High Voltage Coupling-Capacitors are used mainly for Partial Discharge Measurements in High Voltage Testing as per IEC 60270. The Measurements of Partial Discharge according to IEC is based on measurement of High Frequency Voltage Drop across a Measuring Impedance in the Ground lead of the Test Object or of the Coupling Capacitor. Any partial Discharges appearing in or on a Test Object Under High Frequency Charge Transfer between the high Voltage Potential and ground give rise to a High Frequency Current. This current produces a voltage drop across the measuring impedance which is connected to the partial discharge meter for evaluation, measurement and display.
The Coupling Capacitors are insulated for indoor use. The Capacitor CK 60 to CK 600 are Insulated. The low inductance wound capacitor elements are installed in an insulating Cylinder and held in position with special fixtures. They are carefully dried in high vacuum and impregnated with EHV grade oil. The insulation of the capacitor elements and the dimensions of the insulating cylinder are designed for a test voltage of 120% of rated voltage.
Type CK 120, CK 150 have aluminium cast flanges, CK 300 and above are provided with suitably dimensioned aluminium to toroidal electrodes for corona free operation up to rated voltage.