Practice has proved that, combined with the needs of users in the design of the motor protection (motor protection) should meet the following requirements:

    1, using the current sampling

    This will not only take into account the different characteristics of the flow and phase failure protection, but also fully reflect no matter where phase failure should be reflected in the fact that in the current of the power supply line; avoid the shortcomings and limitations of the sampling program. Use of voltage sampling is low cost, but only to protect the power supply to the sampling access at between off, can not protect sampling access at the motor phase failure. Neutral point or artificial neutral point current or voltage of the zero line sampling, the single-phase load on or off, is bound to make the neutral point voltage or current change of the zero line, which will enable the protection setting value is difficult to determine.

    2, the choice of the responsive electronic protection program

    Ensure that off phase starting refused to switch on, run-off phase instantaneous trip. As for the implementation of delay off protection and overheating protection point of view is stale, one-sided.

    3, with the the protection normally closed contact action to protect the

    This is claimed in the main circuit does not work and the normal working hours to perform the relay does not operate when a fault occurs in the motor starter and Actions. This protector is suitable for group control circuit with the computer output and logic multi-speed and reversing motor, as well as with the main switch interface, use limitations.

    4, there is a wide range of current adaptation

    Motor no-load current is approximately 0.3 times the rated current, seven times the starting current of the rated current. For motor protection (motor protection) should be from low to high at least 20 times or 30 times the current allowable range for single-phase protection, the current adaptation range should be even greater.

    5, do not use the required power supply motor protection (motor protection)

    Does not need power supply, making it common to any occasion. Supply voltage from the world is not the same, at the same time prevents the motor from the power failure will result in motor protection (motor protector) is no electricity, causing the relay does not operate, would not achieve the protective effect

    6, motor protection (motor protection) off phase and overcurrent should be controlled so as not to involve each other refuse to move or malfunction.