Cascading simulation techniques in Europe: the PRACTICE

experienceE. Ciapessoni, D. Cirio, A. Pitto

2013 IEEE PES General MeetingVancouver, British Columbia, Canada

July 21-25, 2013

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PRACTICE• Tool for probabilistic assessment of operational risk operational risk in

power systems• Based on risk concept

– Combination of probability and severity of a disturbance (contingency)

• Assessing cascading evolution …– important task

• Cascading engine has two operation modes:– Single path– Multi path

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Cascading engine: general features• Robust power flow program Robust power flow program enhanced with steady-

state models of:– frequency regulation (5% default droop) – main protection and defence systems,

• e.g. line and transformer overcurrent, minimum impedance for lines, minimum and maximum voltage for generators and loads, under-frequency load-shedding (pumps and loads).

• Able to assess an “impact” for the contingencies which cause load-flow divergence load-flow divergence – adopting suitable load reduction techniques

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“Single path” mode

• Uncertainty only related to initiating event• Check violations of currents/voltages • One element tripped at a time

– The element with highest violation

• Does not take into account the uncertainty on protection systems response

• Fast algorithm

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“Multi-path” mode• Considers also uncertainty in protection systems response• Probabilistic models are defined for:

– Hidden failures Hidden failures (HF) of protections exposed by the initial contingency or by overloads

– Correct operation of the overcurrent relaysovercurrent relays

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Benchmark for cascading engine• Italian EHV transmission grid with

foreign equivalents:– 1400 electrical nodes– 1000 lines– 700 transformers– 300 generators

• Peak and off peak load early 2000’s• Goal: comparing time sequence of

events given by T-D simulator with the sequence of trippings by the single path cascading

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Benchmarking

• Dynamic model:– Prime movers & AVRs– Automatic load shedding– Overcurrent protections

for branches (120% Imax)– No secondary frequency

control– Standard model for loads

(50% dyn 50% static)

• Quasi static model (in PRACTICE):– Primary control– Automatic load shedding for

power deficits– Overcurrent protections for

branches (set to 120% Imax)– Constant power model for

loads– Under/over voltage for

loads and generators

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Benchmarking results (I)8

Loss of an important 400 kV line in the North East

Time domain simulator[tripping time, s] – line ID

Quasi static approachTripping cause / line ID

28 - VV2196-UDNV21 Overloading / BUIV211-UDNV21142 - OV2215-LNZO21 Overloading / SOVV212-LNZO211

Tripping of BUIV-UDNV 220 kV line

Tripping of SOVV-LNZO 220 kV line at 42 s

eliminates violation on this line!

Benchmarking results (I)9

Loss of an important 400 kV line in the North East

Time domain simulator[tripping time, s] – line ID

Quasi static approachTripping cause / line ID

28 - VV2196-UDNV21 Overloading / BUIV211-UDNV21142 - OV2215-LNZO21 Overloading / SOVV212-LNZO211

Tripping of BUIV-UDNV 220 kV line

Tripping of SOVV-LNZO 220 kV line at 42 s

eliminates violation on this line!

Mutual relief mechanisms taken

into account in quasi static approach

Benchmarking results (II)

Three most probable cascading paths identified by multi-path cascading engine (future time interval=5 minutes)

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Cascading Path Probability of occurrence [over future 5-min interval]

(1) BUIV211-UDNV211 --> SOVV212-LNZO211 8.610-7

(2) No cascading 7.910-7

(3) BUIV211-UDNV211 3.910-7

Loss of the first line BUIV211-UDNV211 implies a very high overloading (140%) on branch SOVV212-LNZO211

Prob. of tripping of both lines (path # 1) >> prob. of tripping only of the first line (path # 3)

Benchmarking results (III)11

Quasi static tool Time domain simulator

Step nr. Tripped branch Due to ... Time [s] Tripped branch

1 Soverzene-Vellai overload 51.5 Soverzene-Vellai

2Musignano-Lavorgo

overload 55.0Musignano-

Lavorgo3 Bulciago-Soazza overload 62.5 Bulciago-Soazza

4 Sondrio-Cislago overload 64.0 Sondrio-Cislago

5Baggio-Castelnuovo

overload67-68

Many EHV lines, due to instability

6 Loadflow diverges

Cascading trippings well caught by PRACTICE

Loss of a large thermal power plant

Benchmarking results (III)12

Loss of a large thermal power plant

Cascading trippings well caught by PRACTICE

(angle, voltage) instability mechanisms

Quasi static tool Time domain simulator

Step nr. Tripped branch Due to ... Time [s] Tripped branch

1 Soverzene-Vellai overload 51.5 Soverzene-Vellai

2Musignano-Lavorgo

overload 55.0Musignano-

Lavorgo3 Bulciago-Soazza overload 62.5 Bulciago-Soazza

4 Sondrio-Cislago overload 64.0 Sondrio-Cislago

5Baggio-Castelnuovo

overload67-68

Many EHV lines, due to instability

6 Loadflow diverges

Remarks• Proposed a benchmark Proposed a benchmark for cascading tools

– A model of the Italian EHV transmission system with foreign equivalents (early 2000’s)

• Quasi static «single path» cascading engine cascading engine tested against time domain simulator– Very good matching with the sequence of events by time

domain simulation at least in the early stages of cascading

• Multi-path cascading Multi-path cascading engine provides probability of different sequences of trippings– Taking into account hidden failures and uncertainties on

protection relay settings

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Contact: Dr. Andrea Pitto, PhD e-mail: andrea.pitto@rse-web.it