ge digital energy multilin

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GE Digital Energy Multilin

Terrence [email protected]

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Transformers

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• Who was the better actor in a transformer movie:

• A – Marky Mark

• B- Shia Labuff.

Pole Question

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Power Transformer -- an expensive device

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Generator Step-Up (GSU) Transformers

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• 1300 MVA • 343 ±2x1.9% / 25 kV • 60 Hz • 3-phase • ODAF (oil-immersed, forced oil - forced air cooling)

GSU xfmr

Aux. xfmr

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Step-Down Distribution Substation Transformers

• 24 MVA • 138 / 13.8 kV • 60 Hz • 3-phase • FOA

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1000 MVA346 ±17x3.66 kV / 225 kV60 Hz3-phaseOA/FA/FA (self-cooled/ forced air cooled)

Autotransformers

ADVANTAGES: reduced weight and size per kVA lower cost lower leakage reactance lower losses and better eficiency lower exciting current

DISADVANTAGE: no electrical isolation between

primary and secondary sides

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Transformer Differential Protection (87) compares the current going into the transformer zone against the current leaving the transformer zone

CT Polarities are show as pointing away from the transformer or protected zone

Protected Zone Protected Zone

No-Fault ConditionsI1 + I2 = 0

I1 I2 I1 I2

Fault ConditionsI1 + I2 > 0

• Phase-to-phase faults• Three-phase faults

• Ground faults• Core faults• Tank faults

Differential Protection Principle (87T)Active internal faults detected by 87T protection:

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Transformer Differential ChallengesAccount for unequal CT performance by sloped differential characteristicAccount for different currents with magnitude compensationAccount for phase difference and zero seq current with phase compensation.

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Transformer Differential Settings

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Transformer Differential Challenges

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• Why does polarity matter:

• A – it properly determines direction relative to another quantity

• B- You always have to have the dot awayfrom the equipment

• C – It doesn’t really matter.

Pole Question

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CT Connection…Polarity doesn’t matter as long as

its right

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Harmonic currents—percentage of total harmonicsTypical ratios of 2nd harmonic

to fundamental are 10%–60%

CT saturation limits sensitivity

1428 May 2020Transformer Protection |

Inrush currents

2nd-harmonic ratio during inrush

2nd-harmonic ratio

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Harmonic Restraint Mode should be set to:

• A – per phase

• B- two out of three

• C – average

Pole Question

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Typically H Winding leads X winding by 30 degrees

What I expect to see for ABC rotation?

A

C

B

a

b

c

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What I expect to see for ABC rotation?

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Typically H Winding leads X winding by 30 degrees

What I expect to see in secondary current?

H Winding H Secondary H sec ang X Winding X secondary X sec ang100 2.5 0 1000 2.5 -210100 2.5 -120 1000 2.5 -330100 2.5 120 1000 2.5 -90

200/5

200/5

200/5

2000/5

2000/5

2000/5138KV/13.8KV

100A<0

100A<-120

100A<-240

A

C c

a

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Transformer phase compensation in the relay is performed by:

• A – magically shifting the current by the correct angle

• B- using the angle with respect to setting to mathematically determine how the shift is occurring a combination of current to get the shift.

• C – it depends

Pole Question

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28 May 2020Transformer Protection | 20

Delta CTs

Wye CTs

Wye CTs

Wye CTs

Wiring CTs for transformer phase compensation

Old connection to cancel 30° phase shift externally

Modern connection—wire as wye and compensate internally

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CT and transformer-winding settings

Angle compensation

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Differential setup

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Sloped differential adds security from CT inaccuracies

Low region

High region

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Two breakpoints tune differential characteristic

BREAK 1 (B1)—safe limit of linear CT operation

BREAK 2 (B2)—minimum current level that causes large spurious differential signals from CT saturation


S1

S2

Diff

eren

tial

RestrainingMin PKP

B1 B2

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DIR = 1 Internal fault: no current source is greater than 90 degrees apart

DIR = 0External fault: one or more current sources are greater than 90 degrees apart


Phase-comparison element (PCE) detects internal / external fault

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DIF

L

DIR

SAT

DIF

H

OR

AN

D

OR Percent Diff OP

AN

D

Irest

Idiff

U.S. Patent 6442010, General Electric Co.

Directional principle—low region, small restraint

Restraint current is small

Relay trips when Idiff / Irest percentageis greater than Slope 1 AND direction is true


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Flux cannot change instantly, so CTs cannot saturate instantly— t

Fast DSP recognizes swing from restraint to operate region

CT Saturation Detector blocks tripping on external faultIrest

Idiff

External fault with saturationInternal fault

Saturation detector—high region, large restraint


DIF

L

DIR

SAT

DIF

H

OR

AN

D

OR Percent Diff OP

AN

D

U.S. Patent 6442010, General Electric Co.

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How the Relay Compensates for Phase Angle and Zero Sequence Removal

H Winding H Secondary H sec ang X Winding X secondary X sec ang100 2.5 0 1000 2.5 -210100 2.5 -120 1000 2.5 -330100 2.5 120 1000 2.5 -90

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Where do I operate???

For a slope of 25% you should operate when you drop to 75% of original value

Does it operate……..Depends on pickup setting. 0.63/5 is 0.13per unit. So it will operate as long as the pickup is less than 0.13

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What Happens if I only inject single phase values?????

For a slope of 25% you should operate when you drop to 75% of original value

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Transformer Differential

200/5

200/5

200/5

2000/5

2000/5

2000/5138KV/13.8KV

100A<0

100A<-120

100A<-240

A

C c

a

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