Digital Overcurrent & Ground Overvoltage & Selective Ground Relay (GDR-AEF01) User's Manual
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Kyongbo Electronics Co., Ltd.
3.3 Selective Ground Function
This relay has the selective ground protection element to protect from ground accidents
by detecting zero-phase rated voltage generated at GPT 3 phase side and zero-phase
current generated through ZCT, in case of ground accidents in non-grounded system or
resistance grounded system.
Also, it has inverse time and definite time characteristics and designed so that there is
no difficulty in operation time setting. Inverse time characteristic is the function between
current and time, and the bigger the current, the shorter the operation time.
The time and voltage relationship function of the inverse time characteristic is as
follows.
×
sec
T = Operation time
I = Relay input current / Relay operatio setting value
M = Operation time ratio
Logic Diagram for selective ground protection element operation is as follows.
【
Figure 3.14
】
SGR Logic Diagram
