Maintenance of a Constant Voltage Transformer (CVT)

Routine maintenance

Routine checks should be made to ensure that the ventilation for the power conditioner is properly maintained.

The unit should be positioned in a well ventilated location as power ratings assume natural air cooling. Annual checks of capacitor integrity may be worthwhile once the unit is more than five years old.

Preventative maintenance

Visual examination of capacitors on large units can often indicate a local fault through leakage of oil - in this case replace the faulty part. To prolong usable life it can be beneficial to replace the capacitor bank every five years. Some larger power conditioners are fitted with fans to assist with cooling. Under normal circumstances the only preventative maintenance required is the cleaning of fans if fitted.

Replacement of capacitors

We are occasionally asked to supply replacement capacitors for old CVTs.

Capacitors are subject to two characteristics which affect the use of these spare components in CVTs.

a value and tolerance

b physical dimensions

a - changes in capacitance value will result in differences in the CVT output voltage.

In general terms we expect normal production tolerances in the value of a spare capacitor to make less than a 1% change to the original output voltage nominal setting. This situation can be improved when a coloured dot is noted on the failed capacitor and it's colour dot is defined at the time of ordering a spare. The output voltage variation expected with CVTs using a spare capacitor of the same colour dot will be less than 0.3%.

b - the physical dimensions of commercial capacitors change over extended periods of time. In general terms our capacitors will be of similar size or smaller. In case of any anticipated problem we recommend a factory repair for units up to 3 kVA. Care must be taken when handling high voltage capacitor installations. Replaced capacitors must have an adequate Vac rating for duty with high harmonic currents.