Power Grids

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Power Grids

Normal Operation and Failures

A.M.Kulkarni

IIT Bombay

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My talk…

 Power System

- Structure, Operation and Control

 An example of a Power Grid: India

 An example of a Grid Failure

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"

Except for a few islands and some small isolated systems, the entire electric grid is really one big circuit.

The humble wall outlet is actually a gateway to one of the largest and most complex objects ever built. The grid encompasses

billions of individual components, tens of millions of miles of wire and thousands of individual generators

"

Thomas Overbye,

Re-engineering the Electric Grid, American Scientist, 2000, Vol. 88, Iss. 3.

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Bulk Power Systems

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Common Doubts for a non-specialist

 Why interconnect to form large grids ?

 Why AC and not DC ?

Role of DC in modern power grids

 Why 50 Hz / 60 Hz ?

 Why Three phase ?

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Synchronous Links

 Synchronous Grid:

 Synchronous machines interconnected with AC lines

DC DC

Transmission Lines

Induction Generators ?

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Synchronous Links

 Synchronous Grid:

 Synchronous machines interconnected with AC lines

 Power Flow in AC lines - function of Voltage phase Angle Difference (determined by the relative rotor position in synchronous

machines)

 Frequency throughout grid is the same in

steady state (why ?)

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Synchronous Links

 Synchronous Grid:

 Synchronous machines interconnected with AC lines

DC DC

Transmission Lines

Induction Generators ?

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Dynamics in a Synchronous Grid

Relative motion (swing)

Centre of Inertia motion

( depends on sum of forces : Fg1+Fg2+Fg3-FL1-FL2-FL3 )

Fg1 Fg3 Fg2

FL3 FL2

FL1

Relative motion (swing)

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Dynamics in a Synchronous Grid

Sudden Load Throw Off

Stable Common and Relative Motion

Sudden Generation Trip

Stable Common and Relative Motion

Large Disturbance Angular Instability : Loss of Synchronism

Small Disturbance Angular Instability : Growing Oscillations

(triggered by any disturbance: big or small)

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Effect of Lack of Synchronism in AC ties

Not Acceptable ! Distance Relays trip Uncontrolled

System Separation

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Asynchronous Links

 Asynchronous Interconnects

 HVDC links: Power flows not a function of Phase Angle Difference

 Frequencies of connected regions could

“happily” be different

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Synchronous Links

Tie Line 2 (AC)

(AC)

(P^GEN1-P^LOAD1) - (P^GEN2-P^LOAD2) = P1 + P2

Frequency of Area 1 and 2 is the same (in steady state)

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Asynchronous Link

Frequency of Area 1 and 2 need not be the same

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Synchronous or Asynchronous ?

(PGEN1-PLOAD1) - (PGEN2-PLOAD2) = P1 + P2

Frequency of Area 1 and 2 is the same (in steady state)

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Issues in Interconnected Systems

 Ownership

 Monitoring & Control Hierarchy

 Cooperation and Coordination is

necessary!

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Subsystems : Generator Control

ROTOR MECHANICAL

EQUATIONS

MACHINE WINDING EQUATIONS

GENERATOR

FIELD VOLTAGE

MECH POWER



V



EXCITER TURBINE

+ BOILER

Valve / Gate control

Power Electronic

Control

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Static Excitation: Voltage Control

DC AC

Controlled Rectifier

Main Generator

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AVR

ROTOR (MECHANICAL

EQUATIONS)

GENERATOR

FIELD VOLTAGE

MECH POWER



V



EXCITER TURBINE

and/or BOILER

Gate/ Valve (mech) Control by governor

Power Electronic

Valve Control

AVR

NETWORK

Terminal Voltage of Generator

Reference Voltage

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Frequency Control

 Frequency Depends on Cumulative Load- Gen Balance in a Synchronous Grid

 Load is Weakly Frequency Dependent

 Generation-Load Balance has to be Maintained.

