corto entre espiras

7/28/2019 Corto Entre Espiras

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Detection of inter-coil short circuits

in wind generator windings

Ante Elez Ph.D.

Mate Jelavi Ph.D.

Prof. Stjepan Car Ph.D.


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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.


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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.

FEM

calculations

Calculation

results

Confirmation of

calculation results

on real machine.

FAULT

DETECTION

METHODS

Evaluation of calculated magnetic field

waveforms in correct and faulty condition.

1

2

3

4


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Inter-coil short circuit detection methods

Working condition No load Nominal load

No fault

Excitation winding fault

Armature winding fault

Nominal excitation current

Decreased excitation current

Description of calculated

and measured model1 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,



List of analyzed machine conditions for witch calculations and measurements

have been performed.


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Inter-coil short circuit in excitation winding

t

pole 1

p 2p 3p 4p

-

pole 3 pole 4 pole 5 pole 60pole 59pole 58pole 57pole 6pole 2

t

a1

a2

t

even

odd

fault

MAIN EMF ADDITIONAL EMF

MAIN EMF TOTAL EMF

t

Beven

TOTAL B1

MAIN B1BoddBfault


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pole pitch p

t

a1

a2

ADDITIONAL EMF

a1 p = a2 p a1 = a2

For 60 pole machine:

a1 + a2 = N

a2 = ( N)

a1 = ( N)

S = S

For 2p pole machine:

n = - (Nknl)pp

ni) = - (Nknl)

p

ni) = + (Nknl)

p

knl factor determined by the slope ofgenerator open circuit characteristic.


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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.


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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.

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.

I0=45 A,I0=25 A,

I0=15 A.


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- 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 forunsaturated

machine gives reliable detection of inter-coil short circuit in excitation winding

coils.

- Direct measurement and analysis of magnetic field waveform forsaturatedmachine 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.


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N NN

N

N

N

S S

S

S

S

S

S, N rotor pole

Ms2p

wedge

U1

U2

U1 U20 symmetric condition

U1 U2 0 possible inter-coil short circuitsU1 U2

Differential magnetic field measurement in air gap.


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U1, U2 voltage induced in measuring coil wires placed on stator winding wedge,

U1-U2 total measuring coil voltage.


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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.

Voltage waveform induced in measuring coil Ms2pfor wind generator.


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- 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.


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Inter-coil short circuit in armature winding


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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.


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1 with presence of armature inter-coil short circuits,

2 without presence of armature inter-coil short circuits.

Frequency analyses of the flux density waveform monitored from a rotor pole shoe.


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- 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 failuredetection. 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 inarmature winding coils can be detected.


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Measurement results

1

2

3

analog data,

digital data.

RF

on rotor

1

3

2 on stator

to control

system

1 Hall sensor, measuring coil

2 processing units,

3 wireless bridge.


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Measurement results

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.

Measured and calculated flux density waveform in wind generator air gap.


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Measurement results

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.

Integrated voltage waveform induced in measuring coil Ms2p


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Measurement results

Curve 1 measurement,

Curve 2 FEM calculation.

Flux density waveform monitored from rotor pole shoe with inter-coil

short circuits in armature winding.


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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.


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