10
Instruction manual
5. Maintenance and overviews during exploitation.
5.1 Maintenance
Excessive dust or other kind of pollution must be brushed off the
transformer. Polluted transformers can be cleaned with spirit,
petrol or toluene. Traces of arcs and minor surface damages can
be easily removed with sandpaper after which the surface is to be
treated by applying a thin layer of silicone paste on it. Instruction
for repairing greater surface damages must be requested from the
manufacturer.
5.2 Overviews during exploitation
Medium voltage instrument transformers in resin insulation are
maintenance-free. However, because of work under different
environmental conditions during the transformer operation it is
advisable to carry out:
– overview of the instrument transformer during operation – only
visual control,
– overview of the instrument transformer disconnected from
power supply.
Time periods between inspections is regulated by standards,
by operation and maintenance manual of switchgears or user
requirements.
Overview of the instrument transformer during operation
The review is based on visual control in accordance with the
principles of safety. During the inspection should pay attention to:
– condition of resin body,
– condition of primary terminals,
– condition of support structures.
Overview of the instrument transformer disconnected from
power supply
The overview should be done every time before restarting. The
overview should include:
– cleaning the surface of instrument transformer,
– checking condition of the transformer resin body surface,
– checking condition of mounting screws and checking the
condition of all electrical connections (on primary and secondary
terminals and earthing terminals),
– measurement of main insulation resistance,
– measurement of secondary winding insulation resistance.
Cut off the power supply of transformer before
attempting cleaning or repairing operations.
6. Instruction for use
The main tasks of voltage transformers are:
– to transform voltages from a usually high value to a value easy to
handle for relays and instruments, while maintaining appropriate
accuracy class, and to power supply to the metering circuit,
– to insulate the metering circuit from the primary high voltage
system,
– supply other low voltage devices do not require a high standard
of accuracy, such as disconnectors drives
For applications that use a power supply
transformer, the transformer is recommended to
use double-pole voltage transformer. In the case
of single-pole voltage transformer secondary side
can rise to 190% of rated voltage, which can cause
permanent damage to the powered device and the
transformer. Using double-pole voltage transformer
should be one of the ends secondary winding
grounded. An example of such a connection is
shown below in Fig. 16.
Using voltage transformers for purposes other than described
above is forbidden, if not otherwise agreed with its manufacturer.
Figure.16. An example of connecting the receiver to the secondary terminal
winding of the double-pole voltage transformer.