What is Overload?
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Every electrical device used in the power grid or in our daily life will have a rated power, and when the power of the equipment is higher than the rated power, we call it overload.
Again, we refer to this protection in excess of the rated power as overload protection.
It is also important to mention here that when the equipment is overloaded, it is easy to cause a short circuit in the electrical equipment.
We refer to these protections as short-circuit protections that specifically protect against short-circuit faults inside the device.
What is Overcurrent?
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Overcurrent and overload are both a state, in which overcurrent is a state of operation of electrical equipment when the motor or other electrical components are higher than the rated current.
In general, the overcurrent is not higher than the short-circuit current and is within six times the rated current.
Overload protection
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The overload operation state is within the scope of the overcurrent operation state, because it is a state in which the motor operating current exceeds the rated current and is within 1.5 times.
If the electrical equipment is in an overload state for a long time, its winding temperature rise will exceed the allowable value, resulting in aging or damage to the winding insulation.
Overload protection is often achieved by thermal relays, which can operate instantaneously without being affected by the short-term overload impulse current or short-circuit current of the motor.
However, it is also necessary to use a fuse or a low-voltage circuit breaker at the same time, because when more than 6 times the rated current passes through the thermal relay, it will slow down, at least after 5 seconds.
As a result, the heating element of the thermal relay will be burned out at the time of operation.
Overcurrent protection
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As we mentioned earlier, overcurrent is a state, and when there is an overcurrent, it is often smaller than the short-circuit current, and it is within six times.
In general, in electrical circuits, the probability of short circuits and overcurrents is much smaller, especially when the motor is frequently started and reversed.
It should be mentioned here that when there is an overcurrent in the line, if the current value can be restored to normal before the maximum temperature rise is reached, then the electrical components can still operate normally.
However, there is one point, the overcurrent here may cause the impulse current to damage the motor, and the instantaneous electromagnetic torque will damage the mechanical transmission parts, so it is necessary to cut off the power supply in time.
Overcurrent protection should use the overcurrent protection relay, which is installed in the protected line, when the current reaches a set value, the relay will act, its normally closed contact is connected in series in the branch where the contactor coil is located, so that the contactor coil is de-energized, and then disconnected through the main contact of the contactor in the main circuit, so that the motor power supply is cut off in time.
Short-circuit protection
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Many novices don't know that in the power system, if the electrical equipment in the line or the insulation of its wiring is damaged, there may be wiring errors or load short circuits, etc., then, when such a situation occurs, the equipment will be short-circuited.
When a short-circuit fault is caused, the instantaneous current of the appliance is not only a little higher than the rated current, but more than dozens of times.
Such a consequence may be due to the strong electrical power of the electrical line and damage to the electrical equipment, and at the same time generate an electric arc, which can lead to a fire.
Therefore, we need to take some measures to avoid the harm caused by short-circuit faults, which is short-circuit protection. This requires us to quickly cut off the power supply after a failure, and the method often used here is to install a fuse or a low-voltage circuit breaker in the power line.