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CORE REPAIR AND TEST
Its not so simple to answer, because its need depth experiences
to repair this part,however the damaged core as in the figure is
still possible to repair.
Following step may can helping you to repair:
1. Remove the stator coil and surge ring support2. Remove the
compression bolts and finger plate from frame3. Remove the damaged
stator core (if need to replace)4. Clean out by dry air5. Cut the
damaged stator teeth core6. Grinding the damaged stator surface
core, do careful and avoid the metal dust fill
in side7. Clean up by using clean cloth and by dry air8.
Separated the damaged core lamination by using thin knife (round 1
mil thick)9. Sprayed by insulation varnish onto separated
lamination sheet
10. Dry out11. Pull back the lamination onto its position12.
Applied the epoxy / resin or RTV onto these lamination13. Repair
all damaged finger plate or replaced14. Re assy the compression
bolt acc to the torque required.15. Test the core looseness after
compression bolts has been tighten, found loose on
the lamination is indicate loose on compression bolts16. Test
and analysis the core repair result with EL CID or Loop17. Any
unsatisfactory result must be repaired.18. Clean up and spray paint
coating19. Core ready to refitting coils
Following is figures as references.
Compression bolts
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INSPECTION AND TESTING
1. Core Looseness
Core looseness usually will occur at the inside diameter near
the ends of the core.However, it is possible for looseness to be
general and/or exist on the core outsidediameter.
If looseness is suspected, degree of looseness can be evaluated
by carefully inserting aknife blade between punchings at several
locations. If a 10-mil (1 mil = 0.0254 mm)blade penetrates more
than round a quarter of an inch (6mm), the core may be
notsufficiently tight.
EXTREAME CARE SHOULD BE TAKEN NOT TO BREAK THE BLADE, LEAVING A
PIECE INTHE LAMINATIONS !
Looseness may be accompanied by dust generation, punching and
spacer movement, orsmall pieces of punchings flaking or cracking
off.
1. Digital ELCID
Electromagnetic Core Imperfection Detection (EL CID) is used to
check the integrity ofinter-lamination insulation for stator cores
of generators and motors. A fault currentoccurring within the
laminated stator core results in a hot spot and can cause
acatastrophic failure of a generator and motor
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1. Loop Test
Loop is also to test the interlamination core, but its require
high current power supplyand voltage (normally 220 380 V), its very
dangerous, special attention for electricalshock must be care.
Loop test is required Ampere Turn looping entire stator
core,
Ilustration,
How many turns of cable is depend on the stator core dimensions,
such as:
Core Outside diameter, core inside diameter, slot depth, core
length. Following formulae
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n : no of space duct / air duct
Instruments and equipment / tools required:
1. Thermo vision2. Cables3. Regulator Power supply4. Clamp
ampmeter5. Cable support
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Standard req. taken from VDE 0530
PART OF MACHINE A E B F H A.C. Winding of turbine type generator
with rated output of 5000kVA or more 60 70 80 100 125
A.C. Winding of salient pole and induction machine with rated
output of 5000 kVA or more, or having core length of 1 M or more 60
70 80 100 125
If by way of an exception the embedded temperature
detectormethod be used on machines under 5000 kVA, the limit
oftemperature rise given in this item shall apply
60 70 80 100 125
A.AC. Winding of machine with rated output smaller than in item
1.Field winding of a.c. and d.c. machine with d.c. excitation
exceptionmachine in items 3 and 4. Winding of armature of a.c. and
d.c.machine with commutator
60 75 80 100 125
Field winding of cylindrical rotor with d.c. excitation 65 80 90
110 125Multi layer field winding of low resistance and compensating
winding 60 75 80 100 125Single layer winding with exposed bare
surfaces 65 80 90 110 125Permanently short-circuited insulated
windings 60 75 80 100 125Permanently short-circuited uninsolation
windingsIron core and other parts not in contact with the
windingsIron core and other parts in contact with the windings 4)
60 75 80 100 125 Commutator and Slipring, open or enclosed 5) 60 70
80 80 80Journal bearing and rolling bearings 50 50 50 50 50Rolling
bearings using special grease 60 60 60 60 60
1). A correction is necessary for a.c. winding for rated voltage
above 11 kV
2). The temperature rise of parts of machines rated at 5 MVA and
above or having corelength of 1 M or more, which are insulated with
class F or class H materials, shall notexceed the limit of
temperature rise for class B materials3). Where the thermometer
method is used, the limit of the temperature rise is thatgiven for
the resistance methd less 10 deg.C in the case of classes A, E. B.
15 deg.Cwith class F and 20 deg.C with class H materials4). The
limit of temperature rise is detrmined by the class of the
insulating material ofthe embedded winding5). If no marked thermal
interaction between the commutator, or the sliprings, and
thewinding connected thereto is to expected, the limit of
temperature rise applicable tothese parts are those assigned to
their respective insulation classes6). In the case of commutator
and slipring the limit of temperature rise may beexceeded by 10
degC with class F, and by 20 deg.C class H materials.
Core analysis by using loop test for big machine is very
dificult, its require big powersupply, cables, too many man power.
imperfection lamination underneath of core teethcan not detected,
ELCID is the best to analysis your stator core.
Pls be careful, and GOODLUCK......
Rgds
Siswanto
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[email protected]
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