Selective Coordination of Power Systems

Qazvin Seminar on

Selective coordination of power systems Tehran, 26 –27 January 2008

Lecturer: Gerhard Ziegler Siemens Erlangen

Copyright © Siemens AG 2007. All rights reserved.

Seminar Contents: 1. Tasks and principles of power system protection 2. Typical protection schemes 3. Protection of MV and LV Distribution networks 4. Transformer protection 5. Basics of Current and Voltage transformers

Page 1

2007-08

Author: G. Ziegler

Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI

Tasks and Principles of Power System Protection

Page 2

2007-08

Author: G. Ziegler


Tasks of Power System Protection Protection cannot prevent faults, but: minimise the consequences by: fast and selective tripping of the faulted system component automatic reclosing in case of transient faults providing information for fast fault analysis and system restoration in case of permanent faults

This would not have happened with appropriate protection!

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2007-08

Author: G. Ziegler


Requirements on system protection

Fast means: As fast as necessary, i. e. tripping of short-circuit within the critical fault clearing time (z. B. <100 ms in transmission networks) to minimise damage and to ensure system stability Negative example: Reliable means: New York dark (1965 u. 1977) Reliable tripping in case of internal faults (high availability,no under-function) Reliable non-tripping, in case of load or external faults (high security, no over-function) Selective means: Tripping of only faulty system components, leaving the healthy parts in service to continue energy supply

Page 4

2007-08

Author: G. Ziegler


Typical protection objects

Generators

G

< 1MVA to 1500 MVA

Transformers

0,1 MVA to 1000 MVA

Busbars

MV to EHV

Lines

1kV to 750 kV

Motors

Page 5

M

2007-08

Author: G. Ziegler

ca. 100 kW to ca. 20 MW


Fault current, influencing factors (three phase short-circuit as an example) Infeed

Load

Line

Example (RF neglected):

G

1,1× 110kV = 70kV 3 110kV 2 = 2,4Ohm ZS = 5000MVA

E=

ZS

E E=

1,1× U N 3

ISC-3-ph

ISC

USC 2

U ZS = N SK ''

ZSC

RF

Z SC = z L ' [Ohm / km]× l (km)

Z SC = 0,4[Ohm / km]× 20(km) = 8Ohm 70kV (2,4 + 8,0)Ohm = 6,7kA

ISC-3-ph =

E = ZS + ZSC + RF

• Short-circuit power of the infeed (source impedance ZS) • Line impedance to fault location (short-circuit impedance ZSC) • Fault resistance (RF) • Neutral earthing (earth current limitation, e. g. to 2 kA) Page 6

2007-08

Author: G. Ziegler


Fault currents: Ph-Ph and Ph-E short-circuit

Generator

Transformer

Busbar

Load

Grid

In case of ph-ph faults, the short-circuit current is normally much higher thn the load current. The earth short-circuit current can be higher or lower than laod current dependent on system neutral earthing and the fault resistance. High resistance neutral earthing: IE< 10% of nominal CT current

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2007-08

Author: G. Ziegler

IE


Earth fault – System neutral earthing

ZE

ISC

Compen sation coil

ICE

Free star point

ICE

ILE

Low impedance (solid) grounding • Earth fault = short-circuit ZE=0: normal over-current protection trips . • ZE>0 (IE < In): Sensitive earth-current step (0.1 to 0.5 x In) required Page 8

2007-08

Compensated

Isolated system

• Earth fault = no short-circuit • Small current ⇒ service can be continued • Fault indication by sensitive directional earth fault relays • Normally no tripping, only alarm • Manual tripping

Author: G. Ziegler


Capture of earth-current IE und and neutral displacement voltage UE for earth-fault protection

IE

Core balance CT 60/1 A

IL1 IL2 IL3

ZE

IE

For sensitive directional earthfault relaying

IE ‘

UE

I E = I L1 + I L2 + I L3 Page 9

2007-08

UL1 UL2 UL3 Mp

Author: G. Ziegler

U E = U L1 + U L2 + U L3 Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI

Typical Fault criteria

¾Overcurrent I> ¾Earth-current IE> ¾Undervoltage U< ¾Unterimpedanz Z< ¾Overvoltage U> ¾Leakage (Differential) current ∆I ¾Over- and Under-frequency ¾Current unbalance (negative sequence current I2>) ¾Special criteria for machine protection

Page 10

2007-08

Author: G. Ziegler


Protection Criterion: “Overcurrent“ Applicable when:

ISC-min > 2,5 x Iload-max. ISC-min

Infeed

G

I>, t2

I>, t1 Iload-max.

