Business SolutionsData Centre's, Server Room's, Managed Services & Cloud

31NOVEMBER 2012

Power QualityMeasurement Guide1. Why Do We Measure Power Quality?Why Measure Power Quality?

Power Quality (PQ) is a huge concern because of the increasein usage of non-linear loads, mainly power electronic devicessuch as variable speed drives & UPS, critical power distributionmethods, and an increase in decentralized power supply fromgreen energy sources such as wind and photo-voltaic.

Poor PQ causes trouble in receptacle/transmission equipmentand causes malfunction in electrical & electronic equipment.

For example, harmonics are known to burn-out reactors andcause overload and damages to PFC capacitors. Also, impulsenoise and voltage drops, can stop control systems that aredependent on computerised systems.

Power supply network problems, caused by poor PQ is acommon problem for both electric utility suppliers and end users.However, it is not easy to identify whether the cause of poor PQis at the supplier’s system or the end user’s system.

Based on this situation, effective PQ measurement torecognized international standards, is necessary to understandthe actual cause of PQ problems as well as to consider andanalyze for effective countermeasures.

The GridVis® Software package from Janitza, offers PQmonitoring, analysis & reporting with detailed & comprehensiveoverviews of all levels of an enterprise, both local and global.

2. IEC61000-4-30What is the standard IEC61000-4-30?IEC61000-4-30 is the international standard stipulating how PQ

should be measured,with modern PQMonitoring devices,both in measurementand accuracy, andmeasuringinstruments such asthe UMG511 fromJanitza, are certified,in compliance withIEC610004-30 andgive reliable andrepeatablemeasurement resultsregardless of the PQproblem.

The measurementsincluded in thisIEC61000-4-30

standard include all kinds of PQ parameters and phenomenaspreading in the electrical system, which are the frequency,supply voltage amplitude (RMS value), flicker,dip/swell/interruption of supply voltage, transient overvoltage,supply voltage unbalance, harmonics, inter-harmonics, signallingon supply voltage, and rapid voltage fluctuation.

IEC61000-4-30 classifies the measurement methods andcapabilities of measuring instruments into 3 classes; A, S, and B.The most reliable PQ measurement can be made by Class A

instruments, such as the UMG511.Class A measurement is used when precise measurements are

necessary, for example, for contractual applications that mayrequire resolving disputes and verifying compliance withstandards etc. The detailed measurement methods andtechniques are defined by the standard, such as the time-clockaccuracy, method of RMS value calculation and data processing.Time accuracy is critical, as it means, two class A devices performthe same result and measurement (in line with the definedaccuracy in the standard) at the same point in time, and aretherefore comparable.

3. Power Quality Survey ProceduresTips to help Identify the Cause of PQ Problems1.Record the trend of voltage and current at your Power

Incomer!If the voltage dropssimultaneously,with the increase ofcurrent consump-tion in a building,the cause isconsidered to beinside the building.On the other hand,if both the voltageand current dropsimultaneously, thecause is attributedto equipment oreither an electricalanomaly outsidethe building. It isimportant to determine where to measure as well as tomeasure the current accurately.

2.Check the power trendEquipment in overload condition is often the cause of trouble.By knowing the power trend, itis much easier to identify the precise equipment or locationthat is causing the problems.

3.Check WHEN the event occurred!By accurately identifying what time the event (e.g. voltage sag)occurred and when the problem subsided, it can be easier todetermine which equipment or location could have caused theproblem.e.g. In case a voltage sag and simultaneously a current risecomes every morning while production is starting, it may be awork process problem, such as a large compressor.

4.Check for excess heat in equipment!Overheating of servers, motors, transformer and cables are keysigns that there are problems due to overload or harmonics.

Power Quality Parameters and EventsTypes of PQ OccurrenceThe PQ occurrences outlined below, are the key requirements forsurveying or analyzing power trouble. By measurement of the

HELPFUL TIPS FOR MEASUREMENT

GridVis® Power Quality & EnergyManagement Software

UMG511 Power Quality Analyzer (Class Adevice)

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Business SolutionsData Centre's, Server Room's, Managed Services & Cloud

32NOVEMBER 2012

these PQ problems, you can gain a thorough understanding ofthe PQ status for your site.

Threshold values for these occurrences are set within the PQanalyzer, UMG511 todetect the “faultvalue” or “faultwaveform” for thepower qualityparameters. Then,the UMG511identifies an “event”when the inputexceeds thethresholds.

FrequencyFluctuationsThis occurs due to achange of effective

power balance between supply and consumption, or an excessiveincrease or decrease of the load. Varying rotation speeds ofsynchronous generators, the most common type of generatorused in utility power systems, may be the cause of frequencyfluctuations.

