What other application scenarios are there for transformers?

 

Instrument transformers, an electronic device, play a vital role in the power system. It is not only used to connect the meter for power measurement, but also plays a key role in many aspects. Instrument transformers are mainly divided into two categories: voltage transformers and current transformers. The core function of voltage transformers is to reduce high voltage according to a certain ratio, and then provide the required voltage signal for various measuring instruments and relay protection devices. Therefore, it plays an indispensable role in the voltage, power and electric energy measurement of high-voltage lines.

The core task of the current transformer is to reduce the large current according to a predetermined ratio in order to provide the necessary current signal for various measuring instruments and relay protection equipment. For this reason, the current transformer plays an indispensable and important role in the current, power and electric energy measurement of low-voltage and high-current lines.

 

 

In our daily life, low-voltage equipment is the most frequently used equipment. Therefore, what we usually call transformers actually refer to current transformers.

 

1.Working principle of current transformer

What is it? When the current in the circuit is too large, it is not only extremely inconvenient to measure directly, but also there is a high safety risk. At the same time, general instruments can hardly withstand such a large range. However, by using current transformers, we can effectively expand the measurement range of the instrument, reduce energy consumption during the measurement process, and ensure personal safety. The structure of the current transformer is similar to that of the transformer, both of which contain an iron core and a primary and secondary coil. The number of turns of its primary winding is designed to be relatively small, usually only one or a few turns, and is directly connected in series in the measured circuit; while the number of turns of the secondary winding is more, usually connected in series in the measurement circuit or instrument.

According to the transformer principle, the working relationship of the current transformer can be expressed as: I1÷I2=N2÷N1=K. Among them, I1 represents the primary current, I2 represents the secondary current, N1 and N2 represent the number of turns of the primary coil and the secondary coil respectively, and K is the transformation ratio of the current transformer. Since the number of turns of the current transformer coil remains fixed after leaving the factory, its transformation ratio also remains unchanged. By measuring the current in the secondary circuit of the current transformer, we can accurately calculate the current in the primary circuit.

Next, we will explore the practical applications of current transformers.

 

 

2.Current measurement

In low-voltage power distribution systems, it is crucial to monitor the line current. By measuring the current, we can determine whether the three phases are balanced and whether the line switch is overloaded, thereby ensuring the stable operation of the system. For example, on the distribution cabinet, we often see three ammeters and one voltmeter, which together constitute an important means of current monitoring.

When measuring the circuit current, the measured wire needs to pass through the current transformer, and ensure that the secondary side S1 and S2 of the current transformer are connected to the ammeter. In addition, to prevent the current transformer from generating high voltage due to an open circuit, one end of S1 or S2 must be grounded.

 

3.Electric energy measurement

In the measurement of electric energy, the wiring method of the current transformer and the three-phase meter is the key. The maximum specification of the three-phase meter is 30 (100) A. If the current exceeds this limit, the meter may burn out due to overload. In order to measure large currents safely and effectively, we can use current transformers to expand the range of the meter. Next, we will introduce the specific wiring steps of the three-phase meter and the transformer:

 

4.Relay protection

For large-capacity motors, if there is a lack of appropriate thermal relays, we can cleverly use current transformers to reduce the current, and then connect the thermal relay to the secondary circuit of the transformer to achieve the overload protection function.

In addition, current transformers can also be widely used in relay protection of power supply lines. Once the line has abnormal conditions such as overcurrent or short circuit, the current transformer can respond quickly and cut off the power supply to ensure the safe operation of the line and avoid potential damage.

 

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