Add-on criterion: Time (t) (to gain selectivity)

Protection methods: Fuse Definite time (DT) over-current relay Inverse time (IT) overcurrent relay

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2007-08

Author: G. Ziegler

t

DT Fuse

IT

ISC


Typical fault causes

Line faults Atmospheric impact (lightning, icing, wind) Growing plants (trees, bush fire) Mechanical impact (crane, flying objects) Thermal overload (too large sag of line conductors)

Cable faults Insulation flash through (for example due to water treeing, water in cable sealings) Mechanical damage (for example during digging works ) Thermal overload

Power transformer faults and instrument transformer failures Insulation failure (due to aging, transient overvoltages) External short-circuits Thermal overload

Busbar faults Short-circuits caused by foreign objects (dropping line conductors, animals) False switching actions (e. g. switching to earth, opening an isolator under load)

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2007-08

Author: G. Ziegler


Causes of Faults German Disturbance Statistics, 1986

20 kV:

110 kV:

380kV

18042 2385 357 disturbances (13 per 100 km) (4,9 per 100 km) (3,4 per 100 km) of which:

of which:

of which:

60 %

31 %

51 %

11 %

4%

4%

foreign impact

2%

5%

8%

internal reasons

23 %

40 %

11 %

no obvious reason

4%

20 %

26 %

reaction from other networks

Page 13

2007-08

Author: G. Ziegler

atmospheric impact


Fault types

3-phase short-circuit

3-phase interruption

HV

EHV

5%

1%

2-phase short-circuit 25 %

2-phase interruption 6%

1-phase earth short-circuit 70 %

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2007-08

1-phase interruption

93 %

Author: G. Ziegler


Requirements on system protection Fast means: As fast as necessary, i. e. tripping of short-circuit within the critical fault clearing time (z. B. <100 ms in transmission networks) to minimise damage and to ensure system stability Negative example: New York dark (1965 u. 1977)

Reliable means: Reliable tripping in case of internal faults (high availability,no under-function) Reliable non-tripping, in case of load or external faults (high security, no over-function)

Selective means: Tripping of only faulty system components, leaving the healthy parts in service to continue energy supply Page 15

2007-08

Author: G. Ziegler


Overcurrent protection, Fuses, Current limitation

Maximum possible assymetric peak on bolted fault without fuse

Fault occurs

Peak let through current

Time

a

b c

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2007-08

a = Melting time b = arcíng time c= Total clearing time

Author: G. Ziegler


Overcurrent protection, Fuses, Coordination

Minimum melting time

Time

Infeed

Maximum clearing time Fuse

t2 Fuse 2 Fuse 1

t1 Fuse 1 I

Current Criteria for fuse-fuse coordination: t1< 0.75 t2

The maximum clearing time of main fuse 1 should not exceed 75% of the minimum melting time of the backup fuse 2. Page 17

2007-08

Author: G. Ziegler


Overcurrent protection, Current-Time graded Protection : (Example definite time)

A

20 MVA

20 kV

100 kV Grid

1700 A 0,7 s I>, t

Time grading

1700 A 0,4 s

B

I>,t

6000 A

350 A 3500 A

C

0,3 s I>,t

1 MVA

M I>,t 0,7 s

1700 A 0,1 s I>>,t0 150 A I>,t 1,0s

0,1 s I>>,t

0,3 s I>,t

I>>,t

M

Current grading

3500 A

ISC

1700 A 350 A

A Page 18

2007-08

B Author: G. Ziegler

C

150 A

I>>C, I>A, I>B I>C


Protection criterium “Impedance“

The relay determines the impedance:

Z = U/I

from voltage and current at the relay location.

In the fault case, the

measured impedance corresponds to the fault distance

I Grid E

Page 19

2007-08

D

U

ZL

RF

Z2, t=0,4 s

X

Time is used as

additional criterion (for selectivity and backup)

ZS

Z1, t=0 Operating

characteristic:

Author: G. Ziegler

Fault area

Load area

R


Distance protection: Graded zones

A

B

C

Infeed

Z<

Z<

t

Z3

t3 Z2 t2 Z1

t1 A

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2007-08

B Author: G. Ziegler

C

l


Line protection using communication (Signal transmission) Absolutely selective! Instantaneous fault clearance on 100% line length

A

B

Forward

U N D

ZOR-A

Forward

Protection Relay A

Protection Relay B Communication (Signal transmission)

