Transformer at base of Tower Critical link to successful Wind - - PowerPoint PPT Presentation

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Transformer at base of Tower Critical link to successful Wind - - PowerPoint PPT Presentation

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Wind Power Transformer Design By Philip J Hopkinson, PE Wind Power Transformer at base of Tower Critical link to successful Wind Turbine connection to the grid Subject of Many complaints 1. Gassing 2. Winding Failures 3. Contact

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SLIDE 1

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 1

Wind Power Transformer at base of Tower Critical link to successful Wind Turbine connection to the grid Subject of Many complaints

1. Gassing 2. Winding Failures 3. Contact coking 4. Arc-Flash 5. Low liquid level

Doble Engineering Conference 021913

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SLIDE 2

Wind Power Transformer Design

By Philip J Hopkinson, PE

1. Consideration focused on Generator step-up Transformers from 600 volt to 34,500 volt 2. Inputs from field experience 3. Standards work within IEC TC 14 and IEEE 4. Arc-Flash Safety considerations from NFPA 70E 2009 5. Work with Manufacturers of Transformers 6. Analytical studies 7. Attempt to develop meaningful universal standard requirements for transformers rated up to 10 MVA. 8. IEEE Transformer Working Group P60076-16 9. IEC Document 60076-16

  • 10. Currently 100 members on IEEE Working Group

1/22/2013 2 Doble Engineering Conference 021913

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SLIDE 3

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 3

Typical Wind Turbine transformer

  • 1. 3-Phase Pad mounted
  • 2. 600 volt low voltage Gr Y
  • 3. 34,500 volt high voltage
  • 4. Commonly Wye high voltage
  • 5. Sometimes Delta high voltage
  • 6. Most with 5-leg wound cores
  • 7. Some with 3-leg stacked cores
  • 8. Nearly 100% liquid filled
  • 9. Nearly all with sheet low voltage
  • 10. All with wire high voltages

Doble Engineering Conference 021913

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SLIDE 4

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 4

Typical Wind Turbine transformer concerns

  • 1. High Hydrogen gas
  • 2. High voltage winding failures
  • 3. Safety of HV load-break switch
  • 4. Carbonized HV Switches and Tap

changers

  • 5. Low liquid levels in cold

temperatures

Doble Engineering Conference 021913

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SLIDE 5

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 5

High Hydrogen Gas

  • 1. Present in Up to 50% of

transformer populations

  • 2. Hydrogen as high as 20,000 ppm
  • 3. Small amounts Ethane and

Ethylene and Methane

  • 4. Windings apparently OK
  • 5. Most transformers returned to

factories pass Routine Tests, including Impulse.

Doble Engineering Conference 021913

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SLIDE 6

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 6

High Hydrogen Gas always partial discharge related

  • 1. But windings not involved
  • 2. Leads not involved in most cases
  • 3. Hot spots in windings OK
  • 4. Some gassing improves with time
  • 5. If not windings or leads then what

else?

Doble Engineering Conference 021913

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SLIDE 7

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 7

What about the iron core?

  • 1. Magnetic energy reservoir
  • 2. Voltage generator from changing

flux

  • 3. Many laminations of thin steel
  • 4. Very thin inter-laminar insulation
  • 5. High inter-laminar capacitance
  • 6. Susceptible to static charge

Doble Engineering Conference 021913

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SLIDE 8

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

1. The issue is gassing and Partial Discharge 2. Dielectric Breakdown in windings not the problem 3. Gassing and PD worst at 34.5 kV 4. Gassing not an issue at 5 kV 5. Gassing at 15 kV an annoyance only 6. Gassing coming from Core 7. Solution via grounding or shielding

1/22/2013 8 Doble Engineering Conference 021913

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SLIDE 9

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

1/22/2013 9

Ground Lead Vi Outer Core Vi Inner Core Vi Inner Core Vi Outer Core C5 C2 C1 C3 C4 C1 C1 C4 C4 C1 C1 C4 C3 C1 C2 C3 C5 C5 C5 C5 C5 LV

Grounded Clamp

HV L L

Doble Engineering Conference 021913

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SLIDE 10

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

1/22/2013 10

Ground Lead Vi Outer Core Vi Inner Core Vi Inner Core Vi Outer Core C5 C2 C1 C3 C4 C1 C1 C4 C4 C1 C1 C4 C3 C1 C2 C3 C5 C5 C5 C5 C5 LV

