Electric: basic knowledge of 16 transformers. (Ⅲ)

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

Losses during the transformer work include two parts：

(1) This is caused by an iron core. When the coil is voltage, the magnetic field lines alternate, causing vortex currents and losses of hysteresis in an iron core. This loss in aggregate is called iron loss. 

(2) This is caused by the resistance of the coil itself. When the current passes through the primary and secondary coils of the transformer, there is a loss of electric energy, which is called the loss of copper.The amount of iron and copper losses is the loss of the transformer that are associated with the power of the transformer, the voltage and the use of equipment. Therefore, when choosing transformers, it is important to make sure that the power of the equipment corresponds to the actual use in order to improve the use of the equipment, and be careful not to operate the transformer under a small load.

What is a named transformer plate? What are the main technical data on the passport plate?

The transformer plate indicates the performance, technical characteristics and the situation of using the transformer, which is used to meet the needs of the user. The main technical data that you should pay attention to when choosing:

(1) KVA contains passport plate. The output power of the transformer is in a nominal state. For example, the capacity of the passport plate of a single -phase transformer = line U × line I; Three -phase transformer power = line U × line I.

(2) Nominal voltage in volts. Indicate the voltage on the findings of the primary coil and the voltage on the conclusions of the secondary coil (when they are not connected to the load) separately. Please note that the voltage on the terminals of a three -phase transformer belongs to the value of the line U linear voltage.

(3) rated current in amperes. This applies to linear current I, the value of which is the primary coil and secondary coil for a long time in the passport capacity and an acceptable increase in temperature.

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

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

How to choose a transformer? How to determine the reasonable power of the transformer?

Firstly, it is necessary to investigate the voltage of the power source in the electricity consumption zone, the actual electrical load of the user and the location conditions. Then you should make a link to the technical data indicated on the transformer passport plate to select one after another. As a rule, the power of the transformer, voltage, current and environmental conditions should be comprehensively considered, and the choice of power should be based on the capacitance, nature and time of using the user’s electrical equipment to determine the required load in order to choose the power of the transformer.

During normal operation, the power load transferred by the transformer should be about 75 ~ 90% of the power of the transformer passport plate. When the actual load on the transformer bearing is measured 50 % less than % during operation, the low -power transformer should be replaced. If it is more than the passport capacity of the transformer, a large transformer must be immediately replaced. At the same time, when choosing a transformer, the voltage value of the primary coil of the transformer is determined on the basis of a linear power source, and the voltage of the secondary coil is selected on the basis of electrical equipment. It is best to choose a low -voltage three -phase four -wire power source. This can provide both power and lighting at the same time.

To select a current, it is important to pay attention to whether the load can comply with the engine requirements when starting (after all, the engine current is 4-7 times more than when working in a sinking mode).