relaying 101 - college of continuing & professional...

Relaying 101

by: Tom ErnstGE Grid Solutions

[email protected]

Relaying 101

The abridged edition

Too Much to Cover• Power system theory review

– Phasor domain representation of sinusoidal waveforms

– 1-phase and 3-phase power– Symmetrical components

• Zones of protection• Relaying principals

– Over-current– Differential– Distance

Power system theory review• Phasor domain representation of sinusoidal waveforms

– Vectors: multi-dimensional, static

N

ESt Paul

Duluth

Power system theory review• Phasor domain representation of sinusoidal waveforms

– Phasors: multi-dimensional, time-variant, rotate at constant angular velocity (ω=2πf)

– Projection onto the Re axis plots as cos(ωt+θ)– Projection onto the Im axis plots as sin(ωt+θ)– m*cos(ωt+θ) => M@ θ => re + jim

• where M=m/√2 (RMS value)• j operator = 90 degree phase shift

– Useful for showing lead/lag relationships• M leads N by (θ+φ)

Im

Re

ωM(ω)

θre

im

N(ω)

φ

Power system theory review• 1-phase power

– Ohms law:• V=I*Z (time or phasor domain)• S=V*I*=p+jq (V and I are phasors, S is a vector)• S=V*(V/Z)* ; |S|=|V2/Z|• S=I*I*/Z ; |S|=|I2Z|

– Power factor• pf = p/S = cos(θ) for pure sinusoids• Leading/lagging (current relative to the voltage)

Ppage 6

Power system theory review• Balanced 3-phase power

– Phase quantities are equal magnitude and 120o

displaced– |AB| = √3*|A|

A

B

C

AB

CA

BC

AB=A-B

-B

Power system theory review• 3-phase power

– Ohms law:• VPN=IP*ZPN

• S1P=VPN*IP*

• S3P=SA+SB+SC

• For balanced systems: S3P = 3*S1P

|S3P|=|VPP2/ZPN|

|ZPN|=|VPP2/S3P|=|VPN

2/S1P||IP|=|S3P/(√3*VPP)|

I’ll try to keep this simple.Hopefully, most of it will be correct!

Power system theory review• Symmetrical components

– Mathematical trick for unbalanced systems• Superposition theorem• Break original system into 3 balanced sub-systems

– Positive sequence (phase rotation same as original)– Negative sequence (phase rotation opposite of original)– Zero sequence (no phase rotation)

• Perform balanced analysis on each sub-system and then add the results to get the total


– Definition: VA=VA1+VA2+V0

+ VB=VB1+VB2+V0

VC=VC1+VC2+V0

VA+VB+VC= 3V0

IA=IA1+IA2+I0

+ IB=IB1+IB2+I0

IC=IC1+IC2+I0

IA+IB+IC= 3I0


C1 A1

B1

A2

C2

B2

A0=B0=C0=0

Positive seq (ABC)

Negative seq (ACB)

Zero seq

A

A=A1+A2+0

ω ωω


C1 A1

B1

A2

C2

B2

A0=B0=C0

Positive seq (ABC)

Negative seq (ACB)

Zero seq

B

A

B=B1+B2+0


C1 A1

B1

A2

C2

B2

A0=B0=C0=0

Positive seq (ABC)

Negative seq (ACB)

Zero seq

A

B

C

C=C1+C2+0


C1 A1

B1

A2

C2

B2

A0=B0=C0=0

Positive seq (ABC)

Negative seq (ACB)

Zero seq

A

B

C

Phase system rotation is ABC

ω


– Physical meaning (intuition)• Positive sequence is “normal” balanced system• Zero sequence is “ground current”• Negative sequence creates reverse rotating fields in motors

and generators– Slip frequence = 2*f– Rotor is cutting many lines of force– Induces heating in the rotor

• Phase-phase unbalances/faults create negative sequence• Phasae-ground unbalances/faults create zero sequence

Relaying: An addiction that is hard to break!

Zones of Protection• Goals of protective systems

– Detect and isolate all faults (reliability)– Never mis-operate (security)– Isolate the minimum amount of equipment– Time is of the essence– Some protection systems operate to prevent a fault (ex:

overload)• Requires selectivity

– Each protection device is assigned a zone of protection

Zones of Protection

52 52

52

52

T-Line Bus

Bus

Trans

Radial Fdr

52 52

Radial Fdr

Radial Fdr

• Highly selective• Over-lapping• Back-up “blurs” the zone boundaries

52

What breakers are tripped for each zone?

Relaying principals• Over-current relaying

– Instantaneous (50)• Definite time

– Time (51)– Phase – Neutral/Ground (zero sequence)– Directional (67)

CHOICES, CHOICES, CHOISES.....

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7CURRENT (A)

SECONDS

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1

.01

.02

.03

.04

.05

.07

.1

.2

.3

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1

TIME-CURRENT CURVES @ Voltage 13.8 kV By TWE

For Instantaneous Over-current relay Characteristic No. M2008

Comment Date 11/6/2008

1

1. 50 Instant. RelayCTR=400/5 Inst.=5000A

No Operate

Operate

No intentional delay

Instantaneous over-current element (50)

Is this really instantaneous?

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7CURRENT (A)

SECONDS

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1


For Definite Time Over-Current Relay Characteristic No. M2008


1

1. 50 Instant. RelayCTR=400/5 Inst.=5000A

No Operate

Operate

0.5 Second intentional delay

Instantaneous over-current element with definite time delay (50)

Time over-current element (51)

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7CURRENT (A)

SECONDS

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1


For Time Over-current Relay Characteristics No. M2008


1

1. 51 (Extreemly Inv) UR-IEEE-EI TD=2.000CTR=400/5 Pickup=5.A No inst. TP@2=19.043s

2

2. 51 (Very Inv) UR-IEEE-VI TD=2.000CTR=400/5 Pickup=5.A No inst. TP@2=14.055s

3

3. 51 (Moderatly Inv) UR-IEEE-MI TD=2.000CTR=400/5 Pickup=5.A No inst. TP@2=7.6065s

Why do we use this inverse time characteristic?

