reactive power -sscet- 1024- final

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Reactive Power Management and VoltageStability

Sharma Kolluri, IEEE Fellow

Manager of Transmission PlanningEntergy Services Inc

Presentation at2012 Southeast Symposium on Contemporary Engineering

Topics (SSCET)

October 26, 2012

New Orleans, Louisiana


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Outline

Background/Introduction

VAR Basics

Voltage Stability

FIDVR

Technology

Summary

.


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Recommendation#23

Strengthen Reactive Power andControl Practices in all NERC Regions

Reactive power problem was a

significant factor in the August 14outage, and they were alsoimportant elements in the several ofthe earlier outages

-Quote form the outage report


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Reactive Power Basics


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Laws of Reactive Physics

Complex Power called Volt Amperes (VA) is comprised

of resistive current IR and reactive current IQ times the

voltage.

VA = VIT* = V (IR jIQ) = P + jQ

Power Factor (PF) = Cosine of angle between P and

VA

P = VA times PF

System Losses

Ploss = IT2 R (Watts)

Qloss = IT2 X (VARs)

VA

P

Q

North American Electric Reliability Corporation


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Reactive Physics VAR loss

Every component with reactance, X: VAR loss = IT2 X

Z is comprised of resistance R and reactance X

On 138kV lines, X = 2 to 5 times larger than R.

One 230kV lines, X = 5 to 10 times larger than R.

On 500kV lines, X = 25 times larger than R.

R decreases when conductor diameter increases. X increases

as the required geometry of phase to phase spacing increases.

VAR loss

Increases in proportion to the square of the total current.

Is approximately 2 to 25 times larger than Watt loss.

North American Electric Reliability Corporation


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Transmission Line Real and Reactive

Power Losses vs. Line Loading

Source: B. Kirby and E. Hirst 1997,Ancillary-Service Details: Voltage Control,

ORNL/CON-453, Oak Ridge National Laboratory, Oak Ridge, Tenn., December 1997.


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Static and Dynamic VAR Support

Static Reactive Power Devices Cannot quickly change the reactive power level as long as the

voltage level remains constant.

Reactive power production level drops when the voltage leveldrops.

Examples include capacitors and inductors.

Dynamic Reactive Power Devices Can quickly change the MVAR level independent of the voltage

level.

Reactive power production level increases when the voltagelevel drops.

Examples include static VAR compensators (SVC), synchronouscondensers, and generators.


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Reactive Power Management

Effectively balancing capacitive and inductive components of

a power system to provide sufficient voltage support.

Essential for reliable power system operation.

Prevention of voltage collapse

Benefits

Improves efficiency of power delivery.

Improves utilization of transmission assets.

Reduces congestion and increases power transfer capability.

Enhances grid security.


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Reactive Power for Voltage

SupportReactive

LoadsVARs flow from High voltage

to Low voltage; import of

VARs indicate reactive

power deficit


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Voltage Stability


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What is Voltage Instability/Collapse?

A power system undergoes voltage

collapse if post-disturbance voltages are

below acceptable limits

voltage collapse may be due to voltage or angularinstability

Main factor causing voltage instability is the

inability of the power systems to maintaina proper balance of reactive power and

voltage control


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Voltage Instability/Collapse

The driving force for voltage instability isusually the load.

The possible outcome of voltage instability:

loss of loads

loss of integrity of the power system

Voltage stability timeframe:

transient voltage instability: 0 to 10 secs

long-term voltage stability: 1 10 mins


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Key Concerns

Minimize

motortripping

Limit UVLSactivationVoltage

(pu)


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P-V Curve

Q V C


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Q-V Curve

200

Q-V Curve with Detailed Load Model

Peak Load with Fixed Taps

-80

-60

-40

-20

0

20

40

60

80

100

120

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Voltage (p.u.)

Mvars

Base Case

Contingency


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Voltages at Goslin 138kV Station

Time (seconds)

Voltage(volts)


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Common Solutions for Voltage Instability

Install/Operate Shunt Capacitor/Reactor Banks

Add dynamic Shunt Compensation in the form of

SVC/STATCOM/DVAR to mitigate transient voltage dips

Add Series Compensation on transmission lines in theproblem area

Construct transmission facilities

Coordinate Voltage Schedules/Reactive Power Flows

Implement UVLS Scheme


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Fault Induced Delayed VoltageRecovery (FIDVR)


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Fault Induced Delayed Voltage

Recovery (FIDVR)

What is it? After a fault has cleared, the voltage stays at low levels

(below 80%) for several seconds

Results in dropping load / generation or fast voltage

collapse 4 key factors drive FIDVR:

Fault Duration

Fault Location

High load level with high induction motor

load penetration

Unfavorable Generation Pattern


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A Near Fast Voltage

Collapse in Phoenix in

1995

North American Electric

Reliability Council, SystemDisturbances, Review of

Selected 1995 Electric System

Disturbances in North

America, March 1996.


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Technology

for Addressing Reactive

Power/Voltage Stability

Problems


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Porter SVC


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Porter Static Var Compensator (SVC)

Maintains

system

voltage by

continuously

varying VAR

output to meetsystem

demands.

Controls

capacitor

banks on the

transmissionsystem to

match reactive

power output

to the load

requirements.


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Series Capacitor

Dayton Bulk 230kV Station

The Capacitor

offsets

reactance in

the line,

making it

appear to the

system to be

half of its

actual length.

Power flows

are redirected

over this largerline, unloading

parallel lines

and increasing

transfer

capability.

Static compensator


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Static compensator

(STATCOM)

Voltage source converter

device

Alternating voltage source

behind a coupling reactance

Can be operated at its fulloutput current even at very low

voltages

Depending upon

manufacturer's design,STATCOMs may have

increased transient rating both

in inductive as well as

capacitive mode of operation

Transformer

DC-AC switching converter

I

X

System bus

Cs

Vdc

V

E

Schematic diagram of STATCOM


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Natchez DVAR


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D-VAR

MT

Metro138 kV

34.5 kV

FDR

34.5 kV25.2

MVAR

480 V34.5 kV


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Summary

The increasing need to operate the transmission

system at its maximum safe transfer limit has

become a primary concern at most utilities

Reactive power supply or VAR management isan important ingredient in maintaining healthy

power system voltages and facilitating power

transfers

Inadequate reactive power supply was a majorfactor in most of the recent blackouts


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Questions?

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