Advanced Concepts Power Quality FLUKE [email protected]

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Advanced Power Quality Concepts


Standards

• Primary international standards for power quality

• How they affect our business

• How they influence the market


Cat IV• Outside and

service entrance• Service drop from

pole to building• Run between

meter and panel• Overhead line to detached building

• Underground line to well pump

IEC 61010 safety ratings – CAT {x}


NFPA 70E

Hazard/Risk Category 2: 240 – 600V electrical environments

• FR long sleeved shirt with sleeves rolled down and front fully buttoned up• FR work pants (not denims) or coveralls over natural fiber• 600 V rated leather over rubber gloves• Leather work boots• Switching hood containing hearing protection • No jewelry or watch


IEC 61000-4-30

First Edition February 2003

Testing and measurement techniques

– power quality measurement methods


Scope Of IEC 61000-4-30

• IEC 61000-4-30 defines the methods for measurement and interpretation of results for power quality parameters in 50/60 Hz a.c. power supply systems.

• Measurement of parameters covered by this standard is limited to those phenomena that can be conducted in a power system, including the voltage and/or current parameters, as appropriate.


The Standard Identifies Measured Parameters Relating To Power Quality

• Power frequency• Magnitude of the supply voltage• Flicker• Supply voltage dips and swells• Voltage interruptions• Transient voltages• Supply voltage unbalance• Voltage and current harmonics • Inter-harmonics• Mains signaling on the supply voltage • Rapid voltage changes• Measure of underdeviation and overdeviation


• Class A Performance - where high precision measurements are necessary, for example:• Contractual applications• Compliance with standards• Resolving disputes

• Class B Performance – where less uncertainty is required, for example:• Statistical surveys• Troubleshooting

Two classes of performance


Testing PQ Instrumentation• The standard defines the critical PQ parameters that must be varied to

insure proper measurement performance• For Class A measurements, IEC 61000-4-30 identifies 9 different power

quality parameters of the input signal that can affect measurements due to their variation• Frequency• Voltage Magnitude• Flicker• Unbalance• Harmonics (THD)• Interharmonics• Mains signaling voltage• Transient voltages• Fast Transients

• It also identifies their range of influence• The intention is that a proper measurement is made under realistic

variations of all these parameters• For Class B the number of parameters is reduced to 6


• IEC 61000-4-30 require that the measurements tests are repeated under three different states of overall power quality• 1 state with clean & balanced power quality• 2 other states with differing power quality conditions

(Note for class B measurements, there are no special power states defined.)

Testing PQ Instrumentation


• In addition, all tests in each state are repeated while each influence is individually changed through a range of 5 equally spaced points• For example on the voltage magnitude influence, the test range

is from 0 to 200% of the nominal value. Tests are done at 0%, 50%, 100%, 150% and 200% of the normal input value while all the other influences are held steady

• The Class A test is very thorough – including 3 states, individually testing all 12 types of measurements while individually varying each of 9 parameters over a 5 point range



• Class A required accuracies• Power Frequency - ± 10 mHz• Magnitude of Supply Voltage - .1% of Nominal• Flicker - Per IEC 61000-4-15 • Voltage Dips & Swells - measured to ± 0.2%• Voltage Interruptions - measured within 2 cycles• Supply Voltage Unbalances - ±.15%• Voltage & Current Harmonics and Interharmonics - Per IEC

61000-4-7• Mains signaling voltage – less than 7% of reading

(Note: For Class B, the original manufacturer’s recommendations are used for the instruments tested.)



Flagging

• During a dip, swell, or interruption, the measurement algorithm for other parameters might produce an unreliable value. The flagging concept therefore avoids counting a single event more than once in different parameters and indicates that an aggregated value might be unreliable.

• Flagging is only triggered by dips, swells, and interruptions.

• The flagging concept is applicable for Class A measurement performance .

• If during a given time interval any value is flagged, the aggregated value including that value shall also be flagged.