ZOR-B

ZOR-B

U N D

ZOR-A

R

Protection range

B

A

ZOR-A

ZOR-B

Page 21

2007-08

Author: G. Ziegler


Options for signal transmission

Wire - Short distances up to 20 km (50/60 Hz oder voice frequency), (Influence of ground short-circuit currents to be considered) - Pilot wire differential protection, distance teleprotection, protection command transmission

PLC (Power Line Carrier)) - up to 400 km - for transmisiion of binary (YES/NO) signals - distance teleprotection, protection command transmission

S/R

S/R

Microwave 2 - 10 GHz (digital) - up to about 50 km (Sight connection) - Digital communication (n times 64 kbit/s), Line differential protection, Digital line differential protection, Distance teleprotection, protection command transmission

- Optic Fibers - Digital communication (n times 64 kbit/s), PCM coded data transmission Save against electromagnetic interferance, - Direct relay-to-relay communicatin up to ca 100 km with dedicated fibers - Communication via data communication networks -Digital line differential protection, Distance teleprotection, protection command transmission Page 22

2007-08

Author: G. Ziegler


Principle of “Differential Protection“ Detection of a leakage (current difference) ∆

I1 i1

I2 Protected object

∆I>

2007-08

Protected object

i2 i1

∆I=I1 - I2 =0

∆I>

∆I=I1 + I2

i2

External fault or load (Through flowing current)

Page 23

I2

I1 i1

i2

Leakage current

Author: G. Ziegler

Internal fault


Stabilised Differential Protection

Node criterion (Kirchhoff‘s law): I1 + I2 + I3 + ... In = Idiff = 0; ΣI ≠ 0 ¼Fault In creased security by current dependent restraint: |I1|+|I2|+ ... |In| = Irestraint Operating characteristic: Iopertion = Idiff – k•Irestraint

Idiff

Protection objekt

Trip Istab

Advantage: Absolute zone selective (zone borders are CT locations) Disadvantage: No backup protection for external faults Application: Differential protection for Generators, Motors, Transformers, Lines/Cables and busbars Page 24

2007-08

Author: G. Ziegler


Pilot wire differential protection

I1

I2

Current differential I2

Three pilot wires

∆Ι ∆I

up to ca. 15 km

∆I

I1 I1

Two pilot wires (Twisted pair) up to ca. 25 km

Page 25

2007-08

I2

Voltage comparison ∆I

∆U

U1

Author: G. Ziegler

∆I U2


Digital line differential protection using data communication

Line differential relay 87L

I1

I2

∆I

∆I

O.F.

Modem

Dedicated optic fibers up to ca. 100 km Communication options

G703-Interface

Other Services

Page 26

2007-08

PCM MUX

Line differential relay 87L O.F.

Modem G703-Interface

Data communication network

Author: G. Ziegler

PCM MUX

Other Services


Transformer differential protection

∆I *)

ZweiwickelTrafo

∆I

87T

87T

87T

∆I

*)

*)

Zweiwickel-Trafo mit doppelter Einspeisung

DreiwickelTrafo

*) Intermediate CTs for ratio- and vector group adaptation (not necessary with digital relays, as they perform these functions internally by numerical calculation )

Page 27

2007-08

Author: G. Ziegler


Transformer Differential Protection Three-phase function diagram

UA

L1

IA1

IB1

L2

IA2

IB2

L3

IA3

IB3

(110 kV)

UB (20 kV)

Digital relays contain: Adaptation of ∆I

7UT6

∆I

∆I

• Voltage ratio(s) UA / UB • vector group(s) e.g. Ynd1

Numerical adaptation

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2007-08

Author: G. Ziegler


Busbar differential protection

Digital Protection 7SS52

Electromechanical and static relays 7SS10/11/13

∆I Central Unit Optic fibers

∆I

BU

BU

BU

BU

0 BU: Bay Unit

G

M Grid infeed

Page 29

G

Consumers

2007-08

Author: G. Ziegler

M Grid infeed

Consumers


Protection of multiple busbar configurations Double busbar as an example

Bus 1 Bus 2

Isolator Replica

∆I1 ∆I2

G

Page 30

2007-08

M

Author: G. Ziegler

The digital busbar protection (7SS5) uses a software based isolator replica. Contact switching is therefore no more necessary! Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI

High impedance differential protection: Principle Behaviour during external fault with CT saturation

with ideal current transformers

RCT

ISC

RCT

ISC

ISC

ISC

UR

ECT −1 = (RL + RCT ) ⋅ iSC

ECT −1 = 2 ⋅ (RL + RCT ) ⋅ iSC

UR = 0 ECT −2 = (RL + RCT ) ⋅ iSC

Page 31

2007-08

Author: G. Ziegler

U R = (RL + RCT ) ⋅ iSC


High impedance differential protection: Principle Behaviour during internal fault

