In coils of windings of excitement there can sometimes be mezhvitkovy short circuits. As the reason of this malfunction of coils serves mechanical damage of a winding or destruction of isolation when overheating. Reduction of resistance of a chain of a winding results that, in turn, increases current. Temperature of a winding increases and leads to short circuit of a bigger number of rounds of the coil. Therefore it is necessary to reveal existence of short-circuited rounds as soon as possible.
It is required to you
- - ohmmeter;
- - ampermeter;
- - voltmeter;
- - portable defectoscope.
Instruction
1. Define short circuit of rounds in the coil of a winding of excitement, having measured coil resistance by an ohmmeter or having taken readings of the ampermeter (voltmeter) at a winding power supply from the accumulator. Write down indications of the measuring device. Divide tension size into current and calculate resistance. If resistance of the coil became less (in comparison with nominal), short circuit of rounds takes place. Eliminate malfunction with rewind of the coil or its replacement.
2. For check of the coil on existence of short circuit use also other method. Connect it via the ampermeter to the accumulator. Measure current in a winding chain. Now measure current in a chain of a winding of other similar coil, obviously serviceable. If short circuit is absent, both measurements will show approximately identical current.
3. For identification of mezhvitkovy short circuit in windings of electrical machines use the portable defectoscope. Connect the device to the power supply and place it in boring of the stator that the groove of section of the checked winding was located between air gaps of steel packages of the defectoscope. Mezhvitkovy short circuit will be demonstrated by the lamp which lit up on the device.
4. For production of the simplest defectoscope collect the core from electrotechnical steel. Pull together core plates with bolts, having isolated from steel laying. Reel up on the core of 800 rounds of a wire of the PEV brand with a section of 0.8 mm.
5. For check of a winding lay it on device core "shoulders". Put on plates a steel plate from tin. Connect the device coil to network. Now slowly rotate a winding, holding a plate. If in one of couples of rounds the isolation is damaged, the steel plate is attracted.
6. At visual inspection determine existence of mezhvitkovy short circuit without special equipment by local destruction of windings. Pay attention also to such sign as "coking up" of oil and the internal surfaces of the device. Quite often at mezhvitkovy short circuit circuit breakers at launch of the unit work.