The three-phase motor winding ends, in addition to the control of the insulation between the turns of the electric motors coils themselves in the same phase.
It also involve the insulation between the coils in the opposite phase and the insulation between the coils and the core, chassis, end caps and other related parts in electric motor maintenance.
Inter-phase insulation is the key to end insulation control.
The shape, size and tying of the inter-phase insulation, the thickness and diameter of the insulation sleeves of the cross-phase coils, the quality of the welding in case of welding of the cross-phase coils, and the handling process, the permeability and curing effect of the insulation paint during the dipping process are all key to quality control.
In addition to the insulation characteristics of the winding core itself, the dimensional conformity of the whole assembly process, the effect of the tooling on the protection of the winding ends and the conductive foreign bodies derived from the processing of parts are all issues that must be attended to.
Some three phase motor windings, in the static insulation performance testing good, but the process of power operation, due to vibration and other reasons, the original weak link, because of the impact of the current and voltage and insulation breakdown failure.
Thus, the motor winding end treatment process is very critical and the assembly process control is a key element in preventing faults.
Phase to phase insulation motor failure in motor windings
Phase to phase faults of motor failures are an electrical fault content specific to three phase electric motors windings, and are electrical insulation problems that occur between the phases of the winding.
At the winding ends, the phases are separated from each other by inter-slot insulation, and the inter-phase winding lines involved are insulated with insulating sleeves for the motor operation.
However, during the winding tie fixing and winding end shaping process, the phase insulation may be displaced to varying degrees, and the phase insulation hose, especially where the leads are welded to this line, may be damaged by factors such as irregular welding joints, broken power line from the power supply , and these unavoidable factors are the main cause of phase faults.
During the dipping and baking process of the phase windings, some innate manufacturing defects are compensated for by the penetration of the insulating varnish, but the original damaged part is still a weak link in the electrical insulation of the motor ac winding.
Particularly for 2-pole three phase motor windings, because of the objective nature of the relatively large span of the winding resistance, end shaping of the winding is relatively difficult, resulting in a relatively high chance of phase-to-phase failure of the stator winding typically.
In view of this specificity, the disposal of the phase slot insulation breakdowns insulation during the production and processing of three phase motors windings should be guaranteed by the necessary tyre tools to reduce and eliminate the problem of damaged phase insulation.
Interlayer insulation of motor windings
Modern low-voltage electrical coils, as long as the quality and stability of the choice of high-strength enameled wire, and in the coil winding process to strictly control the uniformity of the alignment of the wire turns, control the insulation layer of the electromagnetic wire itself pinhole degree, elasticity, common winding breakdown voltage and softening breakdown and other performance indicators, generally rely on the enameled wire insulation layer can meet the requirements of interlayer insulation.
There is no need to add another layer of insulation liner for motor's internal connection.
However, due to the voltage surge gradient between the layers, and considering that the coils may be subject to a number of complex factors such as thermal stress, mechanical stress, electromagnetic forces and solvent vapour pressure during operation, this may lead to a reduction in the interlayer insulation capacity of the coils.
In order to improve the operating stability and service life of the coils, there are still many coils that require the selection of a suitable thin film insulation material as an interlayer insulation liner.
Selection of interlayer insulation materials for electric motor
For coils that need to be impregnated with insulating varnish, it is usually advisable to use insulating fibre films that are highly absorbent to the varnish as interlayer insulation in order to enhance the penetration of the impregnation into the deeper layers of the stator winding and to increase the amount of solid components of the impregnating varnish adsorbed between the turns (amount of hanging varnish).
For coils with a high interlayer voltage gradient and without insulating paint impregnation, a variety of insulating impregnated fibre products such as lacquer cloth and lacquer silk can be used.
This film composition of the stator winding interlayer insulation dielectric properties and heat resistance is higher, but because the thickness is relatively large.
So that the filling factor of the stator winding correspondingly reduced, generally applicable to large and medium-sized low-voltage electrical stator winding interlayer insulation liner
Interlayer and phase-to-phase insulation of electric motors
In the slot of the double winding, there exists a heterogeneous upper and lower layer of coils, which are subjected to line voltage between them, so the interlayer insulation material and structure is the same as the slot insulation.
The width of the interlayer insulation should be able to wrap around the coils so that the coils between the upper and lower layers are separated, and its length should be 40 to 70 mm longer than the core length.
When the coil ends are in phase, there is no additional inter-phase insulation, but when the power or 2-pole motor coil size is large, in order to strengthen the insulation, the nose of each coil is wrapped with glass ribbon (commonly known as "wrap tip").
Between the coils of the heterogeneous group, the triangular end of the pad into the interphase insulation, so that the adjacent heterogeneous coils are separated, bearing the line voltage, so its insulation material and slot insulation is the same.
For low-voltage motors, the minimum distance from the winding to ground is 10 mm in order to prevent flying arcs.
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