Grounded Clamp

HV L L

HV = 34500 LV = 600 Gr Y kVA = 1850 Frequency = 60 Hz C1-C5 calculated In EXCEL

Doble Engineering Conference 021913

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SLIDE 11

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

1. Outside core grounds at 34.5 kV result in high core volts 2. Inside core grounds eliminate static charges and drop core volts to volt/turn levels

1/22/2013 11

Vi Outer Core Loop Inside Surface 804 Volts LV Start is Grounded 0 Volts

C2 C1

L-G Volts 19919 Core Ground

C3

0 Volts Case I, Core Ground Connected to Frame Voltage drop in Outer Core stacks = 804 Volts HV

Doble Engineering Conference 021913

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SLIDE 12

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

1. Outside core grounds at 34.5 kV result in high core volts 2. Inside core grounds eliminate static charges and drop core volts to volt/turn levels 3. Core shields equally effective

1/22/2013 12

0.030" thick static shield 0.020" thick paper Outside Core Leg Core Ground

Grounded Electrostatic Shield

Doble Engineering Conference 021913

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SLIDE 13

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

With Outside Core Ground and no core shield:

  • 1. Hydrogen at 15 kV typically 100-300 ppm
  • 2. Hydrogen at 34.5 kV typically 3,000-10,000 ppm
  • 3. Hydrogen accompanied by small amounts of
  • a. Ethane
  • b. Ethylene
  • c. Methane

1/22/2013 13 Doble Engineering Conference 021913

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SLIDE 14

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

With Outside Core Ground and no core shield:

  • 1. Partial discharge best detector
  • 2. PD should be conducted per Class II transformers
  • a. Start at 50% of rated volts
  • b. Go to 100% of rated volts and record

c. Go to 110% of rated volts and record

  • d. Go to 150% of rated volts and hold for 1 hour
  • e. Drop back to 110% of rated volts and hold for at

least 10 minutes and record. f. Drop back to 100% of rated volts and record.

  • g. Drop back until pd extinguishes below 100 pc
  • 3. Transformer fails test if extinguish Pd (< 100 pc)
  • ccurs at less than 110% of rated volts

1/22/2013 14 Doble Engineering Conference 021913

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SLIDE 15

Transformer Core Grounds in Wound Cores

By Philip J Hopkinson, PE

Conclusions:

  • 1. Wound Cores most responsible for High

Hydrogen with Outside Core Grounds

  • 2. Absolute Inside Core Grounds OK
  • 3. Shielded Cores OK
  • 4. 3-Leg Stacked Cores generally immune

1/22/2013 15 Doble Engineering Conference 021913

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SLIDE 16

Transformer Core Grounds

By Philip J Hopkinson, PE

Recommendations:

Specify Core Precautions in Standard

  • 1. For 5 Leg Wound Cores
  • a. Absolute inside core grounds or
  • b. Shielding
  • 2. 3 Leg Stacked Cores
  • 3. 4 and 5 leg stacked cores May need some

shielding

1/22/2013 16 Doble Engineering Conference 021913

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SLIDE 17

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 17

Load-break Switching often fails transformers

  • 1. Switching often not done at

transformer

  • 2. Groups of ~15 transformers

switched by vacuum breakers

  • 3. First and / or Last transformer

in Group most vulnerable

  • 4. Current Chopping and

Reignition Transients are failure-initiators

  • 5. IEEE C57.142 Addresses Issues
  • 6. Resistor-Capacitor Snubbers

needed

Doble Engineering Conference 021913

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SLIDE 18

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 18

Common Denominators for switching-induced problems

  • 1. Switching done at Vacuum

breaker

  • 2. Transformers connected to

vacuum breakers by shielded cables

  • 3. No arresters at transformers..

but it wouldn’t help

  • 4. Switched currents < 6 amps
  • 5. Current chopping and

reignition transients present

Winding failures in tap section

  • r at line ends

Doble Engineering Conference 021913

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SLIDE 19

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 19 Doble Engineering Conference 021913

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SLIDE 20

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 20

Vacuum breakers compact, clean, efficient, generally safe.. But Transformers often in trouble!

