ABB REG316 4 Series - Page 281

REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-243
REs and MTR in the case of secondary injection at the
generator terminals
An injection transformer block Type REX 011-2 is needed for this
circuit.
The bias voltage can also be injected across part of the
grounding resistor connected to the broken-delta secondaries of
a grounding v.t’s at the generator terminals (see Fig. 3.5.24.3).
The two resistors R'
Es
and R'
Ps
limit the maximum current at the
star-point which must not exceed 20 A. The total resistance is
thus :
Condition 1:
R' R'
U
3I
3N
N
Es Ps
Gen
Emax
2
1
2
+³
´
´
´
æ
è
ç
ö
ø
÷
where: U
Gen
phase-to-phase voltage at the generator
terminals
I
Emax
max. star-point current = 20 A
N
1
/N
2
ratio of the grounding transformer.
The grounding resistors R'
Es
and R'
Ps
must fulfil the following
conditions:
Condition 2:
R' 130
3N
N
Ps
2
1
2
³´
´
æ
è
ç
ö
ø
÷
W and R' 500
3N
N
Ps
2
1
2
£´
´
æ
è
ç
ö
ø
÷
W
Condition 3: R' 4.5 R'
Es Ps
³´
Condition 4:
R' 0.7 k
3N
N
Es
2
1
2
³´
´
æ
è
ç
ö
ø
÷
W
and R' 5.0 k
3N
N
Es
2
1
2
£´
´
æ
è
ç
ö
ø
÷
W
The v.t. must be designed such that for a solid ground fault at
the generator terminals, the rated frequency component voltage
Us
= 100 V ±20 %, i.e. the ratio MTR' = N'
12
/ N'
11
must lie within
the following range:
Condition 5:
1.2 n
N'
N'
0.8 n
12
11
´³ ³ ´, where
n
U
3 100 V
3N
N
R'
R' R'
Gen
2
1
Es
Es Ps
=
´
´
´
´
+
A v.t.
N'
N'
U
3100V
3N
N
12
11
Gen 2
1
=
´
´
´
will fulfil condition 5 in most cases.
The settings for R
Es
and MTR must be entered via the HMC, i.e.
the values of R'
Es
and MTR' reflected to the primary of the
grounding transformer: