AC LV MOTORS REWINDING
1. Preliminary Expertise
a) The engine is subjected to visual examination. As assessment is made through the examination of structures and accessories such as Couplings, Shafts, Connectors on its body and the findings are recorded.
b) The location of the coupling or the pulley is measured by vernier calliper and recorded. The coupling/pulley, if present, are drawn and disassembled from the shaft. The pulley is disassembled by dismantling its screws in case it is of screw-tightened type. If any, the locking bolt is dismantled if the coupling/pulley hosts shrink fit.
The coupling/pulley are pulled by a 120-degree special pulling machine. Disassembly is performed by the application of heat via oxygen in order not to damage the materials in couplings/pulleys, which have close tolerances.
c) Regarding with the information taken from the customer, a preunderstanding is reached about the causes of the problem, after which the standard and advanced expertise methods to be applied are identified.
d) The deflection on the coupling location is measured via comparator after the coupling/pulley are disassembled. As a standard, the deflection on the coupling location is performed through the middle of the shaft’s coupling location during which it is checked whether the deflection is within the 3-5% limit value.
a) The bolts of the covers are dismantled, after the covers are marked with dots. If any, the covers are disassembled by the help of drawing bots or levers. In a manner not to drop them on the shaft, heavy covers are disassembled by crane or light ones are done so manually, after which they are placed over the universal palette.
b) Bearings and greasing flanges are disassembled by rollers. Heat by oxygen welding is applied for close tolerances. If any, locking bolts on the greasing flanges are loosened.
c) If any, the coals in the Ring groups are dismantled and if necessary, the coal housing is disassembled.
d) A pipe in appropriate dimensions is attached to the rotor shaft, and it is disassembled from the stator’s interior by the help of a double crane or by the creation of a balance weight with a single crane.
a) The tolerances of the cover and bearings together with the tolerances of the couplings/pulleys are measured via internal and external radius micrometers and they are recorded on the mechanic expertise form.
b) The isolation of the sturdy windings are measured by a megger devices are recorded on the electric expertise form. If the isolation is low, then energy cables are dismantled from the connector joints, and if the measured item is the rotor, then the energy connections are dismantled from their rings and the cause of the isolation lowness is identified.
c) The calorimeters and heaters are measured by multimeter and their resistance checks are performed. In case it is a synchronous machine, its diodes and varistors are measured and checked by multimeter.
4. Preparation for Winding
a) The existing windings are disassembled by the drawing or combustion method without damaging their nuclei.
b) If problems occur during the heating tests on the nucleus, its repair and isolation is performed by partially or wholly dismantling it prior to winding. The dismantled nuclei are compressed in the press following repair and they are later assembled by bringing them into their original dimensions.
d) After the nucleus is cleaned by pressurized air and solvents following the cleaning operation, it is rendered ready for winding by being dyed with prime paint.
a) Cavity isolation is performed with minimum F class nomex pressband. Both two head sections of the pressband are cut in a manner to protrude approximately 1 cm out of the cavity and by using glass or macaron isolators, support is made for the bobbin wires by using its lower section in a completely in circular shape. The resistance of the isolations at the cavity outlet is thus increased against the magnetic loads in the bobbins.
b) Wire selection is important for the bobbins. For ensuring quality, we use “Theic Polyesterimide and above Polyamide-Imide” enameled grade2 class wires that are resistant against corrosion and temperatures at 210 °C. This wire is manufactured by special order, ordered in reels conforming to the number of parallels necessary for the engine and the bobbin is prepared without the making of any additions.
d) The bobbin wires are descended to the cavities with the accompany of polyester guides for ensuring that their enamel does not scratch by contacting nucleus when the bobbins are thrown into the cavities.
e) Nomex pressband is placed between the two bobbin groups in the cavity. Its purpose is to isolate the intervals between the two phases in the same cavity and also to isolate the bobbins of the same phase that have high voltage differences.
f) The phases at the bobbin heads are isolated via specially cut nomex pressbands. Both cavity outlets are isolated in this manner if the engine is driven by the frequency converter.
g) The bobbins are closed and their resistance against electromagnetic impacts are increased by shaping H Class glass or F Class fiberboards in a manner to rigidly telescope the cavities.
h) The bobbin heads are bound with silk or glass band and for high engines, the startup moments are bound by using polyglass band.
j) The bobbin connections are made by using silver welding and copper ring.
l) Heat detector RTD is mounted on each phase of the stator winding, whose wrapping has been completed, their cables are extracted to the connector by using silicon macaron and the cable terminals are lugged.
m) Further to the aforesaid, the winding heads are bandaged with polyglass band in order that they can resist against centrifugal forces in cases where the engine is a ringed one the winding is a rotor one. Special benches and apparatus, which provide tensioning at an appropriate torque, are required for this operation.
n) The winding is kiln-dried by being heated up to 130 °C for a period of 15 hours.
o) The windings are removed from the kiln and when they are still hot, they are varnished with kiln-dried-varnish that is applied via immersion and spraying method. This method allows the spreading of the varnish until the winding’s interior.
r) After the varnish has dried-up, its residues are cleaned from the nucleus.
s) Special moist removing heaters, the exterior sheaths of which can resist up to 200 °C, are mounted on winding heads in powers conforming to that of the engine. The heaters are bound to the windings using F class polyglass band, their cables are migrated to the connector by using silicon macaron, and the cable terminals are lugged.
6. Winding Tests
a) Isolation tests are performed for the windings using megger.
b) The DC resistance of the windings are measured up to maximum 15 amperes and on 1/10000 sensitivity level.
c) Hi-POT and SURGE tests together with high voltage and isolation resistance tests against the chassis and the bobbin-spirs interval are performed for the windings.
d) Resistance checks are performed for the windings, the RTD calorimeters and the heaters.
7. Cleaning, Maintenance and Repair Operations for the Windings and Parts
a) Unwrapped windings and engine parts are cleaned with pressurized hot water, detergent and solvent in a special washing cabinet. Following cleaning, windings are subjected to the kiln-drying operation performed on the engines and following kiln-drying, they are varnished with protective varnish.
d) The jag sockets of bolts, which have been corroded and which have filled with varnish, are cleaned by guide.
e) Malfunctioning housing locations and flanges are repaired by the bushing method and using a micrometer, it is checked whether it is in the specified tolerance.
f) The balance of the rotor and all its rotating parts is measured by half-wedge or full-wedge according to the ISO 1940-1 standard, the wedging manner of the coupling/pulley, and the manner of balancing. The balances of the coupling/pulley are measured separately by considering the same standard and wedging method.
a) Apipe in appropriate dimensions is attached to the rotor shaft, and it is assembled inside the stator by the help of a double crane or by the creation of a balance weight with single crane.
b) Internal grease covers are telescoped inside the shaft.
d) The oil sump inside the bearing and the grease covers are greased with sufficient amount of grease oil.
e) The oil sump inside the bearing and the grease covers are greased with sufficient amount of grease oil.
f) The brushes are installed after adjusting the distance between the brush holders and the ring between 2-2,5 mm.
9. Final Test
a) Isolation tests of the windings are performed using megger.
b) In case of slip-ring engines, the stator is given nominal voltage when the rings are in open circuit and checks are performed on the stator current, power loss and rotor voltages. It is checked whether appropriate and equal voltage emanate from the rotor windings. The lost powers represent the iron loss of the engine.
c) The stator current and power losses are recorded by rotating the engine in its nominal voltage. This power represents the iron, wind and friction losses of the engine.
d) The engine shaft is locked and the stator’s voltage and power is recorded by passing a rated current through the stator. This power represents the copper loss of the engine.
e) Vibration analysis and balance check are performed and the bearing performances are measured by making a vibration measurement on the housings when the engine is in its nominal revolution.
f) The sounds of the bearing flap and the bearings are listened.
g) The housing temperatures are measured and checked after 30 minutes of operation.
a) The engine trunk that has passed the test is cleaned and dyed.
b) The engine, the dye of which has dried, is covered by stretch film, bound on the universal palette by a special tie and rendered ready for shipment.