 Generation Control or Load Shedding

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Subsystems : Generator Control

ROTOR MECHANICAL

EQUATIONS

GENERATOR

FIELD VOLTAGE

MECH POWER



V



EXCITER TURBINE

+ BOILER

Valve / Gate control

Power Electronic

Control

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Primary Control

Speed Control (Governor)

Load Sharing by different generators: Droop Control

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Power Flow (Synchronous Grids)

500

200 400

300

Line Flows Depend on Line Parameters 100

200 100

300

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Power Flow (Synchronous Grids)

600

400 200

800

500

300 100

300

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Power Flow Control in AC lines

Modulation also possible with these devices

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Control Centre

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RTU SUB LDC

SLDC RLDC

NLDC

Nos. 31

Nos. 51

1649 Nos.

5 Nos.

Plant/Sub Station Level Group of

District Level

State HQ Level Region

Level National

Level

Unified Load Despatch &

Communication

Present SCADA/EMS – Multi way information Flow

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Preventive Control

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Un-Synchronized Measurements

Location 1

Location 2

Magnitude of the two phasors can be determined independently but phase angle difference cannot be measured

without synchronization of measurements

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Synchronized Measurements

Location 1

Location 2

Phase angular difference between the two can be determined if the two local

clocks are synchronized.

Synchronizing pulses obtained from GPS satellites.

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WAMS

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The Indian Power

Grid

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Indian Power System : Among the Largest in the World

National Grid (UK) 68GW

MidWest ISO (USA) 159GW

RTE (France) 93GW

PJM (USA) 165GW

Red Electrica (Spain) 93GW

ONS (Brazil) 100GW

SO - UPS (Russia) 146 GW

Tepco (Japan) 64GW

KPX (South Korea) 70GW

Terna (Italy) 57GW

SGCC (China) 900GW

PGIL (India) 163GW Eskom

(South Africa) 43.5GW

Source: VLPGO (~2011)

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Some Typical Numbers (~2011)

 Generating Units :~ 1600

 400kV & above Trans. Line :~ 700

 Transformers (High Voltage) :~ 2000

 Busses (Extra High Voltage) :~ 5000

 Control Areas :~ 100

 Inter-State Metering Points :~ 3000

 Open Access transactions typical daily :~ 100

 Captives participating in market :~ 125

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The Indian Grid

NEW grid

South grid

Installed Capacity: ~ 180 GW

By 2027: ~575 GW

~2014 one synchronous grid

Courtesy: Power Grid Corporation of India Ltd. / Ministry of Power

Thermal 65%

Hydro 21 % Nuclear 3 % Renewable 11 %

Renewables: Wind, Small Hydro, Biomass etc

Wind Energy: 14 GW (Fifth Largest)

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NEW Grid

South Grid

South West North

East

Northeast

Five Regional Grids Five Frequencies

October 1991 East and Northeast

synchronized

March 2003 West synchronized With East & Northeast

August 2006

North synchronized With Central Grid

Central Grid

Five Regional Grids Two Frequencies

MERGING OF MARKETS

SR Synch By 2013-14

Inter – Regional Capacity:

22 GW

Courtesy: POSOCO

Installed Capacity: ~ 180 GW

By 2027: ~575 GW

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The Indian Grid: HVDC

HVDC (Long Distance)

1. Rihand – Dadri

2. Chandrapur – Padge 3. Talcher – Kolar

4. Balia - Bhiwadi

BACK To BACK 1. Vindhyachal

2. Bhadravati 3. Gazuwaka 4. Sasaram

(1500 MW)

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The Indian Grid

Courtesy: Power Grid Corporation of India Ltd. / Ministry of Power

Major Load Centres

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ROURKELA RAIPUR

HIRMA TALCHER JAIPUR

NER ER

WR NR

SR

B'SHARIF ALLAHABAD

SIPAT

GAZUWAKA JEYPORE CHANDRAPUR

SINGRAULI

VINDHYA-

2000MW 2000MW 2500MW

1000MW

500MW LUCKNOW

DIHANG

CHICKEN NECK

TEESTA

TIPAIMUKH BADARPUR

MISA

DAMWE

KATHAL- GURI

LEGEND

765 KV LINES 400 KV LINES HVDC B/B HVDC BIPOLE

EXISTING/ X PLAN NATIONAL ZERDA

HISSAR

BONGAIGAON

DEVELOPMENT OF NATIONAL GRID

KOLHAPUR

NARENDRA KAIGA

PONDA

IX PLAN

MARIANI

NORTH

KAHALGAON

RANGANADI

SEONI CHEGAON

BHANDARA DEHGAM

KARAD LONIKAND VAPI

GANDHAR/

TALA

BANGLA

BALLABGARH A'PUR

(DELHI RING)

