GE MiCOM P142 Agile User Manual

2 CT REQUIREMENTS
The current transformer requirements are based on a maximum fault current of 50 times the rated current (In) with
the device having an instantaneous over
current setting of 25 times the rated current. The current transformer
requirements are designed to provide operation of all protection elements.
Where the criteria for a specific application are in excess of this, or the lead resistance exceeds the limiting lead
resistance shown in the following table, the CT requirements may need to be modified according to the formulae in
the subsequent sections:
Nominal Rating Nominal Output Accuracy Class Accuracy Limited Factor
Limiting Lead
Resistance
1A 2.5 V
A 10P 20 1.3 ohms
5A 7.5 VA 10P 20 0.11 ohms
The formula subscripts used in the subsequent sections are as follows:
V
K
= Requir
ed CT knee-point voltage (volts)

f
= Maximum through-fault current level (amps)

n
= Rated secondary current (amps)
R
CT
= Resistance of current transformer secondary winding (ohms)
R
L
= Resistance of a single lead from relay to current transformer (ohms)
R
st
= Value of stabilising resistor for REF applications (ohms)

s
= Current setting of REF elements (amps)
V
S
= Required stability voltage
2.1 PHASE OVERCURRENT PROTECTION
2.1.1 DIRECTIONAL ELEMENTS
Time-delayed phase overcurrent elements
V
I
R R R
K
cp
CT L p
= + +
2
( )
Instantaneous phase overcurrent elements
V
I
R R R
K
fp
CT L p
= + +
2
( )
2.1.2 NON-DIRECTIONAL ELEMENTS
Time-delayed phase overcurrent elements
V
I
R R R
K
cp
CT L p
= + +
2
( )
Chapter 9 - Current Transformer Requirements P14x
200 P14xEd1-TM-EN-1

GE MiCOM P142 Agile Specifications

General

Brand	GE
Model	MiCOM P142 Agile
Category	Control Unit
Language	English