© 2015 Mirus International | All Rights Reserved
Harmonic and Energy Saving Solutions
Power Quality You Can Trust | Real W...
© 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International
Preventing Circulating Curr...
© 2015 Mirus International | All Rights Reserved
Preventing Circulating Current in
Parallel Generator Applications
© 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International
Scope of Presentation
•  Ge...
© 2015 Mirus International | All Rights Reserved
Generator Pitch and Harmonics
Coil Pitch:
The angular distance between
th...
© 2015 Mirus International | All Rights Reserved
Generator Pitch and Harmonics
Fractional Pitch Winding:
When Coil Pitch i...
© 2015 Mirus International | All Rights Reserved
Generator Pitch and Harmonics
•  Voltage waveform produced by a generator...
© 2015 Mirus International | All Rights Reserved
Generator Pitch and Zero Sequence
Impedance
•  Generator impedances vary ...
© 2015 Mirus International | All Rights Reserved
How Paralleling Dissimilarly Pitched Generators creates
Neutral Circulati...
© 2015 Mirus International | All Rights Reserved
How Paralleling Dissimilarly Pitched Generators
creates Neutral Circulati...
© 2015 Mirus International | All Rights Reserved
Traditional Methods for limiting
Circulating Currents
•  Ensure that gene...
© 2015 Mirus International | All Rights Reserved
Traditional Methods for limiting
Circulating Currents (cont.)
•  Add impe...
© 2015 Mirus International | All Rights Reserved
Traditional Methods for limiting
Circulating Currents (cont.)
•  An ungro...
© 2015 Mirus International | All Rights Reserved
GENLINK Dissimilar Pitch Neutral Limiter
•  Multiple winding reactor inst...
© 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International
•  Paralleled generators wi...
© 2015 Mirus International | All Rights Reserved
Application of GENLINK DPNL in 4-Wire
System
•  DPNL is used when 2 or mo...
© 2015 Mirus International | All Rights Reserved
Application of GenLink DPNL on 4-Wire
System with Utility Transformer
•  ...
© 2015 Mirus International | All Rights Reserved
Cascaded System for Multiple Generators
•  DPNL’s can be cascaded in appl...
© 2015 Mirus International | All Rights Reserved
DPNL Fault Current Path
•  Fault current passes through the shoulder of t...
© 2015 Mirus International | All Rights Reserved
GENLINK Effect on 1-Ph Fault Level
3000A DPNL
•  1-ph impedance
–  Normal...
© 2015 Mirus International | All Rights Reserved
GENLINK Dissimilar Pitch Neutral Limiter
•  Circulating current inductanc...
© 2015 Mirus International | All Rights Reserved
Application of GENLINK DPNL in 3-Wire
System
•  In a 3-Wire application w...
© 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International
•  Paralleled generators wi...
© 2015 Mirus International | All Rights Reserved
How to Size GENLINK for a Specific
Application
•  Determine total capacit...
© 2015 Mirus International | All Rights Reserved
How to Size GENLINK (cont.)
•  This will size the DPNL for a return neutr...
© 2015 Mirus International | All Rights Reserved
Total neutral current = 160A
Case Study: Martin Brower Distribution Facil...
© 2015 Mirus International | All Rights Reserved
Case Study: Martin Brower Distribution Facility
Neutral Grounded at one l...
© 2015 Mirus International | All Rights Reserved
Case Study: Martin Brower Distribution Facility
•  1-Ph load return neutr...
© 2015 Mirus International | All Rights Reserved
Case Study: Boca Hospital, S. Florida
•  Generator configuration
–  2 x 1...
© 2015 Mirus International | All Rights Reserved
Case Study: Boca Hospital, S. Florida
“Reading went from 400 amp
to zero ...
© 2015 Mirus International | All Rights Reserved
Case Study: 13.8kV System, Waterloo Illinois
- Differently pitched Genera...
