Measuring voltage transformers are used to convert high voltage to low standard values, which is used to power measuring instruments and various protection and automation control relays. They, like current transformers, isolate measuring devices and relays from high voltage, ensuring the safety of their maintenance.
The device of measuring voltage transformers
According to the principle of the device, the switching circuit and the operating features, voltage transformers practically do not differ from power transformers. The power of voltage transformers does not exceed tens or hundreds of volt-amperes. At low power, the operation mode of voltage transformers approaches the idle mode. Opening the secondary winding does not lead to dangerous consequences. With the transformateur a sec this is the best deal now.
Switching schemes for voltage measuring transformers
At a voltage of 35 kV and below, voltage transformers are usually switched on through fuses so that they do not cause accidents if the voltage transformer is damaged. For personnel safety, voltage transformers must be earthed one of the terminals of the secondary winding.
Operation of voltage measuring transformers
Maintenance of voltage measuring transformers
Maintenance of voltage transformers and their secondary circuits is carried out by personnel and consists in overseeing the operation of voltage transformers themselves and monitoring the operability of the secondary voltage circuits.
- Voltage transformers are supervised during equipment inspections. At the same time, they pay attention to the general condition of the voltage transformer, the presence of oil in them, the absence of discharges and cod inside the voltage transformer, the absence of traces of overlap on the surface of insulators and porcelain tires, the degree of contamination of insulators, the absence of cracks and chips of insulation, as well as the condition of reinforcement joints. When cracks in porcelain are detected, voltage transformers must be disconnected and subjected to detailed inspection and testing.
35 kV voltage transformers with a small oil volume do not have expanders and oil indicators. They do not add oil to the cover by 20 to 30 mm. The resulting space above the surface of the oil acts as an expander. Detection of traces of oil leakage from such voltage transformers requires urgent removal of them from work, checking the oil level and eliminating leakage.
Maintenance of voltage measuring transformers
During operation, make sure that the fuse links are correctly selected. The reliability of the fuses is ensured if the rated current of the fuse-link is 3 to 4 times less than the short-circuit current at the most remote point from the voltage transformers of the secondary circuits.
- On the control panels, it is necessary to systematically monitor the presence of voltage from voltage transformers by voltmeters and signal devices (displays, signal lamps, bell).
In the event of the disappearance of the secondary voltage due to blown low voltage fuses, they should be replaced, and the disconnected circuit breakers should be turned on.
