Knee Point Voltage Calculation of Ct

CT Knee Point Voltage Calculation Sheet

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CT ratio of the trasformer REF Protection Transformer Rating, MVA % Impedance, %Z Voltage of Line Side, KVLV

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CT Secondary Resistance, RCT (ohm) Resistance of control cable of 2.5 Sq. mm. Loop Length of Control Cable

In MVA 20 -

Primary Secondary Volt Resistance Resistance Length In AMP In kV In ohm In ohm/km in Meter In % 1200 1 13.9 11 -

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Calculation: 1) Fault Current at Primary Side of CT (kA) = MVA/*100(%Z*1.732*KLV)

7.55

2) Fault Current at Secondary Side of CT, If (A)=

6.29

3) Cable Lead Resistance, RL (Ohm)=

1.02

4) Knee Point Voltage Vk (Volt) = 2If(RCT+2RL)

6 -

101.2

REMARKS : Knee Point Voltage of CT provided by CGL for REF CT = 115V and for Differental CT = 200V are in order.

8.5 -

120

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