3 RESTRICTED EARTH FAULT PROTECTION IMPLEMENTATION
3.1 ENABLING REF PROTECTION
A REF element is available for each of the windings (HV, LV, and if applicable, TV) as well as one for
Autotransformer
s. For each of these windings you can disable REF protection or set it to Low Impedance or
High Impedance using the settings REF HV Status, REF LV Status, REF TV Status and REF Auto Status in the
REF PROTECTION column.
Low impedance REF is blocked if:
● Current Transformer Supervision operates
● Stub Bus protection is activated (on a per-winding basis)
High impedance REF is not blocked by Current Transformer Supervision or Stub Bus Protection.
3.2 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:
P64x Chapter 8 - Restricted Earth Fault Protection
P64x-TM-EN-1.3 173
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