Power QualityJulie E. VanDyne, P.E.

Power QualityDefine Power QualitySteady State VoltageWaveshape/HarmonicsLoad Issues Related to Waveform DistortionConsequences of Harmonic Distortion Source Issues Related to Waveform DistortionCapacitance/Power Factor CorrectionTransients/Transient Protection

Power QualitySection I - Steady State VoltageDefine Power Quality Identify Voltage LevelsSection II - Waveshape Harmonics Define what they are Causes ImplicationsSection III - Harmonic Control Source Issues MitigationSection IV - Transient Voltage Surge suppression Devices Application Design

Power QualitySection I Steady State Voltage

Power Quality Defined Quality of VoltageSufficient MagnitudeFrequencyWaveshape

Power Quality Defined Quality of VoltageSufficient MagnitudeFrequencyWaveshapeSufficient Power Quality Equipment Should Operate Properly

Alternate Definition Power Quality We have Quality Power when the user is satisfied with the cost, and with the operation of equipment.Qualitative!

Power QualityMagnitudeWaveshape (Harmonics)Frequency

Voltage TransientSteady State

Magnitude VoltagesClassified as Low, Medium, or HighLow - 600 Volts and belowIncludes 480, 240, 120 etc.Medium > 600 Volts; <34,500 VoltsTypically 4 and 12 KVHigh > 34,500 VoltsDelta / Wye

Magnitude Levels (Steady State) Voltage Quality can be affected by equipment ratingsPlant equipment: 440 v.s. 460 v.s. 480Source generally 480

Power QualityVoltage MagnitudeSteady State VoltageIEEECBEMAUtilityCBEMA Curve

CBEMA Curve

CBEMA CurveCBEMA is falling from favorITECANSIRemember that all curves are a tool to help evaluate, none are definitive

Magnitude Levels (Steady State) Engineering StandardsIEEE Typically +/- 5%CBEMA +6% -13%UtilityTypically +/- 5% though varies

MagnitudeItems to rememberVoltage level ranges often dictated by individual equipmentSteady State over/under voltage often the problemEquipment doesn’t always subscribe to CBEMA or IEEE+6 to -10% as a Guideline

Magnitude

Power QualitySection II Waveshape Harmonics

HarmonicsPrimer Fourier - French Mathematician Describe any waveshape as the sum of a fundamental sinusoidal wave and an infinite series of harmonic sinusoidal waves

HarmonicsHarmonicsDefine what they areHow they come about in Power SystemsCharacteristics of Individual HarmonicsMotor Drive SystemsEffects on power systems - Consequences

HarmonicsFundamental

HarmonicsFundamental and Third Harmonic

HarmonicsFundamental and Fifth Harmonic

HarmonicsFundamental and Seventh Harmonic

HarmonicsLinear Load  Linear Voltage DropNo Waveshape DistortionNon Linear Loads  Non Linear Voltage DropWaveshape Distortion

HarmonicsLinearNon - LinearLinear vs. Non Linear Loads

HarmonicsSwitching Mode Power Supply

HarmonicsLinear Vs. Non-LinearLoad (I) and Source (V)(Combined System Impedance (Z))Ohms LawE = I * Z

HarmonicsLinearNon - LinearLinear vs. Non Linear Loads

Harmonic DistortionDistorted Voltage Waveform - Voltage Drop at the Third Harmonic

HarmonicsImplications of Individual Harmonics & Effects on Power System Need to further refine understanding of individual waveforms that make up the overall waveshape, and how they combine.

Harmonic DistortionFundamental Minus Third Harmonic

Harmonic DistortionFundamental Minus Third Harmonic

Harmonic DistortionDistorted Voltage Waveform - Voltage Drop at the Third Harmonic

Drive Harmonics

Drive Harmonics

Harmonic Distortion Fundamental With Voltage Drop at the Fifth and Seventh Harmonic

Harmonic RotationFundamental

Harmonic RotationThird Harmonic

Harmonic RotationThird Harmonic

Harmonic RotationFifth Harmonic

Harmonic RotationFundamental PositiveSecond NegativeThird ZeroFourth PositiveFifth NegativeSixth ZeroSeventh PositiveEighth NegativeNinth ZeroTenth PositiveEleventh NegativeTwelfth ZeroThirteenth PositiveFourteenth NegativeFifteenth Zero

ConsequencesMotorsReverse TorqueOverheating Shortened lifeTransformersIncreased LossesOverheatingShortened lifeCapacitorsIncreased CurrentOverheatingShortened lifePlant ElectronicsMisoperationFailureDowntime

Distortion LevelsIEEE 519-1992All Harmonics - Voltage (THD) <5% (<10%)

Distortion LevelsCurrent Distortion

HarmonicsReviewHarmonics are a way to describe the result of non-linear loads on the power systemBasic Limit of 5% (10%) for Voltage DistortionCurrent Distortion Limit Depends on System, Currently under review

