Solution
Solutions for global temperature control systems
Motor
subcategory： Solution
2024-09-12
With the development of technology, the application range of motors is becoming more and more extensive, especially the use of motors in daily life and production is becoming more and more important. However, the accident of motor burning also occurs from time to time. In real life, the motor burning is mainly caused by the following reasons such as overheating of the locked rotor coil, overload of the motor and lack of phase. The installation of thermal protector is one of the effective ways to protect the motor. Thermal protector, also called temperature switch, temperature control switch, etc. It is a temperature switch that uses a bimetallic strip as a temperature sensing element. When the electrical appliance is working normally, the bimetallic strip is in a free state and the contact is in an open state. When the temperature rises to the operating temperature value, the bimetallic element is heated to generate internal Stress and act quickly, open the contact, cut off/on the circuit, thereby playing a thermal protection role. When the ambient temperature drops to the reset temperature of the protector, the contact will close the circuit again and the motor will work again.
How to choose the right protector is very important, otherwise not only can not play a protective role, but will cause the motor to fail to work or even burn because of the wrong selection.
1. Determination of voltage and current
Motors have different voltage ranges of 380V 230V 220V 110V, DC motors also have 36V 24V 12V, etc. Protectors with different rated voltages are selected according to different working voltages. In principle, the actual application voltage should be less than or equal to the rated voltage of the protector. For example, a 380V motor cannot use a protector with a rated voltage of 220V, while a protector with a rated voltage of 220V can be used in a 110V motor.
The current of the motor is divided into three types: starting current, normal working current and locked-rotor current. The rated current of the protector should be greater than the maximum value of the three currents, and a margin should be left. For example, if a motor has a normal working current of 1A, a starting current of 1.5A and a locked-rotor current of 2A, the rated current of the selected protector is at least 2A, and it is better to select a rated current of 3A or 5A to keep the margin. Some motor starting current is greater than the rated current of the protector, but the starting time is short, and the normal working current and the locked-rotor current are less than the rated current of the protector. In this case, the protector can also be selected. Because the starting current is greater than the rated current, but due to the short time, the current thermal effect has not had time to make the two-piece heating lead to protector protection, which will not cause misoperation.
2. Selection of protection temperature
The choice of protection temperature is related to the three factors of enameled wire insulation level, installation location and protector type
|
Temperature class of insulation |
A |
E |
B |
F |
H |
|
Maximum allowable temperature (℃) |
105 |
120 |
130 |
155 |
180 |
|
Winding temperature rise limit (K) |
60 |
75 |
80 |
100 |
125 |
The protection temperature shall be lower than the maximum allowable temperature. For example, the maximum temperature of Class F is 155 degrees. The actual selection can be 145 degrees or 150 degrees.
The installation position is divided into built-in inside the coil and tied to the outside of the coil, because when the motor blocks heat, overheating spreads from inside and outside. If the protector is buried inside, the protection temperature is slightly lower than the maximum temperature of the enameled wire. If it is tied to the outside of the coil, the temperature difference between the inside and outside should be considered and the protector with lower temperature should be selected. For example, if the insulation grade is F-grade enameled wire and the temperature difference between the inside and outside of the coil is 20 degrees, a protector with 155-20=135 degrees is selected;
3. Selection of protector
The installation position is limited: the coil is buried in the locked rotor or abnormal. Generally, the heat starts from the inside of the coil and is gradually conducted to the surface of the coil. If it is placed on the surface of the coil, there will be delay. Or the same model winding turns more, squeezing the internal space, resulting in the protector can not be installed. KSD button type: the KSD-B is directly wave soldered on the circuit board, and the protector microphone is close to the surface of the coil.
Anti-reshaping pressure after burial: the current solution in the industry is to dig a slot and plug it in after reshaping or use a fake protector to build in reshaping and then put it in. The real protector damages the coil and delays the production efficiency.
Vacuum and paint: in order to provide insulation performance, the stator is put into the paint tank to immerse and vacuum, and the pressure reaches-0.09mpa, especially water-based paint, which has good fluidity and is especially easy to enter the inside of the protector, and the paint enters between contacts, thus causing product failure. The unique sealing structure design and process treatment of KSD button products, in the case of-0.085mpa, the paint rate is below 1.
When using a thermal protector with current passing through two pieces, the advance amount of jump caused by current heating should be considered in the design, and the advance amount is also different at different ambient temperatures, which is more painful to design. However, for the pure temperature protector, the working current passes through the reed instead of the double sheet, which has no great influence on the jump-off temperature and will not lead to the jump-off in advance. The design is relatively simple.
The installation space is limited, but the blocking current is large and the service life is very long.
The KSD-D diameter is 9mm and the thickness is 7.5mm. Under the condition of AC250V, the current 25A life exceeds 100 times, and the current 35A life exceeds 2000 times. The smaller the current, the higher the life.
The traditional current passes through the double-chip protector, because the double-chip has a very slow creeping process when approaching the jump-off temperature, resulting in too small contact pressure and large contact resistance, which slightly cuts off when reaching the jump-off temperature. Due to the small opening distance, the arcing phenomenon is serious when jumping off, resulting in limited service life.
Baozhu BAOZHU thermal protector, the contact is welded or placed on the reed, the double piece and the reed are independent. However, the temperature is close to the breaking temperature, and when the two pieces creep, the contact pressure will not change, and the contact resistance will not change, so it will not lead to the arc phenomenon during micro-cutting. When the double piece reaches the tripping temperature, it reverses rapidly, driving the moving contact on the reed and the static contact on the cover plate to separate. Due to the large opening distance, the arc ablation phenomenon is not obvious.
Three-phase motors cannot cut off the three phases at the same time. Traditionally, one for each phase or one for any two phases cannot be protected at the same time. It is easy to cut off the three phases at the same time due to phase loss KSD-S at a voltage of 400V and a current of 6.3A/12A. The service life exceeds 3000 times.
The high-power motor uses an external overload protector. There is no blocked rotation. When the current is too large, the coil will also generate heat. The traditional high-current protectors 5AM, 7AM and 8AM are square in size and cannot be installed on the surface of the coil. The temperature of the coil is slow. KSD-D 250V30A blocked 50A high current protector diameter 10mm thickness 7.5mm.
The insulation layer of the protector is sharp after heat shrinkage, which is easy to cut the enameled wire, causing short circuit or insufficient insulation withstand voltage. The KSD button series shell epoxy encapsulation, round and smooth, will not cause damage to the enameled wire.
Protector for explosion-proof motor, due to poor sealing performance and arcing problem during protector action, KSD button series shell can be epoxy encapsulated.
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