Sices D-PRO, Technical Manual

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20 D-PRO Protection relay Technical Manual
2 - Neutral on genset.
4.6.10
The auxiliary current can be used as a protection of restricted earth fault (or maximum current
differential). In order to calculate the differential current
(A
∑),
the CT of the auxiliary current
should measure the current on the neutral of the generator and the P.0122 parameter should
be set as “2 – Neutral on the generator”.
That way, the device calculates the vector sum of all the four currents measured and therefore
detects and calculates any imbalance, allowing you to implement, by means of the parameters
P.0368 and P.0369 a threshold for the restricted earth fault or maximum current differential
protection (64).
The triggering of the protection generates a lock.
The P.0123 parameter determines where the auxiliary current is measured:
0- Not used.
1- On currents side A.
2- On currents side B.
4.6.11
The sequence current zero “I0” is calculated as the vector sum of the three phases current
divided by three.
The positive sequence current “1+” or “I1” is calculated as 1/3 module of the vector sum of the
three phase currents, aligned in the same direction (120° rotation of L2 phase and 240°
rotation of L3 phase, depending on the rotation sense).
The negative sequence current “I2” is calculated as 1/3 module of the vector sum of three
phase currents, with a 120° rotation of L2 phase in one direction and a 120° rotation of L3
phase in another direction (depending on the rotation sense).
If the load and the cos(ɸ) on the
three phases is balanced, the “I2” current is 0. Basically, it is an unbalance index