Ⅰ.Basic knowledge of transformer tap changer
The tap changer of a power transformer is used to regulate the output voltage of the transformer. Due to the fact that the voltage in various parts of the power system grid is not exactly the same, in order to ensure that the transformer can output the rated voltage no matter where it is installed in the grid, multiple taps are set in the high-voltage winding of the transformer, and the taps are connected to the tap changer, which is connected to the grid through the switch. In this way, the tap changer can be connected to different transformer winding taps to change the turn ratio of the high and low voltage windings of the transformer, thereby achieving the purpose of regulating the output voltage of the transformer. It is divided into no-load voltage regulating tap changer and on-load regulating tap changer
Ⅱ.ommon faults and cause analysis of transformer tap changer
⒈Common faults of on load tap changer
⑴The transition resistance in the auxiliary contact is broken down and burnt out during the switching process, causing a flashover at the burnt out point, causing the arc between the contacts to become longer and longer, and emitting abnormal sounds
⑵Due to poor sealing of the tap changer, water ingress caused flashover during phase contact
⑶Due to the roller in the contact getting stuck, the tap changer stopped in the transition position, causing a short circuit between phases and burning out
⑷Due to the lack of tightness in the oil tank of the voltage regulating tap changer, the oil tank of the tap changer is interconnected with the oil tank of the main transformer, and the indicators of the two oil level gauges are the same, resulting in false oil levels in the tap changer, endangering its safe operation
⒉Analysis of common fault causes of on load tap changer
⑴The transition resistance in the auxiliary contact is broken down and burned during the switching process
⑵The tap changer is not tightly sealed, causing the same short circuit due to water ingress
⑶Due to the contact roller getting stuck, the tap changer stopped in the transition position, causing a short circuit between turns and burning out
⑷Tap changer oil tank is out of oil
⑸Crossing fault current encountered during voltage regulation process
⒊Analysis of common fault causes of on load tap changer
The main reasons for the malfunction of the on load voltage regulating device
⑴The operating power supply voltage disappears or is too low
⑵The motor winding is broken and burned, and the starting motor loses voltage
⑶Poor contact of interlocking contacts
⑷Rotating mechanism tripping and pin detachment
