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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 reliability At present, industrial and mining enterprise thermal relays 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. Easy to use the more advanced electronic motor protectors, the detection elements generally use current transformers, and the emergence of the core structure. Since the introduction of the core-type motor protector, it has attracted a lot of interest from the electrical industry due to its many advantages compared to thermal relays. 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, at present, only large-size protectors are used at home and abroad, and small-size ones can only use wiring. The electronic motor protector solves the problem that the thermal relay has a single function, and it newly generates the disadvantages of the need of working power. Although the requirements of electronic circuit amplification and driving need working power are reasonable, the application of the protector brings a series of problems, such as the user must look for the power terminal before use, understand the power supply voltage level and many other inconveniences. In addition, because the protector needs to work continuously, this causes the failure rate to be high because of the fluctuation of the voltage of the electrical network, interference, self-heating and other factors. According to incomplete statistics of the used electronic motor protectors of our factory, more than half of the faults of the protector itself are from the power supply, which greatly dampened the enthusiasm of electrical workers in using electronic motor protectors. In addition, the electronic motor protector has 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 Circuit used for automatic control; Second, use the relay's normally closed contact action to implement the protection scheme, although its control contact can be directly connected to the control circuit like a thermal relay, but due to its automatic reset, it 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 and large production volume, the cost is extremely low; while the electronic motor protector generally consists of signal detection, amplification, processing, execution, power supply and other components, and its production cost is far higher than the thermal relay. Bringing certain pressure on the user's initial investment also brings certain difficulties for the full promotion of electronic motor protectors. As a manufacturer, while improving product performance, reducing production costs is a constant effort. Novel Motor Protector From the above, we can see that the electronic motor protector is characterized by its reliable function, but it has the disadvantages of complex structure, inconvenient use and maintenance, large size, and high cost. Here, I will introduce the UL-E2 series motor protectors manufactured by Ningbo Julong Electric Works after more than two years of use. This product retains all the advantages of the electronic motor protector and completely overcomes the shortcomings of this type of protector. The following also compares the conventional electronic motor protector from three aspects. Function: The protector has a phase-off, over-current protection function. The protector has been used in our factory for more than two years. It has used the equipment of UL-E2 series protectors. Basically, no damage has been found to the motor. In particular, the protector is used in the induced draft fan in the 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 protector has the following features in addition to the general electronic motor protector with multiple functions, sensitive operation, and stable performance; the protector-phase-off signal and the over-current protection signal are independent, so even if the over-current setting value is improper No matter whether the motor is deactivated or stopped before starting, the protector can operate reliably. The current setting of the UL-E2 series protector is represented by a dial, which is very eye-catching and convenient. When used, it is only necessary to adjust the scale to a value corresponding to the rated current of the motor. Overcame the difficulty of full load debugging of similar products in the country. After using the protector in this way, it can not only make the motor fully exert overload capacity, but also enable the motor to be reliably protected. Easy to use: UL-E2 series motor protector is very convenient to use. The whole series adopts string type (only need to wear 1 inch), no external power supply structure, and Japan's OMRON company's similar product small size protection The device needs 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. And this protector has the intelligence characteristic, the protector not only can directly connect in the control loop, but also can automatically identify the manual control loop and the automatic control loop. 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. This protector is small in size and installation size and can be interchanged with the JR16 thermal relay. The overall circuit of the 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 applied to any harsh environment. Our protector has been used for more than two years, and it has been found so far. Damaged protector. Unfortunately, this protector has no fault indication function and cannot intuitively determine the cause of the fault. In the end, the price of this product is only about 1/2 of the domestic similar products.
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