Difference between voltage transformer and voltage relay - News - Global IC Trade Starts Here.

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

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Voltage relay

It is a relay that operates when the voltage in the circuit reaches a predetermined value. The structure is basically the same as that of the current relay, except that the number of turns of the electromagnet coil is large, and it is used in parallel with the power supply. It is widely used in voltage loss (zero voltage) and undervoltage (low voltage) protection. The so-called voltage loss and undervoltage protection is that when the power supply voltage is reduced too much or the power is temporarily cut off for some reason, the motor is automatically disconnected from the power supply; when the power supply voltage is restored, if the start button is not pressed, the motor cannot start by itself. If the relay control is not used, but the manual control is directly performed by the knife switch, since the switch is not pulled off in time during the power failure, when the power supply voltage is restored, the motor starts automatically, which may cause an accident. There is also an overvoltage relay, which is a relay that cuts off the power supply due to the suction of the electromagnet when the voltage of the circuit exceeds a certain value. It is used for overvoltage protection (such as protection of silicon tubes and thyristors).

The current relay has fewer solenoid coils. If the current through the coil is lower than the rated value, the suction force of the electromagnet is insufficient to overcome the elastic force of the reaction spring, and the armature does not operate. If the current exceeds the rated value, the suction of the electromagnet is greater than the elastic force, and the armature is sucked. Thus, the normally closed contact in the contact system is opened and the normally open contact is closed. Since the relay will only operate when the current exceeds a certain rated value, it is also called an overcurrent relay. Adjust the spring force of the reaction spring to adjust the value of the operating current.

The current relay is mainly used for overload and short circuit protection. It is more complicated than the fuse structure, but the overload protection performance is better than the fuse, and it is not necessary to replace the component like a fuse after the accident, and it can be reused. Therefore, it plays a key role in protecting the motor from overload and short circuit in the power system.

Voltage transformer

A voltage transformer, also known as an instrument transformer , is a voltage conversion device. Its working principle, construction and wiring method are the same as those of the transformer. The main difference is that the voltage transformer has a small capacity, usually only tens of VA or several hundred VA, and in most cases, its load is constant high impedance, quite When the transformer is operated at a low load, the secondary voltage is substantially equal to the secondary induced electromotive force value. Therefore, the voltage transformer is used to indirectly measure the voltage, which can accurately reflect the magnitude of the high voltage side and ensure the measurement accuracy.

Regardless of how high the primary voltage of the voltage transformer is, its secondary rated voltage is typically 100V. Thus, the voltage transformer secondary winding connected to the relay and a variety of instruments, can be manufactured uniform standardized.
In an ideal voltage transformer, the excitation current is zero, and the impedance of the coil is not counted. At this time, the ratio of the primary and secondary voltages is equal to the ratio of their turns, and the phase is not offset. However, in actual voltage transformers, there are always voltage errors and angular errors due to the presence of the excitation current and the influence of the coil impedance. According to the allowable error range of the voltage transformer, the accuracy of the voltage transformer can be divided into 0.2, 0.5, 1 and 3, which is the accuracy level of the voltage transformer. See Table 2.

Voltage transformers have their corresponding rated capacity at each level of accuracy, so the same voltage transformer can operate at different levels of accuracy depending on the size of the secondary load. For example, JDZJ-10 type voltage transformer has an accuracy level of 0.5 and a capacity of 50 VA in the case of a load power factor of 0.8; an accuracy level of 1 and a capacity of 80 VA; and a level of 200 VA. . If the accuracy level is not considered, only the allowable heat condition is met, and its maximum capacity is 400 VA.