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1. What is a transformer?

In AC circuit, the voltage will be increased or decreased equipment called transformer, transformer can be any value of voltage into the frequency of the same voltage value we need to meet the transmission of electric energy, distribution and use requirements. For example, the voltage level of the electricity emitted from the power plant is low, so the voltage must be increased before it can be transmitted to the distant power area, and the power area must be reduced to the appropriate voltage level to supply the power equipment and daily use of electricity equipment.

2. How does the transformer transform the voltage?

Transformers are made according to electromagnetic induction.

It consists of an iron core made of sheets of silicon steel (or silicon steel) and two coils wound around the core. The core and coils are insulated from each other and have no electrical contact with each other.

The coil connecting the transformer and the power supply side is called the primary coil (or the original side), and the coil connecting the transformer and the electrical equipment is called the secondary coil (or the secondary side). When the primary coil of the transformer is connected to the AC power supply, changing lines of magnetic force are created in the core.

Since the secondary coil is wound on the same iron core, the magnetic wire cuts the secondary coil, and the induction electromotive force must be generated on the secondary coil, so that the voltage appears at both ends of the coil. Since the magnetic field lines are alternating, the voltage in the secondary coil is also alternating. And the frequency is exactly the same as the power frequency.

It has been proved by theory that the voltage ratio between the primary coil and the secondary coil is related to the ratio of turns between the primary coil and the secondary coil, which can be expressed by the following formula: the voltage of the primary coil/the voltage of the secondary coil = the number of turns of the primary coil/the number of turns of the secondary coil. Therefore, it can be seen that the secondary coil is less than the primary coil, is the step-down transformer. On the contrary, it is a booster transformer.

3. What are the types of transformer designs?

Divide by phase

There are single-phase and three-phase transformers

By use

There are power transformers, special power transformers, regulating transformers, measuring transformers (voltage transformers, current transformers), small power transformers (for small power equipment), safety transformers

By structure

Core type and shell type. The coil has double winding and multiple winding, autotransformer

According to the cooling method

There are oil - immersed and air - cooled

4, what are the main parts of the transformer?

Transformer components are mainly composed of iron core, coil, in addition to the oil tank, pillow, insulation sleeve and tap start, etc.

5, what is the use of transformer oil?

The role of transformer oil is:

(1) insulation effect

(2) Heat dissipation effect

(3) arc elimination

6. What is an autotransformer?

The autotransformer has only one set of coils, the secondary coil is tapped from the primary coil, its electric energy transfer, in addition to the electromagnetic induction transfer, there is also the transmission of electricity

The difference between the autotransformer and the general transformer is that the number of silicon steel sheet and copper wire is less than the general transformer, commonly used for regulating voltage.

7, the voltage regulator is how to adjust pressure?

The structure of the voltage regulator is the same as that of the autotransformer, but the core is made into a ring coil on the ring core.

The secondary coil tap uses a sliding brush contact to make the contact slide annular along the surface of the ring to achieve smooth voltage regulation.

8, transformer primary coil and secondary coil current relationship is what?

When the transformer is running with load, the change in the secondary coil current will cause the corresponding change in the primary coil current. According to the principle of magnetic potential balance, the current of the primary secondary coil is inversely proportional to the number of turns of the coil, the side with more turns is small current, the side with fewer turns is large current.

It can be expressed as follows:

Primary coil current/secondary coil current = turns of secondary coil/turns of primary coil.

9. What is the voltage change rate of the transformer?

The voltage change rate of the voltage regulator is one of the main performance indexes of the transformer.

When the transformer supplies power to the load, the voltage at the load end of the transformer will inevitably drop. Compared with the rated voltage value, the voltage change rate is taken as a percentage, which can be expressed by the formula

Voltage change rate = [(secondary rated voltage - load terminal voltage)/ secondary rated voltage] x 100%. The usual power transformer, when connected to the rated load, the voltage change rate is 4 ~ 6%.

10, how to ensure that the transformer has a rated voltage output?

Voltage is too high or too low will affect the normal work and service life of the transformer, so it must be regulated.

The voltage is regulated by drawing out several taps in the primary coil, connected to the tap start, which changes the number of turns of the coil by turning the contacts. The desired voltage rating can be obtained by turning the position of the tap switch.

It should be noted that voltage regulation should usually be carried out after cutting off the load of the transformer!

11, usually used small transformer is what?

Small transformer refers to the capacity of less than 1 kV single-phase transformer, mostly used for electrical equipment control power transformer, power transformer for electronic equipment and power transformer for safety lighting.

