real-time stability management under stressed conditions: voltage … novosel & vahid... ·...

© PG&E and Quanta Technology LLC Proprietary and Confidential

Damir Novosel, Quanta

Vahid Madani, PG&E

Mevludin Glavic, Quanta

Amsterdam, October 2012

Real-time Stability Management Under

Stressed Conditions: Voltage Stability

http://www.td-europe.eu/


Voltage Related Issues

Voltage Instability: Short- and Long- Term

Fault Induced Delayed Voltage Recovery (FIDVR)


Inability to maintain voltage so that power and voltage

are controllable

• High system loading,

followed by a fault,

line overload or

generators hitting

excitation limits

• Grid gets overloaded, more

reactive power is consumed

and voltages drop

• Followed by motors stalling

Real

Power

Voltage

Margin

Pre-contingency case Post-contingency

case

PV Curve

108% Peak

- in 3 years

100% Peak

Margin

108% Peak

3 Wide Area Events: Voltage Instability


Disturbances: Understanding What Happened

220

225

230

235

240

245

170 175 180 185 190 195 200 205 210 215 220

Vo

ltag

e (

kV

)

Power (MW)

Power - Voltage Curve

Alarm when measured “PV-curve” slope approaches a critical level Source: Dmitry Kosterev, BPA

4


Dynamic Reactive Power: Practical Measures

• Additional generation and transmission lines

• Switching on shunt capacitors and

switching off shunt reactors

• Exhaust generation reactive

resources, e.g. AVR set points

• Dynamic reactive power devices

• On-line tap changer control

• Fast unit start up

• Demand Side Management

• Wide Area Monitoring, Protection

and Control Control

Some voltage collapse examples:

• Brazil-Paraguay, 11/11/09

• Greece, 07/12/04

• NE US and Canada, 8/14/03

• WECC, 7/2/96

• Japan 7/23/87 and 8/22/70

• Sweden, 12/27/83

• France, 12/19/78


Voltage Stability Monitoring & Assessment

Simple voltage-only measurements

Dynamic, model-based simulation tools

• Voltage Stability Assessment (VSA) based on State Estimation

contingency analysis

• Tracking the relative distance from voltage instability continually in

real-time:

Distance to the nose of the PV curve

State Estimation based stability boundary

• Important to validate model correctness

Measurement-based indicators

• Identify composite low voltage violations simultaneously over a broad

area

• Monitor available reactive power levels (capacitor/reactor reserves,

tap-changers)

• Distance of the load’s apparent impedance to the Thevenin

impedance

x Under-

voltage

signal

#1

#2

r

Voltage

instability

region #1: inaccurate under-voltage detection

#2: under-voltage fails to detect

Source: ABB


Measurement-Based Voltage Instability Detection

Simple, real time, voltage instability margin

detection, e.g. VIP*

Better than voltage-only methods, but simpler

than any other method • Much faster than EMS/SE contingency analysis

and not model dependent

Enabling tracking both slow changes and

system dynamics using PMUs (10-120

frames/s)

New Real-time Voltage Instability Indicator

(RVII) • Major improvements in accuracy, numerical

stability, implementation variants, and ease of use

Maximum power transfer

|Zapp | = |ZThev |

Point of collapse

* K. Vu and D. Novosel, “Voltage Instability Predictor (VIP) - Method

and System for Performing Adaptive Control to Improve Voltage

Stability in Power Systems,” US Patent No. 6,219,591, April 2001.

Z Thev Z app

Thevenin Load E


New RVII Advantages 1 (2)

Model-free, fast real-time voltage instability detection method*, independent of state

estimation

Implementation in several variants: bus, load center, transmission line, transmission

corridor

• Calculates Q-margin & other indices

for proximity to voltage collapse

• Stability boundary calculated with

real-time PMU data refresh rate

Easily combined with other

methods and indices

• Reactive power monitoring

• Could initiate model-based

contingency analysis,

e.g. by alarming the operator

New Q-margin Loading margin


Ability to process data from different sources (PMUs, SCADA, simulation outputs (static

and dynamic))

• Takes immediate advantage of available PMUs

• Scales up well with increased number of PMUs

Excellent results from actual system tests on slowly changing system operating

conditions (load ramp) and in tracking system dynamics after large disturbances

Able to distinguish FIDVR from voltage

instability even if voltage is very low

Simple implementation in Control Center

tools local and/or IEDs for:

• Operator tools to increase

situational awareness

• Local automated actions

• Addition to SIPS

New RVII Advantages 2 (2)

Load center


Real-Life System Test Results

Alarm when measuring real-time Q margins

Realistic PQ-curve slope before and after the disturbance


Real-Time Simulation Results: PG&E Line switching – Two T-lines (Sequentially) Lines switched are from outside of the single line

The P-Q plane - Use of 5 PMUs for A-B Corridor

@ B

Reactive Margin Computation and Observability

- Time evolutions of margins for different PMUs

available


Comprehensive tests using real-life PMU and SCADA measurements and off-line

time-sequence simulation tools

Ability to detect instability even if voltage close to nominal

• Accurate results for load centers, transmission lines, and corridors

• Detection at highly-meshed high voltage systems (e.g. 500 kV) is more difficult

Results comparable to detailed, model-based off-line QV analysis; very

accurate closer to instability boundary

Discriminates between FIDVR and fast voltage instability

• FIDVR cases (no voltage collapse) are accurately detected despite the fact the

voltage is low for some time

No false alarms

Test Results


Deploy real-time application software based on RVII as part of

comprehensive WAMPAC system in control room

Design monitoring and control strategies based on RVII

Present and Future Activities

New

MEASUREMENT-BASED VOLTAGE STABILITY

Identification

RPM Methodology

Other Indices

Traditional

MODEL-BASED

VOLTAGE STABILITY Analysis

(EMS) SCADA

& Alarms WAMS

State Estimator

State Measurement

Other EMS Applications

New Applications

Small Signal Stability

Oscillation Monitoring

Transient & Voltage Stability

Stability Monitoring & Control

Island

Management

Island Detection,

Resynchronization,

& Blackstart

New Real-time Voltage Instability Indicator Solution

Alstom e-terravision

approach with new

RVII

real-time stability management under stressed conditions: voltage … novosel & vahid... ·...

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