Power Quality Monitoring - IITKhome.iitk.ac.in/~spdas/rvenk1.pdf · Power Quality Monitoring R Venkatesh Crompton Greaves Ltd. PDF created with pdfFactory trial version : David G

Power Quality Monitoring

R VenkateshCrompton Greaves Ltd.

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Power Quality Monitoring

• Why monitor?• What to monitor?• What are the limits?• When to monitor?• Where to monitor?• How to monitor?• Who should monitor?• What to do with data?



Why Monitor?



The Transition & Drivers• From 2D power to 3D power

Cost

Quantity

Cost

QuantityQuality

•Increasing cost of poor PQ •Awareness of poor PQ •Standards & Regulations•Increased sensitivity of equipment•Energy conservation & SD



Implications of Poor Power Quality

• Increased currents & losses in the system

• Lower Energy efficiency

• Blocked capacity / Higher Investment

• Additional heating and lower reliability / life

• Failure of equipment

• Mal-function of equipment

• Poor operational efficiency

• Poor quality of products manufactured



Implications of Reactive Power

• Increase in currents• Increase in T & D and equipment loss• Blocked capacity• Reduction in voltage stability margins• Over heating and loss of life of equipment• Resonance!?



Implications of Harmonics

• Increase in currents• Increase in T & D and equipment loss• Blocked capacity / higher investment• Over heating and loss of life of equipment• Resonance!?• Equipment Failure /mal-function• Poor Quality of production



Benefits of Reactive Power Compensation

• Reduction in currents• Reduction in losses - energy savings• Reduction in demand - Reduction in demand

charges• Release of blocked capacity - better utilization • Better voltage stability margins• Improvement in power factor - avoided penalty /

incentive



Benefits of Harmonic Filtering

lReduced currents - sizing, capacity - released & deferred

lLower losses in lines & equipment (Copper, core & stray)

lReduced demand

lElimination of failure & mal function

lCompliance to standards

lBetter quality production

lHigher operational efficiency



Benefits of power quality Improvement• Direct Benefits / Technical Benefits

– Energy Savings– Release of blocked capacity– Reduced temperature rise– Increased reliability / Life of equipment (e.g. Transformer,

Motors, electronics, capacitors...)– Reduced mal-function of equipment (e.g. Drives, Relays,

Meters)

• Indirect / Regulatory Benefits– Penalty savings / Incentives (e.g. Demand charges, pf penalty)– Tax benefits– Compliance to standards & Regulations (e.g. IEEE 519)



A basic requisite for costing (quantification) of poor power quality and also for the formulation of proper standards, guidelines & regulations is the measurement of power quality and the availability of power quality data. PQ variations such as momentary interruptions, voltage sags, switching transients and harmonic distortion can impact customeroperations, causing equipment damage and significant costs in lost production and down time. Electric utilities must be able to characterize and assess the system performance at all levels of the system. Especially in a deregulated environment it is very important to assess the system performance and identify the sources of power qualityproblems as to plan system improvements and also to track performance indices.



Power Quality Monitoring-Benefits• Understanding PQ and reliability • Prioritizing system improvements• Identifying problem conditions• Information services• Enhanced quality of delivery• Formulation of Regulations• Formulation of Standards



Power Quality Monitoring-Industrial

• Energy & demand profiling• Harmonic evaluation• Voltage sag & ride through conditions• Power factor correction • Transient & Switching problems• Unbalance conditions



Power Quality Monitoring-PS

• Equipment performance trends• Switching transients• Performance indices monitoring & Benchmarking• Equipment loading & loss of life• Feeder load monitoring & projections



What to monitor?



