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Generator Reactivity Limit

Testing

Workshop Presentation

WECC Generator Testing Task Force

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What it is and what it isnt

It is a quick and relatively easy test. It verifies reactive capability for only

one set of conditions at 2 points.

It does not verify generator capabilityfor all conditions.

It does not verify all points in thegenerator capability curve.

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Letter Defining Requirement

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Testing Requirements

All synchronous machines greater than 10 MVA

Operating conditions should be as close to

normal as practicable, including loading, unittemperatures, and pressures.

Tests should be performed during periods of

operation which maximize the MVAR in/outputof the machine (when system voltage is mostadvantageous to yield these results).

When possible, other synchronous machines orpower system components should be used toobtain the most advantageous terminal voltage

during these tests.

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Testing Requirements

While operating in a steady state mode at netdependable MW capability (near rated output),

raise excitation in automatic voltage control untilone of the following conditions occurs:

The 100% MVA rating of the machine isreached (reached capability curve)

Rated field current or field voltage is reached

Terminal voltage limit is reached

Generator temperature limits are reached

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Testing Requirements

Maximum/over excitation limiter is

reached/alarms Maximum reference adjuster travel or limit is

reached

Maximum auxiliary bus voltage is reached

Hold unit at this level for a minimum of 15minutes (30 minutes is a preferable duration),then take measurements

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Testing Requirements

While operating in a steady state mode at netdependable MW capability lower excitation in

automatic voltage control until one of thefollowing conditions occurs:

UELs are activated

100% MVA rating is reached Generator temperature limits are reached

Minimum reference adjuster travel or limit isreached

Minimum auxiliary bus voltage is reached

Minimum terminal voltage limit is reached

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Example Hydrogenerator

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Nom Voltage

Min Voltage

Max Voltage

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Application to Testing

The rated MVA and 95% PFoverexcited point is at nominalterminal voltage. (blue line)

This machine will not producerated MVA and 95% PF whenterminal voltage is at the

maximum. (turquoise line) This unit passes the reactive

capability test because Tests

should be performed duringperiods of operation whichmaximize the MVAR in/outputof the machine (when system

voltage is most advantageousto yield these results). (red)

Min

Nom

Max

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Application to Capability

The Generator Capability Curve should stateminimum capability for all rated conditions:

terminal voltage, ambient temperature, etc.

Internal and external events that limit capability

normally considered separately. It may not bepossible to produce all limiting conditionssimultaneously.

The reactive capability test does not validatethe machine capability curve.

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Machine Capability Maintenance

Owners should be aware of changes and updatemachine capability curves.

Operational events that indicate potentialcompromise of capability should be investigated.

Due to the complicated nature of validatingcapability for all operational conditions andconsidering the potential impact to system

operation, it is not prudent to mandate re-validation of capability.

Operational events and routine maintenancenormally reveal potential problems.

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Benefits of Reactive Capability Testing

Testing can detect significant degradation.

Tests are simple and cause little risk.

Tests confirm capability under nominal

conditions. If the unit fails to meet the reactive capability

under the most favorable conditions, it isproven to fail to meet the machine capabilitycurve on record.

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Reactive Capability Testing Limitations

Passing reactive capability testing is a necessarybut not sufficient condition to assure machinecapability curve is accurate.

May not detect outer loop control (SCADA) limits

if tested under local control.

Tests are done steady state with gentle moves

approaching limits. Design for abnominalconditions may require more restrictive SCADAlimits.

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The End