Combined instantaneous and time over-current element (50/51)

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7CURRENT (A)

SECONDS

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1


For Time Over-Current Relay With Instantaneous Characteristic No. M2008


1

1. 50/51 UR-IEEE-EI TD=2.000CTR=400/5 Pickup=5.A Inst=5000A TP@2=19.043s

Phase (50/51P) and Neutral (50/51N) over-current elements(composite coordination)

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7

10 2 3 4 5 7 100 2 3 4 5 7 1000 2 3 4 5 7 10000 2 3 4 5 7CURRENT (A)

SECONDS

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

2

3

45

7

10

20

30

4050

70

100

200

300400500

700

1000

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1

.01

.02

.03

.04

.05

.07

.1

.2

.3

.4

.5

.7

1


For Phase and Ground Over-current Relay Characteristics No. M2008


1

1. 50/51P UR-IEEE-EI TD=2.000CTR=400/5 Pickup=5.A Inst=5000A TP@2=19.043s

2

2. 50/51G UR-IEEE-MI TD=12.000CTR=400/5 Pickup=2.A Inst=5000A TP@2=45.639s

Full Load

Why can the neutral pick-up be set less than full load?

Time coordination is achieved through selection of curve shapes, pick-ups and time delays.

Relaying Principals

52 52T-Line 1

Bus

52 52

52 52

T-Line 2

T-Line 3

67

• Directional Relay (67)– Compares angle between operating and polarizing

quantities• Operating = line current• Polarizing = something stationary

– Healthy phase-phase voltage– Sequence voltage– Sequence current

Relaying principals• Bus differential relay (87B)

– Kirchhoff's current lawI1 + I2 = I3

52

Bus

52

52

87B

I1

I3

I2

Relaying principals• Bus differential relay (87B)

– CT error will cause operating current• Poor quality CTs• CT saturation due to very high fault currents

– Use percentage slope characteristics for security• Operate on difference current• Restrain operation with through-load current• Minimum operating current = Irest * Slope

– Minimum pick-up to avoid “divide by zero” issues– Directional element and CT saturation detection add security– Will not operate for faults outside the zone of protection

• No coordination required

Bus differential relay slope characteristic

Minimum Pick-up = 0.1 pu

TRIP Region

Slop

e1=25

%

Slop

e2=80

%

TRIP

NOTRIP

Relaying principals• Transformer differential relay (87T)

– Same principal as bus except SIN = SOUT• Account for turns ratio and phase shifts

– Includes additional restraint• 2nd harmonic for in-rush• 5th harmonic for over-excitation

– May include:• directional element • CT saturation detection

52

87T

SIN

SOUT

Relaying principals• Line differential relay (87L)

– Same principal as bus: IS = IR• Account for CT ratio differences

– Uses magnitude and angle of differential and restraint

– May include differential for line termination transformer

– Requires high bandwidth communication channel

• Fiber• Digital microwave• Digital radio

IS

IR

52

Line

52

87L

87L

Conn Chan

Relay Engineers get used to the abuse,Given enough time...

Relaying principals• Distance relay (21)

– AKA: Impedance– Measures the complex impedance to the fault

• Z=V/I• Operates “instantaneously” if Z is within the

characteristic– Offset MHO– Quadrilateral

21

52 52T-Line 1

21

line21

R

jXDesired reach @ line angle

Offset MHO Characteristic

Most fault impedances are on or near the line angle

Operating Voltage = V-I*ZRPolarizing Voltage = V

line21

R

jXDesired reach @ line angle

Quadrilateral Characteristic

Most fault impedances are on or near the line angle


– Uses pre-fault memory voltage for directional control on zero-voltage faults

– Phase• Phase-phase element• 3-Phase element• Phase or sequence component based

– Ground• Measures positive sequence impedance• Uses a K0 scaling factor to approximate zero sequence

impedance


• Typically applied using stepped zones– Zone 1 (21-1) under-reaching: ZR=85% of ZL Instantaneous– Zone 2 (21-2 ) over-reaching: ZR=125% of ZL Time delayed to

coordinate with remote zone 1 elements

21-1

52 52T-Line 1

21-1

21-2 21-2

Relaying principals• Pilot schemes (communication assisted)

– Permissive over-reaching transfer trip (POTT)• Send permission to remote end(s) if 21-2 operates• Local instantaneous trip if 21-2 operates while receiving

permission from remote end(s)

21-2

52 52T-Line 1

21-1Trip zone

Relaying principals

21-R

52 52T-Line 1

21-R

21-2 21-2

• Pilot schemes (communication assisted)– Directional comparison blocking (DCB)

• Send block to remote end(s) if 21-R operates• Local instantaneous trip if 21-2 operates while not receiving

block from remote end(s)

Trip zone

Relaying principals• Pilot schemes (communication assisted)

– Direct under-reaching transfer trip (DUTT)• Local instantaneous trip if 21-1 operates• Send direct transfer trip to remote end(s) if 21-1 operates

21-1

52 52T-Line 1

21-1

Trip zone

Lots More to Talk About• Generator protection• Motor protection• Capacitor bank protection and control• Reactor protection• Over-voltage coordination• IEC-61850••

Save it for Relaying 102, 103, ......

It’s finally over! Time to grab a beer.

Thanks for Your Time!

Any Questions?

relaying 101 - college of continuing & professional...

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