First, the basic principles of selection

At present, the low-voltage motor protection products on the market do not have the same standard, and the model specifications are varied. Manufacturers in order to meet the different needs of users to derive a large number of products, a wide variety of users to bring a lot of inconvenience to the selection of users, users should be in accordance with the actual needs of motor protection in order to achieve the expected use value and effect.

Second, the basic method of selection

(1) Conditions related to selection:

The selection of motor protection has a fair relationship between the motor and the protector. The following provides several conditions and factors related to protection, which provides a reference for users to choose the protector.

1. Motor: First understand the model specifications of [1], motor function characteristics, protection type, rated voltage, rated current, rated power, power frequency, and edge. 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, corrosion, vibration, sand, altitude, electromagnetic pollution.

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

4. Control system: The control mode includes manual, automatic, local or centralized remote control, single unit independent operation, or production line interlocking automation program. 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 and control is relatively random or rigorous, and the abnormal shutdown affects the severity of production.

There are a number of factors related to the selection of protectors, such as installation location, connection lines and system electrical appliances, but mainly the variation of motor operating conditions and the impact of control changes on production, according to the actual working conditions mentioned above. And the actual changes, the protection of the fair selection and adjustment.

(ii) Common types of low voltage motor protectors

1. Ordinary type: The structure is relatively simple. The setting of the current value is controlled by potentiometer knob or dial switch. The circuit is generally analog, and the action protection curve adopts inverse time or definite time. The main function is to highlight the fault protection such as overload, phase loss (three-phase unbalance), fault type using indicator light, and running power using digital tube display.

2. Digital monitoring type: The internal circuit of the protector uses single-chip microcomputer to realize intelligent comprehensive protection of the motor, integrating protection, measurement, communication and display. The setting current is digitally set and manipulated by the operation panel button. The user can modify various parameters on the spot according to his actual use requirements and protection conditions. The digital tube is used as the display window. The information displayed by the digital tube is not rich enough. This type of protector is medium to high-end.

3, intelligent monitoring Chinese Han Xian type: Compared with the above digital monitoring type, it has more perfect functional features and humanized configuration. Such products have various parameters, status and information directly on the control panel unit. The interface is more intuitive and eye-catching, and can support a variety of communication protocols, such as ModBUS, ProfiBUS, etc., to meet a variety of startup methods, view a variety of Information governance records and more. Such protectors are of the high quality type on the market today.

4, special type: structural features, basic protection functions, circuit control mode, etc. are roughly the same as ordinary type and digital monitoring type, except that the internal circuit output control wiring method of the protector is different, to highlight the special control, such as fan, water pump, lathe. , pumping unit, etc.

(3) Selection of protector type under motor operating conditions

1. For the single-machine independent running motor with low requirements on working conditions, simple control, simple monitoring and control, and no impact on production, the ordinary type protector can be used. Because the structure of the ordinary protector is simple, the wiring is installed on site. It is simple, convenient, and cost-effective.

2, for the working conditions are very high, safety and continuity are critical, and the degree of automation is high, and requires special personnel to control, monitor, and manage. In the MCC system that requires network monitoring, high-end or high-grade protection should be selected. Device.

3. For those motors with special load characteristics and frequent light and heavy load, special protection devices should be selected for the purpose of protection control and display monitoring.

(4) Selection of wiring method for protector main current

The main current wiring method is divided into:

1. Once through the core (you can also use the secondary current transformer secondary circuit)

2, the terminal type (can also use the peripheral current transformer secondary circuit)

3, direct insertion

One-time core-type wiring is convenient and safe, and avoids contact resistance heating caused by poor contact of the terminal. The rated current of the motor is above 5A, and it is generally possible to use one-time core wiring.

It is convenient to connect directly into the wiring mode, especially for those cases where the space is small and suitable for the installation position, the plug-in protector can be directly connected to the main contact of the contactor output.

(5) Selection of protector setting current range

In order to adapt to the selection of different power motors, the protector basically has a certain current adjustment range. When the protector is selected, the value of the middle region of the set current range is selected as much as possible according to the rated current value of the motor.

(6) Working power selection

The working power supply is mainly for the internal circuit of the protector. Except for the working power type, the working power level is generally divided into: AC380V, 220V, 110V, 36V. There is no special requirement for the working power supply selection, because it is an independent power supply unit, and the user only needs to select according to the voltage level of the motor control circuit.