Contactors are common electrical components in frequency converter control, mainly used for switching buffer resistors and connecting and disconnecting circuits. The correct selection of contactors directly affects the working quality of the frequency converter and the operating condition of electrical equipment, thus impacting the normal production and safe and stable operation of the entire system. Paying close attention to contactor-related issues is of great practical significance for improving the overall operating level and product quality of frequency converters.
What kind of contactor does a frequency converter actually need?
(1) It can meet the insulation requirements of the frequency converter and improve the safety of the frequency converter.
To address the insulation characteristics of frequency converters, the contactor housing is made of reinforced flame-retardant nylon 66, with an insulation voltage of 1500V DC and a power frequency withstand voltage of 3500V. This eliminates safety hazards, allowing the product to be directly installed on the housing and improving the safety of the frequency converter.
(2) Unipolar DC
Since the contactor operates on the DC bus, switching a buffer resistor only requires one pole. Therefore, it is designed as a single-pole DC circuit. Based on the characteristics of using buffer circuit contactors in frequency converters with power ratings of 18.5kW and above, the contactor's current rating should be 50A, 100A, 200A, 265A, 400A, 600A, 800A, etc.
(3) High temperature resistance and dustproof
Low-voltage frequency converters use IGBTs as their power components, which generate heat during operation. To dissipate this heat, fans are installed on the converter housing, significantly reducing its internal dust protection. This means the contactors installed inside the converter operate in a high-temperature, high-dust environment. To address these issues, the contactor coils are wound with enameled wire resistant to 180℃, and both the contact system and magnetic system are enclosed within the housing.
(4) Meets the control voltage specifications of various standards
In frequency converters, contactors are categorized into two control voltage types: DC and AC. DC control primarily uses 24V DC, mainly because they believe that 24V DC cooling fans have more stable performance. Therefore, the contactors also use 24V DC, allowing them to share a switching power supply with the fan.
AC control primarily uses AC 220V and 380V. AC 220V requires a control transformer, which improves the reliability of the contactor but also increases the cost, while AC 380V does not require a control transformer.
Opinions vary on the control voltage; 24V DC, 220V AC, and 380V are all acceptable.
(5) The installation method complies with the current specifications for frequency converters.
Currently, there are many brands of three-phase AC contactors used in frequency converters, making it difficult to find a suitable shape and installation size for the industry. However, both screw and clamp mounting methods can be considered during the design process.
There are not many manufacturers of single-pole DC contactors, and the installation dimensions of their products are relatively uniform. Therefore, the shape and installation dimensions can be kept consistent with existing products during the design phase, allowing frequency converter manufacturers to use them directly without any modifications.
