What is connected to the primary circuit of your frequency converter? Fine tasting, do you really need it? This article will discuss this issue. So let's talk about it one by one from top to bottom.

Firstly, a circuit breaker is essential as it can not only isolate the power supply, but also serve as a protective device.

When repairing the frequency converter, it is necessary to disconnect the power supply for safety. Opening the circuit breaker and hanging the tag is the most appropriate measure to isolate the power supply while avoiding personnel from mistakenly closing it. This is the boldest way to conduct maintenance.

The circuit breaker also has overload and short circuit protection functions, which can quickly remove faults and effectively provide short circuit protection and other protections for the frequency converter circuit.

However, the price of a circuit breaker is also not cheap, especially for large capacity switches, but it is not possible to connect an isolation switch. If one day there is a harmless one, it is not worth it to have a load pull switch! So, what should be, still needs to be!

Below is the contactor, which mainly cooperates with the fault output of the frequency converter. When the frequency converter fails, the contactor can be disconnected to power off the frequency converter. When there is no fault, it can be used as the power on of the frequency converter. In fact, there is really no need for it, it is optional. If the frequency converter malfunctions and shuts down, the output will be locked, and short circuit protection is not needed, which is more like adding insult to injury.

Contactors have instinctive undervoltage protection. When encountering power grid shaking, I originally wanted to let the frequency converter avoid the shaking process. Who had thought that when the contactor was released, everything became useless.

Then there is the fast fuse, which is also necessary. Its function is to quickly cut off the short-circuit current, which can be said to be eye-catching. Its action speed is faster than that of the circuit breaker. Sometimes, when encountering a short circuit, it almost melts, but the circuit breaker does not act, which can indicate its fast action speed.

To be clear, some frequency converters are equipped with fast melting in the DC bus as part of the frequency converter. At this time, equipping the peripheral main circuit with fast melting would be a bit expensive!

Next is the incoming reactor, which is mainly used for filtering and improving power factor. It is quite large and heavy, and when installed in a cabinet, it always feels that it is not very coordinated. So for the incoming reactance, if the frequency converter is equipped with a built-in DC reactor, there is no need for it to exist, because in terms of DC reactance, it not only has the effect of filtering and improving power factor, but also has a higher and lower noise than the incoming reactance. Why not!

The above is the input side, take a look at its output side.

First of all, there are contactors. Some devices with single drag orders are often equipped with contactors, which is really expensive to burn! What do you want it for? If the frequency converter starts to engage, if the engagement is slow, it may also cause overcurrent protection. Even if the motor insulation is measured at its lower port, it does not meet safety requirements, as there is a risk of misoperation at any time.

Of course, the above is for single drag orders, but for variable frequency and power frequency, as mentioned earlier, as switching contactors, it is another matter! There is also a situation where one frequency converter drives multiple motors and can only be switched through contactors, and in both cases, a heating relay is required as overload protection.

Then there is the output reactor, which is necessary and strongly recommended. It can effectively filter out the high-order harmonics output by the frequency converter and protect the motor.

In some cases, in order to facilitate the measurement of motor insulation, an isolation switch is added, which is understandable. It can be added for convenience, but to avoid the risk of accidentally pulling the switch, it is best to have electrical locking conditions.

This article will focus on the main circuit and related protection of the frequency converter. If there are any issues, please criticize and correct them, with a focus on communication.

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