GE P645

3.3 SELECTING THE CURRENT INPUTS
The P642 has two current terminal inputs (T1 and T2), the P643 has up to three terminal current inputs (T1 to T3),
and the P645 has up to fiv
e current terminal inputs (T1 to T5).
For the P642, you associate one terminal current input with the HV (High Voltage) winding and the other with the
LV (Low Voltage) winding.
For the P643 and P645 you can choose to associate more than one terminal current input with particular windings.
In cases where more than one terminal CT is associated with a winding, the input to the differential protection
function uses the vector sum of the current terminal inputs (on a phase by phase basis) as the input to the
calculation for that winding.
You associate these current inputs with the system transformer windings with the settings HV CT Terminals, LV CT
Terminals and TV CT Terminals in the SYSTEM CONFIGURATION column as follows:
Setting P642 P643 P645
HV CT Terminals 01
001
011
00001
00011
00111
01011
01111
LV CT Terminals 10
100
110
10000
11000
11100
11010
11110
TV CT Terminals 010
00100
01100
00110
01110
Where the terminals T1 to T5 correspond to the bits in the binary string as follows (1 = in use, 0 = not in use). The bit
or
der starts with T1 on the right-hand side. For example:
If a CT is assigned to more than one winding, then an alarm is issued (CT Selection Alm). When this DDB signal is
asserted, the protection is also blocked.
Winding associations for the P643
If an overcurrent element is assigned to the HV winding then the associated setting I>(n) Current Set is relative to
the T1 CT. Therefore if if the T1 CT setting is changed, then I>(n) Current Set will be affected accordingly.
The same is true for the LV winding and its associated T3 CT as well as for the TV winding and its associated T2 CT.
Winding associations for the P645
If an overcurrent element is assigned to the HV winding then the associated setting I>(n) Current Set is relative to
the T1 CT. Therefore if the T1 CT setting is changed, then I>(n) Current Set will be affected accordingly.
The same is true for the LV winding and its associated T5 CT as well as for the TV winding and its associated T3 CT.
P64x Chapter 9 - Current Protection Functions
P64x-TM-EN-1.3 203