Instruction For Installation; General; Checking Voltage Transformers Upon Arrival; Preparations Before Installation Of Voltage Transformers - ABB TDO 6 Instructions For Installation, Use And Maintenance Manual

4. Instruction for installation

4.1 General

A voltage transformer is a piece of electrical equipment and its
electrical installation shall be done by skilled person only. Observe
the provisions of local legislation regarding the minimum age and
the competence criteria for personnel working with or in vicinity of
electrical installations.
If local legislation is not applicable, the guidelines set forth in EN
50110-1 shall be observed.

4.2 Checking voltage transformers upon arrival

Inspection shall be made upon arrival of voltage transformer for
any signs of damage or tampering incurred during shipment.
Make sure that voltage transformer parameters
indicated on the rating plate comply with the
parameters specified on the order!
If:
– there are any damages in the shipment,
– voltage transformer has been damaged,
– or voltage transformer ratings do not comply with order
specification,
notify the carrier and contact the voltage transformer
manufacturer. Keep the written record of damages until complaint
resolution.

4.3 Preparations before installation of voltage transformers

Perform a visual inspection of the voltage transformer prior to
installation paying particular attention to the following points:
– cast resin (enclosure) is in good condition,
– voltage transformer terminals and surfaces of housing and base
are clean and without visible mechanical damages,
– there are no signs of moisture on the voltage transformer; in
case of visible signs of moisture, the voltage transformer must
be dried,
– voltage transformer ratings comply with technical specification of
connection.
Prior to installation of the voltage transformer perform the following
measurements:
a) measurement of insulation resistance of primary
winding:
– insulation resistance of unearthed transformer (with
two insulated primary terminals) shall not be lower than
1000 MΩ, use 2,5 kV coil megaohmmeter to measure
the resistance between short-circuited terminals of
primary winding and base,
6 Instruction manual
– insulation resistance of earthed transformer (with one insulated
primary terminal) shall not be lower than 200 MΩ. Use 1 kV coil
megaohmmeter to measure the resistance between short-
circuited terminals of primary winding and base.
Prior to measurements of insulation resistance for
earthed transformer (with one insulated primary ter-
minal) remove an earthing screw from "N" terminal
in terminal strip and remember to reattach it after
completing measurements.
b) measurement of insulation resistance of secondary
windings:
– insulation resistance of secondary windings insulation
shall not be lower than 50 MΩ. Use 1 kV coil
megaohmmeter for measurements.
Prior to measurements of insulation resistance of se-
condary windings remove earthing screws in one of
the terminals of each secondary winding, if screwed
in. Reattach these earthing screws and ground one
of the terminals according to voltage transformer
connection diagrams.

4.4 Safety instructions

a) Installed voltage transformer shall be always considered as part
of interconnected circuit. Never attempt to touch the leads,
terminals or other parts of the voltage transformer unless they
are known to be properly connected and ground.
b) Always ground the metal base of voltage transformer.
c) If secondary winding is earthed at several points, only the same
terminal of secondary winding may be used for grounding.
Check with care if both terminals of the same secondary
winding are not grounded by accident. Grounding both
terminals of secondary winding can result in damage of voltage
transformer over a short period of time. Any claims for resulting
transformer damages will be void.
d) If auxiliary secondary windings of earthed transformers (single-
pole insulated) are connected to open delta, only one node of
open delta circuit may be earthed.
e) If two unearthed voltage transformers (double-pole insulated)
operate in V-connection, only one of the two terminals of
secondary winding may be earthed.