BANGALORE

KOZHIKODE COCHIN KAYAMKULAM

TRIVANDRUM

PUGALUR

KAYATHAR KARAIKUDI

CUDDALORE SOUTH CHENNAI

KRISHNAPATNAM CHITTOOR

VIJAYAWADA

SINGARPET PIPAVAV

LIMBDI

KISHENPUR

DULHASTI WAGOORA

MOGA URI

BHUTAN

RAMAGUNDAM SATLUJ RAVI

JULLANDHAR

DESH

VARANASI /UNNAO

M'BAD

PURNEA

KORBA NAGDA

SILIGURI/BIRPARA

LA KS

HADW

EE P

TEHRI

MEERUT

BHIWADI

BINA

SATNA MALANPUR SHIROHI

KAWAS

AMRAVATI AKOLA

AGRA

SIRSI

CHAL

JETPUR AMRELI

BOISAR TARAPUR PADGHE DHABOL

KOYNA

BARH G'PUR

HOSUR MYSORE

KUDANKULAM

M'PUR

KARANPURA

MAITHON JAMSHEDPUR

PARLI

WARDA

BEARILLY

SALEM GRID

XI PLAN

765 KV LINES IN X PLAN. TO BE CHARGED AT 400KV INITIALLY TO BE CHARGED AT 765 KV UNDER NATIONAL GRID

765 KV RING MAIN SYSTEM

THE POWER

‘HIGHWAY’

CHEAP HYDRO POWER FROM THE NORTH-EAST AND PIT

HEAD THERMAL POWER FROM THE EAST ENTERS THE

RING AND EXITS TO POWER STARVED REGIONS

Cheap Thermal

Courtesy: POSOCO

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The Grid Collapse of 30 ^th July 2012

2:33:11:9 hours

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From Geet Ramayana (G.D.Madgulkar)

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MP antecedent trippings

00.10 hrs overload

00.05 hrs trip, 01.35 hrs revived Xmer

00.20 hrs Hand tripped

00.10 hrs overload

~02.34 hrs overload

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-278 MW 2654 MW

832 MW 975 MW

835 MW 962 MW

-33 MW 95 MW 1192 MW

3123 MW 2710 MW

2650 MW

Scheduled vs Actual Flows 02:30 hours

Frequency : 49.68 Hz

(asynchronous tie) (asynchronous tie)

Bhutan

Demand met > 70 GW in NEW grid

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DR of Bina-Gwalior

Zone3 tripping of Main-II

Approx impedance seen: 110 ohm

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“Distance Protection”

I V1

V1 is normally much greater than the impedance of the line ZL. Normal

V2

I

ZL

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Distance Protection

I V1

Voltage at fault point is ~zero

Fault

V1 will be equal to Z

Relay setting to detects fault on this line V1 < Z^L ; immediate trip

Relay setting (back-up) for faults on neighbouring line V1 < Z^L + Z^L1 Z

I

(Slow trip setting) I

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PMU data 30-7-2007, 2:33 hours

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30-7-2007: WAFMS (NTP synchronized)

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PMU data 30-7-2007, 2:33 hours

(Zone 1)

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First Conclusion

 The critical event leading to large angular separation was Gwalior-Bina 400 kV trip

 From DR, PMU, WAFMS : Tripping time is established to be 2:33:11:9

 Trip was NOT on fault.

 Zone3 tripping (back-up protection)

 “Load encroachment”

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x

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Zone-1 trippings at ~2:33:15, due to large angular separation ---- NR becomes an island

Balia-Biharsharif Balia-Patna

Grkpr-Muzzpr.

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Zone -1 tripping (Gorakhpur-Muzaffarpur)

Zone 1 implies V1/I < Z^L

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Cut-Set

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Birds-eye view (WAFMS)

System separation at this point.

Most generators will trip at 47.5 Hz

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