The connection of a restricted earth fault function is shown in Figure
. It is connected across
each directly or low impedance earthed transformer winding.
Id
IEC05000177-2-en.vsd
IEC05000177 V2 EN-US
Figure 38: Application of HZPDIF function as a restricted earth fault protection for a star
connected winding of an YNd transformer
Setting example
It is strongly recommended to use the highest tap of the CT whenever high
impedance protection is used. This helps in utilizing maximum CT capability,
minimize the current, thereby reducing the stability voltage limit. Another
factor is that during internal faults, the voltage developed across the selected
tap is limited by the non-linear resistor but in the unused taps, owing to auto-
transformer action, voltages much higher than design limits might be induced.
Basic data:
Transformer rated current on HV winding:
250 A
Current transformer ratio:
300/1 A (Note: Must be the same at all locations)
CT Class:
10 VA 5P20
Secondary resistance:
0.66 ohms
Cable loop resistance:
<50 m 2.5mm
2
(one way) gives 2
ˣ
0.4 ohm at 75° C
Max fault current:
The maximum through fault current is limited by
the transformer reactance, use 15
ˣ
rated current of
the transformer
Section 6
1MRK 505 343-UEN B
Differential protection
106
Application manual
Содержание Relion 670 series
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