What is the frequency converter connected to in one circuit?

Oct 31, 2023

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.

Adleman Limited is a control system components company,which located in Xiamen,a beautiful coastal city. 

We are specialized in providing world-reknowed brands: Allen Bradley , ABB , General Electric , Triconex , Honeywell , Bently Nevada , Schneider , Hima ,etc. Even some discontinued ones,such as A-B 1785/1771 and so on.

Adleman Limited is a professional manufacturer of global famous brand modules and spare parts.

Our main products are: distributed control system (DCS), programmable logic controller (PLC), large servo control system.

The spare parts we sell are guaranteed for one year and are rigorously tested and certified.

We are now a global manufacturer of industrial automation spare parts and components.

Rockwell: Allen-Bradley

1) ControlLogix 1756 series controller

2) CompactLogix 1769 series controller

3) SLC 500 1747 1746 Series Controller

4) PLC-5 1771 1785 series controller5)

5)ProSoft :MVI69/PS69/MVI56/MVI94/MVI71/MVI46/31506)

6)ICS TRIPLEX trusted system


1) AC800M series controller I/O module

2) AC800F series controller module

3) AC31 series controller module

4) 800xA series modules

5) Bailey INFI 90 module

6) DSQC robot module spare parts

7) Advant OCS system spare parts

8) H&B Freelance

Bentley Nevada :

1) Bently 3500 Monitoring system

2) Bently 3300 Monitoring system


Quantum 140 series :Modicon M340

Modicon Premium :CPU Processor Module,Communication module,etc


1) Ovation System DCS Card

2) DeltaV system Dual Channel Redundancy Safety System, Redundancy Controller

General Electric:

1) IS200/DS200 series Excitation system card

2)IC693/IC695/IC697/IC698/IC200/IC660/IC670 CPU module,Communication module, Analog Digital module

Triconex Card: Tricon System Card

Foxboro: I/A Series System Module


1) Alcont

2) Experion LS  

3) Experion PKS

4) Experion HS

5) Plant Scape

6) TDC 2000

7) TDC3000  

8) TPS

Siemens :

1) Siemens MOORE

2) Siemens S5

3) Siemens  6SN/6FC/6FXseries

4) Siemens  CNC system 810、802D SL、810D、840D

5) Siemens MOORE S7系列S7-200、S7-300、S7-400;6AV/6GK


CS3000 System CPU Controller Module, Analog Module


Robot Servo Controller, Servo Motor, Servo Drive.

Rexroth Indramat:

I/O module, PLC controller, drive module


VM600 MPC4 VM600 CMC16 VM600 IOC4T Vibration Sensor, Speed Sensor, Vortex Sensor, Monitoring System Module Gateway Communication Module.

We can provide equipment and spare parts from different countries and manufacturers, solve your troubles in many places or worry about quality problems, and has great price advantage.

Welcome to call us to get more product detail information.

Please note: The business regions corresponding to the main activities with an annual business volume of more than 20%: Indonesia, the United States, Germany and Saudi Arabia. Excluding Hong Kong, China.

Need Help? Chat with us

leave a message
For any request of information or technical support, fill in the form. All fields marked with an asterisk* are required.
Looking for FAQs?
Contact us #
+86 -15259245292

Our hours

Mon 11/21 - Wed 11/23: 9 AM - 8 PM
Thu 11/24: closed - Happy Thanksgiving!
Fri 11/25: 8 AM - 10 PM
Sat 11/26 - Sun 11/27: 10 AM - 9 PM
(all hours are Eastern Time)




Contacts Us