Em

10%

UKN

RCT

ISC

RCT

ISC

50%

URS

Relay set point = IR-pick-up⋅RR ImR

Im

CT requirement: UKN ≥ 2 times URS E CT −1 = U KN

Page 32

U R ≈ U KN

2007-08

E CT − 2 = U KN

Author: G. Ziegler


High impedance differential protection: Calculation example (busbar protection) Given:

n = 8 feeders rCT = 600/1 A UKN = 500 V RCT = 4 Ohm ImR = 30 mA (at relay pick-up value)

Pick-up sensitivity:

RR = 10 kOhm Ivar = 50 mA (at relay pick-up value)

Stability:

(

I F −min = rCT ⋅ I R − pick −up + IVar + n ⋅ I mR

I F − min =

RL= 3 Ohm (max.) IR-pick-up.= 20 mA (fixed value)

)

600 ⋅ (0.02 + 0.05 + 8 ⋅ 0.03) 1

I F − min = 186 A ⋅ (31% )

I F −through − max < rCT ⋅

I F −throuh − max <

RR ⋅ I R − pick −up RL + RSW

600 10,000 ⋅ ⋅ 0.02 1 3+ 4

I F −through − max < 17 kA = 28 ⋅ I n

Page 33

2007-08

Author: G. Ziegler


High impedance differential protection: Application notes •HI protection can only be used for a galvanically connected circuit (not for transformer differential protection!) •Other protection relays cannot be connected in series as the CTs saturate heavily in case of internal faults •Special CT requirements: CTs must all have the same ratio and construction, normally Class PX according to IEC 60044-1 with low secondary resistance and leakage reactance •A voltage limiting device (varistor) may be necessary because high voltage occurs in case of internal faults •Preferred Application cases: Restricted earth fault protection (winding earth-fault protection) Differential protection of single busbars Differential protection of motors and generators

Page 34

2007-08

Author: G. Ziegler


Backup protection

Remote backup Infeed Protection

Protection

Backup zones

Local backup Infeed

Protection

Protection

Protection

Protection

Local Backup protection

Page 35

2007-08

Author: G. Ziegler

Breaker failure protection


Local backup protection

If the circuit breaker fails, the infeeding CB is tripped after tBFP

t BFP=100-200ms dependent on CB time and I> reset time

I>, t

I>, t

I>, t

BFP

BFP

BFP

I>

AUS & t BFP

Trip

M

Page 36

2007-08

Author: G. Ziegler

BFP Logic


Protection system

CTs and VTs

Circuit breaker 600 A

110 kV

Wiring 1A

100 V

Distance protection Battery

Protection relay

S R

Remote end

Communication

Each system is only as strong as its weakest component !

Page 37

2007-08

Author: G. Ziegler


Current and Voltage transformers

i1

G

i1 ⋅ w1 = i2 ⋅ w2

Φ

Load

w1

w1

u1

w2

u2

w2 Φ

u1 u 2 = w1 w2

i2

Protection relay

Page 38

2007-08

Author: G. Ziegler


Current transformers for protection

Current transformers • transform from primary to 1 or 5 A secondary • define the position of the relay

Relays can be connected in series to the CT cores

• define the border of the protection range 87 BB

21

CT burden in operation:

POB = Pleads +

On transmission level, each main protection is connected to a separate CT core (redundancy), for example 87BB and 21

CT cores Page 39

∑ PRe lays

2007-08

Author: G. Ziegler


Current transformer: Principle, transformation ratio, polarity

i1

i2

i1 w1

u1 i2

1 Φ

u2

i1 ⋅ w1 = i2 ⋅ w2

Function principle i1

u2

u1 u 2 = w1 w2

2

w2

u1

Polarity marks

P1

P2

i2 i1

u1

i2

u2 S1 Equivalent electrical circuit

Page 40

2007-08

Author: G. Ziegler

S2

Designation of CT terminals according to IEC 60044-1 Copyright © Siemens AG 2007. All rights reserved. PTD SE PTI

Design of protection CTs

CT standard: IEC 60044-1: 5P oder 10P CT specification:

300/1 A

Pi = I sec .2 × R CT

5P10, 30 VA RCT ≤ 5 Ohm

Ratio: In -prim. / In -sec.

