GE P645

Parameter Description Value
IH2 Diff Set This setting defines the second harmonic blocking threshold. 20%
Cross blocking
This setting enables or disables cross blocking (cross blocking is where a 2nd harmonic
block
ing signal from any one phase, blocks all three phases).
Enabled
CT Saturation This setting enables or disables CT saturation detection. Enabled
No Gap This setting enables or disables CT Gap detection. Enabled
IH5 Diff Set This setting defines the fifth harmonic blocking threshold. 35%
A series of external faults were simulated to determine the CT requirements for the differential function, by using a
state of the ar
t Real Time Digital Simulation system (RTDS). We performed these tests with different X/R ratios, CT
burdens, fault currents, fault types and points on the current waveform.
To achieve through-fault stability, the K dimensioning factor must comply with the following expressions:
System Conditions K Kneepoint voltage (VK)
In < I
F
<= 40In
5 <= X/R <= 20
16
V
K
=> 16In(R
CT
+ 2R
L
+ R
r
) (ear
th fault)
V
K
=> 16In(R
CT
+ R
L
+ R
r
) (phase fault)
40In < I
F
<= 64In
5 <= X/R <= 20
30
V
K
=> 30In(R
CT
+ 2R
L
+ R
r
) (ear
th fault)
V
K
=> 30In(R
CT
+ R
L
+ R
r
) (phase fault)
In < I
F
<= 40In
20 <= X/R <= 120
17
V
K
=> 17In(R
CT
+ 2R
L
+ R
r
) (ear
th fault)
V
K
=> 17In(R
CT
+ R
L
+ R
r
) (phase fault)
40In < I
F
<= 64In
20 <= X/R <= 120
34
V
K
=> 34In(R
CT
+ 2R
L
+ R
r
) (ear
th fault)
V
K
=> 34In(R
CT
+ R
L
+ R
r
) (phase fault)
where:
● V
K
= kneepoint v
oltage
● K = CT dimensioning factor
● I
n
= rated current
● R
CT
= resistance of CT secondary winding
● R
L
= resistance of a single lead from device to current transformer
● R
r
= resistance of any other protection devices sharing the current transformer
● I
F
= maximum external fault level
5.10.2 CT REQUIREMENTS - SMALL BUSBAR APPLICATION
We strongly recommend Class X or Class 5P current transformers for this application.
The curr
ent transformer knee-point voltage requirements are based on the following settings:
Parameter Description Value
Is1
This sets the minimum differential current threshold required for the transformer differential
pr
otection to trip.
1.2 pu
Is2
This defines the bias current threshold at which the second slope of the bias current
characteristic becomes active.
0.4 pu
K1 This setting defines the gradient of the first slope in the bias current characteristic. 20%
K2 This setting defines the gradient of the second slope in the bias current characteristic. 80%
Is-HS1
This setting defines the first High set threshold on the bias current characteristic. This setting
is only used in advanced mode.
10 pu
Is-HS2
This setting defines the second High set threshold on the bias current characteristic. This
setting is only used in advanced mode.
Disabled
P64x Chapter 6 - Transformer Differential Protection
P64x-TM-EN-1.3 139