Power System S8 - Power System Security

30
June 7, 2022 GEC Thrissur 1 Power System Power System Security Security

Transcript of Power System S8 - Power System Security

Page 1: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 1

Power System Power System SecuritySecurity

Page 2: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 2

Electrical Power SystemElectrical Power SystemSystem which

Generates ………………..…generators Controls ……………….…transformers Transmits …………..transmission lines Consumes Electric Energy ……….load

Power system should be • Economic• Reliable • Secure

Page 3: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 3

Power System SecurityPower System Security

Degree of risk in power system’s ability to survive imminent disturbances (contingencies) without interruption to customer service

Depends on • System operating condition – reserve

capacity available (unused generators & no. of parallel lines)

• Contingent probability of disturbances

Page 4: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 4

Necessity for securityInsufficient degree of security leads to

• severe system failures• enormous economic cost• loss of life

To ensure system reliability1. Proper design with security as primary

consideration2. Monitored during operation to ensure

sufficient security margin exists at all times

Page 5: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 5

In small power system, security assessment can be conducted in an off line operating –planning environment in which performances were determined aso Steady state performance……..power flowo Dynamic performance………..time domain

simulation

System security involves:Practices designed to keep the system operating when component fails

Page 6: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 6

Generator taken off-line because of auxiliary equipment failure

Remaining units on the system can make up the deficito By maintaining proper amounts of spinning

reserveo without too low frequency dropo without load shedding

ExampleExample

Page 7: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 7

ExampleExample

Transmission line damaged by storm taken out by automatic relaying

Committing & dispatching generationo Transmission flows is maintainedo Remaining transmission lines can take the increased

loading o Lines still remain within limits

Page 8: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 8

BlackoutBlackout

• Typical feature of PS Security• Cascading failure of equipments leads

to entire system collapse

Power system equipment is designed to be operated within certain limits, most of them are protected by automatic devices & switched out of the system if limits are violated, may lead to cascading failures.

Page 9: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 9

ExampleExampleNew York City July

13,1977

2000 hr : Electrical load peaking around 6000 MW (half is being imported via overhead tie-lines & underground cables), system in Normal state.

2031 hr : Severe lightning hits transmission tower carrying two 345 kV lines causing permanent tripping of both.Network losses 1000 MW, remaining lines loaded, system in Alert state.

2055 hr : City generation raised by 550 MW to strain off tie-lines which are still below their thermal limits, still in Alert state.

Page 10: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 10

2056 hr : Second lightning stroke cripples a third 345 kV line, within fraction of a second a fourth line trips due to power transients, remaining lines are pushed above their thermal limits, system in Emergency state, every serviceable generator is running.

2119 hr : Thermal expansion of one 345 kV line, sag deep to cause short circuit via small tree, the line trips further overload to few remaining ties which one by one break open, system in Extremis state.

Page 11: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 11

2129 hr : Last tie trips, system with deficiency of 1700 MW resulting in rapid loss of frequency, under frequency relays automatically initiate preset load shedding of section upon section of the city, loss of frequency cannot be halted & generators are tripped automatically & manually to avoid catastrophic machine damage.

2136 hr : New York City goes totally back

Page 12: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 12

Examples of Major System Examples of Major System Disturbances/BlackoutsDisturbances/Blackouts

• July 2, 1996 disturbance of WSCC (Western North American Interconnected) System

• August 10, 1996 disturbance of WSCC system• 1998 power failure of Auckland business

districts, New Zealand• March 11, 1999 Brazil blackout• July 29, 1999 Taiwan disturbance• August 14, 2003 blackout of Northeast U.S.

and Ontario

Page 13: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 13

POWER SYSTEM OPERATING STATES

E,I

Normal

E,I

Restorative

E,I

Alert

E,I

Extremis

E,I

Emergency

RestartsLoad Pickup Preventive

control

Emergency control Resynchroni-

zation

Page 14: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 14

Preventive control:Start-up of stand-by units/ generation

rescheduling/change in interchange schedule

Emergency control:Lowering bus voltage, starting quick start

unitsLoad shedding, network rearrangement

Restorative state:Rescheduling of active & reactive power unit

restraintsResynchronization & gradual load pick-up

Page 15: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 15

Normal operation of power Normal operation of power systemsystem

Conditions to be fulfilled:1. Load demands are met & load flow equations are

satisfied2. Frequency is constant3. Bus voltage magnitude are within prescribed

limits (+6%)Power equipment are supposed to operate at a given rated voltage

4. No power system element is overloadedOverloading results in higher temperatures & component is likely to be damaged.

Page 16: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 16

If tried to transmit more power than static power limit synchronism is lost & transmission system will collapse.

For short lines (300 kms) thermal limit fixes the loading of the line.

For long lines static power limit becomes the limiting factor

Page 17: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 17

DEFINITIONSDEFINITIONS

Security: An instantaneous time-varying condition reflecting the robustness of the system relative to imminent disturbances.

