Do you know how many? 16 common knowledge about transformers, it's not easy to answer 12 correctly!

1. What is a transformer?

In communication circuits, devices that increase or decrease voltage are called transformers. Transformers can convert any value of voltage into the voltage value we need with the same frequency to meet the requirements of energy transmission, distribution, and use.

For example, the electricity generated by a power plant has a low voltage level and must be raised in order to be transmitted to a distant power consumption area. The power consumption area must then be reduced in voltage to a suitable voltage level for use by power equipment and daily electrical equipment.

2. How does a transformer transform voltage?

Transformers are made based on electromagnetic induction. It consists of an iron core made of stacked silicon steel sheets (or silicon steel sheets) and two sets of coils wound around the iron core. The iron core and coils are insulated from each other and have no electrical connection.

The coil connecting the transformer and the power supply side is called the primary coil (or primary side), and the coil connecting the transformer and the electrical equipment is called the secondary coil (or secondary side). When the primary coil of a transformer is connected to an AC power source, magnetic field lines will change in the iron core.
Due to the secondary coils being wound around the same iron core, magnetic field lines cut through the secondary coils, which inevitably generates induced electromotive force on the secondary coils, resulting in voltage at both ends of the coils. Because magnetic field lines are alternating, the voltage of the secondary coil is also alternating. And the frequency is exactly the same as the power frequency.

The manager argued that the voltage ratio between the primary and secondary coils of a transformer and the ratio of the number of turns between the primary and secondary coils are related, which can be expressed as follows: primary coil voltage / secondary coil voltage = primary coil turns / secondary coil turns, indicating that the more turns there are, the higher the voltage. Therefore, it can be seen that there are fewer secondary coils than primary coils, which is a step-down transformer. On the contrary, it is a step-up transformer.

3. What are the types of transformer designs?

There are single-phase and Three-Phase Transformers according to the number of phases

According to their purposes, there are Power Transformers, specialized power transformers, voltage regulating transformers, measuring transformers (Voltage Transformers, current transformers), small power transformers (used for small power equipment), and safety transformers

There are two types of structures: core type and shell type. The coil has dual windings and multiple windings, and is an autotransformer.

There are two types of cooling methods: oil immersed and air-cooled.

4. What are the components of a transformer?

The transformer components are mainly composed of iron core and coils, as well as oil tank, oil pillow, insulation sleeve, and tap changer.

5. What is the use of transformer oil?

The function of transformer oil is to:
(1) Insulation function

(2) Heat dissipation function

(3) Eliminate the arc effect

6. What is an autotransformer?

An autotransformer has only one set of coils, and the secondary coil is tapped out from the primary coil. Its electrical energy is transmitted not only through electromagnetic induction, but also through electrical transmission. This type of transformer has fewer silicon steel sheets and copper wires than ordinary transformers, and is commonly used for voltage regulation.

7. How does a regulator regulate pressure?

The structure of a voltage regulator is the same as that of an autotransformer, except that the iron core is made into a circular coil and wound around it.

The secondary coil tap uses a sliding electric brush contact to make the contact slide in a circular manner along the surface of the coil, achieving smooth voltage regulation.

8. What is the current relationship between the primary and secondary coils of a transformer?

When a transformer operates with a load, changes in the secondary coil current will cause corresponding changes in the primary coil current. According to the principle of magnetic potential balance, the current of the primary and secondary coils is inversely proportional to the number of turns in the coil. The side with more turns has a smaller current, while the side with fewer turns has a larger current.

It can be expressed as follows: primary coil current/secondary coil current=number of secondary coil turns/number of primary coil turns.

What is the voltage change rate of a transformer?

The voltage change rate of a voltage regulator is one of the main performance indicators of a transformer. When a transformer supplies power to a load, the voltage at the load end of the transformer will inevitably decrease. Comparing the decreased voltage value with the rated voltage value, the percentage is taken as the voltage change rate,

Can be expressed using a formula; Voltage change rate=[(secondary rated voltage - load terminal voltage)/secondary rated voltage] × 100%. A typical power transformer has a voltage change rate of 4-6% when connected to a rated load.

10. How to ensure that the transformer has a rated voltage output?

High or low voltage can affect the normal operation and service life of transformers, so voltage regulation is necessary.

The method of voltage regulation is to draw several taps from the primary coil and connect them to the tap head. The tap head changes the number of turns of the coil by rotating the contact. Simply rotate the position of the tap changer to obtain the desired rated voltage value. It should be noted that voltage regulation should usually be carried out after cutting off the load connected to the transformer.

11. What are the commonly used small transformers? In which occasions is it applied?

Small transformers refer to single-phase transformers with a capacity of less than 1 kVA, mostly used as power transformers for electrical equipment control, electronic equipment, and safety lighting.

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, due to the alternating magnetic field lines, eddy currents and hysteresis losses occur in the iron core, which are collectively referred to as iron losses.

(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, the equipment capacity should be as consistent as possible with the actual usage to improve equipment utilization, and care should be taken 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 scenarios of the transformer, which is used to meet the user's selection. The main technical data to be noted during selection are:

(1) The kilovolt ampere rating of the rated capacity. The output capacity of the transformer under rated conditions. For example, the rated capacity of a single-phase transformer is equal to the U line multiplied by the I line; Three Phase Transformer capacity=U line x I line.

(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 a load) separately. Pay attention to the terminal voltage of the three-phase transformer, which refers to the U-line value of the line voltage.

(3) Rated current amperage. The line current I-line value that allows the primary and secondary coils to pass through for a long time under rated capacity and allowable temperature rise conditions.

(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 high and low voltage coils, which are only used for single-phase, while three-phase transformers have Y/△ type. 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 of the place where the electricity is used, the actual electricity load of the user, and the conditions of the location. Then, refer 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. 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 transformer should withstand an electrical load of approximately 75-90% of its rated capacity. When the actual load borne by the transformer during operation is less than 50%, the small capacity transformer should be replaced. If it is greater than the rated capacity of the transformer, the large transformer should be replaced immediately.

At the same time, when selecting a transformer, the primary coil voltage value of the transformer is determined based on the line power supply, and the secondary coil voltage value 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.

When selecting the current, it is important to ensure that the load meets the requirements of the motor during start-up (as the starting current of the motor is 4-7 times higher than during sinking operation).

15. Why can't transformers operate under overload?

Overload operation refers to the operation of a transformer exceeding the current value specified on the nameplate.

Overload is divided into two types: normal overload and accident overload. The former refers to the increase in user electricity consumption under normal power supply conditions, which often causes the temperature of the transformer to rise, promotes insulation aging of the transformer, and reduces its service life. Therefore, transformer overload operation is not allowed.

Under special circumstances, the overload operation of transformers in a short period of time should not exceed 30% of the rated load (in winter), and should not exceed 15% in summer.

16.What types of tests should transformers undergo during operation?

To ensure the normal operation of the transformer, the following tests should be conducted regularly: