What are the phenomena of motor winding turn-to-turn short circuits?
1) A large loop current (often 2-10 times the normal current) will flow in the short-circuited coil, causing the coil to heat up seriously;
2) The three-phase current is unbalanced, and the motor torque is reduced;
3) Produce murmurs;
4) When the short-circuit is serious, the motor cannot start with load.
At the beginning of a turn-to-turn short circuit, there may be only two wires in contact due to worn insulation at the overlap.
As a result of the short-circuit turns generated within the loop current, so that the coil heats up quickly, further damage to the insulation of neighboring wires, so that the number of turns of the short-circuit is increasing, the failure to expand.
When the number of short-circuit turns is sufficiently large, it will cause the fuse to burn out, and even the winding burns and smokes.
When a three-phase winding turn-to-turn short-circuit occurs, the equivalent of the phase winding turns to reduce the stator three-phase current imbalance. The unbalanced three-phase current makes the motor vibrate, and at the same time emits an abnormal sound explosion-proof cloud platform.
The average torque of the motor drops significantly, and it becomes weak when dragging the load.
Motor winding turn-to-turn short circuit causes
(1) poor manufacturing process. For example, in the next line, shaping and other processes to damage the turn insulation; copper wire with hard pieces, burrs, will also cause turn insulation damage.
(2) operation, in the electric, thermal and mechanical stress, the winding deformation, displacement, resulting in inter-turn insulation fracture, wear and tear, detachment; in addition, due to dirt, etc., may also cause a short-circuit between the turns (especially between the end of the rotor winding).
(3) Run for a long time, insulation aging, can also cause turn-to-turn short circuit.
Treatment of motor winding turn-to-turn short circuit
When the short circuit occurs in the winding, it will usually be manifested as motor power supply circuit fuse blown or switch tripped; motor winding short circuit occurs when a large current is generated to make the coil quickly heat up and burn, which will have a burnt flavor; uneven distribution of the magnetic field; current imbalance makes the motor vibrate or make the noise intensified, or even make the motor can not function normally, and so on. In the event of a short circuit, we can deal with the following methods:
1, induction method
This method is the use of the principle of electromagnetic induction, a special short-circuit transformer – short-circuit detectors across the stator slot, short-circuit detectors energized, if placed on the slot on the iron vibration, indicating that there is a short-circuit phenomenon.
2, observation method
That is, observe the end of the winding, wire groove inside the insulation is not damaged or burnt, whether there is an odor. 3, multimeter or megohmmeter inspection method
3, multimeter or megohmmeter inspection method
That is, with these two tables to test the insulation resistance between any two-phase winding, the reading is very little or zero, there is a short circuit between the phases.
4、Detecting temperature checking method
Make the motor run unloaded for a certain period of time, and feel the temperature of the winding parts of the normal. If there is a turn-to-turn short circuit, then the temperature of the place will generally be higher.
5、Electrification test method
This is a fairly simple way, is to use an ammeter test, if there is a short circuit between the phases, the current through the general is relatively large. The above are the most common treatment methods, the following we explain through examples to illustrate.
When a short-circuit in the winding occurs, the method should be screened according to the actual situation and the corresponding measures should be taken to deal with it.