Security Monitoring:The on-line measurement of system and environment variables that affect system security; provides base case conditions for analysis of the effects of contingencies.

Page 18: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 18

DEFINITIONSDEFINITIONS

Security Assessment:The evaluation of data, provided by security monitoring, to estimate the relative robustness (security level) of the system in its present state. (determination of whether the system is in the normal or Alert operating state).

Security Enhancement:Specific operations taken on-line to improve system robustness. Includes security control, corrective rescheduling, preventive actions etc.

Page 19: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 19

DEFINITIONSDEFINITIONSSecurity Control:It is an umbrella term comprising security monitoring, assessment and enhancement.

Emergency control:Control taken after one or more operating constraints have been violated in order to return the system to the normal state. May include or be referred to as remedial action, determined in advance relative to one or more possible contingencies for which security enhancement is not feasible.

Page 20: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 20

DEFINITIONSDEFINITIONS

Reliability :National Electric Reliability Council (NERC) defines reliability as comprising of two components, adequacy and security.

Adequacy is the ability to supply energy to satisfy load demand.

Security is the ability to withstand sudden disturbances.

Page 21: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 21

Factors affecting power system Factors affecting power system securitysecurity

Characteristics• Aging transmission

infrastructures

• Lack of new transmission facilities

Impact• Increased probability of

component failures and malfunction leading to system disturbances

• Overloading of transmission facilities leading to protection operation or contributing to phenomena such as voltage collapse

Page 22: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 22

Characteristics• Cutbacks in system

maintenance

• Increased dependence on controls and special protection systems

• Large numbers of small and distributed generators

Impact• Component failures and

disturbances such as flash overs to trees

• Increased probability of inadvertent/incorrect operation of protections

• Increased unpredictability of cascading events

• Increased difficulty in adequate system design due to uncertainty in generation plans

Page 23: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 23

Characteristics• Market-driven

transactions

• Increased dependence on communications and computer systems

Impact• Unpredictable power

flows and system usage leading to congestion and/or poor dynamic behavior, New forms of stability problems such as voltage and small signal stability

• Software/hardware failures may leave large portion of the system unobservable to operators, leading to inappropriate, or lack of, control actions during disturbances

Page 24: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 24

Characteristics• Limited integrated

system planning

• Trend toward interconnection

Impact• Insufficient/improper

generation and transmission resources

• Exposure to cascading disturbances brought on by events in neighboring systems

• New forms of stability problems such as small signal stability

Page 25: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 25

Characteristics• New technologies

such as advanced control systems, wind power, biomass, fuel cells, etc

• Aging and downsized workforces

Impact• Lack of operating

experience with technologies which may have unique dynamic characteristics

• Unpredictable behaviors during disturbances

• Lack of experienced personnel that may lead to the inability to deal appropriately with emergency conditions

Page 26: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 26

SECURITY ASSESSMENT SECURITY ASSESSMENT APPROACHAPPROACH

Two approaches• Direct - probabilistic view point

- analysis of a fixed set of contingencies

- classify the system as insecure if any member of the set would

result in transition to the emergency state

• Indirect - deterministic view point - tracks a variety of reserve

margins (MW,VAR reserves)- determined by off-line studies

Page 27: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 27

Important & Probable Contingencies considered:

o Outage of a circuito Outage of a unit o 3-phase or L-G fault

Security monitoring: (continuous activity)o Energy control centre/Load despatch centreo On-line identification of actual operating

condition of power system

Page 28: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 28

• Static state estimation (computer based technique) provides database for analysis – gives bus voltages at any instant from telemetered data & breaker status.

• Security analysis by security analyzer then finds out impact of contingencies using fast load flow method (FDLF)

• If system is found insecure, system engineer determines preventive control.

• If in emergency state due to cascading events corrective emergency controls are to be applied

Page 29: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 29

Methods of Enhancing SecurityMethods of Enhancing Security Impractical to achieve complete immunity to blackouts

– need to strike a balance between economy and security

Good design and operating practices could significantly minimize the occurrence and impact of widespread outages– Reliability criteria– On-line security assessment– Robust stability controls– Coordinated emergency controls– Real-time system system monitoring and control– Wide-spread use of distributed generation

Page 30: Power System S8 - Power System Security

April 10, 2023 GEC Thrissur 30

ReferencesReferences1. Allen J.Wood and Bruce F.Woolenberg, “Power

generation, operation and control”, John Wiley & sons Inc.

2. A. K.Mahalanabis, D.P.Kothari, S. I. Ahson,”Computer aided power system analysis and control”, Tata McGraw-Hill publishing company limited, New Delhi.

3. Olle l. Elgerd,”Electric Energy Systems theory An Introduction”, T M H Edition.

4. Kip Morison, Lei Wang, Prabha Kundur,” Power System Security Assessment”,IEEE power & energy magazine, sep/oct 2004, pp30-39.