Customer : Project : ABB Ref.no. :

Vk Value calculation forTransformer Diff. Protection ( Relay used : CAG34)

System Voltage in kV 11CT Primary 1200CT Secondary ( 1 or 5A) 1Trasnformer rating in kVA 500Rct (CT Sec.) 8RL (Lead Resistance) 100

Formula : Vk = 40 I (Rct+2RL) Vk 394.40 Vk value required is 414 Volts

Magnetising current, Ie < 30mA at VK / 2

Customer : Project : ABB Ref.no. :

Vk Value calculation forTransformer REF Protection ( Relay used : CAG14)

System Voltage in kV 6.6CT Primary 250CT Secondary ( 1 or 5A) 1Trasnformer rating in kVA 2250Percentage Impedence ( Z %) 6.5Rct (CT Sec.) 2RL (Lead Resistance) 5

196.83

3028.15

If 12.11

Formula : Vk = 2 If (Rct+2RL) Vk 50.70 Vk value required is 56 Volts

Magnetising current, Ie < 30mA at VK / 2

Full load current = Transformer Rating / ( V3 / System Voltage)

Fault current = Full load current / Percentage Impedence

Fault Current reflected to CT Sec. = (Fault current / CT Primary) x CT Secondary

Customer : Project : ABB Ref.no. :

Vk Value calculation forMotor Diff. Protection ( Relay used : CAG34)

System Voltage in kV 6.6 KVCT Primary 350 ACT Secondary ( 1 or 5A) 1 AMotor rating 2555 kWPower factor 0.8 Cos Percentage Impedence ( Z %) 8 %Rct (CT Sec.) 2 OhmRL (Lead Resistance) 5 Mtrs.

279.39

3492.36

If 9.98

Formula : Vk = 2 If (Rct+2RL) Vk 41.77 Vk value required is 46 Volts

Magnetising current, Ie < 30mA at VK / 2

Full load current = Transformer Rating / ( V3 / System Voltage)

Fault current = Full load current / Percentage Impedence

Fault Current reflected to CT Sec. = (Fault current / CT Primary) x CT Secondary

Customer : Project : ABB Ref.no. :

Vk Value calculation forStabilising Resistors & Metrocils ( Relay used : CAG34)

System Voltage in kV 6.6 KVCT Primary 250 ACT Secondary ( 1 or 5A) 1 AMotor rating 1805 kWPower factor 0.8 Cos Percentage Impedence ( Z %) 8 %Rct (CT Sec.) 2 OhmRL (Lead Resistance) 5 Mtrs.Relay rated current (1 or 5A) 1 AAssuming relay setting (10-40%) 0.1Relay burden at setting current 1 VARelay setting in Amp (Is) 0.1 A

197.38

2467.21

If 9.87

Formula : Vk = 2 If (Rct+2RL) Vk 41.31 Vk value required is 45 Volts

Magnetising current, Ie < 30mA at VK / 2

Voltage across relay Vr 20.66 Formula : Vr = If (Rct+2RL)

Stabilising Resistor Rs 106.55

Vk 2038.45

V Peak 812.30

Full load current = Transformer Rating / ( V3 / System Voltage)

Fault current = Full load current / Percentage Impedence

Fault Current reflected to CT Sec. = (Fault current / CT Primary) x CT Secondary

Formula : Rs = {Vr-Is - VA Burden of Relay / (Is) Sq.}

Vf = Maximum volts that would produce if CT did not sature under internal faults.

Formula : Vf = If {Rs + VA Burden of Relay / (Is) Sq.}

V Peak = Peak Volts developed by CT under internal faults

Formula : V Peak = 2 V2 Sqrt ( Vk ( Vf -Vk ) )

Since Peak Voltage is less than 3kV Metrocil is not required.