ABB RET 541 - Page 54

Fig. 9 Protection, control, measurement and supervision functions of YNyn-connected power transform-
ers, implemented with RET 543 transformer terminals, REF 543 feeder terminals and REA 101 arc
protection. The neutral point of the low-voltage network is earthed via a low resistance. The
scheme is also applicable to other types of low-impedance earthed networks, where the neutral
point is earthed effectively or via a low reactance. This sceme can be applied also for parallel con-
nected transformers.
RET/3I
REF/3I
REF, REA/3I
RET/3I
RET/1I
REF/1I
REF/1I RET/1I
REF/3U REF/3U
REF/3U RET/1U
RET/RTD
P>
Θ
Θ
df/dt
I >
CBFP 62BF
51N
50N
0
R
TCS
CBCM
MCS
E
27
59
3U<
3U>
3U
0
I3I
REF 54_
67
3I>
f> 81O
pf
f
3I>
&
REA 101
81O-R
000
3
U
R
TCS
U
3ΔI >
87T
RET 54_
3I
U
513I>
50
51N
50N
I >
0
62BFCBFP
49T
513I>
50
HV
LV
HV
HV
62BFCBFP
LV
87TN
LV
51N
50N
I >
0
LV
I
0
ΔI >
0
87TN
HV
ΔI >
0
I
0
3I
O
T
w
T
90
3I >
2f
68
HV
000
000
TCS
R
3I> 51
50
68
3I >
2f
I >
0
50N
51N
62BF
CBFP
REF 54_
3I I
0
3U
3U< 27
59
3U>
000
YNyn transformers impedance earthed LV neutral
M
MF
M
M
MF
M
Transformer Terminal RET 541, RET 543, RET 545
1MRS755543
54