PROTECT ION TR I P UNI TS
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t
I7
t7
I
t
steady state
start-up
t
I7
I
t7
I
Neutral protection : available at 50%, 100% or 200% of the phase currents, or disabled, it is applied to the overcurrent protections L, S and I.
t
100% 200%
50% 150%
L
t
steady state
start-up
S
I
I
I
t t t
Instantaneous Ground Fault (G-ANSI 50N) : with trip curve without instantaneous delay.
100% 200%
50% 150%
L
I4
I4
t4
S
I
I I I
t
Ground fault on toroid (G ext - ANSI 51G & 50GTD) : with trip time independent of the current (t = k) or with constant specific let-through energy (t = k/l 2 ). Pre-alarm that 90% threshold has been reached permits the fault to be reported to supervision systems without interruption of continuity. The protection uses the exter- nal toroid installed, for example, on the star center of the transformer, and is an alternative to the G and Rc functions. The function is active with an auxiliary supply.
t
I3
I4
t4
I
I
t
t
Modified Differential Ground Fault (MDGF): Available with the trip time independent of the current (t = k) or constant specific let-through energy (t = k/l 2 ). This protection function is designed for systems with solidly grounded multi-source ground fault schemes (refer to instruction manual 1SDH001330R005). The complete equipment level solution includes third-party phase current transformers, summing current transformers, and a dedicated terminal (please refer to 1SDA114800R1 or 1SDA114798R1).
I2
t
I3
t2
I
I7
I
t7
t t
I
I1
t1
Start-up function : enables protections S, I and G to operate with higher trip thresholds during the starting phase, avoiding untimely trips due to high inrush currents of certain loads (motors, transformers, lamps). The starting phase lasts 100 ms to 30 s and is recognized automatically by the trip unit: • at the closing of the circuit breaker with a self-supplied trip unit; • when the peak value of the maximum current exceeds the set threshold (0.1…10 x In) with an externally supplied trip unit; a new start-up is possible after the current falls below the threshold.
t
steady state
start-up
I2
t2
I I
I
t
I1
t1
t
Current unbalance (IU – ANSI 46) : with constant trip time (t = k), protects from an unbalance between the currents of the single phases protected by the circuit breaker.
100% 200%
50% 150%
t
L
S
I7
I
I
t7
I
I
t
t
steady state
start-up
I4
t4
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