© 2015 Mirus International | All Rights Reserved
Case Study: 13.8kV System, Waterloo Illinois
•  Virtually no neutral circ...
© 2015 Mirus International | All Rights Reserved
Case Study: 13.8kV System, Waterloo Illinois
•  Required continuously rat...
© 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International
Summary
•  Paralleling of d...
© 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International
Questions
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Preventing circulating current in parallel generator applications

As the need for secure and reliable electricity has gown, many opportunities for distributed generation have appeared. Diesel, Natural Gas, Biofuel or other generators used for these applications often run in parallel with themselves or with Utility transformers. This can result in high levels of triple frequency (180Hz in 60Hz systems) circulating current in the common neutrals or ground connections. These circulating currents can cause overheating in the generator windings and false tripping of overcurrent protection devices, especially ground fault schemes. Mirus’ GenLink Dissimilar Pitch Neutral Limiter (DPNL) is a uniquely wound, multiple coil reactor which can be very effective in blocking the flow of circulating current without negatively impacting system fault levels. MIRUS’ President & CEO, Tony Hoevenaars P.Eng, covered how paralleling generators can lead to very high neutral circulating currents and what can be done to control them. The problem is particularly evident when the generators are built with dissimilar pitches but is also very common when generators are paralleled with Utility transformers for Distributed Generation. In the webinar, attendees learned about: - Understanding Generator Pitch and Harmonics - How Circulating Current Problems Start - Effective Method for Reducing Circulating Current - Adding Circulating Path Impedance without Effecting Ground Fault Path - Sizing Neutral Blocking Solution for Specific Applications - Real-World Case Studies
Published on: Mar 4, 2016
Published in: Engineering      
Source: www.slideshare.net


Transcripts - Preventing circulating current in parallel generator applications

  • 1. © 2015 Mirus International | All Rights Reserved Harmonic and Energy Saving Solutions Power Quality You Can Trust | Real World Experience | A History of Innovation
  • 2. © 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International Preventing Circulating Currents in Parallel Generator Applications Today’s Presenter •  Prior to joining Mirus, Tony was the Chief Facilities Electrical Engineer at an IBM manufacturing facility in Toronto •  Tony is a professional engineer •  Tony is also a member of IEEE, and has published multiple research papers on power quality
  • 3. © 2015 Mirus International | All Rights Reserved Preventing Circulating Current in Parallel Generator Applications
  • 4. © 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International Scope of Presentation •  Generator Pitch and Harmonics •  How paralleling dissimilarly pitched generators creates neutral circulating current •  Traditional methods used to prevent generator circulating current •  GENLINK Dissimilar Pitch Neutral Limiter (DPNL) •  Case Studies: –  Martin Brower Distribution Facility •  750kW and 1000kW Generators –  Arkansas University •  2 x 800kW Generators with 1500kVA Utility Transformer –  City of Waterloo Power Plant Expansion •  New 7200kW 13.8kV Turbine Generator •  Summary
  • 5. © 2015 Mirus International | All Rights Reserved Generator Pitch and Harmonics Coil Pitch: The angular distance between the two sides of an individual coil of an AC armature winding Pole Pitch: The angular distance between centers of adjacent field poles Winding Pitch: The ratio of Coil Pitch to Pole Pitch Full Pitch Winding: When Coil Pitch is exactly equal to Pole Pitch Full Pitch Generator Coil Pitch = 90°, Pole Pitch = 90° Generator  Pitch  &   Harmonics   Circula4ng  Currents   problems   Preven4ng  Generator   Circula4ng  Current   GENLINK  DPNL   Case  Studies
