Relays in frequency converters are typically used to control the on/off state of circuits, enabling various control functions such as starting, stopping, and speed regulation. There are many types of relays; based on the input signal, they can be classified as voltage relays, current relays, and time relays; based on their working principle, they can be classified as electromagnetic relays, induction relays, and transistor relays.
A relay works on the principle of electromagnetic induction. Changes in the input signal alter the magnetic circuit inside the relay, causing the contacts to actuate. When the coil is energized, a magnetic field is generated in the iron core, creating an electromagnetic force that drives the contacts to move. Once actuated, the contacts connect or disconnect the circuit, thus achieving the control function.
Anyone familiar with this industry will be no stranger to relays. It is an electrical control device.
What are electrical control devices?
A relay contains both a control system and a controlled system. It can automatically adjust and switch circuits, and provide safety protection based on factors such as current and voltage. It can promptly reflect the current status of the frequency converter and send signals to the control system.
For example: when the inverter is powered on, the relay activates; when the inverter is not powered on, the relay does not activate. Operation indicators can also be set: when the inverter is running, the relay activates; when the inverter is not running, the relay does not activate. This allows us to know the motor status and, based on different settings, output signals for ready, running, fault alarm, forward/reverse, mains frequency conversion, sleep mode, and extended functions, etc.
The inverter also has a high-current relay or contactor inside, used to control the external braking unit or braking resistor.
Although it comes in many different styles, the basic principle is the same.
During maintenance, the coil should be removed, and its contact surfaces filed or ground smooth; any oil stains should be cleaned. Loud noise may be caused by a short circuit or a broken ring; repairing or replacing the short-circuit ring will resolve the issue. If the armature does not release immediately after power is off, this may be due to the moving iron core being stuck, the air gap being too small, spring wear, or oil stains on the iron core contact surface. During troubleshooting, the cause of the fault should be addressed accordingly; adjustments may be made to the air gap to maintain a protection level of 0.02–0.05 mm, the spring may be replaced, or the oil stains may be cleaned with gasoline.
Common relay faults and troubleshooting methods
Poor contact: Poor contact is one of the common relay faults. Troubleshooting methods include checking the contact surface for dirt or oxides, cleaning the contacts with alcohol or gasoline, or replacing the contacts.
Open circuit in the coil: An open circuit in the coil is also a common fault. Troubleshooting methods include checking if the coil is broken or detached, resoldering, or replacing the coil.
Core breakage: A broken magnetic core will cause the relay to malfunction. Troubleshooting methods include replacing the magnetic core.
Parameter mismatch: Parameter mismatch can lead to unsatisfactory relay control performance. Troubleshooting methods include adjusting the parameters to match the actual requirements.