Mains Signaling

• Mains signaling voltage measurement shall be based on• either the corresponding 10/12-cycle rms value

interharmonic bin;• or the rms of the four nearest 10/12-cycle rms value

interharmonic bins • For example, a 316.67 Hz ripple control signal in a 50 Hz power

system shall be approximated by an r.m.s. of 310 Hz, 315 Hz, 320 Hz and 325 Hz bins, available from the FFT performed on a 10-cycle time interval.

• FFT on 10/12 cycles provides 5Hz resolution

300 Hz 350 Hz

316,67 Hz

325 Hz


EN50160

• Followed primarily in Europe• Adopted in some countries

• Modified in others• Focus is mostly on minimum distribution limits


EN50160

• Specifies the quality of electricity• Intended for Service Entrance Monitoring• Sets limits for:

• Frequency, Voltage Magnitude and variations ,Transients, Rapid voltage changes, Flicker severity, Voltage dips, Voltage Interruptions, Unbalance, Harmonic Voltage, Main signaling

• Concept: You can’t blame the electricity supplier when still having problems.

• Some parameters are assigned a tolerance they must meet 95% of the time, so they can be out of tolerance over 8 hours per week!

• Most measurements are “Averages of Averages” so short variations are smoothed out

• Staying within limits doesn’t guarantee good power quality


Phenomena Parameter Limit Not exceeding probability

Power frequency Mean value over 10 sec +1%/-1%+4% / - 6%

99.5% of a year100% of the time

Supply voltage variations Mean rms over 10 min +10%/-10%+10% / -15%

95% of one week100% of the time

Rapid voltage changes Number of events Short duration and 5%UnShort duration and 10% Un

NormalSeveral time per day

Flicker severity Plt (2hr) ≤ 1 for 95% of one week

Voltage dip Number of events duration < 1 second and < 60% Un 10..1000 events per year> 50% of all dips

Short Interruptions Number of events duration < 1 second and < 1% Un 10..1000 events per year> 70% of all interruptions

Long interruption Number of events with duration >180 secondsand <1% Un

10...50 events per year

Overvoltages (50Hz) Number of events with few sec duration > 110% Un and ≤ 1.5kV

Transient Overvoltages Number of events μsec to msec duration > 1.5kV and < 6kV

Unbalance Uneg/Upos over 10 min <2% 95% of one week

Harmonic voltage Mean rms over 10 minTHD ≤ 8%

See harmonic Limits Table≤ 8%

95% of one week95% of one week

InterHarmonic Under consideration

Mains signaling Mean rms over 3 sec 99% of a day day

EN50160


Upper limits for individual harmonic voltages at the supply terminals in % of nominal voltage. 95% of 10-minute average Vrms over 1 week must be below limits

Odd harmonics Even Harmonics

Not multiples of 3 Multiples of 3

Orderh

Relative voltage Orderh

Relative voltage Orderh

Relative voltage

5 6 % 3 5 % 2 2 %

7 5 % 9 1.5 % 4 1 %

11 3.5 % 15 0.5 % 6…24 0.5 %

13 3 % 21 0.5 %

17 2 %

19 1.5 %

23 1.5 %

25 1.5 %

EN50160 Harmonics


How to Read EN50160

• RMS voltage readings over every 10 cycles (50Hz)• These readings are averaged over non-overlapping 10-minute intervals (50 x 10

cycles avg)• 168 hours x 6 = 1008 average voltages• 95% of the readings (958 readings) must be within 10% of nominal. • No readings may be 10% above or 15% below nominal. • So up to 5% of the readings (50 readings) may be below 207V, but no lower than

195.5V.

