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Selection principle and method of motor protector
The basic principle of selection
At present, the low voltage motor protection products in the market have not the same standard, the model specifications are various. Manufacturers in order to satisfy the user's different requirements to derive a lot of series of products, a wide variety to the general user selection to bring inconvenience, when users in the selection of motor protection based on the actual demand, to achieve the use of the expected value and effect.
The basic method of selection
(I) conditions related to selection:
Motor protection type motor and protector exist two relation, how to reasonable with the following several conditions and factors related to the protection provided, provide a reference for users how to selection protector.
1. Motor aspects: first understand the model specification, motor function, protective type, rated voltage, rated current, rated power, power supply frequency, etc. These contents can provide a reference basis for the user to use and maintain and select the protector correctly.
2. Environmental conditions: mainly refers to normal temperature, high temperature, high cold, corrosion degree, vibration degree, wind sand, altitude, electromagnetic pollution, etc.
3. Motor use: mainly refers to the characteristics of mechanical equipment, such as fan, water pump, air compressor, lathe, oil pumping unit, etc.
4. Control system: control mode has manual, automatic, local or centralized remote control, single unit operation, or production line chain automation program. The starting mode includes direct, step-down, star delta, frequency sensitive rheostat, frequency converter, soft starting and so on.
5. Other aspects: the user's control over the production monitoring of the site is more casual or serious, and the non-normal downtime affects the severity of production.
And the selection of protector has certain there are many related factors, such as installation location, connecting lines and the matching between system use electric appliances, but mainly motor working condition the influence extent of variation and controlling changes to the production according to the requirement of the actual working conditions and the actual change, for reasonable selection and adjustment of the protector.
(2) common types of low-voltage motor protectors
1, ordinary: structure is simple, setting current value set using potentiometer knob or code switch control, generally USES the analog circuit, action using inverse time protection curve or definite time job characteristics. The main functions are to highlight the failure protection such as overload and missing phase (three-phase imbalance). The fault type adopts the indicator light to show that the running power is displayed in the digital tube.
2. Digital monitoring type: the inner circuit of the protector USES a single chip microcomputer to realize the intelligent comprehensive protection of the motor, which integrates protection, measurement, communication and display. Setting current adopting digital set, through the control panel buttons to hold the vertical, the user can according to your actual use requirement and protect themselves at the scene for the various parameters setting, using digital tube as a display window, due to the information not enough rich digital tube display, this kind of protector into high gear.
3. Intelligent monitoring of Chinese hanexplicit: compared with the above digital monitoring type, it has better feature and humanized configuration. Such products for a variety of parameters, status, information directly on the manipulation of the face plate unit HanXian Chinese LCD display, make the interface more intuitive, can support various communication protocols, such as ModBUS, ProfiBUS, meet many startup mode, view a variety of information management records, and so on. Such protectors are of high quality in the present market.
4, special: structural characteristics, basic protection function, circuit control mode, roughly the same with the regular and digital surveillance, just inside the protector circuit output control wiring methods, in order to highlight special control is given priority to, such as fan, water pump, lathe, pumping unit, etc.
The choice of protector type in working conditions of the motor
1, low requirements for the working conditions, simple operation control, monitoring, governance, more casual, downtime for production of little influence on single independent motor operation, can choose ordinary protector, because ordinary protector has simple structure, in the field wiring installation, replacement, manipulation is simple, convenient, high cost-effective, etc.
2, for the high requirement of working conditions, and it's key security and continuity, and high degree of automation, and control, monitoring, treatment, and needs the MCC system network monitoring, should choose middle-grade or high-grade protector.
3. The special type protector should be chosen for the dual purpose of protection control and display monitoring for those with special load characteristics, light weight and heavy overload.
(4) the connection mode of the main current of the protector
The main current connection mode is divided into:
1. The core type (also can be used to use peripheral current transformer secondary loop)
2. Terminal type (peripheral current transformer secondary loop can also be used)
3. Direct interpolation
It is convenient and safe to wear the core type wiring, which avoids the heating of contact resistance due to the contact of the terminal. The rated current value of the motor is above 5A, and it can be used for a single core.
It is easy to connect directly into the connection mode, especially for those with small space and suitable for installation, the insertion type protector can be directly connected with the main contact of the contactor.
(5) selection of the range of setting current of the protector
Matching, in order to adapt to different power motor protector basically have certain current adjusting range, when choosing protector, according to the motor rated current value as far as possible choose setting current value of the middle area.
(6) selection of working power supply
The working power supply is mainly for the internal circuit of the protector, except for the work power type, which is generally divided into: AC380V, 220V, 110V, 36V. There is no special requirement for working power supply, since it is an independent power supply unit, the user can choose according to the voltage level of the motor control circuit.
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