Views: 7 Author: Site Editor Publish Time: 2022-11-01 Origin: Power Grid Technology
Every electrical device used in the power grid or in our daily life will have a rated power. When the power of the device is higher than the rated power, we call it overload.
Likewise, we will call this protection over rated power overload protection.
Another point to mention here is that when the equipment is overloaded, it is easy to cause a short circuit in the electrical equipment.
We call those protections that specifically protect against short-circuit faults inside the device as short-circuit protection.
Both overcurrent and overload are a state, in which overcurrent is an operating state of electrical equipment when the motor or other electrical components are higher than the rated current.
Normally, the overcurrent is not higher than the short-circuit current and is within six times the rated current.
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The overload operating state falls within the category of the overcurrent operating 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 overload operation for a long time, the temperature rise of its winding will exceed the allowable value, resulting in aging or damage to the winding insulation.
Overload protection is often achieved by thermal relays, which can act instantaneously without being affected by short-term overload impulse current or short-circuit current of the motor.
However, fuses or low-voltage circuit breakers should also be used synchronously, because when a current exceeding 6 times the rated current passes through the thermal relay, it will act slowly, at least after five seconds.
This will cause the heating element of the thermal relay to be burnt out when it operates.
We mentioned earlier that overcurrent is a state. When overcurrent occurs, it is often smaller than short-circuit current, and it is within six times.
Usually, in the electrical circuit, the probability of short circuit is much smaller than that of overcurrent, especially when the motor is frequently started and reversed.
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In the power system, if the electrical equipment in the line or the insulation of its wiring is damaged, there may be a wiring error or a load short circuit. Then, when such a situation occurs, the equipment will be short-circuited. Fault.
When a short-circuit fault occurs, at this time, the instantaneous current of the appliance is not only a little higher than the rated current, but exceeds dozens of times.
The consequence of this may be that the electrical equipment is damaged due to the strong electric power in the electric line, and an arc is generated at the same time, and the serious consequence will lead to the occurrence of a fire.
Therefore, we need to take some measures to avoid the harm caused by short-circuit faults, which is called short-circuit protection. Here we need to cut off the power supply quickly after a fault occurs. The method often used here is to install a fuse or a low-voltage circuit breaker in the electrical circuit.