The intelligent motor protector integrates the functions of measurement, control, protection, network communication, etc., and can protect the three-phase asynchronous motor. The modular design of the fully intelligent motor protector, the main controller and the display operation module are separated, according to the actual situation whether to use the display operation module. The product is small in size, compact in structure and easy to install. It can be directly installed in various low-voltage control cabinets and various drawer cabinets of 1/4 module and above.
The current transformer in the motor mainly cooperates with the relay device. When a fault occurs in the circuit, such as a short circuit, the relay device sends a signal to cut off the faulty circuit to protect the safety of the motor.
Current transformers can be divided into:
1. The measuring winding of the current transformer: within the normal operating range, it provides the current information of the power grid for measuring, metering and other devices.
Current transformer for precise measurement (or precise measurement winding of current transformer): within the current range in normal operation, the current information content of the power grid is given to precise measurement, metrological verification and other equipment.
2. Current transformer for protection: in the case of power grid fault, the information content of power grid fault current is given to relay protection devices and other equipment.
Current transformers for protection are further divided into:
(1) Current transformer for grounding protection (zero sequence current transformer)
(2) Overload protection current transformer
(3) Differential protection current transformer
The protection transformer usually starts to operate when the current is several times or tens of times of the normal operating current. Operational requirements for protective inductors:
1. Reliable insulation.
2. Sufficiently large accurate limit coefficient.
3. Thermal stability and dynamic stability.
The rated accuracy limit of the protective transformer is the primary current that can meet the requirements of the accuracy level under the rated load. The accuracy limit coefficient is the ratio of the rated accurate primary current to the rated primary current. Accurate limit coefficient characteristics When the primary current is large enough, the iron core will saturate and cannot reflect the primary current. The accuracy level of the protection transformer is 5P and 10, which means that the allowable current error when the rated accurate limit primary current is 1% and 3%, and the composite error is 5% respectively.
The inrush current that fails when the motor is running generates heat and electromagnetic force, which are borne by the protective transformer. Under the condition of short-circuit fault of the secondary winding, the rms value of the primary current that the current transformer can withstand without damage in one second is called the rated short-time thermal current. Under the condition of short-circuit fault of the secondary winding, the peak value of the primary current that the current transformer can withstand without damage is called the rated stable current.
Transformer function for protection:
This series of low-voltage protection devices have the functions of load, phase failure, unbalance, underload, grounding/leakage, and locked rotor. It can be combined with contactors, motor starters and other components to form a motor control and protection module, which has the functions of remote control automatic control, on-site direct control, panel marking, data signal alarm, and computer interface communication.
Application scope of protective transformer:
Power distribution equipment industry in coal mining, petrochemical, smelter, power engineering, engineering construction and other fields.
At this stage, there is no unified standard for motor protection products on the market, and there are various specifications and models. In order to better meet everyone’s different application requirements, manufacturers have derived many product series with various types, which brings a lot of inconvenience to many customers’ model selection; customers should comprehensively consider the actual requirements of motor protection when choosing, and effectively select protection Function and protection measures can achieve better protection effect, enhance the stability of facility operation, reduce unplanned parking, and reduce accident losses.