Voltage Swells (Surges)This is the instantaneous voltage increase caused by events, suchas lightning strikes, opening or closing of a power supply circuit,high capacitor bank switching, ground (earth) fault, or switchingoff a heavy load.

It may also occur due to the grid connection of a new energysource (wind, photo-voltaic, etc.). A sudden increase in voltagemay damage or reset the power supply of equipment.

Transient Overvoltage (Impulse)This is the voltage changes, caused by events such as lightningstrikes, contact problems and closing of a circuit breaker /contactors etc. It is often a rapid change and consists of highpeak voltage. Damage to equipment’s power supply or resetfunction often occurs nearer the generation point due to the highvoltage. Insulation damage due to high dV/dt levels are theconsequence in many cases, especially if transients are of arepeating nature.

FlickerFlicker is a periodically repeated voltage fluctuation caused by afurnaces, arc welding or a thyristor controlled load. It may causelights to flicker and IT equipment to malfunction. When theflicker value is high, most people working within an officeenvironment feel uncomfortable (head ache) because of theflickering lights.

Voltage Dips (Sags)Most sags are caused by natural phenomena such as thunder andlightning. It is represented by an instantaneous voltage dropcaused by the cutting off of the power supply circuit due to ashort circuit to earth or high inrush current generation whenstarting a large motor, etc.

Due to the voltage drop, it may cause a stop or reset of PLC’s& IT equipment, turn off lighting, speed change or stop ofmotor, and synchronization error of synchronous motors orgenerators.

Interruption (black out)This is a power outage over an instantaneous, short or longperiod. It can be caused by incidents such as lightning strikes ortripping of the circuit breaker due to short-circuit. UPS are nowwidely used to protect PCs, but this type of equipment may alsocause a stop or reset of equipment.

HarmonicsHarmonics are preliminary generated by semi-conductor controldevices in the power supply of equipment as a result of distortedvoltage and current waveforms. When the harmonic componentis big, it may cause serious accidents such as overheating in

motors or transformers and burn out reactors and capacitors inPFC systems.

High-Order Harmonic ComponentThis is a noise component higher than several kHz generated bythe semi-conductor control device in the power supply ofequipment, and may contain various frequency components.High-order harmonic components may damage the powersupply of IT equipment, reset equipment or introduce abnormalnoise into equipment such as PC’s or Servers. A typical source ismodern IGBT converters with switching frequencies of up to20kHz.

Inter-HarmonicsThis is generated by a voltage/current waveform distortioncaused by devices such as electronic frequency converter,inductive motors, welding or arc furnaces, and consists of non-integer orders of the fundamental frequency. Inter-harmonicsmay cause damage, malfunction or deterioration of equipmentdue to the zero-cross shift of the voltage waveform.

UnbalanceUnbalance is generated by the increase or decrease of loadconnected to each phase, partial running equipment,voltage/current waveform distortion, voltage drop, or reversephase voltage, etc. Unbalance may cause revolution faults,overheating, and less torque in a motor. Also, it may cause circuitbreakers to trip, transformers to overheat, or a loss increase in acapacitor smoothing rectification.

Inrush currentThis is an instantaneous high current flowing at the timeequipment is powered/switched on, especially capacitive loadscause very high inrush currents if not damped properly. Inrushcurrent may cause relays to malfunction, circuit breakers to open,impact on the rectifier, unstable power supply voltage, and/orequipment to malfunction or reset.

With an integrated,integral PQmanagement system,you can also centrallymonitor andcompare(benchmark)branches at variousgeographicallocations. Practicallyat the push of abutton, the relevantsoftware can be usedto prepare the various data and create PQ reports with statisticsand tables in a format, for indebt analysis.

End-to-end power quality management systems create networktransparency on the various network levels, which allow theidentification of possible ‘sinners’, uncovering inefficientprocesses and initiation of corresponding PQ efficiency measures.Many PQ efficiency measures can be achieved with low financialinvestment and scalable solutions are the best approach in manycases. And even with real capital investment, a return ofinvestment can often be expected quickly. Case Studies

Article by David Gilligan, Janitza Electronics UK Ltd.

For more information on our PQ Solutions, contact:

GridVis® Software, multiple screen analysis

Voltage sag captured by a UMG poweranalyzer.

Janitza Electronics UK LtdThird Floor, 207 Regent StreetLondon, W1B 3HHTel (UK): +44 78 3311 1985Tel (Ireland): +353 87 982 3103david.gilligan@janitza.comwww.janitza.com

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