12. What are the losses of transformer in operation? How to reduce the loss?

Loss in transformer operation includes two parts:

(1), is caused by the iron core, when the coil is energized, because the magnetic force line is alternating, causing eddy current and hysteresis loss in the iron core, this loss collectively referred to as iron loss.

(2), is caused by the resistance of the coil itself, when the transformer primary coil and secondary coil current through, it is necessary to produce power loss, this loss is called copper loss.

The sum of iron and copper losses is transformer losses, which are related to transformer capacity, voltage and equipment utilization. Therefore, in the selection of transformer, should try to make the equipment capacity and the actual use of the same, in order to improve the utilization of equipment, pay attention to not make the transformer light load operation.

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

Transformer nameplate indicates the performance of the transformer, technical specifications and use occasions, to meet the user's selection, usually choose to pay attention to the main technical data are:

(1) kilovolt-amperes of rated capacity. That is, the output capacity of the transformer in rated state. For example, single-phase transformer rated capacity =U wire x I wire; Three-phase transformer capacity =U wire x I wire.

(2) Rated voltage volts. The terminal voltage of the primary coil and the terminal voltage of the secondary coil (when not connected to the load) are indicated respectively. Note the U-line value of the terminal voltage of the three-phase transformer.

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

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

(5) Wiring mode. Single-phase transformer only high and low voltage each group of coil, only supply single-phase use, three-phase transformer Y/△ type. In addition to the above technical data, there are transformer rated frequency, phase number, temperature rise, transformer impedance percentage, etc.

14, how to choose the transformer?

First of all, it is necessary to investigate the power supply voltage of the place where the power is used, the actual power load of the user and the local conditions, and then choose one by one according to the technical data marked on the transformer nameplate.

Then how to determine the reasonable capacity of the transformer?

Generally, the transformer capacity, voltage, current and environmental conditions should be considered comprehensively. The capacity selection should be based on the capacity, nature and use time of the user's electrical equipment to determine the required load, so as to choose the transformer capacity.

In normal operation, the transformer should be subjected to electrical load of 75 ~ 90% of the rated capacity of the transformer. If the actual load borne by the transformer is less than 50% in operation, the small-capacity transformer should be replaced. If the transformer is larger than the rated capacity, the large transformer should be replaced immediately.

At the same time, in the selection of transformer according to the line power supply to decide the voltage value of the transformer primary coil, according to the electrical equipment to choose the voltage value of the secondary coil, the best choice for low-voltage three-phase four-wire system power supply. This provides electricity for both power and lighting.

For the selection of current, attention should be paid to the load when the motor starts to meet the requirements of the motor (because the motor starting current is 4 ~ 7 times larger than the sinking operation).

15. Why can't the transformer run under load?

Overload operation is when the transformer is running in excess of the current value specified on the nameplate.

Overload is divided into normal overload and accident overload two kinds, the former refers to the normal power supply, the user caused by the increase in power consumption, it often makes the transformer temperature rise, promote the transformer insulation aging, reduce the service life, so do not allow the transformer overload operation.

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

16, transformer in operation should do what kind of test?

In order to ensure the normal operation of the transformer, the following tests should be frequently carried out:

(1) Temperature test.

Transformer running state is not normal, the temperature is very important. The regulations stipulate that the upper oil temperature shall not exceed 85C(i.e., 55C temperature rise). General transformers are equipped with special temperature measuring devices.

(2) Load measurement.

In order to improve the utilization rate of the transformer and reduce the loss of electric energy, it is necessary to determine the power supply capacity that the transformer can bear in the operation of the transformer. The measurement work is usually carried out in the peak period of each season, and is measured directly with a clamp ammeter. The current value should be 70 ~ 80% of the rated current of the transformer. If it is more than that, it indicates overload and should be adjusted immediately.

(3), voltage measurement.

The regulation requires that the voltage range should be within the rated voltage ±5%. If this range is exceeded, tap should be used to adjust the voltage to reach the specified range. Voltmeter is generally used to measure the terminal voltage of the secondary coil and the terminal voltage of the end-user.

(4) insulation resistance measurement.

In order to keep the transformer in normal operation, it is necessary to measure the insulation resistance to prevent insulation aging and accidents. Measurement should try to make the transformer stop running, using the meter to measure the transformer insulation resistance value, the resistance measured is not less than 70% of the previous measured value, the selection of the meter, low voltage coil can be used 500 volt voltage grade.