  • 6. © 2015 Mirus International | All Rights Reserved Generator Pitch and Harmonics Fractional Pitch Winding: When Coil Pitch is less than Pole Pitch Advantages of Fractional Pitch Generators: –  Shorter end connections to reduce copper –  More sinusoidal waveform and therefore, less harmonics 2/3 Pitch Generator Coil Pitch = 60°, Pole Pitch = 90°
  • 7. © 2015 Mirus International | All Rights Reserved Generator Pitch and Harmonics •  Voltage waveform produced by a generator will vary slightly with respect to winding pitch •  Harmonic content in voltage will also vary based on winding pitch –  Pitch factors below are used to predict harmonic voltages based on respective harmonic fluxes Reference: ‘Generator Winding Pitch and Harmonics, Engine Data Sheet EDS 70.4, Caterpillar, March 1993 ’ Pitch Fund. 3rd 5th 7th 9th 2/3 0.866 0.0 0.866 0.866 0.866 4/5 0.951 0.588 0.0 0.588 0.951 5/6 0.966 0.707 0.259 0.259 0.966 6/7 0.975 0.782 0.434 0.0 0.782
  • 8. © 2015 Mirus International | All Rights Reserved Generator Pitch and Zero Sequence Impedance •  Generator impedances vary with respect to winding pitch, especially zero sequence impedance •  Generator zero sequence impedance directly impacts the amount of circulating neutral current •  Many claim that a 2/3rd pitch generator is better for 3rd harmonic, but this is not entirely true –  it has very low zero sequence impedance which results in less 3rd harmonic voltage distortion under non-linear loading, but –  the low zero sequence impedance presents little resistance to the flow of circulating currents
  • 9. © 2015 Mirus International | All Rights Reserved How Paralleling Dissimilarly Pitched Generators creates Neutral Circulating Current •  Generators with different pitch configurations will have slightly different voltage waveshapes •  Differences in Phase-Neutral (Ph-N) instantaneous voltages will appear as triple frequency •  Can also apply when paralleling alternate energy sources with the Utility 5/6P Gen1 2/3P Gen2 Generator  Pitch  &   Harmonics   Circula4ng  Currents   problems   Preven4ng  Generator   Circula4ng  Current   GENLINK  DPNL   Case  Studies
  • 10. © 2015 Mirus International | All Rights Reserved How Paralleling Dissimilarly Pitched Generators creates Neutral Circulating Current (cont.) •  Difference in instantaneous voltages drives neutral circulating current •  Flow is restricted only by zero sequence impedance of generators and cables which is usually quite low
  • 11. © 2015 Mirus International | All Rights Reserved Traditional Methods for limiting Circulating Currents •  Ensure that generators are of similar pitch –  This is not always possible or even preferred when expanding a site with older, existing generators –  Can be difficult when sourcing from different suppliers or a supplier that has changed their pitch design –  Even identically pitched generators can have slightly different voltage waveshapes Generator  Pitch  &   Harmonics   Circula4ng  Currents   problems   Preven4ng  Generator   Circula4ng  Current   GENLINK  DPNL   Case  Studies
  • 12. © 2015 Mirus International | All Rights Reserved Traditional Methods for limiting Circulating Currents (cont.) •  Add impedance in the common neutral –  Neutral Grounding Resistors or Neutral Reactors can be used but the impedance required to limit circulating current might reduce 1-ph faults to unacceptable levels (ie. such that breakers do not trip) –  These devices must be rated for the residual steady state circulating current –  If NGR’s are required for fault limiting, this can be an effective method but the requirement to handle steady state current will increase size and cost
  • 13. © 2015 Mirus International | All Rights Reserved Traditional Methods for limiting Circulating Currents (cont.) •  An ungrounded system can be used where neutrals are not connected together or grounded –  Ground fault monitoring is required and no neutral return path is available for 1-ph loads –  Sometimes zigzag reactors are used to provide a ground reference •  Internal generator faults may be a problem
