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Power Quality Monitoring

R Venkatesh

Crompton 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?


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Why Monitor?


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

Cost

Quantity

Cost

Quantity

Quality

Increasing cost of poor PQ

Awareness of poor PQ

Standards & Regulations

Increased sensitivity of equipment

Energy conservation & SD


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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


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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!?


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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


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Benefits of Reactive Power Compensation

Reduction in currents

Reduction in losses - energy savings

Reduction in demand - Reduction in demandcharges

Release of blocked capacity - better utilization

Better voltage stability margins

Improvement in power factor - avoided penalty /incentive


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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


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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)


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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 quality

problems as to plan system improvements and also to track

performance indices.


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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


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Power Quality Monitoring-Industrial

Energy & demand profiling

Harmonic evaluation

Voltage sag & ride through conditions Power factor correction

Transient & Switching problems

Unbalance conditions


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Power Quality Monitoring-PS

Equipment performance trends

Switching transients

Performance indices monitoring & Benchmarking

Equipment loading & loss of life

Feeder load monitoring & projections


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What to monitor?


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Power Quality

Power = Voltage x Current

S = V x I

Power Quality = Voltage Quality x Current Quality


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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


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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


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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


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Good voltage quality at the customer bus is the

utilitys responsibility

Good quality for load current drawn from the bus inthe customers 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!)


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0

0

Harmonics Transients

InterruptionsSag

Manifestations of Poor Power Quality


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Power Quality definition

For utility, PQ = reliability and continuity.

For manufacturer, PQ = no rejection of product on accountof 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 ofcustomer equipment.

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


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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


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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


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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


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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


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What are the limits?


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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 customers load

performs properly.

PQ - Requirements


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Types Norms

Standards & Guidelines

Statutory requirements

Utility regulations


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Standards & Guidelines

System Disturbances Deviation from clean voltage

consideration for current drawn

Harmonics For systems

For equipment

Grounding Impact of transients & safety


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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 forunbalance voltage conditions max. unbalance of 3% on no load

Motors to operate at 1% unbalance

Flicker curves - IEEE standard 519-1992


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IEEE draft 1250 on momentary disturbances& guidance for mitigation. No limitsprescribed

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

CBEMA curves

ITIC curves


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Alternative pow er acc eptabili ty curves

C urve Y ear A pplication S ource

FIPS power acceptabil i ty

1978 A utom atic dataprocessing(ADP) equipment

U.S . federalgovernment

C B E M Acurve

1978 C om puter businessequipment

Com puter businessequipmentmanufacturers

associat ionIT IC curve 1996 Inform ation

technologyequipment

Informationtechno logy indus trycounci l

Fa ilure ratecurves forindustrial

loads

1972 Industrial loads IEEE standard 493

A C linevoltagetolerances

1974 M ain fram ecomputers

IEEE standard 446

IEEEEmeraldBook

1992 S ensitiveelectronicequipment

IEEE standard 1100


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Transient over voltage protection of LV

equipment - ANSI/IEEE C62

Recommended practice on surge voltages inLV AC power systems - ANSI/IEEE C62.41

Guide on surge testing for equipment

connected to LV AC power circuits -

ANSI/IEEE C62.45-1987


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IEC - 1000-3-3: Limitation of voltage fluctuationsand flicker in LV supply systems for equipment withrated current < 16A

IEC - 1000-3-5: Limitation of voltage fluctuationsand flicker in LV supply systems for equipment withrated current > 16A

IEC - 1000-3-7: Limitation of voltage fluctuations

and flicker for equipments connected to medium andhigh voltage power supply systems


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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%


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

CBIP recommendations THD = 3%, individual = 1%

No utility norms

CIGRE norms for Voltage distortion


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ANSI / IEEE standard 18 gives limitations forcapacitor 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 transformercapacity when current distortion exceeds 5%

National Electric code gives recommended practicefor sizing of neutral conductors

ANSI C82.1 gives the max. THD ofr HF FL ballast as32%


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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


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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 5

20 - 50 7.0 3.5 2.5 1.0 0.5 8

50 - 100 10 4.5 4.0 1.5 0.7 12

100 - 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).


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Standards for grounding

Grounding implications

Safety of operating personal

Safety of equipment Reduce damage due to transients

Provide signal reference


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Standards for grounding

ANSI / NEPA 70 - 1993: Grounding ofneutral 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 ofsensitive electronic equipment


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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)


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Utility Regulations

Most powerful Pricing as a tool to achieve objectives

Types Monetary Non-monetary

Class

Applicable to Utilities Applicable to customers


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Types of Utility Regulations

Monetary Maximum demand charges

Contract demand Power factor surcharge

Harmonic metering

Non-monetary Grounding requirements

Protection requirements


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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


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Example of monetary regulation

Power factor surcharge

APSEB:

1% of energy bill for ever 0.01 below0.9 + 1.5 5 for every 0.01 below 0.85 +2% for every 0.01 below 0.8 + 3% forever 0.01 below 0.75

TNEB: Re. 1.0 for every kVARh consumed in

windfarms


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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


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When to monitor?


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Before installation of plant / Equipment

Before expansion

After problem occurrence / suspect Annually / Periodically

Formulation of guidelines

Continuously

When


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Where to monitor?


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Close to sensitive /critical equipment

Close to source

PCC / metering point

Major Nodes / Branches

Where


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Examples of Loads


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Harmonics in Power Systems


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Sample Single Line Diagram


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Sample Single Line Diagram


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How to monitor?


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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


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Snap shot

Full cycle

Continuous

How-II


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Who should monitor?


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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


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What to do with data?


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Collection of raw data

Compilation of data

Analysis of data

Trending

Limit analysis

Correlation

Advanced AI systems

Diagnosis, Recommendations & Actions

Data Analysis


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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


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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, RVenkatesh & 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


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Thank You

Dr. R Venkatesh

Crompton Greaves Ltd.Email: [email protected]

mailto:[email protected]://www.pdffactory.com/http://www.pdffactory.com/mailto:[email protected]

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