In the modern industry production, the application of the motor is very extensive, but in production are due to the lack of function and form a temporary motor burned holds a large share in the production of the issue, how to reduce these problems, the use of comprehensive progress motor power, is a question worthy of careful thinking, I according to his many years of practice and relevant materials, beware of motors single phase operation measures are put forward, for reference only, the lack of place, please put forward valuable opinion.

　　I. causes and precautions of single-phase operation of the motor

　　1, fuse fuse

　　(1) fault fuse: mainly because the main circuit of the motor single-phase grounding or phase to phase short circuit and form a fuse fuse fuse.

　　Precautions: select motors that are suitable for the surrounding environment and low-voltage electrical appliances and circuits with correct devices, check them regularly, strengthen daily protection and maintenance operations, and eliminate all kinds of hidden dangers in time.

　　The non-fault fuse: mainly is the melt capacity selection is not appropriate, the capacity is small, when the motor is started, the impact of the starting current, fuse attack fuse.

　　Fuse non-fault fuse is able to prevent, do not assume that in the case of avoiding the motor's starting current, melt capacity as far as possible to choose a smaller, so as to be able to protect the motor. Let's make it clear that the fuse can only protect the single-phase grounding and interphase short circuit of the motor, and it can never be used as the over-load protection of the motor.

　　2, the correct selection of melt capacity

　　In general, the formula for selecting the melt rated current is: rated current =K rated current of the motor

　　After heat resistance capacity of the fuse (packed)K value can be selected 1.5 ~ 2.5.

　　The smaller heat resistance fuse K value can be selected 4 ~ 6.

　　As for the load carried by the motor, the value of K is also correspondingly different. If the motor drives the fan directly, then the value of K can be selected to be larger. If the load of the motor is not large, the value of K can be selected to be smaller.

　　In addition, the fuse melt and fuse holder must be outstanding touch, otherwise it will cause heat at the touch, so that the melt by external heat and the formation of non-fault fuse.

　　Proper wiring method and correct protection method should be adopted in the process of setting up the motor.

　　(1) copper, aluminum connection as far as possible to use copper and aluminum transition joints, such as no copper and aluminum joints, copper joints can be connected to hang tin.

　　For the larger capacity piercing fuse, in the wiring can add pad copper sheet (0.2mm), so the effect will be better.

　　The contact pressure between the melt and the holder is checked and adjusted.

　　(4) of wiring to prevent damage fuse, fastening to moderate, wiring to add gasket spring.

　　3. Faults easy to appear in the main loop

　　(1) the dynamic touch of the touch device is not good touch.

　　The main reasons are: improper selection of the touch device, small arc extinguishing of the contact, making the dynamic contact stick together, the three-phase contact action is not synchronous, resulting in the lack of phase operation.

　　Precautions: choose a suitable touch device.

　　The use of harsh environment such as humid, oscillating, corrosive gas and poor cooling conditions, forming contact damage or oxidation wiring, poor touch and the formation of phase operation.

　　Preventive measures: select electrical components that meet the environmental requirements, take appropriate protective measures, force the improvement of the surrounding environment, and regularly replace the components.

　　3, the timing view, the touch device contact wear is serious, the surface is uneven, make the touch pressure is lack of phase operation.

　　Preventive measures: according to the practice, confirm the reasonable view of the protection cycle, carefully protect the operation.

　　Of improper selection of thermal relays, so that the thermal relay of the bimetallic pieces burned, forming a phase of operation.

　　Precautions: select appropriate thermal relays to prevent overload as far as possible.

　　It is improper to form the wire or the wire is damaged by external force and it is off phase.

　　Precautions: during the construction of wires and cables, "standard" should be strictly implemented and construction should be conducted in a civilized manner.

　　6 electrical component quality is not qualified, the capacity can not reach the nominal capacity, forming contact damage, dead and other abnormal phenomenon.

　　Precautions: select appropriate components and carefully inspect the device before installation.

　　The body quality of the liraglug motor is poor, the coil windings are poorly welded or unwelded. Poor touch of lead and coil.

　　Precautions: select motors of better quality.

　　Analysis and protection of single-phase operation

　　According to the motor wiring method, under different loads, the current of single-phase operation is also different, so the protection method adopted is also different.

　　For example, when a y-type motor is in single-phase operation, the phase current of the motor is equal to the line current, which is related to the load carried by the motor.

　　When delta type break when the internal wiring of the motor, motor into ∨ type wiring, phase current and line current and motor load into share to add, under the rated current load, two phase current should be increased 1.5 times, 1.5 times the phase line current is added to the, the other two phase line current 3/2 times add).

　　External break when train type wiring of motor, the motor at the moment after two phase winding in series with a third group of winding and connection between the two phase voltage and line current is equal to the sum of parallel path winding current and the motor load into share to add, in rated load cases, the line current increase 3/2 times, concatenated two winding current is constant, the other one phase current will increase 1/2 times.

　　In the case of light load, the line current is added from light current to rated current, the current of the two-phase winding is kept unchanged, and the current of the third phase is added about 1.2 times.

　　Therefore, the line current and phase current of the angular connected motor vary not only with the disconnection but also according to the load when the motor is in single-phase operation.

　　To sum up, the reasons for the single-phase operation of the motor are as follows:

　　1, the environment is bad or some reason to form a phase power supply off phase.

　　2, insurance abnormal fuse.

　　3. The engine equipment and wires and contacts are burned or damaged, loose, with poor touch and improper selection, etc., forming a power supply cut-off phase.

　　4. The stator winding of the motor is broken in one phase.

　　5. The new motor itself fails.

　　6. Failure of the engine equipment itself.

　　As long as we carefully device in the construction, in the normal operation and protection maintenance process, strictly in accordance with the standard implementation, will be able to prevent the motor single-phase operation caused by unnecessary economic losses.

　　Iii. Selection of motor capacity

　　The selection of the motor is mainly the selection of capacity, if the capacity is small, on the one hand, can not give full play to the ability of mechanical equipment, so that the production power reduced, on the other hand, the motor in the case of long-term overload operation, premature damage, may also appear together launch difficulties, can not withstand the impact load. Large capacity selection, not only to increase the cost of equipment, and often in light load motor operation, operation power and power factor (for asynchronous motor) will be reduced. Motor capacity should be selected according to the following three principles.

　　Heating: when the motor is running, it must ensure that the maximum practical temperature of the motor is equal to or less than the maximum temperature allowed by the insulation of the motor.

　　Overload ability: the motor must have certain overload ability when running. That is, the maximum torque of the selected motor or the maximum allowable operating current must be greater than the maximum load torque and the maximum load current that may appear during the operation.

　　Ability to start: since the squirrel cage asynchronous motor usually has a small starting torque, the motor must have a reliable starting load torque.

　　As long as we strengthen the repair and maintenance of electrical equipment in the daily production, regular inspection, frequent discovery, frequent use of brain, frequent thinking, careful treatment of the problems presented, about the motor selection, strict treatment of careful analysis, I believe that problems like the above will prevent. In this way, not only the enterprises can reduce unnecessary investment costs and economic losses caused by equipment failure, but also the progress of our own quality, practical ability and level will be correspondingly improved.