Grounding; Inspection Before Energization; Operation - HPS NH Serie Guía De Instalación, Operación Y Mantenimiento

three phase and 100 kVA single phase, to facilitate
cable entry.
For non-ventilated transformers, pre-punched
knockouts are not provided and the appropriate cable
connector suitable for the application must be used.
Please refer to figures 1 and 2 (pages 9 and 10)
for cable entry locations.
Warning: Never attempt to change con-
nections or taps unless the transformer is
de-energized and all windings grounded.
Side entry of cables is recommended as it leaves
the ventilated areas unobstructed.
Cable connection lugs of plated copper or
aluminum may be used to connect to the transformer
terminals. Terminals should be cleaned and electrical
joint compounds are recommended for use on all
electrical connections.
Refer to the transformer nameplate for primary
and secondary voltage connection combinations and
primary and/or secondary tap positions as applicable.
Transformers received from the factory will have
tap leads installed on the nominal, or 100%, voltage
position. The balance of the tap positions will still be
coated with impregnation material and insulation.
To change taps, it is necessary to remove this
insulation by gently removing the protective coating
from the surface appropriately. The surface of the tap
lead should be clean and coated subsequently with
electrical compound.
NOTE: After installation of cables and
connectors, a minimum of 1" clearance
must be maintained from energized parts
to all case parts.

GROUNDING

All core and coil assemblies are solidly grounded
to the enclosure internally to ensure that all conductive
metal parts have the same potential.
The transformer enclosure in turn should also be
securely and effectively grounded as a safety
precaution.
This grounding should be in accordance with
national electrical code standards.

INSPECTION BEFORE ENERGIZATION

For the safe and proper operation of the
transformer, please check and verify the following:
a) The insulation resistance, core to primary, core to
secondary and primary to secondary, should be
greater than 10k ohms.
b) Before energizing and connecting any loads,
please measure and verify the output voltage
matches nameplate specifications.
c) Ensure correct phase connections. Refer to the
nameplate vector diagram.
d) The load on a delta secondary winding with a 120
volt center tap should not exceed the normal current rating of the winding. This center tap is
designed for a max. of 5% of the nameplate kVA.
e) When windings are connected in parallel (as in
the case of dual voltage primaries), the primary
taps for all coils must be connected to the
identical percentage tap positions to avoid the
shorting of turns. For tap positions, refer to the
nameplate on the transformer.
f) The enclosure should be grounded with the
appropriately sized conductor.
g) The total load among all the phases should be
balanced as much as possible for optimum
performance of the transformers windings.
Any three phase or single phase load may be
connected to the transformer but the kVA loading
on each phase must not exceed 1/3 of the
nameplate kVA rating.
h) The clearance and tightness of all electrical
connections should be checked.
i) If there is any reason to suspect that the
transformer has been exposed to moisture during
transit or storage, it should be checked for
dryness before energization. This can be done by
making an insulation resistance test. Dry-out
procedures are on page 6.

OPERATION

For all relatively normal and clean installations,
dry-type transformers will operate satisfactorily under
normal conditions of energization and load.
For your reference, fully loaded dry-type
transformers may appear warm to the touch,
particularly on the cover of the unit.
Standards permit the temperatures of the cover
to be 65°C (149°F) over ambient. This represents
normal loading and should not be of concern.
Dry-type transformers are designed to operate
continuously at their full nameplate kVA rating.
ANSI C57.96 provides guidance for loading
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