Rated power (Rated burden) PRB

5% Accuracy up to I= ALF x In

Accuracy limit factor ALF

The accuracy limit factor in operation depends on the actually connected burden: Pi + PRB Accuracy limit in operation: ALF' = ALF × Pi + POB

Auslegungskriterium: I ALF' ≥ SC − max . × K TF In

KTF (Transient overdimensioning factor) considers the dc offset of the short-circuit current ISC, (Relay specific requirements, as provided by the manufacturer)

Page 41

2007-08

Author: G. Ziegler


Voltage transformes for protection

Voltage transformers (VTs) are necessary for •Direction determination •Impedance measurement, Distance to fault location

100 V 110 kV / 100 V / 100 V / 3

Open delta winding

Micro circuit breakers

•Power measurement •Synchro-check and Synchronising •U<, U>, f<, f> protection

Earth fault relaying Protection 1 Protection 2 Measurement

Practice: In distribution: VTs only at the busbar(s) In HV and EHV: VTs at each feeder Sezification according to IEC60044-2 1% accuracy sufficient for protection

Page 42

2007-08

Author: G. Ziegler


Auto-reclosure Fast clearance of transient faults

x

G

Trip 1-pole 3-pole

x

Close Open

G

Close

Open finally

CB On

Distribution: Further 40 % successful

CB Off tSC-1

Short ARDead time

tK2

Long ARDead time

2nd shot

1st shot

Page 43

2007-08

Tgrading time

Author: G. Ziegler


Success rate of Auto-reclosure (German utilities, 1986)

In Germany:

Disturbances per 100 km line length 68,5%

15

10

MV:

3-pole AR ( multi-shot)

HV:

3-pole AR

EHV:

1-pole AR

Self extinguishing earth faults

59,1%

Unsuccessful AR 85,3%

5

Successful AR 89,1%

Page 44

2007-08

95,1%

Author: G. Ziegler


History of applied protection technology

Electromechanical Technology

Analog electronic Technology

Digital Technology 1950

Page 45

1960

2007-08

1970

1980

Author: G. Ziegler

1990

2000


Historic development of relay design (HV)

statisch StaticAnalog (analog electronic)

digital digital

elektromechanisch

electromechanical

Page 46

2007-08

Author: G. Ziegler


Legacy relaying technology Rectifier bridge comparator with moving coil relay

Induction relay

I1

I2

Protection object

I1 i1

I Re s

i1

∆i

i2

Page 47

2007-08

Op

−I

Author: G. Ziegler

i2

IOp

∆i

I Re s = k ⋅ (I 1 − I 2 ) ∆I = I

I2

Protection object

I Op = I 1 + I 2

+ Re s

N

S


Digital relay structure

Tripping

A AI BO

D

MP

Alarms

System BI

Serial interfaces

Signal from remote line end

Page 48

2007-08

Author: G. Ziegler


Capture of measuring data (principle) 1ms

IN=1A oder 5A UN=(100...125V)/√3 1

1

Input data

S&H

ΙL1 ΙL2 ΙL3 ΙE

2007-08

Digital values

1 1 1 0 1 1 0 1 1 0 A

8

8

8

Analog

Page 49

UL1 UL2 UL3 UE

MUX

UL1 UL2 UL3 UE

8

ΙL1 ΙL2 ΙL3 ΙE

1kHz clock 1 1

D

S&H Sample & Hold MUX Multiplexer A/D Analog/Digital-Converter

Digital

Author: G. Ziegler


Sampling theorem Requirement: fmax <

a) Spectra

fS 2 x(f)

x(f)

- f S/ 2

0

fS/ 2

f

fA

- f S/ 2

0

f S/ 2

f

fS

Sampling theorem violated!

Sampling theorem fulfilled!

b) Sampling of different waveforms (fS = 400Hz) x(t)

x(t)

x(t) = sin (f50,t)

x(t) = sin (f 350,t)

t/ms

t/ms

Page 50

2007-08

Author: G. Ziegler


Dynamic range of A/D conversion 15 bit + sign A/D converter → 15 Bit= 215 =32.768 steps resolution The measuring error corresponds to ± ½ LSB (Last Significant Bit) Currents: 15

Voltages:

32.768 steps = 100 x IN

15

234 steps = 1.0 V → Error: 0.2 % of the measuring value

33 steps = 0.1 x In → Error: 1.5 % of the measuring value

1

Page 51

1 step = 0.00305 x IN = 0.3 % x IN

2007-08

Author: G. Ziegler

32.768 steps = 140 V

1

1 step = 0.00427 V


Fourier analysis of measured values

Processing with two orthogonal filters

Sampled signal i(t)

I(k) = IS(k) + j⋅ IC(k)

