DEVELOPMENT OF BREAKDOWN VOLTAGE TESTER FOR LIQUID DIELECTRICS
Dr. Farhan Mehmood
Liquid dielectrics are basically used to prevent or rapidly quench the electric discharges. They
are used widely to provide insulation in transformers, capacitors, high voltage cables and switch
gears. It is essential to design a device which can measure the breakdown voltage strength of
these liquid dielectrics, in order to understand the reliability of equipment functionality on
dielectrics used in them. The predetermined estimation of dielectric strength can help us to
prevent our appliances from fatal failure, provided that they are operated in optimized range of
voltages that is below the breakdown voltage of dielectrics used in them. The transformer oil
(insulation oil) of voltage and current transformers fulfills the purpose of insulating as well as
cooling. Thus, the dielectric quality of transformer oil is essential to secure operation of a
transformer. As transformer oil deteriorates through aging and moisture ingress, transformer oil
should, depending on economics, transformer duty and other factors, be tested periodically.
Power utility companies have a vested interest in periodic oil testing since transformers represent
a large proportion of their total assets. Through such testing, life of transformer can be
substantially increased, thus reducing new investment of replacement transformer assets.
Measuring the breakdown voltage of liquid dielectrics will give information about their dielectric
strength. Through this test-kit, we will be able to study breakdown voltage characteristics of
liquid dielectrics as well as newly developed nanodielectrics. Transformer designing is the major
and toughest part of our project. We have designed a high voltage single phase transformer with
input from WAPDA utility of 230V and the output will be variable with the range of 0V to 30kV
(RMS). We rectify the AC input with a rectifier. This DC voltage is then inverted to a square
wave with an inverter. This square wave is then converted to a sinusoid through an RLC filter.
The transformer then steps up this voltage. The magnitude of the output voltage is controlled
automatically through MATLAB and voltage rise rate is set to 2kV/ sec which can also be
changed according to the requirement. As soon as, the breakdown of oil sample occurs as the
high voltage, the protection circuit cuts the supply so that the source is not damaged by the short
circuit current. The values of breakdown voltage, applied voltage and rate of rise of voltage can
be monitored as well.