Electrician: Basic knowledge of 16 transformers. Teacher Fu said that 12 is already very impressive!（Ⅲ）

12. What are the losses of transformers during operation? How to reduce losses?

The losses during transformer operation include two parts; (1) It is caused by the iron core. When the coil is energized, the magnetic field lines are alternating, causing eddy current and hysteresis losses in the iron core. This loss is collectively referred to as iron loss. (2) It is caused by the resistance of the coil itself. When there is current passing through the primary and secondary coils of the transformer, electrical energy loss occurs, which is called copper loss.

The sum of iron loss and copper loss is transformer loss, which is related to transformer capacity, voltage, and equipment utilization. Therefore, when selecting transformers, it is important to ensure that the equipment capacity is consistent with the actual usage, in order to improve equipment utilization, and be careful not to operate the transformer under light load.

13. What is the nameplate of a transformer? What are the main technical data on the nameplate?

The nameplate of the transformer indicates the performance, technical specifications, and usage situation of the transformer, which is used to meet the user's selection needs. The main technical data that should be paid attention to during selection are:

(1) KVA of Nameplate capacity. The output capacity of the transformer under rated state. For example, Nameplate capacity of single-phase transformer=U line × Line I; Three phase transformer capacity=U line × Line I.

(2) Rated voltage in volts. Indicate the terminal voltage of the primary coil and the terminal voltage of the secondary coil (when not connected to the load) separately. Note that the terminal voltage of the three-phase transformer refers to the line voltage U line value.

(3) Rated current in amperes. It refers to the line current I line value that the primary coil and secondary coil are allowed to pass for a long time under the conditions of Nameplate capacity and allowable temperature rise.

(4) Voltage ratio. The ratio of the rated voltage of the primary coil to the rated voltage of the secondary coil.

(5) Wiring method. Single-phase transformers only have one set of coils for high and low voltage, and are only supplied for single-phase use. Three-phase transformers have Y/△ types. In addition to the above technical data, there are also the rated frequency, number of phases, temperature rise, and impedance percentage of the transformer.

14. How to choose a transformer? How to determine the reasonable capacity of a transformer?

Firstly, it is necessary to investigate the power supply voltage in the electricity consumption area, the actual electricity load of the user, and the conditions of the location. Then, reference should be made to the technical data indicated on the transformer nameplate to select one by one. Generally, the transformer capacity, voltage, current, and environmental conditions should be comprehensively considered, and the capacity selection should be based on the capacity, nature, and usage time of the user's electrical equipment to determine the required load, in order to select the transformer capacity.

During normal operation, the power load borne by the transformer shall be about 75~90% of the Nameplate capacity of the transformer. When the actual bearing load of the transformer is measured to be 50% less than% during operation, the small capacity transformer shall be replaced. If it is greater than the Nameplate capacity of the transformer, the large transformer shall be replaced immediately. At the same time, when selecting a transformer, the voltage value of the primary coil of the transformer is determined based on the line power supply, and the voltage value of the secondary coil is selected based on the electrical equipment. It is best to choose a low-voltage three-phase four-wire power supply. This can provide both power and lighting electricity simultaneously.

For the selection of current, it is important to pay attention to whether the load can meet the requirements of the motor when starting (because the starting current of the motor is 4-7 times greater than when running in sinking mode).

15. Why cannot transformers operate under overload?

Overload operation