Doble Engineering Conference 021913

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SLIDE 21

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 21

Shielded cables amplify resonances with reflected waves and voltage doubling

Shielded Cables integral part

  • f damaging voltage

transients

  • 1. Act like Transmission

lines

  • 2. Wave velocity half the

speed of light

  • 3. Surge impedance

independent of length

  • 4. Low energy dissipation
  • 5. EPR generally superior

to XLPE due to higher dissipation

Doble Engineering Conference 021913

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SLIDE 22

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 22

Ping test #5 at Tap 4-5 & 9.5 amps Feb. 1. 06 Island Park Substation Unit #2 Line 1 to Gr. Voltage With 20:1 Attenuators & Arc Gap@ 5.5"

  • 120
  • 100
  • 80
  • 60
  • 40
  • 20

20 40 60

  • 200

200 400 600 800 1000 Microseconds kV

  • 1. Circuit breaker

contacts open and transient recovery voltage (TRV) rises by Ldi/dt to (-)100

kV in~90 µsec.

  • 2. Contacts reignite back into

conduction, current rises to peak and decays to chopping level, inducing oscillatory

  • transient. Voltage rises by

+145 kV in <1 µsec., then

  • scillates to zero.
  • 3. Current decays and is chopped out
  • f conduction and voltage oscillates to

zero.

  • 5. Contacts
  • pen

sufficiently to prevent reignition current and interruption is completed

  • 4. Second TRV

voltage rises to (-)80

kV, then breaker

reignites, raising voltage by +120 kV in <1 µsec., etc.

Load-break Switching

  • ften fails transformers

Current chopping unavoidable at light currents < 6 amps Reignition transients likely at low power factor Circuit damping key to solving problems

The higher the system energy efficiency the more likely are winding failures

Doble Engineering Conference 021913

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SLIDE 23

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 23

Resistor-Capacitor Snubbers provide needed damping

  • 1. Can be mounted in

transformer

  • 2. Can also be mounted in

switchgear

  • 3. Current chopping will still

happen

  • 4. Reignition transients will

totally disappear

  • 5. Transformer survives!

Doble Engineering Conference 021913

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SLIDE 24

High Voltage Winding Failures from Switching

By Philip J Hopkinson, PE

1/22/2013 24

Conclusion

R-C Snubbers in Vacuum breaker cabinet can prevent switching failures Recommendation Include brief tutorial and recommendation in the new Wind Power Document P60076-16

Doble Engineering Conference 021913

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SLIDE 25

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 25

Thermal Stability of Electrical Contacts in switches and tap changers

  • 1. Desired stable life for

30+years

  • 2. Many electrical contacts

susceptible to oxidation

  • 3. Key Variables are:
  • a. Contact materials
  • b. Contact pressures

c. Type of fluid

  • d. Current amplitude and

variability

  • e. Temperature

f. Worsened by high current harmonics

Doble Engineering Conference 021913

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SLIDE 26

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 26

Thermal Stability of Electrical Contacts in switches and tap changers

  • 1. Functional life test being

documented in IEEE PC57.157

  • 2. 30 day test with acceleration
  • f 1000 times
  • 3. 2 XN Current daily for 8 hrs.

in 130 C bath followed by 16 hours cool down de- energized.

  • 4. Test passed if:
  • a. Stable
  • b. Resistance change < 25%

Doble Engineering Conference 021913

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SLIDE 27

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 27

Thermal Stability of Electrical Contacts in switches and tap changers

  • 1. Functional life test being

documented in IEEE PC57.157

  • 2. 30 day test with acceleration
  • f 1000 times
  • 3. 2 XN Current daily for 8 hrs. in

130 C bath followed by 16 hours cool down de- energized.

  • 4. Test passed if:
  • a. Stable
  • b. Resistance change < 25%

CuCu Average Resistance 000.0E+0 100.0E-6 200.0E-6 300.0E-6 400.0E-6 500.0E-6 600.0E-6 700.0E-6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Days Resistance in Micro-Ohms CuCu (C147) oil (1-9-96/2-15-96) CuCu (C147) sil (1-9-96/2-15-96) CuCu (C147) sil (3-28-96/6-1-96) CuCu (C110) sil (10-23-97/1-21-98) CuCu FR3 (12-15-04/2-21-05) CuCu FR3 (4-18-05/6-27-05)