10,000 8,000 6,000 4,000

IS =

1 2π

2,000

Ø

∫

I ( ωt) ⋅ sin ωt dt

Ø - 360°

0,000 0

20

40

60

80

100

-2,000 -4,000 -6,000

1 IC = 2π

Page 52

2007-08

Ø

∫

I ( ωt) ⋅ cos ωt

dt

Ø - 360°

Author: G. Ziegler


Fourier analysis: Filtering characteristics

Half cycle (10 ms at 50 Hz)

Full cycle (20 ms at 50 Hz) 1

1

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0

Page 53

50 100

200

2007-08

300

400

500Hz

0

Author: G. Ziegler

50 100

200

300

400

500Hz


Fourier transform Determination of Voltage and current phasors Time domain

diL (t) uL (t) = RL ⋅ iL (t)+ LL ⋅ dt 1 Re{UL } = ⋅ T

+T/2

∫uL(t)⋅ cos(ω0 ⋅ t )dt

−T/2 +T/2

1 Im{U L } = ⋅ ∫ uL (t)⋅ sin(ω0 ⋅ t )dt T −T/2

U L = Re{UL }+ jIm{UL }

−

T 2

+

T 2

+T/2

1 Re{I L } = ⋅ ∫ iL (t)⋅ cos(ω0 ⋅ t )dt T −T/2 +T/2

1 Im{I L } = ⋅ ∫ iL (t)⋅ sin(ω0 ⋅ t )dt T −T/2

I L = Re{I L }+ jIm{I L }

UL = UL ⋅ [cos(ω⋅ t + ϕU ) + jsin(ω⋅ t + ϕU )] = UL ⋅ e j(ω⋅t+ϕU) IL = IL ⋅ [cos(ω⋅ t + ϕI ) + jsin(ω⋅ t + ϕI )] = IL ⋅ e j(ω⋅t+ϕI )

t=0 Data window

U L = U L ⋅ e jϕ U = U L ⋅ e jω t U

Frequency domain ϕU = ω ⋅tU

I L = I L ⋅ e jϕ I = I L ⋅ e jω t I ϕI = ω ⋅ t I t=0

Page 54

2007-08

Author: G. Ziegler


Fault impedance calculation from complex U- and I-phasors for distance protection Impedance plane

U L = U L ⋅ e jϕ U = U L ⋅ e jωt U

X

IL

=

UL ⋅ e

R

t =0 jϕU

I L ⋅ e jϕI

=

U L j(ϕU −ϕI ) ⋅e IL

2007-08

R L = Re{Z L } = X L = Im{Z L } =

= R L + jXL

Page 55

XL ϕ Z = ϕ U − ϕI

ϕI =ω⋅tI

ZL =

ZL

I L = I L ⋅ e jϕI = I L ⋅ e jωt I

ϕU = ω ⋅ tU

UL

RL

Author: G. Ziegler

UL ⋅ cos(ϕ U − ϕ I ) IL UL sin (ϕ U − ϕ I ) IL


Differential protection with current phasors (principle) A

IA

IB

Protection Object

B

∆I trip

∆I IA

j·IAS

restraint

∆I>

ΣI Operating quantity :

∆I

∆I = I A + I B

Restrainin g quantity : Σ I = I A + I B

IBC IAC

j·IBS

IB Page 56

2007-08

Author: G. Ziegler


Power System Protection: Digital relay design (different manufacturers)

Page 57

2007-08

Author: G. Ziegler


Modern digital protection relay, design

Modem

Modem

Page 58

2007-08

Author: G. Ziegler


Relay series SIPROTEC 4 Communication interfaces (1) PC-interface, front side Öelectric RS 232

Analog output 20 mA or teleprotection interface Öelectric or optic

System interface Öelectric or optic ÖIEC60870-5-103,IEC61850, Profibus FMS, DNP3.0 or Modbus; alternatively analog output 20 mA

Page 59

2007-08

Author: G. Ziegler

Service interface Öelectric RS232 / RS485 ÖDIGSI 4 / modem Time synchronisation ÖGPS (IREC-B) Öor DCF-77


Relay series SIPROTEC 4 Communication interface (2)

Teleprotection 1

Teleprotection 2 IEC 870-5-103 61850, Profibus DNP, Modbus,

Local control

Remote operation Local operation

Page 60

2007-08

GPS Synchr.

