Windings for stators and rotors

Winding for stators – AC machinesPossible types of windings:

• According way of insertions in holes/grooves:– axial layout– radial layout

• According shape of wires:– circular (formed after insertion into grooves)– special profile (formed before insertion)

• According number of layers:– single-layer– double-layer

Winding for small drivers (mass-production) up to 500 kW

Limited by voltage 1 kV:

• circular cooper wire cca up to 2 mm

• dispersed winding – cheap fro production, low efficiency of volume of groove, unknown voltage between turns

Higher than 1 kV:

• winding made from profiled wires – better efficiency of grooves

• production process - less automation

Winding-machines:

• complicated movement of arm – for dispersed winding

• Pulling of wires – for profiled wires

Production process• wires are wind-up on templates (via machines, not

manually!)• covering of grooves (textile foil) – isolation function• dispersing/scattering of wires• fixing of wires by wedges• connection of wires at front sides (critical point)• binding/bandages – especially at front sides

Critical issue:

bandages x isolation x mechanical properties

Impregnating process of bandages:– drying (at temperature about 130 °C)

– plunging bandages into solvent (40 °C)

– hardening event. second impregnation

Possible shapes of turns / winding

hexagonal turn

oval/ellipse turn

trapezoidal turn

Possible placement of winding in grooves

Winding for high voltage drivers

• typically up to 6 kV - profiled wires• forming of turns before assembly• grooves – often „opened“, not „closed“• winding – contains integrated isolation system• isolation - based on mica (isinglass)• isolation – resistance up to 3 kV/mm of electrical stress/intensity

Difficult issue:

mechanical properties and stress of isolation during forming of turns!

3 – isolation layer

4 – separation layer or wedge

1 – longitudinal part of turn

2 – front-side parts

View of front side part of stator winding – big AC generator, 6,0kV winding

Winding from rod/bars(artificial Roeble’s rods/bars)

Principle: parallel wires are permutated lower power-losses due to whirling currents

Processing of rods:• Forming of wires• Assembly of rods (including isolation spacing)• Hardening (including of isolation or cement between copper

parts)

Variants of cooling:• Compressed-air cooling (big cross-section of channel),

difficult process of forming of turns• Liquid-based cooling (hollow tubes)

outlets/ connection

longitudinal isolation

- diameter of turning

- „nose“

- front-side parts

Formed single turn for 6,0kV stator

Principle of permutated rod/bars

Decomposition of Roeble’s rod along the stator

Different channels for cooling systems

Cross-section of stator rod with separated/spitted channels Cross-section of stator rod

for water (liquid) cooling

Fixing of rods in grooves (1) and (4)

Different shapes and cross-sections (2), (3), (5), (6)

Detail of front-side parts for 6,0kV driverIsolation desk/board

Separation foil

rope from hemp (plant)

damping circle

Isolation desk/boardCarrier of winding

Protection against partial discharges Basic cause (root cause)• not-fixed isolation on wires• cavity in isolation material• non-homogenous grooves

Examples of solving:• (synthetic) resin with small particles of graphite („smola“)• hardening of isolation system in hot-press or vacuum chambers • conductive layer (painting or foil) on the surface of isolation or on

the surface of grooves

Special issue:• output of wires from grooves – semi conductive layer (painting)

Important issues:• small tolerance 0,5 mm mechanical solidity• filling of cavities by graphite paper

Solution: • isolation desks/boards• axial wedges• fixture/brace circles

Assembly of winding

Very important – mechanical solidity of front-side parts!!!

Winding of rotors of induction (AC) drivers

Smaller drivers: winding made from coilsdispersed /not oriented winding

orSquirrel-cage rotor:

• The motor rotor shape is a cylinder mounted on a shaft. Internally it contains longitudinal conductive bars (usually made of aluminum or copper) set into grooves and connected at both ends by shorting rings forming a cage-like shape. The name is derived from the similarity between this rings-and-bars winding and a squirrel cage.

Bigger drivers: rods with full cross-section (copper)–dispersed (not often),–axially inserted (more often).

Rotors for AC drivers – squirrel cageSmall drivers: pouring-off

Mass production pouring-off (forms, 40 MPa)preheating, melting, pouring-off, cooling

Piece production pouring into mould form (ingot)– preheating up to (500 °C)

AdvantagePouring-off enables to make different and difficult shapes of grooves (double

cage etc.)

Everything is still based on ALUMINUN – Al !!!

Groves for start-up (ramp-up)

Profiled grooves – different distribution of current density

Double cage called „Boucherot“

Shapes of grooves for AC induction drivers

for stators

for rotors

for hard ramp-up (start-up)

Filling of grooves on rotor by stacks of winding