Power Quality

Power = Voltage x Current

S = V x I

Power Quality = Voltage Quality x Current Quality



PQ Aspects• Voltage - shape & magnitude

– Steady state limits– Frequency– Distortion - Frequency content– Sags & Swells– Transients– Unbalance - Phase and magnitude

• Current- shape & magnitude– Magnitude– Distortion - frequency content– Phase angle– Transients– Unbalance



Common Manifestations of Power quality

• Reactive power - Low power factor• Harmonics - current & voltage distortions• Frequency limits - under & over frequencies• Steady state voltage limits - under & over voltages• Transients• Sags & Swells• Unbalance• Sequence components• Black outs & Brown outs• Flicker• Neutral shifts



Symptoms of Harmonics

• Nuisance tripping / operation of switchgear / fusegear• PF improvement not commensurate with capacitor addition• Premature / frequent failure of equipment • Mal function of equipment• Overheating of cables, equipment• Neutral burn outs• Excess energy consumption• Low power factor• Memory loss in electronic equipment• Poor Product quality• Audible noise in cables, busbars, transformers• Difficulty in installing compensation systems



•“Good” voltage quality at the customer bus is the utility’s responsibility•Good quality for load current drawn from the bus in the customer’s responsibility.•Current quality affects voltage quality & vice-versa

-1

-0.5

0

0.5

1

0 180 360

Pure Sine Wave Voltage (Available Only in Textbook!)



0

0

Harmonics Transients

InterruptionsSag

Manifestations of Poor Power Quality



Power Quality definition• For utility, PQ = reliability and continuity.• For manufacturer, PQ = no rejection of product on account

of poor quality - High operational efficiency• for-end-user of equipment, PQ = proper functioning of

equipment.

• Formal definition of PQ:• PQ problem = any power problem manifested in V,I or

frequency deviations that result in failure/mal-operation of customer equipment.

• IEEE: PQ= the concept of powering equipment in a manner that is suitable to the operation of that equipment.



• For Steady State Phenomena– Amplitude

– Frequency, Spectrum & Modulation

– Source impedance

– Notch depth & Notch area

• For non-steady state phenomena– Rae of rise

– Amplitude

– Duration

– Frequency, spectrum

– Rate of occurrence

– Energy potentia

Terms & Definitions



• Transients – Impulsive & oscillatory

• Long duration voltage variations – OV, UV, Sustained interruption

• Short duration voltage variations – Interruption, sags, swells

• Voltage imbalance

• Waveform distortion-DC offset, Harmonics, inter-harmonics, notching, noise

• Voltage fluctuation

• Power frequency variations

Terms & Definitions



• SAIFI=System average interruption frequency index

• SAIDI= System average interruption duration index

• CAIFI= Customer average interruption frequency index

• CAIDI = Customer average interruption duration index

• ASAI =Average system availability Index

• THD

Reliability Indices



• Nature of problem

• Characteristics of sensitive equipment

• History

• Coincident problems

• Possible sources

• Existing power conditioning devices, sources & loads

• System data & electrical diagram

• Implications and benefits of improvement

Site Survey



What are the limits?



• Power quality is driven by customer satisfaction /

requirements.

• What is “ good enough” quality for an arc furnace load

is not enough for a machine with ASD.

• What is “good enough” for ASD machine is not

enough for a computer center.

• Power quality is “good” if the customer’s load

performs properly.

PQ - Requirements



Types Norms

• Standards & Guidelines• Statutory requirements• Utility regulations



Standards & Guidelines• System Disturbances

– Deviation from “clean voltage”– consideration for current drawn

• Harmonics– For systems– For equipment

• Grounding– Impact of transients & safety



Standards for system disturbances

• Steady State voltage limits in ANSI C84.1– +/- 5% nominal & +5.8% to -8.3% short time

• NEMA MG-1-1987 for motor de-rating for unbalance voltage conditions– max. unbalance of 3% on no load– Motors to operate at 1% unbalance

• Flicker curves - IEEE standard 519-1992




• IEEE draft 1250 on momentary disturbances & guidance for mitigation. No limits prescribed

• ANSI C84.1 - temporary under voltages at f0• ANSI/IEEE standard 446-1987.(orange book)• CBEMA curves• ITIC curves



