Analysis of Electronic Motor Protector

Analysis of Electronic Motor Protectors We know that thermal relays have the advantages of simple structure, low cost, small size, and easy to use. However, the thermal relay has a single protection function, low accuracy, unstable operation, and a short heating time constant. Simply put, all thermal relays are good, that is, the protection performance is not reliable, which is its achilles heel. It is precisely because of this that an electronic motor protector with reliable protection performance has emerged. While showing its vitality, it is experiencing a process of gradual maturity. My company's production environment is relatively harsh, high temperature, more dust, moisture, continuous production, high motor damage rate. We have used several forms of motor protectors and we have gained some experience. Below from the reliability, ease of use and economical aspects of the electronic motor protector, talk about their immature experience. Electronic motor protector (motor protector) reliability At present, the thermal relays of industrial and mining enterprises are commonly used, but the phenomenon of damage to the motor is also widespread. According to investigations, more than 90% of the failures of asynchronous motors are due to overheating of the stator windings, and nearly 60% of them are caused by phase failures. This not only indicates that the thermal relay is relatively unreliable as a phase-failure protection, but also shows the protection of the phase failure. The necessity. In addition, due to the impact of the starting current of the motor, the thermal relay also causes its own phase failure to occur occasionally. Therefore, the novel motor protector must have the function of phase failure protection. As mentioned earlier, the thermal relay has a small heat-generating time constant, which is not suitable for motors with heavy inertia and heavy-load starting. The method of short-circuiting the thermal relay at startup is often used. This not only makes the control system complicated in structure, but also increases the cost. The protection of the dead zone. In order to avoid misoperation during start-up, the setting current is increased to make the protection virtually useless, and most of the detection current transformers of the electronic motor protector use a speed-saturation current transformer, so it is generally allowed to have a starting time in the cold state. Long; rapid overload feature when hot. This is exactly matched with the actual protection requirements of the motors of industrial and mining enterprises, and can more reliably protect motor overload. The detection element of the thermal relay is a bimetal. Due to the overcurrent impacts such as starting current and overload, it is easy to cause the bimetal to have a fatigue effect, resulting in offset of the scale value and unstable operation. This is difficult to find on the production site. Eventually causing overload does not work. The electronic motor protector uses a current transformer as the detection element, so there is no heating problem. The operation stability of the electronic motor protector is a qualitative leap compared to the thermal relay. With the use of more advanced electronic motor protectors (motor protectors), the detection elements generally use current transformers, and a core-through structure has emerged. Since the introduction of the core-type motor protector (motor protector), due to its numerous advantages compared with the thermal relay, it has attracted a great interest of the electrical industry. The core-through structure is not only easy to use, but also completely isolated from the main circuit, which will not affect the main circuit and increase its own reliability. At the same time, the problem of heating of the connection terminals is completely solved, and the interchangeability is good. However, currently only large-size motor protectors (motor protectors) are used at home and abroad, while small-size ones can only use wiring. Electronic motor protectors (motor protectors) solve the problem of a single function of the thermal relay and create new drawbacks that require a working Power Supply. Although the requirements for the electronic circuit amplification and driving need working power are reasonable, the application of the motor protector (motor protector) brings a series of problems. For example, the user must look for the power terminal before use and understand the power supply voltage. Grades and other inconveniences.

