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Motor overheating overload protector selection method

Article Source:Thermal protectorAuthor:Kangding MetalPopularity:Published time:2019-07-26 11:17

First, the basic principles of selection
Today, there are no uniform standards for motor protection products on the market, and the model specifications are varied.
In order to meet the different needs of users, manufacturers have derived a large number of series of products, which brings a lot of inconvenience to the selection of users.
Users should fully consider the actual needs of motor protection when selecting the type, and reasonably choose the protection function and protection mode to achieve good protection effect, achieve the purpose of improving equipment operation reliability, reducing unplanned parking and reducing accident losses.

Second, the basic method of selection
(1) Conditions related to selection:
The choice of motor protection has a reasonable relationship between the motor and the protector. The following are some of the conditions and factors related to protection, which provide a reference for users to select.

1. Motor: First understand the model specifications, motor function characteristics, protection type, rated voltage, rated current, rated power, power frequency, insulation level, etc. These contents can basically provide a reference for users to correctly use and maintain and select the protector.

2. Environmental conditions: Mainly refers to normal temperature, high temperature, high cold, corrosivity, vibration, wind and sand, elevation, electromagnetic pollution and so on.

3, motor use: Mainly refers to the characteristics of the mechanical equipment required to drag, such as fans, pumps, air compressors, lathes, oil field pumping units and other mechanical properties of different loads.

4. Control system: The control modes include manual, automatic, local control, remote control, stand-alone operation, and centralized control of the production line. The starting mode includes direct, buck, star triangle, frequency sensitive varistor, inverter, soft start and other starting methods.

5. Other aspects: The user's on-site production monitoring management is relatively random or rigorous, and the severity of the impact of abnormal shutdown on production.

There are many factors related to the selection of protectors, such as the installation location, power supply, and coordination with the power distribution system; Also consider whether the new motor protection configuration, or the motor protection upgrade, or the improvement of the accident motor protection; Also consider the difficulty of changing the motor protection method and the degree of impact on production; The selection and adjustment of the protector should be considered comprehensively according to the actual working conditions on site.

(2) Common types of motor protectors
1, thermal relay: Ordinary small-capacity AC motors, good working conditions, and no severe operating conditions such as frequent start-up. Due to poor precision, reliability cannot be guaranteed and is not recommended.

2, electronic type: The three-phase current value is detected, and the setting current value is operated by a potentiometer knob or a dial switch. The circuit is generally analog, and adopts an inverse time limit or a time limit operation characteristic. The protection function includes fault protection such as overload, phase loss and stalling. The fault type is displayed by indicator light, and the running power is displayed by digital tube.

3. Intelligent type:
The three-phase current value is detected, and the protector uses a single-chip microcomputer to realize intelligent comprehensive protection of the motor, integrating protection, measurement, communication, and display. The setting current is digitally set and operated by the operation panel button. The user can modify various parameters on the spot according to his actual use requirements and protection conditions. Use a digital tube as a display window or a large-screen LCD display. Can support a variety of communication protocols, such as ModBUS, ProfiBUS, etc., the price is relatively high, for more important occasions, today's high-voltage motor protection is intelligent.

4, thermal protection type:
A thermal element is embedded in the motor. According to the temperature of the motor, the protection effect is good, but when the motor capacity is large, it needs to be used together with the current monitoring type. The temperature rises sharply when the motor is blocked, and the motor winding is damaged due to the hysteresis of the temperature measuring element.

5, magnetic field temperature detection type:
The magnetic field detecting coil and the temperature probe are embedded in the motor, and are protected according to changes in the rotating magnetic field inside the motor and changes in temperature. Key features include overload, stall, phase loss, overheat protection and wear monitoring. The protection function is perfect, and the disadvantage is that a magnetic field detecting coil and a temperature sensor are installed inside the motor.

 thermal protection type