5
High Voltage Instrument Transformers | DDB/DFK/DDN/DFN
User manual
ELECTRICAL CONNECTIONS/
Primary connections
The primary terminal material is aluminum or copper. They can
have a tin or silver coating to prevent galvanic pair corrosion and
improve their contact.
Do not bring aluminum into contact with copper-based materials
unless special precautions are taken.
Material
Finish
Cleaning
Copper
Silver or tin plated
We recommend cleaning the contact surfaces with
a soft cloth (avoid brushing with a metal brush)
Aluminum
Aluminum
Unfi nished
We recommended vigorously brushing the contact
surfaces with a soft metal brush (preferably
stainless steel) or sandpaper, until you see the
characteristic shine of the clean metal
Copper/Brass
Only impregnate the contact surfaces to be used with contact
grease, keeping the others clean. Remove excess grease to
avoid contamination.
Tightening must be carried out using a torque wrench, as shown
on the diagram plates and in
Annex II
.
Check the correct external wiring.
Grounding
The ground terminal of the transformer
must be properly
connected to the ground network by a connection capable of
carrying the network’s fault current. Check that the connection
is tightened correctly and that the contact surfaces are clean.
The low voltage terminal of the primary voltage winding
must
always be grounded when the transformer is in service. This
terminal can be located inside the secondary terminal box on
the side of the box (fi g. 7).
The high-frequency terminal (HF)
, which protrudes from
the capacitor unit, must be fi rmly connected to the ground
terminal of the housing (fi g. 8a). If there are carrier accessories,
this high frequency (HF) terminal shall be connected to the
carrier accessory block. While this equipment is not in use, the
grounding switch must remain closed (fi g. 8b).
A faulty contact or a bad connection can lead to rapid transformer deterioration
Avoid excessive torque, as the connector may suff er damage such as cracks which may expand in the future and
cause it to break
An inadequate torque may cause improper contact and cause the terminals to heat up during operation
Secondary connections
The secondary winding(s) must be connected to earth through
one of its terminals, preferably in the secondary terminal box
itself.
In case of secondary with intermediate taps, the common termi-
nal must be grounded.
Check that the secondary connections are correctly tightened
and the contact surfaces are clean.
The screws of the lower cable gland cover, the block cover
and the terminals must be tightened to the torque specifi ed in
Annex II
.
Do not leave the terminal block open after handling. It should
be properly closed with the cover and lid
.
In the terminal box there is a block where the secondary wires
are connected. The disposition of the terminals is indicated on
the secondary marking plate on the inside of the box cover.
Any secondary one that is not loaded must be open and grounded at a single point
The current in a short-circuited secondary can reach dangerous values and can even destroy the device
CAUTION
Do not use the secondary terminal block as a step
A platform lift or ladder should be used to make or check the primary connections,
upholding the necessary safety conditions for work at height. Under no circumstances
may the terminal block be used as a support
