April 21, 2023

1

IEEE Chapter Symposium

Possible Applications of PMUs for Detecting Angle Instability in Power

Systems

Nima Farkhondeh Jahromi Zongyu Liu

April 21, 2023 2

Outline

• Problem Formulation• Angle Stability Classification• First Proposed PMU-Based Algorithm• Second Proposed PMU-Based Algorithm• Conclusion and Remarks

April 21, 2023 3

Problem Formulation• Centralized Power plants

Small number of large scale gen. units • Traditional generator design/const. Not so high efficiency

• Popularity of renewable energy

Large number of small scale gen. units

• Newer Technology in generator design Higher efficiency

Power networks (due to power transfer capacity) get closer to their stability margin

Less tolerance

• Regulated electricity market • Deregulated electricity market

Various power flow directions

More congestions

Contradictory combination

Stability control (instability detection) is (will be) the key challenge

April 21, 2023 4

Angle Stability Classification

[Real-time] Angle Stability Assessment in future Power Systems

Axis 1[Real-time] large disturbance angle stability (transient stability) assessment

Axis 2:[Real-time] small disturbance

angle stability assessment

April 21, 2023 5

1st Proposed PMU-based Algorithm

Detection of transient instability based on the real-time COA

• Concept of Centre Of Angles (COA)

1

1

:

: .

N

i ii

COA N

ii

i

i

H

H

Internal machine rotor angle

H Inertia time cte

Difficult to directly measure

Difficult to access in real time. Number of units being dispatched can vary

April 21, 2023 6

1st Proposed PMU-based Algorithm (1)

• Substitution of the internal angle with the phase angle of the high side bus voltage

• Substitution of the inertia time constant with the high side active power injection

GTU U

Phase Measurement Unit (PMU)

high side injection massP MApproximation! (could be a source of

error)

April 21, 2023 7

1st Proposed PMU-based Algorithm (2)

• Illustration of substitution of the inertia time constant with the high side active power injection

April 21, 2023 8

1st Proposed PMU-based Algorithm (3)

• Real-time Centre of Inertia for area i

• Real-time Centre of Inertia for the whole system

1

1

( )

Ni ij j

jic iN

ij

j

P

g tP

1

1

( )

Ni ic

ic sysN

i

j

Pg t

P

April 21, 2023 9

1st Proposed PMU-based Algorithm (4)

Taking the appropriate remedial action(s) based on the value of

• If > “pre-specified benchmark” (continuously)

1) Area i (in a detailed analysis each gen. can be an area) is speeding up2) Suitable remedial action is to trip some generators

• If < “pre-specified benchmark” (continuously)

1) Area i (in a detailed analysis each gen. can be an area) is slowing down2) Suitable remedial action is load shedding

ic

ic

ic

April 21, 2023 10

1st Proposed PMU-based Algorithm (5)

Alarm mode based on comparing the real-time signals

• A real-time signal for area i

• A signal to be used as a reference: Critically-stable response

( ) ( ) ( )ic c i sys ig t g t f t

( ) ( ) ( )ic crt stab c crt stab i crt stab sys crt stab i crt stabg t g t f t

April 21, 2023 11

1st Proposed PMU-based Algorithm (6)

• Rescue-time definition

Permanent decline

April 21, 2023 12

1st Proposed PMU-based Algorithm (7)

• The method (the reference signal) is fault-location (and also fault-type) dependent.

• The method is dependent on the inertia time constant of the generators (Perhaps in future; lighter machines have higher output)

April 21, 2023 13

2nd Proposed PMU-based Algorithm • Principal idea is to have a real-time energy function (by means of PMUs) for a system divided into two clusters.

• The main question: Based on the real-time energy function, will the system split to more clusters or not?

Area 1M1ω1

Area 2M2ω2

New [temporary] steady-state

2 21 2

1 21 2

1 2

, 1 2

( )1 1( )

2 2

,

( , ) ( ) ( )

K eff eff eff

eff eff

K line line steady state

dE M M

dtM M

MM M

V E P P d

April 21, 2023 14

2nd Proposed PMU-based Algorithm (2)

April 21, 2023 15

Conclusion and Remarks

• It might be possible to perform an on-line transient instability detection and mitigation for a multi-area power systems

• By improving (generalizing) the proposed algorithm, it might be possible to avoid some blackouts happen due to islanding

• Designing the appropriate remedial action, is very much dependent on the system capabilities and is difficult to be generalized

April 21, 2023 16

Discussions

Suggestions

Questions

Criticisms

Ideas

Compliments