  • 14. © 2015 Mirus International | All Rights Reserved GENLINK Dissimilar Pitch Neutral Limiter •  Multiple winding reactor installed in the common neutral of paralleled generators or generators paralleled with Utility •  Inserts ~ 48% impedance in neutral current circulating path at triple frequency –  Reduces neutral circulating current by 70% or more •  Minimal effect on fault level –  Adds < 1% saturated impedance to 1-Ph fault level –  No impedance to 3-Ph fault level •  Designed to meet IEEE Std 32 Requirements for Neutral Grounding Devices Generator  Pitch  &   Harmonics   Circula4ng  Currents   problems   Preven4ng  Generator   Circula4ng  Current   GENLINK  DPNL   Case  Studies
  • 15. © 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International •  Paralleled generators with dissimilar pitches in stand- alone or emergency stand-bye operation •  Generator or other Alternative Energy source that is paralleled with a Utility transformer that can have its neutral-ground bond routed through the DPNL –  Cascaded DPNL’s can be used where there are more than two connected supplies •  Examples are alternative energy generators, standby generators, islanded supplies for drilling rigs, production platforms, pumping stations, etc. Applications for GenLink DPNL
  • 16. © 2015 Mirus International | All Rights Reserved Application of GENLINK DPNL in 4-Wire System •  DPNL is used when 2 or more generators of dissimilar pitch are paralleled together or a generator is paralleled with an alternate source, such as the Utility •  DPNL is inserted in the neutral between the dissimilar groups •  Neutral should be grounded in only 1 location –  Preferred location is neutral bus in switchboard
  • 17. © 2015 Mirus International | All Rights Reserved Application of GenLink DPNL on 4-Wire System with Utility Transformer •  Utility transformer neutral should be grounded through DPNL •  Ground at only 1 location
  • 18. © 2015 Mirus International | All Rights Reserved Cascaded System for Multiple Generators •  DPNL’s can be cascaded in applications where there are more than 2 types of dissimilar pitch generators or dissimilarly pitched generators are paralleled with Utility •  Size each DPNL based on the total generator load connected to it
  • 19. © 2015 Mirus International | All Rights Reserved DPNL Fault Current Path •  Fault current passes through the shoulder of the DPNL (Z-X or Y-X) –  Shoulder impedance is typically 4% – 5% •  During a fault, reactor steel saturates, significantly reducing the impedance Fault current path
  • 20. © 2015 Mirus International | All Rights Reserved GENLINK Effect on 1-Ph Fault Level 3000A DPNL •  1-ph impedance –  Normal Operation ~ 5% –  Above 8000A (saturated condition) < 1%
  • 21. © 2015 Mirus International | All Rights Reserved GENLINK Dissimilar Pitch Neutral Limiter •  Circulating current inductance (Y-Z) is almost 4x the shoulder inductance •  Since the frequency of the circulating current is 3x the fundamental current (180 Hz vs 60 Hz), circulating current impedance is 3x greater •  Net impedance to circulating current is around 48%
  • 22. © 2015 Mirus International | All Rights Reserved Application of GENLINK DPNL in 3-Wire System •  In a 3-Wire application where there is no return neutral current from 1-Ph loads, a smaller size DPNL can be used •  Terminal X may or may not be grounded –  If ungrounded, Ground Fault monitoring will be required
  • 23. © 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International •  Paralleled generators with dissimilar pitches that are tied to a Utility grid supplied by a transformer or multiple transformers that cannot have neutral grounded through DPNL –  DPNL prevents circulating current between the generators –  NGI helps block circulating current between the generators and the Utility transformers –  NGI is not necessary if Neutral-Ground bond on Utility transformers can be routed through DPNL •  Examples are Generating Stations with Alternative Energy sources, Co-generation sites, Peak Shaving generators, etc. •  Also NGI alone can be useful in applications with Alternative Energy sources and Utility when neutral is inaccessible Applications for GenLink DPNL + NGI
  • 24. © 2015 Mirus International | All Rights Reserved How to Size GENLINK for a Specific Application •  Determine total capacity in kW or kVA of all generators connected in parallel •  Select DPNL that corresponds to this value in the appropriate system voltage column
