ABB REG316 4 Series - Contactor; Grounding Resistor R E; Residual Current C.t

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. B
4-34
only a limited damping capacity. The output power of the v.t. in
the example varies at a continuous current of 2 A between 577
and 831 VA.
When the main priority is to prevent mal-operation, the resistor
Rp is chosen according to the maximum continuous rating of the
v.t’s which is usually in the range of 5 to 10 % of the permissible
10 s current. Where the v.t’s are also used for metering, it should
be noted that the voltage and phase errors increase at the
maximum continuous current.
4.2.5.6. Grounding resistor R
e
The grounding resistor must be rated for 10 s. A voltage drop of
20 % is allowed if a v.t. is used as grounding transformer. For a
ground fault current of 20 A and a rated voltage of UN = 10.5 kV,
the recommended value of the resistor is:
U
N
U
broken
D
R
p
R
e
I
2
[V] [V]
[W]
[A] v.t. [A] 10 s
10,500 500 250 2
1.7 W
240
4.2.5.7. Contactor
The contactor switches both ends of the grounding resistor R
e
.
4.2.5.8. Residual current c.t.
Alternative I:
1 core-balance c.t. 100/1 A, rated burden 2.5
W.
Alternative II:
3 bushing c.t’s, .../5 A - 33/1 A, rated burden 1.5
W.
The above burdens apply for c.t. leads of 2 x 100 m with a gauge
of 4 mm
2
.