Doble Engineering Conference 021913

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SLIDE 28

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 28

Thermal Stability of Electrical Contacts in switches and tap changers

  • 1. Functional life test being

documented in IEEE PC57.157

  • 2. 30 day test with acceleration
  • f 1000 times
  • 3. 2 XN Current daily for 8 hrs. in

130 C bath followed by 16 hours cool down de- energized.

  • 4. Test passed if:
  • a. Stable
  • b. Resistance change < 25%

AgCu Average Voltage Drop 000.0E+0 20.0E-3 40.0E-3 60.0E-3 80.0E-3 100.0E-3 120.0E-3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Days Voltage Drop in Volts AgCu sil (10-7-98/12-16-98) AgCu fr3 (8-6-04/10-13-04) AgCu oil (12-15-04/2-21-05) AgCu oil (4-18-05/6-27-05)

Doble Engineering Conference 021913

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SLIDE 29

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 29

Thermal Stability of Electrical Contacts in switches and tap changers

  • 1. Functional life test being

documented in IEEE PC57.157

  • 2. 30 day test with acceleration
  • f 1000 times
  • 3. 2 XN Current daily for 8 hrs.

in 130 C bath followed by 16 hours cool down de- energized.

  • 4. Test passed if:
  • a. Stable
  • b. Resistance change < 25%

AgAg Average Resistance 000.0E+0 50.0E-6 100.0E-6 150.0E-6 200.0E-6 250.0E-6 300.0E-6 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 Days Resistance in Micro-Ohms AgAg (Soft) sil (3-28-96/6-1-96) AgAg (Hard) sil (6-4-96/11-5-96) AgAg (Line 1) fr3 (8-6-04/10-13-04)

Doble Engineering Conference 021913

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SLIDE 30

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 30

Thermal Stability of Electrical Contacts in switches and tap changers

  • 1. Test quite meaningful
  • 2. 40+ years proven to find

stable contacts

  • 3. IEEE PC 57.12.157 Guide

should be helpful to the industry

  • 4. Tests should be performed

by each manufacturer for each switch type

  • 5. These conclusions to be

included in Wind Power Transformer Standard P60076-16

Doble Engineering Conference 021913

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SLIDE 31

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 31

Arc-Flash Concerns

  • 1. NFPA 70E reference for

2009

  • 2. Both HV and LV Cabinets

have concerns with LV worst

  • 3. Suit-up needed to just

check gauges

  • 4. These conclusions to be

included in Wind Power Transformer Standard P60076-16

Doble Engineering Conference 021913

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SLIDE 32

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 32

Arc-Flash Concerns Desire third cabinet

  • 1. Gauges
  • 2. Load-break switch

Handle

  • 3. Schrader valve
  • 4. Sampling port

Doble Engineering Conference 021913

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SLIDE 33

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 33

Arc-Flash Concerns Desire HV Cabinet Door to open first

Doble Engineering Conference 021913

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SLIDE 34

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 34

Low Liquid Level Concerns 1. Meter shows level below minimum 2. No leak evidence 3. Cold temperatures 4. Transformer may be de-energized 5. Critical switchgear and other accessories may not be immersed in the liquid

Doble Engineering Conference 021913

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SLIDE 35

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 35

Low Liquid Level Concerns 1. Volumetric change

  • f mineral oil with

temperature Delta V =0.0007*(C-1) 2. Assume tank filled at +70 C 3. Assume coldest temperature (-) 40 C 4. Temperature change is (-) 110 C 5. Volume shrink = - 7.6%

Doble Engineering Conference 021913

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SLIDE 36

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 36

Low Liquid Level Concerns Suppose original liquid height at 50” A 7.6% volume reduction is (-) 4” Recommendation Specify added liquid level to fully cover switches and accessories

Doble Engineering Conference 021913

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SLIDE 37

Wind Power Transformer Design

By Philip J Hopkinson, PE

1/22/2013 37

Summary IEEE P60076-16 should be an important document for Wind Power Transformers

  • 1. Normal C57.12.00

considerations

  • 2. Core Grounds and

shielding

  • 3. Resistor –Capacitor

Snubbers

  • 4. Stable electrical

contacts

  • 5. Arc-Flash issues
  • 6. Added liquid level

Doble Engineering Conference 021913