Author: G. Ziegler


Main processing bord and communication interface modules (SIPROTEC 4 relay series)

O.F. Double ring Exchangeable communication modules Wired IEC61850 Ethernet 100 Mbit

Page 61

2007-08

Author: G. Ziegler


Development of relay processing hardware

Begin of delivery

Relay generation

Memories RAM/EPROM

Bus width

Clock frequency

Processing power

1992

SIPROTEC 3

256/512 k

16 bit

16 MHz

1.0 MIPS *)

2000

SIPROTEC 4

32 bit

80 MHz

35 MIPS *)

512k/4MB + 4MB D-RAM

*) MIPS: Million Instructions per second

Page 62

2007-08

Author: G. Ziegler


Digital Relay, Data aquisition SIPROTEC 4 relay series

Sampling rate:

1000 Hz (1200 Hz at 60 Hz nominal frequency)

Samples per period:

20

Anti-aliasing filter:

500 Hz (600 Hz) limiting frequency

A/D-conversion:

16 bit, corresponding to 65536 steps

Measuring value storage:

15 s

Program language:

C/C++

Page 63

2007-08

Author: G. Ziegler


Multi-function digital relay Example Feeder protection

Close

+ –

Trip

Backup prot.

59

25

79

ST

=

21

FL

M

FR

49

=

67N

85

59 25 79 ST 21 FL FR M 49 67N 85

Overvoltage Synchro-check Auto-reclosure Control Distance protection Fault locator fault recording Measurement Overload Directional EF protection Teleprotection supplement

Modem Remote line end

Page 64

2007-08

Author: G. Ziegler


Combined Protection and Control devices

Scope of functions:

• Protection • Monitoring • Measuring (Load monitoring) • Control • Automisation • Data capture and storage • Communication

Page 65

2007-08

Author: G. Ziegler


Distribution Switchgear Innovation One IED replaces a conglomeration of “black box” devices Traditional panels with mechanical relays and control

Page 66

2007-08

Author: G. Ziegler

Modern panels with digital multifunction relays


Relays as components of Substation Automation

Remote relay opertion

Substation control

Office DIGSI

DIGSI central relay opertion

Telefon/Modem connection Ethernet, IEC 61850

Modem

RUN

7SJ61-0000ERRORDE

RUN

7SJ61-0000ERRORDE

DIGSI Local relay opertion

F1 F2 F3 F4

Page 67

2007-08

7 4 1 .

8 5 2 0

9 6 3 +/-

Author: G. Ziegler

F1 F2 F3 F4

7 4 1 .

8 5 2 0

9 6 3 +/-


Relay communication options

Protection using communication

0

0

Mobile Service

50 100 %

I O V

50 100 %

I O V

Intranet ISDN, Internet Engineering Office 0

50 100%

Substation control

I O V

Local operation Page 68

2007-08

Author: G. Ziegler


PC controlled relay operation

Page 69

2007-08

Author: G. Ziegler


Software marshalling matrix

Page 70

2007-08

Author: G. Ziegler


PLC (Progammable logic control)

Page 71

2007-08

Author: G. Ziegler


Digital relays: Fault reporting

Detailed information for fault analysis

Fault history Time tagged event recording Fault recording Distance to fault

Î Fast fault clearance SIGRA Fault analysis Programm

Î Short outage times

Page 72

2007-08

Author: G. Ziegler


Protection examples

Page 73

2007-08

Author: G. Ziegler


ANSI Device function numbers (Selection of most important functions) 51, 51N

Time delayed phase and earth overcurrent protection

50, 50N

Instantaneous phase and earth overcurrent protection

21, 21N

Phase and earth fault distance protection

85

Supplement (Logics) for teleprotection

87

Differential Protection

87N

Earth differential protection (Restricted E/F protection)

27

Undervoltage protection

59

Overvoltage protection

79

Automatic reclosing

81

Frequency protection

49

Overload protection

46

Unbalanced load protection

Page 74

2007-08

Author: G. Ziegler


Line protection, Overview

OH-lines

Cables

MV:

Radial: I>, t 51 Ring: I>-directional, t 67 Meshed: Z< 21

∆IL+ I>, t

HV:

Z< with communication 21 + I>-directional, t 67

EHV:

2 x Z< 21 + 21 or ∆IL + Z<

87

+ 21

51 if signalling links available, else as OH-lines

∆IL + Z< 87

21 with communication

∆IL + Z<

87

21

each with communication

each with communication Page 75

2007-08

Author: G. Ziegler


Earth fault protection

Solid grounding

Earth fault current ≈ Phase short-circuit current: Earth overcurrent, distance, differential protection Sensivity IE>: 0.25 to 0.5 x In

Impedance grounded Same as above but higher sensivity: 0,1 to 0,2 x In

High impedance grounded Special earthfault protection necessary!

isolated

Page 76

Compensated (Peterson coil)

