3. 132/11 kv Power Transformer Protection

3.1 Differntial Protection relay P642

3.1.1 Data

a Transformer Data

Rated Voltage 132 11

Rated Power @ 132 KV 20 MVA

Rated Power @ 11KV 20 MVA

Vector Group YNd11

Short Circuit Impedance

Normal Tapping 9.48 ℅

Min Tapping

Max. Tapping

b Relay Data

Relay type P642

Rated Current 1/5A

c CT data Primary in A Secondary in A

At 132 KV side 100 1

At 11 KV side 1200 1

3.1.2 Relay Configuration

a Configuration Parameters

b Configuration function parameters

Eneblinmg the protection relay

Phase Sequence

Nominal Current CT primary

132 kv, end A 100

11kv, end B 1200

Nominal Current CT primary

132 kv, end a 100

11 kv, end b 1200

c Referance Current

At 132 KV side I Ref A 87 A

At 11 KV side I Ref B 1050 A

d Referance Power

At 132 KV side S Ref A 20MVA

At 11 KV side S Ref B 20MVA

e Maching Factor

Maching Factor 132 Kv Side 1.14

Maching Factor 11Kv Side 1.14

3.1.3 Differntial Protection Setting Calculation

a The differntial starting thershold (Idiff>)

The transformer has voltage range of voltage regulation per tap as 1%

(Idiff>) 0.2xIref

b The differntial thershold (Idiff>>)

(Idiff>>) 7xIref

The differntial starting thershold (Idiff>) is set between 0.2xIntrafo and 0.4x intrafo taking in to account the CT accuracy and

the voltage difference due to the voltage regulation.

The threshold (Idiff>>) is used to disable the inrush and overflux restraint functions. It must be set above the magnetizing

current of the transformer.Assuming the inrush current is less than 6 times the rated current in peak value:-

3.2 Back up Overcurrent Protection relay P14DB

3.2.1 132 KV side Back up Overcurrent Protection relay P14DB

3.2.1.1 Data

a Relay data

Relay type P14DB

Rated current 1/5A

Rated Voltage 110-250 V DC

b Configuration Set up

Overcurrent Enabled

Earth Fault 1 Enabled

CB fail Enabled

c CT raito

CT Primary 100

CT secondary 1

E/F CT Primary 100

E/F CT secondary 1

4.1.1.2 Back Up Over current Protection Setting Calculation 132KV Side

a The low thershold (I>)

The low thrershold (I>) is set to protect the Autotransformer against overloading.

The thersholod is set to 120 % of the rated primary current.

Rated primary current of transformer 87 A

Overloading factor 1.2

CT raito 100

The low thrershold (I>) is

(I>) 1.05

Selection of time characterstic IEC E Inverse (IEC Extremely Inverse)

The TMS is set to ensure a tripping time of 40 sec for 2xIref

For IEC E inverse k=80 , L=0 , α=2

TMS 0.56282

For a better safety the TMS shall be 0.33 thus the tripping time will be 35.8 sec

b The High thershold (I>>)

Selection of time characterstic DT

The Maximum three phase fault current at Kanoria seen by 132 kv side is :-

I 3ph 2353 A

The High thershold (I>>) is set 1.2 times If 2823.14

(I>>) 28.2

(t>>) 600 msec

4.1.1.3 Back Up Over current Protection Setting Calculation 11KV Side

a The low thershold (I>)

The low thrershold (I>) is set to protect the transformer against overloading.

The thersholod is set to 120 % of the rated primary current.

Rated primary current of transformer 1050 A

Overloading factor 1.2

CT raito 1200

The low thrershold (I>) is

(I>) 1.05

Selection of time characterstic IEC E Inverse (IEC Extremely Inverse)

The TMS is set to ensure a tripping time of 35 sec for 2xIref

For IEC E inverse k=80 , L=0 , α=2

TMS 0.49246

For a better safety the TMS shall be 0.5 thus the tripping time will be 30 sec

b The High thershold (I>>)

Selection of time characterstic DT

The Maximum three phase fault current at Kanoria seen by 11 kv side is :-

I 3ph 28231 A

The High thershold (I>>) 28231.43

(I>>) 23.5

(t>>) 400 msec