Power QualitySection III Harmonic Control

Source IssuesSo Far - Only Load IssuesSource Impedance has been assumed to be constant/linear

Source IssuesLook at the Source of our loadsDetermine it’s characteristicsHow these characteristics impact the Distortion EquationHow we can affect the characteristicsFilteringCapacitors/Ratings/Issues

Source IssuesSource Impedance Graph - Transformer Impedance only

Source IssuesThevenin Equivalent CircuitXT

Source IssuesNorton Equivalent CircuitXT

Source IssuesNorton Equivalent CircuitXTXC

Source IssuesNorton Equivalent CircuitXTXC

Source IssuesNorton Equivalent CircuitZS

Source IssuesNorton Equivalent CircuitZS

Source IssuesNorton Equivalent CircuitXL

Source IssuesNorton Equivalent CircuitXTXLXCZS

Tuning With CapacitorsCapacitor TolerancesIn harmonic rich environments, capacitors for the low impedance path to source currentIn filter applications, capacitors also must tolerate higher voltages

Tuning With CapacitorsCapacitor TolerancesUnited States: IEEE 18-1992CapabilityLine to Neutral 110% ContinuousLine to Line 120% ContinuousCurrent 180% ContinuousVar Output 135% ContinuousEurope: CE Standards call for 8 hour period

Tuning With CapacitorsRemember that these standards are Recommendations, not Code, and can therefore be ignored by manufacturers

Tuning With CapacitorsCapacitors - Two typesDry - usually polyester film dielectricOil Filled - oil impregnated kraft paper dielectric

Tuning With CapacitorsDry Type CapacitorsPros Inexpensivelightweightenvironmentally friendly

Tuning With CapacitorsDry Type CapacitorsConsDo not meet IEEE 18-1992 standardsShort life in industrial applicationsPoor Thermal CharacteristicsShort Life Cycle: 30,000 to 80,000 Hours Within Ratings, Less Under Harsh Circumstances.Require frequent replacement (3 to 9 years)

Tuning With CapacitorsOil Filled CapacitorsPros:Meet or exceed IEEE 18-1992 StandardExcellent Thermal CharacteristicsCompetent in harsh environmentsExtremely long life - Typically 200,000 Hours > 20 years

Tuning With CapacitorsOil Filled CapacitorsConsEnvironmental issuesHave approximately 8 oz fluid per cell (50 to 100 kvar)

Adding Reactors to DrivesDrives are a non-linear impedanceAdding a reactor adds impedance to source at harmonic frequencies to diminish harmonic current

Drive HarmonicsChoke increases impedance to Drive

Adding Reactors to DrivesStrategy reduces harmonic current, and voltage drop through the supplyCan increase distortion to the driveCan ultimately cause drive not to function

Source IssuesPower System is Basically InductiveAdding capacitance creates tuned systemCareful tuning of capacitors can benefit systemTuning capacitors requires more robust capacitors

Power QualitySection IV Transient Voltage

Power System TransientsDefine TransientsIdentify Types/Categories of TransientsTypes of Problems Associated with TransientsStrategies for Accommodating TransientsGroundingTVSS

Power System TransientsBy definition, any voltage variation that is temporary. Type I or Type II on CBEMA

Power System TransientsITECANSICBEMA

Sources of TransientsLightningOn Supply ConductorsGrounded entrancesSwitching CapacitorsMotor Starting/StoppingXFMR SwitchingFaultsSystem switchingMechanical Load ChangesSCR Operation (Notching)Drive StartupWeldingOthers

Consequences of TransientsEquipment FailureEquipment MalfunctionEquipment Degradation (ultimately lead to failure)Blown Supply FuseDegradation to TVSS (Transient Voltage Surge Suppressor) Devices

Power System TransientsDivided into Two Categories (Noise)Common Mode - Noise that is common to the phase conductors. Cannot be measured line to line, only phase to ground. Often comes in on the GroundNormal Mode - Not balanced on all three phases, may be measured phase to phase or phase to ground.

Power System TransientsCan be further broken down into:Transient OvervoltageTVSSGroundingTransient UndervoltageSystem Design

Coping with TransientsProperly designed system minimizes transients Source With Sufficient Capacity Proper GroundingProperly designed system minimizes problems associated with transientsHarmonic Resonance IssuesInstallation of TVSS devices

System DesignVoltage Drop through system is within NEC (<5%)Voltage Drop during motor starts is within IEEE20 % at motor terminals10% at adjacent electronic devicesProper protective device coordination

System Design (cont.)Switched transformer feeders sized properlyWelding sufficiently isolated System Properly Grounded Often the underestimated and overlooked portion of the system

