
22
Technical guide VUC
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1ZSC000562-AAX en, Rev. 1
a2
a1
b1
b2
e1
g1
b1
a2
a1
b1
b2
e1
g1
b1
a2
a1
f1
d1
b2
g2
e1
g1
b1
c1
f2
d1
Insulation levels
LI is the lightning impulse (1.2/50 µs), and Pf is the power
frequency test voltage (60 s). The insulation levels are
indicated as impulse withstand voltage – power frequency
withstand voltage.
The tests were carried out according to IEC 60214-1,
2014-05, with a new tap-changer and clean insulation
transformer oil LC set -30 °C according to IEC 60296,
2012-02. The withstand voltage value of the oil was higher
than 40 kV/2.5 mm (IEC 60156, 1995-08).
Insulation levels to earth (g1)
For VUC
380-150 kV, 650-275 kV, 750-325 kV,
1050-460 kV, and 1175-510 kV
Lightning impulse levels (LI) and power frequency levels (Pf)
corresponds to the following U
m
-values acc. to IEC:
LI (kV)
Pf (kV)
U
m
(kV)
380
150
72.5
1)
650
275
145
750
325
170
1050
460
300
1175
510
362
Table 4.
1) Covers 76 kV that is not an IEC value.
a1 Between any electrically adjacent contacts in the tap
selector, not connected.
a2 Between the ends of the fine regulating winding (across
range). For coarse/fine switching in minus position, this
means between the freely oscillating end of the coarse
winding and any end of the fine winding.
b1 Between not connected taps of different phases in the
fine selector
b2 Between open contacts of different phases in the diverter
switch.
c1 Between ends of the coarse winding in coarse/fine
switching
d1 Between taps of different phases in the coarse selector
(coarse/fine switching)
e1 Between preselected tap and connected tap of one
phase in the diverter switch and in the tap selector.
f1 Between any end of the coarse winding and connected
tap
f2 Between any end of the coarse winding and the middle
of the fine winding.
g1 Connected tap to earth
g2 Pre-selected tap to earth
Fig. 40. Linear switching (L).
corresponding
contact in
adjacent phase
Fig. 41. Reversing switching (R).
corresponding
contacts in
adjacent phase
Fig. 42. Coarse/Fine switching (D).
corresponding
contacts in
adjacent phase