Standards for system disturbances Alternative pow er acceptability curves

C urve Y ear A pplication S ourceF IPS poweracceptability

1978 A utom atic da taprocess ing(A DP ) equ ipm ent

U .S . federalgovernm ent

C BE M Acurve

1978 C om puterbusinessequipm ent

C om puter businessequipm entm anufacturersassocia tion

IT IC curve 1996 In form ationtechno logyequipm ent

In fo rm ationtechno logy indus trycouncil

Failu re ratecurves forindus tria lloads

1972 Industrial loads IEEE standard 493

A C linevo ltageto lerances

1974 M ain fram ecom puters

IEEE standard 446

IEEEEm eraldB ook

1992 S ens itiveelec tronicequipm ent

IEEE standard 1100




• Transient over voltage protection of LV equipment - ANSI/IEEE C62

• Recommended practice on surge voltages in LV AC power systems - ANSI/IEEE C62.41

• Guide on surge testing for equipment connected to LV AC power circuits -ANSI/IEEE C62.45-1987




• IEC - 1000-3-3: Limitation of voltage fluctuations and flicker in LV supply systems for equipment with rated current < 16A

• IEC - 1000-3-5: Limitation of voltage fluctuations and flicker in LV supply systems for equipment with rated current > 16A

• IEC - 1000-3-7: Limitation of voltage fluctuations and flicker for equipments connected to medium and high voltage power supply systems



Standards for Harmonics

• IEEE standard 519 - 1981– VS < 69 kV, THD < 5%– Lower limits of THD for higher system voltages– IEEE 519 revised in 1992

• 5% limit remains• limits for current distortion at PCC• Limits for current THD ranges from 2.5 - 20%




• Countries where limits are specified– Australia, France, Sweden, UK & USA

• CBIP recommendations– THD = 3%, individual = 1%

• No utility norms• CIGRE norms for Voltage distortion




• ANSI / IEEE standard 18 gives limitations for capacitor banks

• ANSI / IEEE C57.12.00 gives limits for current distortion for transformers at full load (5%)

• ANSI / IEEE standard C57110 gives the recommended practice for establishing transformer capacity when current distortion exceeds 5%

• National Electric code gives recommended practice for sizing of neutral conductors

• ANSI C82.1 gives the max. THD ofr HF FL ballast as 32%



IEEE 519 [5] - Voltage Distortion Limits

Bus Voltage Individual Vh (%) THDV (%)

V < 69 kV 3.0 5.0

69 ≤ V < 161 kV 1.5 2.5

V ≥ 161 kV 1.0 1.5

IEEE Standard for Voltage Harmonics



IEEE Standard for Current HarmonicsIEEE 519 [5]l General Distribution Systems (120V - 69 kV)Isc / IL h < 11 11 ≤ h < 17 17 ≤ h < 23 23 ≤ h < 35 h ≥ 35 TDD (%)-----------------------------------------------------------------------------------------------------< 20 4.0 2.0 1.5 0.6 0.3 520 - 50 7.0 3.5 2.5 1.0 0.5 850 - 100 10 4.5 4.0 1.5 0.7 12100 - 1000 12 5.5 5.0 2.0 1.0 15> 1000 15 7.0 6.0 2.5 1.4 20

l General Transmission Systems ( > 161 kV)Isc / IL h < 11 11 ≤ h < 17 17 ≤ h < 23 23 ≤ h < 35 h ≥ 35 TDD (%)-----------------------------------------------------------------------------------------------------< 50 2.0 1.0 0.75 0.3 0.15 2.5≥ 50 3.0 1.5 1.15 0.45 0.22 3.75

l General Sub-transmission Systems (69 kV - 161 kV)Limits are half those for general distribution systems.

Above current distortion limits are for odd harmonics.Even harmonics are limited to 25% of the odd harmonics limits.For all power generation equipment, distortion limits are those with Isc / IL < 20.Isc is the maximum short circuit current at the point of common coupling “PCC”.IL is the maximum fundamental frequency 15- or 30-minute load current at PCC.TDD is the Total Demand Distortion (= THD normalised by IL).