In addition, because the motor protector (motor protector) needs to work continuously, the failure rate is also high because of the fluctuation of the power grid voltage, interference, and its own heat. According to the incomplete statistics of the used electronic motor protectors (motor protectors) in our factory, more than half of the motor protectors (motor protectors) have their own faults in the power supply, which has greatly dampened the use of electronics by electrical workers. Motor protector (motor protector) enthusiasm. In addition, electronic motor protectors (motor protectors) have two insurmountable contradictions due to the use of electromagnetic relays as actuators. First, use the relay's normally open contact to implement the protection program, which features the contact is always open when the main loop is not working, so the contact must be serially connected to the contactor's self-protection circuit, so that even the user feels inconvenient installation, but also unable to For automatic control circuit; Second, the relay's normally closed contact action to implement the protection program, although the control contact can be directly connected to the control circuit like a thermal relay, but due to its automatic reset, the same can not be applied to automatic Control System. This greatly limits the use of electronic motor protectors. On the one hand, it is necessary to change the control circuit when replacing the thermal relay. On the other hand, it cannot be used in equipment that requires automatic control due to unattended, long-term operation and relatively high failure rate, such as pumps and compressors. Economical Because the thermal relay has a simple structure, the production volume is large and the cost is extremely low; while the electronic motor protector (motor protector) generally consists of signal detection, amplification, processing, execution, power supply, etc., and its production cost is much lower than The thermal relay is high, which brings certain pressure on the user's initial investment, and also brings certain difficulties to the overall promotion of the electronic motor protector (motor protector). As a manufacturer, while improving product performance, reducing production costs is a constant effort. Novel motor protector (motor protector). From the above, it can be seen that the electronic motor protector (motor protector) is characterized by reliable functions, but generally has the disadvantages of complicated structure, inconvenient use and maintenance, large size, and high cost. Here I will introduce the UL-E2 series motor protectors (motor protectors) manufactured by Ningbo Haishu Julong Electric Works after more than two years of use. This product retains all the advantages of the electronic motor protector (motor protector) and completely overcomes the shortcomings of this type of motor protector (motor protector).

The following also compares the conventional electronic motor protector (motor protector) from three aspects. Function: The motor protector (motor protector) has a phase failure and overcurrent protection. The motor protector (motor protector) has been used in our factory for more than two years. It has used UL-E2 series motor protector (motor protector) equipment, basically no motor damage has been found, especially the motor protector ( Motor protector) Induced draft fan used in annealing kiln. Because of the poor dynamic balance of the fan, the fixed foot is often loosened due to vibration, which further causes the power cord to break or the terminal to loosen, but never causes the motor to be damaged. The motor protector (motor protector) has the following features in addition to the general electronic motor protector function, action sensitive, stable performance; motor protector (motor protector) phase-off signal and over-current protection signal independent In this way, the motor protector (motor protector) can operate reliably even if the set value of the over-current is improper, and the motor is de-phased or discontinued before starting. The current setting of the UL-E2 series motor protector (motor protector) is represented by a dial, which is very eye-catching and convenient. When used, it is only necessary to adjust the scale to the value corresponding to the rated current of the motor. Overcame the difficulty of full load debugging of similar products in the country. The use of a motor protector (motor protector) in this way enables the motor to fully exert its overload capacity while enabling the motor to be reliably protected. Easy to use: The UL-E2 series motor protector (motor protector) is very convenient to use. The whole series adopts a string type (only need to wear 1 inch), no external power supply structure, and in this regard Japan's OMRON company's Small-size protectors of similar products need to wear 8 inches. The key to this breakthrough in the Dragon Electric Plant is that their actuator adopts a patented micro-power solid-state relay with a drive power consumption of 1uW and an electromagnetic relay with a drive power of 200mW, compared to the sensitivity. It is several orders of magnitude higher, which completely solves the problem of passivation and string core type of electronic protectors. The motor protector (motor protector) has intelligent characteristics. The protector can not only be directly connected to the control circuit, but also can automatically identify the manual control circuit and the automatic control circuit. It is not necessary to adjust the reset mode like a thermal relay when using it. After the action of the protector, the manual control loop can be automatically reset, and for the automatic control loop, it can also be self-locking to avoid the motor in a fault state, repeat the start, and intensify the damage of the motor. The motor protector (motor protector) has a small size and mounting dimensions and is interchangeable with the JR16 thermal relay. The overall circuit of the motor protector (motor protector) adopts a modular full-seal structure, and the internal solid-state relay is also used. It is waterproof, dustproof, and explosion-proof. It can be used in any harsh environment. Our factory uses the motor protector ( In the past two years or more, motor protectors have been found to have been damaged by motor protectors (motor protectors). Unfortunately, the motor protector (motor protector) has no fault indication function and cannot intuitively determine the cause of the fault. Finally, the price of the motor protector (motor protector) is only about 1/2 that of similar domestic products.