CUMMINS Consideration for Paralling Dissimilar Equipment

Considerations forParalleling Dissimilar Equipment

Paralleling Dissimilar Equipment (2)

General Considerations

• You can parallel anything to anything, BUT:– Genset dissimilarities may result in poorer load

sharing performance or,– Potential for some nuisance tripping of protection– Some problems can be resolved with

modifications in the system sequence ofoperation

• Switchgear to genset “incompatibility” cannormally be resolved with the cooperation ofthe parties.


GenSet Compatibility

• Engine Compatibility• Alternator Compatibility• Control Compatibility

– Governor/kW Load ShareSystem

– Voltage Regulation/kVar loadshare system

– Miscellaneous Controls


Core Compatibility Point

• When two or more machines areparalleled:

• Instantaneous differences in voltagewill cause current (kVar) flow.

• Instantaneous differences infrequency will cause kW flow.


GenSet Compatibility

• Engine Compatibility– Not a big issue for prime power

• High speed engines are generally compatiblewith each other on a steady state basis.

– Review steady state frequency regulation• Typical: plus or minus 0.25% from no load to full

load• Look at “steady state” values


Frequency vs Time

59.7

59.8

59.9

60

60.1

60.2

60.3

25 26 27 28 29 30

time

freq

uen

cy

DQKC

DFLE

Steady State Frequency Regulation

FAE engines tend to have faster, more complex governing systemsthan hydro-mechanically fueled engines.


Engine Compatibility

• Not a big issue for prime power– High speed engines are generally compatible

with each other on a steady state basis.• Review steady state frequency regulation• Typical: plus or minus 0.25% from no load to full load

– Transient Performance Issues• Dissimilar machines accept and reject load at

different rates• Sudden load changes to paralleled machines may

cause load sharing disturbance.• Reverse power on load rejection

– Extend time delay on reverse power trip– Smaller load steps

» each load step ½ the smallest genset rating


GenSet Compatibility:Impact of Harmonics

• All Alternators have “imperfect” sinusoidalwaveforms

• Different alternators have different harmoniccontent


GenSet Compatibility:Impact of Harmonics

• Differences in harmonics cause differentwaveform shapes

• Difference in “instantaneous voltage” causecurrent flow


A

B

C

N

G

CIRCULATING NEUTRAL CURRENTS

• If there is a current path between dissimilaralternators, current will flow


Physical Impact of Pitch(Stator Coil Slot Span)/(# Slots/Pole)


Alternator Compatibility

• Compatible alternators have similar harmonics– 3rd Order and multiple harmonics most problematic– 2/3 Pitch machines, which have no 3rd order

harmonics, are “universally” compatible with eachother

• Deal with Dissimilarities by:– Block flow of neutral current

• 3-wire (no neutral) connection on one or all machines• be careful of neutral connection through ground path for

solidly grounded machines.

– Neutral reactors– Replace alternator


GenSet Compatibility• Control Compatibility

– Load Sharing (kW &kVar)– Load Govern– Master Synchronizer


PowerCommand Compatibility

– PCC Compatible with all that use analogload sharing lines

• Woodward 2301• Barber-Colman• Governors America

– AVR Interface• All PCC, or Reactive Droop


Genset Paralleling Compatibility

• Compatible Engines– Similar Transient Performance– Equal Frequency Regulation

• Compatible Alternators– Same Pitch (2/3 most compatible)– Can Solve Incompatibility with

Compromise

• Compatible Controls– Load Sharing is Key Issue


Conventional Paralleling Architecture

GOVERNORBIAS SIGNAL

GOV

AVREC

GENSET

GOV

AVREC

GENSET

ILS

PLC

SYNC

PROTECTION

METERALARM

CB

ILS

PLC

SYNC

PROTECTION

METERALARM

CB

PLCPROTECTION

METERALARM

LOAD SHARELINES

DISCRETESIGNALS


PowerCommand Systems

CB CB

PCC

GENSET

PCC

GENSET

PLCMETERALARM

LOAD SHARELINES


CB CB

PCC

GENSET

PCC

GENSET

PLCMETERALARM

LOAD SHARELINES

PowerCommand Differences

• No Remote Paralleling ControlNecessary

• Genset Control Operates Breaker• No Governor/Speed Bias Available• Load Sharing Lines Connect GenSet

to GenSet• MasterControl Could Be the Same

•• No Remote Paralleling ControlNo Remote Paralleling ControlNecessaryNecessary

•• Genset Control Operates BreakerGenset Control Operates Breaker•• No Governor/Speed Bias AvailableNo Governor/Speed Bias Available•• Load Sharing Lines Connect GenSetLoad Sharing Lines Connect GenSet

to GenSetto GenSet•• MasterControlMasterControl Could Be the SameCould Be the Same


Situations

• Using All New PCC GenSets withSwitchgear by Others

• New PCC GenSet with ExistingCummins/Onan GenSets (Detector-style Controls)

• Using a New PCC GenSet withExisting Switchgear and GenSets byOthers


Typical Isolated Bus Interface(PCC to Conventional Gear)

PLC

PROTECTION

METER

ALARM

CB

PLC

PROTECTION

METER

ALARM

CB

PCC

GENSET

PCC

GENSET

PLC

PROTECTION

METER

ALARM

LOAD SHARELINES

DISCRETESIGNALS


ILSI: Isochronous Load Sharing Interface

Converts PCC Load Sharing Lines

ILSI

CB

ILS

PLC

SYNC

PROTECTION

METERALARM

CB

PCC

GENSET

GOV

AVREC

GENSET

PLCPROTECTION

METERALARM

LOAD SHARELINES

GOVERNORBIAS SIGNAL

NEW SWGR

SECTION

PLCPROTECTION

METERALARM

OptionalComponents


ILSI Compatibility

• Woodward 2301• Barber Colman Analog• GAC (Governors America)• Others

– using analog load sharing lines– NOT CAN


Paralleling Compatibility

• Genset Paralleling Compatibility– Compatible Engines

• Similar Transient Performance• Equal Frequency Regulation

– Compatible Alternators• Same Pitch (2/3 most compatible)• Can Solve Incompatibility with Compromise

– Compatible Controls• Load Sharing is Key Issue

• Switchgear Compatibility is Non-Issue


Specifications

• New Systems:– 2/3 Pitch Alternators– Analog kW Load Sharing Signals

• Old Systems– Deal with “Odd Pitch” Alternators

• Floating Neutral on “odd” machine, or• Reactors, or• Replace Alternator

– Control Upgrades might be best choice

CUMMINS Consideration for Paralling Dissimilar Equipment

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