Customer : Project : ABB Ref.no. : Vk Value calculation for Transformer Diff. Protection ( Relay used : CAG34) System Voltage in kV CT Primary CT Secondary ( 1 or 5A) Trasnformer rating in kVA Rct (CT Sec.) RL (Lead Resistance)
11 1200 1 500 8 100
Formula : Vk = 40 I (Rct+2RL)
Vk
Vk value required is Magnetising current, Ie < 30mA at VK / 2
394.40 414
Volts
Customer : Project : ABB Ref.no. : Vk Value calculation for Transformer REF Protection ( Relay used : CAG14) System Voltage in kV CT Primary CT Secondary ( 1 or 5A) Trasnformer rating in kVA Percentage Impedence ( Z %) Rct (CT Sec.) RL (Lead Resistance)
6.6 250 1 2250 6.5 2 5
Full load current = Transformer Rating / ( V3 / System Voltage)
196.83
Fault current = Full load current / Percentage Impedence Fault Current reflected to CT Sec. = (Fault current / CT Primary) x CT Secondary Formula : Vk = 2 If (Rct+2RL)
3028.15
If
12.11
Vk
50.70
Vk value required is Magnetising current, Ie < 30mA at VK / 2
56
Volts
Customer : Project : ABB Ref.no. : Vk Value calculation for Motor Diff. Protection ( Relay used : CAG34) System Voltage in kV CT Primary CT Secondary ( 1 or 5A) Motor rating Power factor Percentage Impedence ( Z %) Rct (CT Sec.) RL (Lead Resistance)
6.6 350 1 2555 0.8 8 2 5
Full load current = Transformer Rating / ( V3 / System Voltage)
279.39
Fault current = Full load current / Percentage Impedence Fault Current reflected to CT Sec. = (Fault current / CT Primary) x CT Secondary Formula : Vk = 2 If (Rct+2RL)
KV A A kW Cos % Ohm Mtrs.
3492.36
If
Vk
Vk value required is Magnetising current, Ie < 30mA at VK / 2
9.98
41.77 46
Volts
Customer : Project : ABB Ref.no. : Vk Value calculation for Stabilising Resistors & Metrocils ( Relay used : CAG34) System Voltage in kV CT Primary CT Secondary ( 1 or 5A) Motor rating Power factor Percentage Impedence ( Z %) Rct (CT Sec.) RL (Lead Resistance) Relay rated current (1 or 5A) Assuming relay setting (10-40%) Relay burden at setting current Relay setting in Amp (Is)
6.6 250 1 1805 0.8 8 2 5 1 0.1 1 0.1
Full load current = Transformer Rating / ( V3 / System Voltage)
KV A A kW Cos % Ohm Mtrs. A VA A 197.38
Fault current = Full load current / Percentage Impedence
2467.21
Fault Current reflected to CT Sec. = (Fault current / CT Primary) x CT Secondary
If
Formula : Vk = 2 If (Rct+2RL)
Vk
Vk value required is
9.87
41.31 45
Volts
Magnetising current, Ie < 30mA at VK / 2 Voltage across relay Formula : Vr = If (Rct+2RL)
Vr
20.66
Stabilising Resistor Formula : Rs = {Vr-Is - VA Burden of Relay / (Is) Sq.}
Rs
106.55
Vk
2038.45
V Peak
812.30
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.
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