LEGRAND LE06499AE, Instructions For Installation, Use And Maintenance Manual

Page: 21 / 32

21
Cast Resin Transformers
Installa
tion, use and main
tenanc
e manual
6.2 Tappings for voltage setting on HV windings
The variation of the nominal HV supplied by the electrical authority can be compensated by the tappings setting in order
to keep the nominal LV required and detailed on the rating plate. The voltage setting is made by changing the position of
the adjustment busbars on the tappings. This test must be carried out without load on the transformer.
Standard transformers are equipped with 5 tappings: ±5% in steps of 2.5%.
Before operating on the tappings and modifying the voltage setting, it is necessary that the transformer is off-load.
For transformers with one or two primary voltage windings, the voltage setting indications are detailed on the rating
plate.
The transformer is normally shipped set to the nominal transformation ratio.
NOTE: Any changes made to the adjustments must be identically replicated on all windings.
Example 1: After energising the transformer with a nominal transformer ratio of 20000/400 V, a
no-load secondary voltage of 390 V is detected: 2.5% lower.This means that the voltage at the
primary is 19500 V, or 2.5% lower.To obtain the rated voltage of 400 V at the secondary, it will be
necessary to move the adjustment bar from position 4-7 to position 4-8.
Example 2: The electricity distribution company indicates that in the area where the transformer
will be installed the supply voltage will be 21000 V: 5% higher.To obtain the rated voltage of 400
V at the secondary, it will be necessary to move the adjustment bar from position 4-7 to position
5-6.
It is important to move the adjustment bars on all 3 HV columns so that they are in the same position and con-
nected to the same socket. Any differences would lead to circulating currents that would irreversibly damage
the transformer.
6
7
8
5
4
3
5
4
3
6
7
8
5
4
3
6
7
8
5
4
3
6
7
8
5
4
3
6
7
8