WHAT ARE THE CAUSES OF CONTACT STICKING AND COIL BURNING IN THE CONTACTORS ?
What are the causes of contact sticking and coil burning in the contactors?
Electromagnetic switches, which open the closed contacts and close the open contacts when the energy is applied to the coil ends, are called contactors.
It allows remote control of electrical facilities such as electric motors, compensation and heating systems by cable. When used together with thermal relays, it protects devices and facilities against overload currents.
Malfunctions may occur if the contactors are not used in accordance with the technical data or if overcurrent or short circuit occurs in the supply network. In general, contactors are circuit elements that do not fail easily. The contactor can open and close millions of times if the selection is made correctly and the operating conditions are not impaired. The most common situation in contactor failures is contact sticking and coil burning.
The reason for contact sticking; If more current is passed through the main power contacts than it can carry, the contacts will overheat after a while and the contacts may stick as a result of this warming. Switching at high current, short circuit, or error in star-delta transition can cause this. For example, if the contactor is selected according to AC-1 values in motor application, the contacts may stick. Normally, the choice is to choose according to the AC-3 value. For this reason, contactor selection should be made according to the load that will pass over the contactor. If a short circuit has occurred, the cause of the short circuit must first be found, and the control circuit fuse must be renewed. Since contactors cannot open in case of overload, such as switches, their contacts may stick after a certain current.
For example, for AC-3 in engine application;
Ie: Max. the current value of the contactor’s closing capacity is determined as 10xIe and the breaking capacity as 8xIe. After these current values, adhesion can be observed in the contacts.
Reason for coil burns: Coil may burn when the voltage applied to the contactor coil ends is lower or higher than normal. In addition, dust and foreign bodies in the air gap facilitate this. When coil burning is encountered, voltage and frequency should be checked first and a stable coil voltage should be provided for the contactor. To prevent coil burning, the coil must be fed at the voltage and current values specified in the catalog.
Other major failures encountered in contactors can be summarized as follows:
Excessive length of the control (coil) circuit cables can cause some problems. In long cables, the large voltage drop across the cable makes it difficult to close, while the cable capacitance with excessive cross-section prevents opening.
The presence of dirt or foreign particles in the contactor, difficult atmospheric conditions and corrosion can prevent the contactor closing process, especially with the remote control. When such a mistake is encountered, the contactor should be cleaned with a strong clean air flow against dirt and dust, the enclosure should be made more closed and protected, the circuit should be checked, and if there is a conductive factor, it should be eliminated.
FC type power contactors produced in Federal Electric are produced with 3 and 4 poles AC and DC options up to 750A. FC-DK type compensation contactors are produced up to 80 kVAr.
View Product Catalogue