Universal Relay Family B30 Bus Differential Relay

Universal Relay FamilyUniversal Relay FamilyB30B30

Bus Differential RelayBus Differential Relay

Power Management The The Universal RelayUniversal Relay

Contents...Contents...

Features

CT Saturation Problem

Theory of Operation

Dynamic Bus Replica

Operation Examples (link)

Q&As (link)

Benefits


FeaturesFeatures

• Configuration:Configuration:– up to 5 feeders with bus voltage– up to 6 feeders without bus voltage


FeaturesFeatures

• Protection:Protection:– Low-impedance biased differential protection

• CT saturation immunity

• sub-cycle tripping time

• dynamic 1-out-of-2 or 2-out-of-2 operation

– Unbiased differential protection– Dynamic bus replica– CT trouble monitoring– Undervoltage (2 elements)– Phase Overcurrent (2 elements)


FeaturesFeatures

• Metering:Metering:– Oscillography– Event Recorder– Phasors / true RMS


CT saturation problemCT saturation problem

• During an external fault– fault current may be supplied by a number of

sources– the CTs on the faulted circuit may saturate– saturation of the CTs creates a current

unbalance and violates the differential principle– a conventional restraining current may not be

sufficient to prevent maloperation

• CT saturation detection and a directional principle enhance through-fault stability


diffe

rent

ial

restraining

DIFFERENTIAL – RESTRAINT PointDIFFERENTIAL – RESTRAINT Point

External fault: ideal CTs

DIF – differentialRES – restrainingt0 – fault inceptiont2 – fault conditions

t0

t2


diffe

rent

ial

restraining


External fault: ratio mismatch


t0

t2


diffe

rent

ial

restraining


External fault: CT saturation

DIF – differentialRES – restrainingt0 – fault inceptiont1 – CT starts to saturatet2 – fault conditions

t0

t1

t2


diffe

rent

ial

restraining


Internal fault: high current


t0

t2


diffe

rent

ial

restraining


Internal fault: low current


t0

t2


diffe

rent

ial

restraining


External fault: extreme CT saturation

DIF – differentialRES – restrainingt0 – fault inceptiont1 – CT starts to saturatet2 – fault conditions

t0t1

t2


Operating principlesOperating principles

• Combination ofCombination of– low-impedance low-impedance biased differential– directional (phase comparison)

• Adaptively switched betweenAdaptively switched between– 1-out-of-2 operating mode1-out-of-2 operating mode– 2-out-of-2 operating mode2-out-of-2 operating mode

• byby– Saturation DetectorSaturation Detector


Biased Characteristic: Biased Characteristic: Restraining CurrentRestraining Current

• Restraining Current is a “maximum of” Restraining Current is a “maximum of” the bus zone currents :the bus zone currents :– better stability on external faults (as compared

to the “average of” definition)– better sensitivity on internal faults (as

compared to the “sum of” definition)


Biased Characteristic: Biased Characteristic: ShapeShape

• Two breakpoints

• Two slopes– both slopes provide TRUE percentage restraint,

i.e. they are represented by straight lines crossing the origin of the differential-restraining plane

– if the slopes are different, discontinuity of the characteristic occurs

– the discontinuity issue is solved by a smooth “gluing” function


Biased Characteristic: Biased Characteristic: ShapeShape

0 2 4 6 8 10 120

1

2

3

4

5

6

7

8

RESTRAINING, pu

DIF

FE

RE

NT

IAL

, pu

LOW BPNT HIGH BPNT

HIGH SLOPE

LOW SLOPE

PICKUP


Biased Characteristic: Biased Characteristic: Two distinctive regionsTwo distinctive regions

• low currents • saturation possible

due to dc offset• saturation very

difficult to detect• more security

required

diffe

rent

ial

restrainingA

B 1

K 2

K 1

B 2

DIF 1


Biased Characteristic: Biased Characteristic: Two distinctive regionsTwo distinctive regions