  • 25. © 2015 Mirus International | All Rights Reserved How to Size GENLINK (cont.) •  This will size the DPNL for a return neutral current that will be at least 50% of full phase current rating –  85% for 208V-240V or 380V-440V systems •  It is the Users responsibility to ensure that actual return neutral current will not exceed DPNL rating –  If return neutral current is expected to exceed DPNL rating then a larger DPNL should be selected –  A larger DPNL will be slightly less effective in reducing circulating current •  For 3-Wire applications or where return neutral current is known to be very low, smaller DPNLs can be selected
  • 26. © 2015 Mirus International | All Rights Reserved Total neutral current = 160A Case Study: Martin Brower Distribution Facility Two Dissimilarly Pitched Generators Generator  Pitch  &   Harmonics   Circula4ng  Currents   problems   Preven4ng  Generator   Circula4ng  Current   GENLINK  DPNL   Case  Studies
  • 27. © 2015 Mirus International | All Rights Reserved Case Study: Martin Brower Distribution Facility Neutral Grounded at one location only
  • 28. © 2015 Mirus International | All Rights Reserved Case Study: Martin Brower Distribution Facility •  1-Ph load return neutral current = 38.4A •  Most of the current from generators to DPNL is return neutral current from 1- ph loads •  Almost all generator circulating current was eliminated
  • 29. © 2015 Mirus International | All Rights Reserved Case Study: Boca Hospital, S. Florida •  Generator configuration –  2 x 1375kVA 0.8667 Pitch –  1 x 1200kVA . 0667 Pitch •  Calculation of expected circulating neutral current provided by Caterpillar Distributor •  Circulating 3rd harmonic current –  Ga and Gb ~ 97A –  Gc ~ 194A
  • 30. © 2015 Mirus International | All Rights Reserved Case Study: Boca Hospital, S. Florida “Reading went from 400 amp to zero on all three generators and system has functioned with no problems since then.” Hassan Entezari, Pantropic Power Inc. 2500A GenLink DPNL
  • 31. © 2015 Mirus International | All Rights Reserved Case Study: 13.8kV System, Waterloo Illinois - Differently pitched Generators and Multiple Utility Trans. •  New Generator different pitch than existing –  Existing 6600kW (.722P) –  New 7200kW (.814P) •  No access to Utility transformer neutrals but Mirus was not initially informed of this
  • 32. © 2015 Mirus International | All Rights Reserved Case Study: 13.8kV System, Waterloo Illinois •  Virtually no neutral circulating current between Generators •  Residual current to Utility transformers still too high however
  • 33. © 2015 Mirus International | All Rights Reserved Case Study: 13.8kV System, Waterloo Illinois •  Required continuously rated Neutral Grounding Resistor (NGR) or additional Neutral Grounding Inductor (NGI) between DPNL and ground •  NGR recommended for this application: –  60A continuous duty, Z = 19 Ohms –  36”W x 36”D x 66”H –  Residual circulating current estimated to be < 50A •  NGI recommended for this application: –  100A continuous duty, Z = 6.6 Ohms at 60Hz –  44”W x 38”D x 66”H –  Residual circulating current estimated to be < 25A •  Advantages of NGI over NGR –  More effective in reducing circulating current –  Less effect on fault level –  Much lower losses •  NGR power dissipation is entirely kW –  Lower cost
  • 34. © 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International Summary •  Paralleling of different power sources can cause neutral circulating current –  Dissimilarly pitched generators –  Generator or other alternative energy source with Utility supply –  Different alternative energy sources •  Neutral circulating current is predominantly triple frequency •  Application of GenLink DPNL can reduce triple frequency circulating current by 70% or more without significantly affecting fault levels •  Neutral should be grounded at only one location –  Recommended grounding at Switchboard •  If Utility transformer neutrals are not accessible, Neutral Grounding Inductor will also be needed
  • 35. © 2015 Mirus International | All Rights ReservedPrivate and Confidential | Mirus International Questions

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