REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-239
REs and MTR in the case of secondary injection at the star-
point
An injection transformer block Type REX 011-1 is needed for this
circuit.
The bias voltage can also be injected across part of the
grounding resistor connected to the secondary of a grounding
v.t. (see Fig. 3.5.24.2).
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
N
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 following conditions must also be fulfilled:
Condition 2:
R' 130
N
N
Ps
2
1
2
³´
æ
è
ç
ö
ø
÷
W and
R' 500
N
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
N
N
Es
2
1
2
³´
æ
è
ç
ö
ø
÷
W and
R' 5.0 k
N
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
N
N
R'
R' R'
Gen
2
1
Es
Es Ps
=
´
´´
+
A v.t.
N'
N'
U
3100V
N
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:
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