System GroundingBuilding Systems - FIPS Pub 94Consider Building as an “envelope”should have a contiguous grounding systemAll metallic supplies into or out of that envelope should be bonded to the building ground. Building Ground Bonded at Electric Entrance

System Grounding

Grounding RingEncircles BuildingIEEE Recommended for “Data Centers” 20 years ago, we wouldn’t have considered putting a IBM VM 370 in a plant environment, but today we think nothing of it.30 inches deep, 2 foot out from footer, bonded to building steel at intervals, ground rods.Bonds all incoming and outgoing equipment

Metallic SuppliesGas LinesWater LinesFire Protection LinesTelephone LinesSanitary linesStorm Drains Power Lines Parking lot lightingTruck ScalesData LinesBuilding Sub-Feeds

Ground RingResults:All equipment referenced to a common groundGround borne transient is effectively distributed throughout system simultaneouslyPlant equipment not subjected to overvoltageEffective with Most Common Mode Noise Problems

Surge SuppressionOften we think of LightningShould consider all sources of Transient Over Voltages, including:Motor SwitchingCapacitor SwitchingWeldingX-Ray EquipmentSometimes Suppression will not prevent drive nuisance trips

Surge SuppressionDrive trips on overcurrentCurrent to drive: C x dV/dt Examine the dV/dt

Surge SuppressionNFC 780 Mean Days of Thunderstorm ActivityLightning

Surge SuppressorsANSI 62.4 - 1991 Attempted to establish standards for the industryCategory C 20 kV 50 µs 20 kA 20 µsCategory B 6 kV 50 µs 3 kA 20 µs 6 kV, 500 A, 100kHz Ring WaveCategory A 6 kV, 200 A, 100kHz Ring Wave

Surge SuppressorsManufacturers literature attempts to sell productOften designed to, Differentiate, and CloudUL 1449 approved!! (UL Listed)Response Time < 2 ns (in circuit 20 - 50 ns)Current Capacity 250,000 Amps (ANSI Cat C - 20 kAmps for 20 µs)“Level I, Level II, and Level III protection (ANSI - Category C, B, and A)Category A, B, and C by ANSI, Category D, and E by “us.”Lightning - Approximately 30,000 amps

Surge SuppressorsDevice typesArc Gap devices - Usually Medium Voltage, or for Communication TowersGas tubes - Used widely in communication industryMOV’s - Metal Oxide VaristorsSADS’s - Silicon Avalanche Diode SuppressorHybrids

Surge SuppressorsDevice Response Clamping Capacity Cost TimeGas tubes µs’s 400-900 Volts High LowMOV 35 ns 500-600 Volts High LowSADS 5 ns < 300 Volts Low High

Surge SuppressorsSummary Gas Tubes - Low cost, slower than MOV’s MOV’s - Low cost, high clamping voltage, high capacity : Good for heavy duty application SADS’s - High cost, excellent clamping, low capacity: Good in network products, reserve for specialized applications

Surge SuppressorsConfiguration IssuesBeware of ground sinking devices in the plantCommon Mode / Normal Mode devicesModular v.s. Line to Line ClampingUse Fused Disconnects ahead of SuppressorsEnd of line devicesUse arrestors on Medium VoltageParticularly on end of line and next to end of line devices

Surge SuppressorsUL 1449 is for UL Listing of SuppressorsANSI 62.4 - 1991 Set Standards for Suppressor CapabilityCategory C - Main Entrance, Large SubpanelCategory B - Large Subpanel, Small PanelCategory A - Terminal Device

Surge Suppressors - DesignUse Arrestors on Medium Voltage - Good first “knockdown” device.MOV Devices - Good fundamental equipmentSADS Devices - Use on sensitive electronics where loss costs are high

Surge Suppressors - DesignPerhaps more important than technologyevery foot of lead adds 100 to 300 volts to clamping levellead length is 1/3 the distance from the connection point to protected load (or cascaded protector), minimum three to six feet from protected loadUse fused disconnect or dedicated circuit breaker

Surge Suppressors - DesignCascading - Example (120 V Suppressors) with 6 x 20 Wave1st Stage - 512 Volts - 100 Amps2nd Stage - 286 Volts - 6 Amps3rd Stage - 284 Volts - < 1 ampShort Duration Only - Shunt trip for long duration

Surge SuppressorsSummaryGrounding First Be wary of “Specmanship”i.e. 600,000 Amps (can’t be tested; maximum ever measured in field was 30,000 amps)Design often more important than technology.

SummaryDefined Power QualityMagnitude (Steady State)Waveshape (harmonics, System Impedance, Capacitor Issues)Transients (Sources, Strategies, Issues)GroundingSurge Suppression Devices

Power QualityIDC Engineering, Inc.2633 Adgate Rd.Lima, Ohio 45805P - (419) 999-4705F - (419) 991-0404jvandyne@idcengr.comwww.idcengr.com