What to do if the contacts of the magnetic starter stick?
Good afternoon. There is an electric boiler with a capacity of 120 kW, there are four magnetic starters on it. When the coolant reaches the set temperature, by command from the thermal sensor, the magnetic starters are switched off. But, on one of the starters, two power contacts are disconnected, and the third contact is stuck. As a result, the coolant overheats, melts and fails the temperature and emergency sensors, burns out the wiring and the failure of the heating elements.
Questions:
1. Is this situation a phase imbalance?
2. If you put a thermal relay on the magnetic starters and install a remote release on the circuit breaker, can the thermal relay send a signal to the trip by phase imbalance and turn off the voltage supply to the magnetic starter?
Questions:
1. Is this situation a phase imbalance?
2. If you put a thermal relay on the magnetic starters and install a remote release on the circuit breaker, can the thermal relay send a signal to the trip by phase imbalance and turn off the voltage supply to the magnetic starter?
Hello!
How are the heating elements connected? By star? If the zero is not turned off, and this is exactly so, judging by your description, this cannot be called a phase imbalance. Thermal relays will save from prolonged slight overcurrent. Yes, if the thermal relay has block contacts, it can send a signal to the release. Have you replaced starters? Maybe the starter is just weak? Are the contacts sticking because they are welded in or because you have an old starter and its anchor is skewed? If welded and overloaded - put the starter more powerful.
How are the heating elements connected? By star? If the zero is not turned off, and this is exactly so, judging by your description, this cannot be called a phase imbalance. Thermal relays will save from prolonged slight overcurrent. Yes, if the thermal relay has block contacts, it can send a signal to the release. Have you replaced starters? Maybe the starter is just weak? Are the contacts sticking because they are welded in or because you have an old starter and its anchor is skewed? If welded and overloaded - put the starter more powerful.
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Yes, zero is not interrupted. Contacts stick because they are welded. It is possible to replace the starters, but their frequent operation leads to the melting of the contacts and welding over time, you will have to change a lot and regularly. Yes, and on new starters there is no sticking insurance, there have been cases. Starters are according to the documentation of the equipment manufacturer. I would like to protect the equipment from this trouble.
So in this situation, it does not make sense to install a thermal relay on the starters. Can you advise a device that will respond to the disappearance of voltage on some contacts of the starter and on the presence of voltage on others?
Have there been cases? In more powerful contactors, oddly enough, there is a greater switching ability at the contacts. Why are they welded? Maybe they are initially overloaded with you? This entails both large arcs during opening and greater heating of the contact itself. There is of course to put something like a phase monitoring relay AFTER the contactor, although such a connection is not quite typical, it will “see” all the phases “in place”, but its output must be connected to the same contactor, for example with a much larger nominal current (to be sure), or to various releases for circuit breakers, there are such devices, each of them for "their" tasks.
For example, RMM-47 - when the voltage is exceeded, it turns off the machine. Their correct name is "Independent release".But the “RN-47” tripod (IEK’s has it) seems to be what you need from the description “An independent RN47 trip unit is designed to remotely trip a single, double, triple or four-pole circuit breaker of the BA47 series.”