95% of the average Vrms samples taken during 1 week must be within this range

Average Vrms must never fall outside this range

Let’s assume we are monitoring voltage magnitude on a 230V system.Over a one week monitoring period we will take:


Lower limit as specified by EN50160

Upper limit as specified by EN50160

Small: Maximum voltage measured relative to upper limit

Red indicates upper limit is exceeded.Example: 100% of the 10 min avg readings should be within +10/-15%. At least one reading exceeded this limit

Plt reading

Number of events–Dips, interruptions, “rapid voltage changes” and swells

Wide: Avg voltage measured relative to lower limit

430 EN50160 graphic

Unbalance and frequency


• Bar Graphs have a wide base indicating adjustable time related limits (for instance 95 % of time within limit) and a narrow top indicating a fixed 100 % limit. If one of both limits is violated, the related bar changes from green to red. Dotted horizontal lines on the display indicate the 100% limit and the adjustable limit.

• The 100 % limit means that the 10-minute averages must always (i.e. 100 % of time or with 100 % probability) be within range. The bar graph will turn to red if a 10-minute average crosses the tolerance range. The adjustable limit of for instance 95 % (i.e. 95 % probability) means that 95 % of the 10-minute averages must be within tolerance. The 95 % limit is less stringent than the 100 % limit.

430 EN50160 graphic


430 EN50160 graphic


Value table


Flicker

“Flicker is the subjective impression of fluctuating luminance, caused by the modulation of the RMS supply voltage”.

M. De Koster - E. De Jaeger – W.Vancoetsem

• Defined by standard IEC 61000-4-15• Perceptible flicker in lighting caused by periodic voltage sags. • Measured by a statistical “Lamp-Eye-Brain” model that duplicates

how most people are affected by flickering incandescent lights.• Causes

• Loads that draw in periodic “gulps” (ex: arc furnaces, welders)• The Basic Measurements

• PST -- A statistical figure derived over 10 minutes. A reading of 1.0 causes flicker that can be perceived by 50% of people

• PLT -- A statistical figure derived from PST over 2 hrs• Represents the likelihood that fluctuations will cause annoyance


Flicker

• Penalties applied in South America• Generally unknown in North America• Standards applied in Europe and Asia


(IEC 61000-4-15)Pst : Short time (10 min)Plt : long time (2 hours)

8,4Hz modulation

60 Hz

Effects

Flicker is the effect produced on the visual human perception by a changing emission of light by lamps subjected to fluctuations of their supply voltage.

Flicker


Industry Low Voltage

Eolic Generators

Loads Variations

• Arc furnace (c.a. & c.c.)

• Welding machines

• Business copy machines• Large Motors• X-rays machines

Causes

Flicker sources


IEC 61000-4-15

• “It has been shown in [19] that different digital flicker meter implementations that meet the performance tests defined in IEC 61000-4-15, Amendment 1 can still disagree significantly in some actual measurements. “

• IEC Flicker Meter used in Power System Voltage Monitoring• Prepared by: CCU2 – Cigré C4.05 / CIRED 2 / UIE WG2 Joint Working Group on Power Quality• DRAFT 10 October 2003


61000-4-7

• General guidelines on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected

harmonic order n n+1 n+2 n+3

harmonic subgroup n+1

interharmonic subgroup n+2,5

DFT output


Interharmonics

• IH voltages can cause flicker in electronic ballasts when the frequency is near a multiple of the fundamental.

• IH voltages can cause flicker in incandescent lamps primarily when the frequency is near the fundamental or second harmonic.

• 1%IH near the fundamental frequency can result in a Pst of 5.

• Interference with low frequency power line carrier (PLC) signals.

• IH currents cause IH voltage distortion according to the network impedance in the same manner as harmonic currents.

• IH currents have the same thermal effects as harmonic currents in the same frequency range.

• Can cause undesirable effects with tuned filters.

• IEC presently has a limit recommendation of 0.2% voltage distortion from 0-2 kHz.


230 Vac

Vac

t

10 ms

10 values interval = 100 ms

Vmax

Vmin

Vavg

• A 10 min interval contains 10x60x100=60,000 cycles . • During 1 week 7 x 24 x 6 = 1,008 (x 3) values are recorded .

