Detection of inter-coil short circuits

1
Detection of inter-coil short circuits in wind
generator windings
Ante Elez Ph.D. Mate Jelavic Ph.D. Prof. Stjepan
Car Ph.D.
2
Inter-coil short circuit in wind generators

• - Short circuits in generator windings lead to
  severe damage
• long down time,
• high repair costs.
• Generator malfunction is especially severe for
  direct drive machines,
• Detection of generator short circuit could
  shut-down turbine before short circuit
  escalates,
• Requirements upon detection methods
• on-line processing,
• reliable,
• unambiguous.

3
Inter-coil short circuit detection methods

• - Two fault detection methods are presented
• inter-coil short circuit in excitation winding,
• inter-coil short circuit in armature winding.
• Fault detection methods are result of FEM
  calculations and measurements on real machine.

4
Inter-coil short circuit detection methods

• List of analyzed machine conditions for witch
  calculations and measurements have been
  performed.

Working condition No load No load No load No load No load No load No load No load No load No load No load Nominal load Nominal load Nominal load Nominal load Nominal load Nominal load Nominal load Nominal load
No fault
Excitation winding fault
Armature winding fault
Nominal excitation current
Decreased excitation current
Description of calculated and measured model 1 1 2 2 3 3 4 5 6 1 2 3 4 5 6
1 inter coil short circuits of 10 turns of
excitation winding coil, 2 inter coil short
circuits of 5 turns of excitation winding
coil, 3 inter coil short circuits of 2,5 turns
of excitation winding coil, 4 inter coil short
circuits of 14 turns of armature winding coil, 5
inter coil short circuits of 10 turns of
armature winding coil, 6 inter coil short
circuits of 5 turns of armature winding coil,
5
Inter-coil short circuit in excitation winding
6
Inter-coil short circuit in excitation winding
pole pitch ??p
ADDITIONAL EMF
Q a1
Q a2
t
7
Inter-coil short circuit in excitation winding
Curve 1 Flux density observed from stator
tooth, Curve 2 Voltage induced in small
measuring coil placed on stator tooth, Curve 3
Integrated voltage waveform from Curve 2.
8
Inter-coil short circuit in excitation winding
Flux density over pole pitch monitored from
stator core tooth with inter-coil short circuits
in excitation winding on pole no. 59, for tree
values of excitation current I0.
?I045 A, ?I025 A, ?I015 A.
Curve 1, 1, 1 for all odd poles, Curve
2, 2, 2 for all even poles,
Curve 3, 3, 3 for pole with
inter-coil short circuit.
9
Inter-coil short circuit in excitation winding

• Best sensitivity for excitation winding
  inter-coil short circuit detection can be
  achieved with measurement of magnetic field
  inside air gap. Fault detection sensitivity is
  decreasing with distance between the measurement
  point from the air gap.
• Direct measurement and analysis of magnetic field
  waveform for unsaturated machine gives reliable
  detection of inter-coil short circuit in
  excitation winding coils.
• Direct measurement and analysis of magnetic field
  waveform for saturated machine gives unreliable
  detection of inter-coil short circuit in
  excitation winding coils.
• This is valid for magnetic field and flux density
  measurement in air gap, inside stator tooth and
  inside stator core.
• Best sensitivity for excitation winding
  inter-coil short circuit detection for saturated
  machine can be achieved with differential
  magnetic field measurement in air gap.

10
Inter-coil short circuit in excitation winding
Differential magnetic field measurement in air
gap.
U2
wedge
U1
U1 U2? 0 symmetric condition U1 U2 ? 0
possible inter-coil short circuits
U1 U2
11
Inter-coil short circuit in excitation winding
U1, U2 ? voltage induced in measuring coil wires
placed on stator winding wedge, U1-U2 ? total
measuring coil voltage.
12
Inter-coil short circuit in excitation winding
Voltage waveform induced in measuring coil Ms2?p
for wind generator.
Curve 1 voltage induced in measuring coil with
inter-coil short circuits in one pole, Curve 2
voltage induced in measuring coil without
inter-coil short circuits,
Curve 3 integrated voltage waveform from curve
1, Curve 4 - integrated voltage waveform from
curve 2.
13
Inter-coil short circuit in excitation winding

• Differential magnetic field measurement in
  machine air gap is innovative method for
  detecting excitation winding inter-coil short
  circuits.
• Method is tested on small four pole generator
  model specially adopted for simulation of inter
  coil short circuits. Calculated results have been
  confirmed by measurements on real machine.
• If method is properly applied inter-coil short
  circuits in excitation winding can be
  unambiguously detected.

14
Inter-coil short circuit in armature winding
15
Inter-coil short circuit in armature winding
16
Inter-coil short circuit in armature winding
Flux density waveform monitored from rotor pole
shoe.
Curve 1 with 14 short circuited turns, Curve 2
with 10 short circuited turns, Curve 3 with 5
short circuited turns, Curve 2 without short
circuited turns.
17
Inter-coil short circuit in armature winding
Frequency analyses of the flux density waveform
monitored from a rotor pole shoe.
1 with presence of armature inter-coil short
circuits, 2 without presence of armature
inter-coil short circuits.
18
Inter-coil short circuit in armature winding

• Inter-coil short circuit in armature winding is
  localized magnetic field disturbance, and it can
  bee detected within air gap from stator and rotor
  side.
• If monitored from stator side distance of the
  stator slot comprising the short circuited turn
  and measuring sensor significantly affects the
  success of the failure detection. The pole pitch
  represents a limiting distance. Therefore, to
  ensure a successful and reliable detection of the
  described failure, quite a large number of
  sensors should be incorporated into the machine
  and placed at the distance one from another that
  will enable failure detection.
• In the contrary, when flux density within the air
  gap is measured from a rotor pole shoe, only one
  sensor will be sufficient for a successful and
  reliable detection of the analyzed failure. A
  sensor for flux density measurement should be
  fitted on any of the rotor pole shoes. When the
  sensor, which is rotating together with the
  rotor, faces a failure, from measuring data
  inter-coil short circuits in armature winding
  coils can be detected.

19
Measurement results
1
to control system
2
on stator
3
RF
1
on rotor
3
1 Hall sensor, measuring coil 2 processing
units, 3 wireless bridge.
2
20
Measurement results
Measured and calculated flux density waveform in
wind generator air gap.
Curve 1 measurement with Hall sensor on stator
tooth, Curve 2 calculation, Curve 3
measurement with Hall sensor on rotor pole shoe,
Curve 4 calculation.
21
Measurement results
Integrated voltage waveform induced in measuring
coil Ms2tp
Curve 1 without inter-coil short circuits,
Curve 2 with inter-coil short circuits of 2,5
turns in excitation winding coil, Curve 3 with
inter-coil short circuits of 5 turns in
excitation winding coil.
22
Measurement results
Flux density waveform monitored from rotor pole
shoe with inter-coil short circuits in armature
winding.
Curve 1 measurement, Curve 2 FEM
calculation.
23
Conclusion

• New innovative methods for detection of
  inter-coil short circuits in wind generator
  excitation and armature winding are presented.
• Methods are based on FEM calculation results.
• Methods are confirmed with measurements on real
  machine.
• Fault detection methods are implemented in fault
  detection system which can be implemented in wind
  generator.

24
Thank you for your attention