Standards for grounding

• Grounding implications– Safety of operating personal– Safety of equipment– Reduce damage due to transients– Provide signal reference



Standards for grounding

• ANSI / NEPA 70 - 1993: Grounding of neutral conductors (single point)

• Segregation of neutral & ground conductors for sensitive & other loads

• Running of power & control cables• Use of ground wires and conduit returns• IEEE 1100-1992 (Emerald Book) gives

recommended practice for grounding of sensitive electronic equipment



Statutory Requirements • Graduated standards• Compliance requirements based on

equipment, application and country• Statutory requirements - e.g.

– CE– VDE– FCC– IEC 1000 limits (EN EMC directive)



Utility Regulations • Most powerful• Pricing as a tool to achieve objectives• Types

– Monetary– Non-monetary

• Class– Applicable to Utilities– Applicable to customers



Types of Utility Regulations

• Monetary– Maximum demand charges– Contract demand– Power factor surcharge– Harmonic metering

• Non-monetary– Grounding requirements– Protection requirements



Utility Regulations

• Tariff & Non Tariff • Tariff as a tool for PQ improvement• In appropriate & Obsolete

– Tariff related• Cost of reactive power

– Non tariff related• Cable sizing

• Should be contextual and also futuristic



Example of monetary regulation

• Power factor surcharge• APSEB:

• 1% of energy bill for ever 0.01 below 0.9 + 1.5 5 for every 0.01 below 0.85 + 2% for every 0.01 below 0.8 + 3% for ever 0.01 below 0.75

• TNEB:• Re. 1.0 for every kVARh consumed in

windfarms



Classes of Utility Regulations • Applicable to utilities

– Voltage & limits– Frequency & limits– Unbalance & limits– Distortion limits (voltage distortion)

• Applicable to – Nature of current drawn (harmonics)– magnitude & phase angle of current drawn– Safety & compliance norms



When to monitor?



• Before installation of plant / Equipment

• Before expansion

• After problem occurrence / suspect

• Annually / Periodically

• Formulation of guidelines

• Continuously

When



Where to monitor?



• Close to sensitive /critical equipment

• Close to source

• PCC / metering point

• Major Nodes / Branches

Where



Examples of Loads



Harmonics in Power Systems



Sample Single Line Diagram



Sample Single Line Diagram



How to monitor?



• Level– Basic monitors

• DSO, multimeter, demand meters

– Dedicated monitors • Harmonic analyzer, flicker meter, event/disturbance recorders,

impedance analysers

– Advanced monitors

• Mode– Stand alone

– Integrated

– Continuous

How-I



• Snap shot

• Full cycle

• Continuous

How-II



Who should monitor?



• Supplier of power– Contractual obligations

– System performance monitoring & improvement

• Consumer– Improvement measures

– Compliance

– Monitor performance, new installations

• Regulator– To ensure compliance

– To formulate standards

• Manufacturer– Performance guarantee

– Design & Development

Who



What to do with data?



• Collection of raw data

• Compilation of data

• Analysis of data– Trending

– Limit analysis

– Correlation

– Advanced AI systems

– Diagnosis, Recommendations & Actions

Data Analysis



• Monitoring PQ is important

• Data collection should be systematic

• Data analysis is important

• PQ monitoring equipments are available

• PQ Audit should be made mandatory for specific customers

To summarize



References• Trends in power quality monitoring, Mark McGranaghan,

IEEE power engineering review, October 2001.• Understanding power quality problems – voltage sags &

interruptions, Math H J Bollen, IEEE press. • An integrated approach to power quality improvement, R

Venkatesh & S R Kannan, - ET power tech 2001.• Solutions to the power quality problem, Prof. Ray Arnold,

IEE power engineering journal, April 2001• Power quality issues a distribution company perspective,

IEE power engineering journal, April 2001• Monitoring power for the future, Afroz K. Khan, IEE

power engineering journal, April 2001



Thank You

Dr. R VenkateshCrompton Greaves Ltd.

Email: [email protected]


mailto:[email protected]




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Power Quality Monitoring - IITKhome.iitk.ac.in/~spdas/rvenk1.pdf · Power Quality Monitoring R Venkatesh Crompton Greaves Ltd. PDF created with pdfFactory trial version : David G