Voltage variations

A value each ½ cycle


Dips, swell and interruptions are characterized by duration, magnitude and time of occurrence•Starts when from one of the phases the voltage goes below/above the threshold•Stops when all phases are above/below the threshold + hysteresis.•Levels and duration are specified by EN 50160

DipInterruption

Swell

What’s a Dip (sag), swell or interruption?


Rapid Voltage change

A quick change of the RMS voltage between two steady voltages.


Short Interruption

tShort Interruption

Voltage rms in [%] UN

10 ms 1s 1 h3 min

90%

110%

100%

te ts

1%0%

Duration

Voltage variations


Long Interruption

t


10 ms 1s 1 h3 min

90%

110%

100%

Long Interruption1%0%

Voltage variations


Dips and Swells

1%0% Short Interruption Long Interruption


10 ms 1s 1 h3 min

90%

110%

100%

Dip

1 min

Swell

Voltage variations ± 10%

+10 % / -15 %


Sources and Effects

Causes

Effects• Rebooting of computers and similar• Loss of data• Light flashing

• Short circuits• Overload• Load variations

Voltage variations ± 10%

+10 % / -15 %


PQ Solutions

A quick look into possible solutions and techniques


Branch Circuit Solutions:Performance Wiring

Limit length of feeder and branch runs

Eliminate shared neutralsMax of 3 outlets per branch

Dedicated circuits for problem loads


Sources of Noise: Ground Loops


Bubble Principle


The insidious 3rd harmonic

On a three-phase / four-wire system, triplen (zero sequence) harmonics will add up in the neutral.

This is true for all triplen harmonics including 6th, 9th, 12th, 15th

-400-300-200-100

0100200300400

0 90 180 270 360

-400-300-200-100

0100200300400

0 90 180 270 360

-400-300-200-100

0100200300400

0 90 180 270 360

The third harmonics are all in phase and create unbalance


What to check? • Motors, transformers and neutral conductors serving

electronic loadsHow much is ok?

• Voltage distortion (THD) should be investigated if it is over 5 % on any phase

• Some current distortion (THD) is normal on any part of the system serving electronic loads

• Monitor current levels and temperature at transformers to be sure that they are not overstressed

• Neutral current should not exceed the capacity of the neutral conductor

When is distortion a problem?


• Replace overheating transformers with higher K-factor rated units

• Reduce load on overheating transformers

• Rewire or redistribute loads to reduce source impedance and isolate non-linear loads

• Passive filters

• Active filters

• Zig-zag transformer or zero sequence filter

• Larger conductors will have lower source impedance - less prone to voltage distortion

• Double the size of neutral or pull parallel neutral cable to handle triplens

Solutions to harmonics problems


Transformer Derating Curve


Separately Derived System

Transformer as SDS• Secondary is source• Lower source impedance• Electrical isolation• Ground reference


Single-point ground: single N-G bond at the source

Correct Grounding of SDS


Lightning Protection


Transients

Causes of transients:• Utility transformer tap switching• Capacitors switching on• Lightning• Motors switching off • Switch and relay contact “bounce”Effects of transients:• Damage semiconductor junctions• Damage Insulation• Couple into adjacent circuits because of high

frequency (fast rise times)• Corrupt data signals


Transient waveform capture

• Set a tolerance around an ideal sinewave

• Any event that goes outside the envelope triggers the instrument to capture the waveform

• Products that do peak detect via capacitor charging do not.

Most instruments that support transient capture use Envelope Triggering


Reading the waveforms

Capacitive transients will exhibit some ringing

Switching and lightning transients usually show a single prominent spike with a fast decay


• Transient Voltage Surge Suppressors (TVSS)• Uninterruptible power supply with built-in surge

suppression• Isolation transformer

Protecting against transients


Motors: Inrush Current

•Nuisance breaker tripping•Voltage sags


Application notes


Summary & Questions

• Importance of understanding the standards.• How they effect our business• How they effect the customer• The benefit of our product to the customer

• Being able to relate to the customer.• Know the terminology or lingo• Understand what the customer is trying to relate• Recognize what you see and hear

Advanced Concepts Power Quality FLUKE [email protected]

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