• large currents • quick saturation

possible due to large magnitude

• saturation easier to detect

• security required only if saturation detected

diffe

rent

ial

restrainingA

B 1

K 2

K 1

B 2

DIF 2


LogicLogic

DIF1

DIR

SAT

DIF2

OR

AN

D

OR TRIP

AN

D


LogicLogic

diffe

rent

ial

restrainingA

B 1

K 2

K 1

B 2

1-out-of-2 (DIF) if no saturation2-out-of-2 (DIF+DIR) if saturationdetected

2-out-of-2(DIF+DIR)


LogicLogic

DIF1

DIR

SAT

DIF2

OR

AN

D

OR TRIP

AN

D


Directional principleDirectional principle

• Internal faultsInternal faults - all currents approximately in phase



• External faultsExternal faults - one current approximately out of phase



• Check all the angles

• Select the maximum current contributor and check its position against the sum of all the remaining currents

• Select major current contributors and check their positions against the sum of all the remaining currents



"contributor"(phasor)

differential less"contributor"(phasor)

BLOCK

TRIP

TRIP

BLOCK

BLOCK



BLOCK

OPERATE

BLOCK

pD

p

II

Ireal

pD

p

II

Iimag

Ip

ID - I p

External Fault Conditions

OPERATE



BLOCK

BLOCK

pD

p

II

Ireal

pD

p

II

Iimag

Ip

ID - I p

Internal Fault Conditions

OPERATE

OPERATE


LogicLogic

DIF1

DIR

SAT

DIF2

OR

AN

D

OR TRIP

AN

D


Saturation DetectorSaturation Detector

• differential-restraining trajectory

• dI/dt

diffe

rent

ial

restraining

External fault: CT saturation

t0

t1

t2

t0 – fault inceptiont1 – CT starts to saturatet2 – fault conditions



0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

2

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

3

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

4

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

5

Time, sec

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

2

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

3

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

4

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-40-20

02040

Fe

ed

er

5

Time, sec

Sample External Fault on Feeder 1 (Case 1)

Sample External Fault on Feeder 1 (Case 1)


0 5 10 15 20 25 30 350

5

10

15

20

25

30

35D

iffe

ren

tial [

A]

Restraining [A]

12 3 4 56

789

101112

13

1415

16

171819

2021222324252627282930313233

Phase A (Infms)

0 5 10 15 20 25 30 350

5

10

15

20

25

30

35D

iffe

ren

tial [

A]

Restraining [A]

12 3 4 56

789

101112

13

1415

16

171819

2021222324252627282930313233

Phase A (Infms)


Analysis of the DIF-RES trajectory enables the B30 to detect CT saturation (Case 1)

Analysis of the DIF-RES trajectory enables the B30 to detect CT saturation (Case 1)



0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20F

ee

de

r 1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

2

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

3

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

4

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

5

Time, sec

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20F

ee

de

r 1

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

2

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

3

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

4

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-20

0

20

Fe

ed

er

5

Time, sec

Sample External Fault on Feeder 4 - severe CT saturation after 1.5msec (Case 2)

Sample External Fault on Feeder 4 - severe CT saturation after 1.5msec (Case 2)


0 5 10 15 200

5

10

15

20

Diff

ere

ntia

l [A

]

Restraining [A]

12

3

4

5 6

7

8

91011121314

15

16

1718

19

20

2122

23

24252627282930

313233

Phase A (Infms)

0 5 10 15 200

5

10

15

20

Diff

ere

ntia

l [A

]

Restraining [A]

12

3

4

5 6

7

8

91011121314

15

16

1718

19

20

2122

23

24252627282930

313233

Phase A (Infms)


dI/dt principle enables the B30 to detect CT saturation (Case 2)

dI/dt principle enables the B30 to detect CT saturation (Case 2)


