NON-DIRECTIONAL EARTH FAULT LOGIC
Not applicable for IN1
I2H Any Start
2H Blocks IN>2
IN2>1 Timer Blk
AR Blk Main Prot
AR Blocks IN>3
AR blocking available for DT-only stages
*1 If a CLP condition exists, the I>(n) Current Set threshold is taken from the COLD LOAD PICKUP column
*2 Autoreclose blocking is only available for stages 3,4 and 6 and on selected models
*3 The CTS blocking is not applicable for IN1, however this can be achieved using the PSL
Figure 48: Non-directional EF logic (single stage)
The Earth Fault current is compared with a set threshold (IN1>(n) Current) for each stage. If it exceeds this
threshold, a Start signal is triggered, providing it is not blocked. This can be blocked by the second harmonic
blocking function, or an Inhibit Earth Fault DDB signal.
The autoreclose logic can be set to block the Earth Fault trip after a prescribed number of shots (set in
AUTORECLOSE column). This is achieved using the AR Blk Main Prot setting. this can also be blocked by the
relevant timer block signal IN1>(n)TimerBlk DDB signal.
Earth Fault protection can follow the same IDMT characteristics as described in the Overcurrent Protection
Principles section. Please refer to that section for details of IDMT characteristics.
The diagram and description also applies to the Earth Fault 2 element (IN2).
The IDG curve is commonly used for time delayed earth fault protection in the Swedish market. This curve is
available in stage 1 of the Earth Fault protection.
The IDG curve is represented by the following equation:
5 8 1 35
is the operating time
I is the measured current
IN> Setting is an adjustable setting, which defines the start point of the characteristic
Chapter 6 - Current Protection Functions
Note: This diagram shows the logic for IN2 (derived earth fault ). The logic
for IN1 (measured earth fault ) follows the same principles, but with no CTS
This diagram does not show all stages . Other stages follow similar
AR blocking is only available for stages 3 and 4 .