2007-08

UE> for alarming (20 to 50% of 3xU0) Sensitive directional earth current relays (10 to 50 mA) Core balanced CTs required

Author: G. Ziegler


Application of Time-Overcurrent Protection Example: Radial feeders with Definit Time O/C relays 0.4 kV 20 kV

1 MVA

1 MVA 3 MVA

100 kV

30 MVA

I>, t

t = 1,0 s

I>> I>, t

I>, t

I>, t

t = 0,7 s

t = 0,4 s

tI>> =0,1 s tI> =tLV+ 0,4 s

Fuse

Page 77

Advantage: Simple relays, no VTs required

I>, t

51

Disadvantage: Tripping time increase in infeed direction

I>> I>, t

50

2007-08

Author: G. Ziegler

51


Application of Directional O/C Protection Example: Ring network x I>> I>, t x

x I>, t

t = 1,2 s x I>, t

I>, t t = 0,0 s x

x

x I>, t

t = 0,0 s

I>, t

t = 0,8 s x

I>, t

t = 1,2 s

tI>> =0,1 s tI> =tLV+ 0,4 s

t = 0,4 s x I>, t

I>, t

t = 0,4 s

t = 0,8 s x I>> I>, t

Page 78

2007-08

tI>> =0,1 s tI> =tLV+ 0,4 s

Author: G. Ziegler

x I>> I>, t

tI>> =0,1 s tI> =tLV+ 0,4 s

I>, t

I>, t

I>> I>, t

50

I>, t

I>, t

51 51 67


Application of Distance Protection Example: HV Double circuit lines

x

x Z<

x

Z<

x

Z< x

Z<

Z<

t1 = 50 ms

x

t1 = 50 ms

Z<

x

x Z<

t1 = 50 ms

Z< t1 = 50 ms

Advantage:

Instantaneous fault clearance on protected line and backup for folloeing lines Disadvantage: Higher cost

Page 79

2007-08

Author: G. Ziegler


Application of line differential protection Example: Cable feeders

x

x

∆I

∆I

Backup

Backup

x

x x

∆I

∆I

Backup

Backup

t = 0ms

I>, t

∆I 87L Backup

Page 80

2007-08

Author: G. Ziegler

Pilot wire differential or Digital differential with optic fibers MV:

I>, t

51

HV:

Z<

21


Protection of distribution transformers

> ca. 500 kVA

< ca. 500 kVA Short-circuit and overload protection

x

HH-Fuse Type: GTr

Short-circuit and overload protection

I>> I>, t 2

Relay

I t

2007-08

Author: G. Ziegler

x

x

Page 81

LV-Fuse or ? LV-CB with I>, t

?

LV-Fuse or LV-CB with I>, t


Protection of larger transformers

x

I>> I>, t

50

∆I

51

Main protection: Current differential

ϑ>

Overload protection

I>, t

Backup protection Time-overcurrent

ϑ>

Thermal monitoring

BU

Gas pressure relay (Buchhulz relay)

ϑ>

ϑ>

BU

∆I

49 87T

x

Page 82

2007-08

Author: G. Ziegler


Busbar protection

Single busbars without feedback

Single busbars with feedback

Multiple busbars

MV:

I>, t with reverse interlocking

Busbar differential

Busbar differential

HV/ EHV:

Busbar differential

Busbar differential

Busbar differential

High impedance type

High impedance type or Low impedance type

Low impedance type

High impedance differential protection requires special Class X current transformers!

Page 83

2007-08

Author: G. Ziegler


Busbar protection Reverse interlocking method Infeed I>, t

2

Blocking

x

t0= 50ms t2= 0.3 s

I>, t1 + I>

x

x

x

1

I>, t1 +

I>

I>, t1 +

I>

M

1

Feeder protection blocks 50 ms element of infeed protection and trips faulted feeder

2

Infeed 50 ms step trips bus as there is no protection pick-up in the feeders

Page 84

2007-08

Author: G. Ziegler


Dual service with transformation Choice of protection ranges

A

Infeed 1

B

D

Page 85

2007-08

Author: G. Ziegler

C

Infeed 2

E


Dual service with transformation Protection functions 79

79

A Infeed 1

B

87L

87B 50 50N

21

87N

51 51N

51 51N T>

T>

BU

BU

D 51 51N

87B 51 51N

2007-08

50 50N

21

87T

87N

E

51 51N

51 51N

Author: G. Ziegler

Infeed 2

87L

87B

87T

Remote end

Page 86

C

Remote end 51 51N

87B 51 51N

51 51N


Selective Coordination of Power Systems

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