1656.0

)1j1.0(

Z

ZZ

B

actualpu

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.

The LF report generated by ETAP displays the following percent impedance values in 100 MVA base


Load Flow AnalysisLoad Flow Analysis


1. Accelerated Gauss-Seidel Method

• Low Requirements on initial values, but slow in speed.

2. Newton-Raphson Method

• Fast in speed, but high requirement on initial values.

• First order derivative is used to speed up calculation.

3. Fast-Decoupled Method

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

• Fast in speed, but low in solution precision.

• Better for radial systems and systems with long lines.

Load Flow Calculation Methods


kV

kVAFLA

kV

kVAFLA

EffPF

HP

EffPF

kWkVA

Rated

Rated

RatedRated

1

33

7457.0

Where PF and Efficiency are taken at 100 % loading conditions

kV

kVA1000I

)kV3(

kVA1000I

kVA

kWPF

)kVar()kW(kVA

1

3

22

Load Nameplate Data


TYPE OF LOADS:TYPE OF LOAD PHASOR PHASE

ANGLE

POWER ABSORBED BY THE LOAD

P Q

V

I

R VI Ф = 0° P > 0 Q = 0

V

I

L

V

I

Ф Ф = +90° P = 0 Q > 0

V

IC

V

I

Ф Ф = - 90° P = 0 Q < 0

R

L

R L

I

V

V

ΦV

I 0°<Φ<+90° P > 0 Q > 0


TYPE OF LOADS:TYPE OF LOAD PHASOR PHASE

ANGLE

POWER ABSORBED BY THE LOAD

P Q

-90°<Φ<0° P > 0 Q < 0

LI

V

-90°<=Φ<=+9

0°

P = 0 Q = 0

R

C

RC

V

V

I

IVΦ

C

Ic IL

Tuned to

Resonance

IL = Ic

PL = Pc

Energy travels

Back & forth

Between C&L


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.

• 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 Impedance Loads

© 1996-2008 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis Slide 15


• 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 ETAP by defining Load Duty Cycles used for Battery Sizing & Discharge purposes.

Constant Current Loads


Constant Current Loads


Load Type Summary


Exponential Load

Polynomial Load

Comprehensive Load

Generic Loads


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

Generator Operation Modes


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.


Isochronous Mode


Droop Mode


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

In ETAP Generators and Power Grids have four operating modes that are used in Load Flow calculations.


Generator Capability Curve


Field Winding Heating Limit

Armature Winding Heating Limit

Machine Rating (Power Factor Point)

Steady State Stability Curve

Maximum & Minimum Reactive Power


Field Winding Heating Limit Machine Rating

(Power Factor Point)

Steady State Stability Curve



Load Flow Loading Page

Generator/Power Grid Rating Page

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

Generation Categories


X

V)*COS(

X

*VVQ

)(*SINX

*VVP

X

V)(*COS

X

*VVj)(*SIN

X

*VV

jQPI*VS

22

2121

2121

22

2121

2121

222

111

VV

VV

Power Flow


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.

I

var536535.10X|I|

268j1000)68.2j10)(50j6.86(IV

268j1000)68.2j10(100IV

68.2j10I

5j

)50j6.86(0j100

X

VVI

22

*2

*1

21


2

1

0

1

Real Power FlowReactive Power Flow

Power Flow1

2

V E( )

Xsin

V E( )

Xcos

V2

X

0

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.

S


ETAP displays bus voltage values in two ways

•kV value

•Percent of Nominal Bus kV

%83.97100%

5.13

min

alNo

Calculated

Calculated

kV

kVV

kV 8.13min alNokV

%85.96100%

03.4

min

alNo

Calculated

Calculated

kV

kVV

kV 16.4min alNokV

For Bus4:

For Bus5:

Bus Voltage


Lump Load Negative Loading


Exercise Time

• Open LF-Example-A1

• Follow instructions in LF-Example-A1.PDF


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


Adjustments applied

•Individual

•Global

Temperature Correction

• Cable Resistance

• Transmission LineResistance

Load Flow Study Case Adjustment Page


Allowable Voltage DropNEC and ANSI C84.1


Load Flow Alerts


Bus Alerts Monitor Continuous Amps

Cable Monitor Continuous Amps

Reactor Monitor Continuous Amps

Line Monitor Line Ampacity

Transformer Monitor Maximum MVA Output

UPS/Panel Monitor Panel Continuous Amps

Generator Monitor Generator Rated MW

Equipment Overload Alerts


Protective Devices Monitored parameters % Condition reported

Low Voltage Circuit Breaker Continuous rated Current OverLoad

High Voltage Circuit Breaker Continuous rated Current OverLoad

Fuses Rated Current OverLoad

Contactors Continuous rated Current OverLoad

SPDT / SPST switches Continuous rated Current OverLoad

Protective Device Alerts

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

© 1996-2009 Operation Technology, Inc. – Workshop Notes: Load Flow Analysis Slide 44


Exercise Time

• Open LF-Example-B1

• Follow instructions in LF-Example-B1.PDF

Load Flow Example B1 Part 1

© 1996-2009 Operation Technology, Inc. - Workshop Notes: Load Flow AnalysisSlide 46