Saturation Detector: Saturation Detector: State MachineState Machine

NORMAL

SAT := 0

EXTERNAL

FAULT

SAT := 1

EXTERNALFAULT & CT

SATURATION

SAT := 1

The differentialcharacteristic

entered

The differential-restraining trajectoryout of the differential

characteristic forcertain period of time

saturationcondition

The differentialcurrent below thefirst slope forcertain period oftime



• Operation:Operation:– The SAT flag WILL NOT set during internal

faults whether or not the CT saturates– The SAT flag WILL SET during external faults

whether or not the CT saturates– The SAT flag is NOT used to block the relay

but to switch to 2-out-of-2 operating principle


ExamplesExamples

• The oscillograms on the next two slides were captured from a B30 relay under test on a real-time digital power system simulator


B30 Bus Differential Relay: B30 Bus Differential Relay: External Fault ExampleExternal Fault Example

0.06 0.07 0.08 0.09 0.1 0.11 0.12-200

-150

-100

-50

0

50

100

150

200

time, sec

curr

en

t, A

~1 ms

The bus differentialprotection elementpicks up due to heavyCT saturation

The CT saturation flagis set safely before thepickup flag

Despite heavy CTsaturation theexternal fault currentis seen in theopposite direction

Thedirectional flagis not set

The elementdoes notmaloperate


B30 Bus Differential Relay: B30 Bus Differential Relay: Internal Fault ExampleInternal Fault Example

The bus differentialprotection elementpicks up

The saturationflag is not set - nodirectionaldecision required

The elementoperates in10ms

All the fault currentsare seen in one

direction

Thedirectionalflag is set


Dynamic Bus ReplicaDynamic Bus Replica

• The dynamic bus replica mechanism is provided by associating a status signal with each current of the differential zone

• The status signal is a FlexLogicTM operand

• The status signals are formed in FlexLogicTM – including any filtering or extra security checks – from the positions of switches and/or breakers


Dynamic Bus ReplicaDynamic Bus Replica

BUS SECTION 2

F1

U7a

SOURCES

SRC 1

FLEXLOGICTM

Cont Ip 1 On BUSZ1

BUS ZONE 1A STATUS

BUS ZONE 1A SOURCE

BUS SECTION 1


Dynamic Bus Replica: Dynamic Bus Replica: ExampleExample

NORTH BUS

SOUTH BUS

CT-8

B-5

B-6

CT-5

CT-6

S-5

S-6

B-4CT-4

S-3

S-4

B-3CT-3

S-1

S-2

B-2CT-2

CT-1

B-1

C-1 C-2 C-4

C-3 C-5

CT-7

B-7



NORTH BUS

SOUTH BUS

CT-7

CT-8

B-7

B-5

B-6

CT-5

CT-6

S-5

S-6

B-4CT-4

S-3

S-4

B-3CT-3

S-1

S-2

B-2CT-2CT-1

B-1

C-1 C-2 C-4

C-3 C-5

B30 #1



NORTH BUS

SOUTH BUS

CT-7

CT-8

B-7

B-5

B-6

CT-5

CT-6

S-5

S-6

B-4CT-4

S-3

S-4

B-3CT-3

S-1

S-2

B-2CT-2CT-1

B-1

C-1 C-2 C-4

C-3 C-5

B30 #2


Dynamic Bus Replica: Dynamic Bus Replica: ZoningZoning

NORTH BUS

SOUTH BUS

CT-8

B-5

B-6

CT-5

CT-6

S-5

S-6

B-4CT-4

S-3

S-4

B-3CT-3

S-1

S-2

B-2CT-2

CT-1

B-1

C-1 C-2 C-4

C-3 C-5

CT-7

B-7

B30 #2

B30 #1D60 #1


BenefitsBenefits

• Sensitive settings are possible

• Very good through-fault stability

• Fast operation: – fast form-C contacts and FlexLogicTM operands:

typically 10-12ms– form-A trip rated contacts: typically 13-15ms

• Benefits of the UR platform (metering and oscillography, event recorder, FlexLogicTM, fast peer-to-peer communication, etc.)

Documents

Universal Relay Family B30 Bus Differential Relay