The motor protection circuit breaker is used to protect the windings from short circuits, overloading, and also when one of the three phases of the supply circuit is interrupted. The last condition arises in the event of a malfunction of the switching equipment or a violation of the integrity of the cable connecting the boron motor to the relay circuit.
Appointment
The motor protection circuit breaker is placed as the first link in the motor supply network. Next is the electromagnetic starter, after which a thermal relay can be additionally used . Modern models have the ability to adjust the cutoff current.
More often considered types of machines are used to protect three-phase motors. Each winding clings to its contact, but the device is disconnected in all phases. This principle of operation distinguishes the device from circuit breakers of types B and C. Revolving motors start under load in difficult conditions. In this case, the starting current often exceeds the rating up to 6 times. Conventional circuit breakers will trip instantly, but the circuit breaker will turn off only after a steady increase in current strength.
Electrical Device Parameters
The selection of a motor protection circuit breaker begins with the determination of the following characteristics:
- The operating current of the motor.
- The magnitude of the supply voltage.
- The number of windings.
- An important characteristic is the ability of the circuit breaker to disconnect the short circuit current. In conventional machines it does not exceed 6 kA, in recent versions it exceeds 50 kA. The response time is taken into account: selective - up to 1 s, normal - up to 0.1 s, high-speed - not more than 0.005 s.
- Dimensions. Most machines are connected to the mains via a fixed bus. It is often problematic to insert the first switch of a different design.
- Type of release mechanism: the possibility of thermal and electromagnetic protection.
Motor Failure Warning
It is important to know not only what protective functions the motor circuit breaker performs, but also take into account the technical nuances of the connected electrical circuit. In the case of using high-speed motors, malfunctions can occur when a slightly higher current flows through one contact of the switching relay. After prolonged use, this will lead to the failure of one winding. You will need a more sensitive switch that can break the circuit when the wire is heated.
Some motors are critical to the short-term loss of one of the supply phases. Even if you use a motor protection circuit breaker and thermal protection, you will need to install models that turn off when the power supply fails at one of the contacts. Accordingly, such devices have a more complex structure, which affects their cost. Manufacturers strongly do not recommend connecting multiple power circuits to one device.
Additional properties of switching equipment
The motor circuit breaker is designed to operate in a certain range of ambient temperatures. After exceeding the maximum limit set by the manufacturer, false alarms can occur. If the switch is put in a too cold place, then it will not turn off at all at the right time. Therefore, if necessary, installers provide for appropriate technical compensation.
In production, situations may arise when the machine itself fails, and the remaining elements remain operational. Some models have a trip protection function on the front panel of the switch. This is a temporary measure until a new device is installed in order to ensure continuous product delivery. However, there is a risk of damage to the expensive element - the engine.