Load Flow Example B1 Part 2


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


Under-Voltage Example

• Create Under Voltage Condition

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

– Run LF

– Bus8 Turns Magenta (Under Voltage Condition)

• Method 1 - Change Xfmr

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

– Too Expensive and time consuming

• Method 2 - Shunt Capacitor

– Add Shunt Capacitor to Bus8

– 300 kvar 3 Banks

– Voltage is improved

• Method 3 - Change Tap

– Place LTC on Primary of T6

– Select Bus8 for Control Bus

– Select Update LTC in the Study Case

– Run LF

– Bus Voltage Comes within specified limits


Advanced LF TopicsAdvanced LF Topics

Voltage Control

Mvar Control

Load Flow Convergence

Load Flow vs. Optimal Power Flow


Mvar Control

• Vars from Utility

– Add Switch to CAP1

– Open Switch

– Run LF

• Method 1 – Generator

– Change Generator from Voltage Control to Mvar Control

– Set Mvar Design Setting to 5 Mvars

• Method 2 – Add Capacitor

– Close Switch

– Run Load Flow

– Var Contribution from the Utility reduces

• Method 3 – Xfmr MVA

– Change T1 Mva to 40 MVA

– Will notice decrease in the contribution from the Utility



Voltage Control

Mvar Control





• Negative Impedance

• Zero or Very Small Impedance

• Widely Different Branch Impedance Values

• Long Radial System Configurations

• Bad Bus Voltage Initial Values


Exercise Time





Voltage Control

Mvar Control




Review of Load Flow Solution

• Given generation, loading and control settings (Mwgen, Vgen, LTC, Capacitor Bank, …)

• Solve bus voltages and branch flows

• Check over/under voltage, device overloading conditions

• Reset controls and run Load Flow again

• Iterative process


Optimal Power Flow Approach

• Given control setting ranges

• Specify bus voltage and branch loading constraints

• Select optimization objectives (Min. P Losses, Min. Q Losses, …)

• Solve bus voltages, branch flows and control settings

• Direct solution


Control Variables

• Load Tap Changer (LTC) Settings• Generator AVR Settings• Generator MW Generation• Series or Shunt VAR Compensator Settings• Phase Shift Transformer Tap Positions• Switched Capacitor Settings• Load Shedding• DC Line Flow• …


Objective Functions

• Minimize Real Power Losses

- To minimize real power losses in the system

• Minimize Reactive Power Losses

- To minimize reactive power losses in the system

• Minimize Swing Bus Power

- To minimize real power generation at the swing bus(s)


Objective Functions

• Minimize Shunt var Devices

- To minimize var generation from available shunt var control devices

• Minimize Fuel Cost

- To minimize total generation fuel cost

• Minimize Series Compensation

- To minimize var generation from available series var control devices


Objective Functions

• Minimize Load Shedding

- To minimize load to be shed from the available bus load shed schedule

• Minimize Control Movement

- To minimize total number of controls

• Minimize Control Adjustment

- To minimize overall adjustment from all controls


Objective Functions

• Maximize Voltage Security Index

Where,

AllBuses

i

n

i

avgii

dV

VV2

,IndexSecurity Voltage

2min,max,

,ii

avgi

VVV

2min,max, ii

i

VVdV


• Maximize Line Flow Security Index

Where, is the line rating

• Flat Voltage Profile- Voltage Magnitude difference between all

buses is minimum

Objective Functions

sAllBranche

i

n

i

i

S

S2

IndexSecurity Flow Line

iSd


Other Constraints

• Bus Voltage Constraints

• Branch Flow Constraints

• Interface Flow Constraints

• …


Exercise Time




Comparison of LF and OPF


Panel SystemsPanel Systems


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 OLVDouble-Click to drop multiple panels


A panel branch circuit load can be modeled as an internal or external load

Advantages:1. Easier Data Entry2. Concise System Representation

Representation


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

Pin Assignment


Assumptions

• Vrated (internal load) = Vrated (Panel Voltage)

• Note that if a 1-Phase load is connected to a 3-Phase 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


Line-Line Connections

Load Connected Between Two Phases of a3-Phase System

A

B

C

Load

IBCIC = -IBC

A

B

C

LoadB

IB = IBC

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

PBC = VBC.IBC.cos θ

QBC = VBC.IBC.sin θ

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


3-Phase 4-Wire Panel3-Phase 3-Wire Panel1-Phase 3-Wire Panel1-Phase 2-Wire Panel

NEC SelectionA, 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, 4-wire delta connected system (midpoint grounded)

Info Page


Intelligent kV CalculationIf 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

Rating Page


Schedule Page

Circuit Numbers with Column Layout

Circuit Numbers with

Standard Layout


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


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)


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


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.


Feeder Tab


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.


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


Output Report


Panel Code Factors

Code demand load depends on Panel Code Factors

The first fourteen have fixed formats per NEC 1999

Code demand load calculation for internal loads are done for each types of load separately and then summed up

loadflow panel

Documents