Simply put, a transformer is a device that uses alternating electromagnetic fields to achieve conversion of different voltage levels (actually the conversion of electrical energy), and the voltage before and after the conversion does not change in frequency. There are many types according to their uses, such as power transformers, rectifier transformers, voltage regulators, isolation transformers, and CT, PT, etc. What we often encounter at the project site is a three-phase power isolation transformer.
Some main technical parameters related to transformers include:
Rated capacity: refers to the rated output capacity of the transformer under the rated working conditions (equal to U×I, unit is kVA);
Rated voltage: under no-load, rated tap, the value of terminal voltage (namely the voltage value of primary and secondary side);
No-load loss: Under no-load conditions, the loss of the transformer (also called iron loss);
No-load current: under no-load conditions, the current value flowing through the primary coil;
Short-circuit loss: the rated current on the primary side, the loss caused by the secondary short circuit (mainly caused by the coil resistance);
The concept of tapping (tap): In order to meet the needs of power grid operation, regulator has a tap on the high voltage side of the transformer, and the voltage value of these is expressed as a percentage of the rated voltage. This is the so-called tap voltage. For example, a high-voltage 10kV transformer has a tap of ±5%, which means that the transformer can operate at three voltage levels: 10.5kV (+5%), 10kV (rated), and 9.5kV (-5%). Generally speaking, there are many taps (tap points) of on-load voltage-regulating transformers, such as 7-point contacts (±3×2.5%) and 9-point contacts (±4×2%). Since the synchronous switching of the tap-changer cannot be fully guaranteed, the on-load voltage-regulating transformer cannot generally be operated in parallel.