Drying of electrical machines. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Drying of electrical machines. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electric motors

Humidification of the insulation of electrical machines can occur due to the environmental conditions in which the machine is located during transportation, storage, installation or operation. Therefore, it is necessary to check the insulation resistance of electrical machines before their installation, after working outdoors or in a room with high humidity, before a new season of work in these conditions (agriculture), after breaks in work and periodically within the time limits set by those responsible for electrical facilities.

The GOST recommends that the allowable insulation resistance be taken equal to one kiloohm per volt of the operating voltage of the machine, and for machines designed for voltages up to 1000 V, 500 kOhm is considered the norm.

Common methods for drying electrical machines are drying by heating from an external heat source and heating by current flowing in the machine winding.

Drying by external heating is carried out with disassembly of the machine. Disassembly of the machine is necessary not only to improve drying and reduce its time, but also to completely remove moisture and rust from the gap of the machine when it is strongly moistened.

The simplest method of drying by external heating is heating with incandescent lamps placed inside the stator of the machine on a sheet of iron or asbestos. It is better to take two lamps, the power of which depends on the engine power, for example, with an engine power of 30 kW, you can take two 300 W lamps, for a 75 kW engine - two 500 W lamps, for a 110 kW engine - two 1000 W lamps.

Instead of incandescent lamps, external heating can also be carried out using tubular electric heaters - heating elements of appropriate sizes and power, installed inside the stator on a heat-resistant lining.

The heating of the machine can also be a jet of hot air from an air heater, for example, an electric heater, in a drying cabinet or near a powerful heat source.

Drying in the open air under the rays of the sun in summer benefits.

Drying by heating the winding of the machine with the current flowing in it is carried out with a suitable current source, while the machine is not disassembled. This method is suitable when the insulation is slightly damp, when no drops of moisture are visible on the winding.

At the same time, when drying a three-phase motor, its rotor slows down, with a phase rotor, the rotor rings are connected together.

A three-phase current of such a voltage is supplied to the stator winding in order to obtain a current in the winding equal to approximately 0,5 In (In is the rated current of the motor). To maintain such a current, the drying voltage can be equal to 0,1 Un (Un is the rated voltage of the motor).

For drying, three-phase transformers with a secondary voltage of 36V, manufactured by the industry, for example, type TC3-2,5 / 1, can be used, with which a motor with a power of 30 kW can be dried. For drying motors with a power of 30 to 55 kW, two such transformers are needed, connected in parallel. If a three-phase transformer is not available, the motor can be dried using a welding transformer.

In this case, if the motor has six output ends, then the windings of its phases are connected in series.

Drying of electrical machines
Rice. 1. The motor has six winding leads

Connecting a single-phase voltage to the three output ends when connecting the motor windings with a star or a delta gives an unequal current in the motor windings, while when connecting with a star, two output terminals must be connected together.

Drying of electrical machines
Rice. 2. The motor has three winding outputs (star)

Therefore, with three output ends of the motor windings, it is necessary to periodically reconnect the wire to different motor terminals.

Drying of electrical machines
Rice. 3. The motor has three winding leads (triangle)

Publication: electro.narod.ru

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