Using Test Equipment to Detect and Measure

Power Quality Issues

PQ03

Related Presentations:

PQ01 – Harmonic Solutions for VFD’s

PQ02 - Power Quality and Monitoring with

iSense/iGrid/DySC & Surge/Sag/Transient Protection

2

Power Quality

• Effects of bad power quality are not immediately obvious

• Bad power quality can come from anywhere

• Consequences could be severe (production loss)

• Power quality problems are a root cause:

Malfunction

Shutdown

Excessive energy cost

Decreased lifetime of equipment

3

Power Quality

1. Safety

2. Power Quality Measurement PQ Issues

Measurement of Harmonics

The effect of distortion on simple test tools

Power Factor

Transients

Unbalance

Basic Measurements

4

Measurement Safety

5

Measurement Safety

• Example:

DMM fitted with low energy fuse used

incorrectly on a high energy circuit

• EN61010 is based on overvoltage transients, as

well as steady-state voltages.

• All instruments have to be tested by an

independent test house

• Each instrument must be marked with an

Overvoltage Category ( CAT I, II, III, IV )

• As well as a voltage level (300, 600, 1000 Volts)

6

EN61010 LV Directive

CAT IV “Origin of installation” Utility level and any outside

cable run, Electricity meters and primary connection

CAT III Distribution wiring, including “mains” bus, feeders

and branch circuits, permanently installed loads.

CAT II Receptacle outlet circuit, plug-in loads.

CAT I Protected electronic circuits.

7

Category Rating

8

Voltage Rating per Category

Nominal Voltage

(VAC)CAT I CAT II CAT III CAT IV

300 1500 2500 4000 6000

600 2500 4000 6000 8000

1000 4000 6000 8000 12,000

Source Impedance 30 Ω 12 Ω 2 Ω 2 Ω

Isolation and Safety Standards for Electronic Instruments, Test Impulse Rating, Transient Voltage Tolerated

• Regulations are not an option

• Second edition EN61010 ( 2004 ) requires

independent testing

• Remember Test leads are CAT rated ...

9

IEC 1010 / EN61010

1. Safety

2. Power Quality Measurement PQ Issues

Measurement of Harmonics

The effect of distortion on simple test tools

Power Factor

Transients

Basic Measurements

10

PQ Measurement

• Lightning

• Non-Linear Loads – VFD’s, SMPS

• Capacitor switching transients

• Inrush Currents from Motors

• Sags, Surges

• Undersized Neutrals

• Electrical Noise

• Gen-Sets not sized for Harmonics

11

Power Quality Culprits

Fre

qu

ency

of

Occ

urr

ence

$ $$ $$$ $$$$

Low

V

ery

Low

M

ediu

m

Hig

h

Notching (Constant)

Swell (0.5 cycles – 60s)

Noise (Constant)

Harmonics (Constant) Transient (<50 ns – 5 ms)

Unbalance (Fluctuating)

Undervoltage (>1 minute)

Overvoltage (>1 minute)

EPRI (Electrical Power Research Institute)

• Monitored 300 sites for 2+ years.

• 1993 study: 92% of all events were voltage sags under 2 seconds

• 1995 study: 96% of all events were voltage sags less than 2 seconds

Grid

Related

Facility

Related

Sag (0.5 cycles – 60s)

Interruption (0.5 cycles – >1 hr)

12

The PQ Story

Harmonics are …... Deviations from the Ideal Fundamental AC line voltage and current waveforms

Non-linear loads contain ….. Current Harmonics which cause Voltage Harmonic problems for other users

AC

Drive

Input

Current

Input Current

Fundamental Current

Amplitude

time

Time Domain Analysis

Frequency Domain Analysis

1 pu Current magnitude (RMS)

60 Hz

Fundamental

Frequency [Hz] 300 420 660 780

Harmonics

5th 11th 7th 13th 19th 17th

780 780

Frequency [h]

13

Harmonics Are …

Linear Load, sinusoidal waveform,

no harmonics

Non-linear Load, non-sinusoidal

waveform, harmonics present

14

Linear vs Non-Linear

Non-linear Commercial loads

generally come from:

• Computers and CRT’s

• Electronic Ballasts

• And other single phase office equipment

Non-linear Industrial loads generally come from:

• Welders

• Arc furnaces

• UPS and DC power supplies

• AC & DC Drives

15

Non-Linear Loads

Converter

AC to DC

Inverter

DC to AC

DC

Bus

Filter

AC DriveA

C M

oto

r Outp

utA

C L

ine I

nput

Input =

Fixed V

Fixed freq

Output =

Var Voltage

Var frequency

480Vac

60Hz

0-460Vac

0-60Hz ~650Vdc

Bus = Fixed Vdc

16

Adjustable Speed Drive

Harmonic Measurement of Current

Waveform

Volt, Amp Measurement of Phase A

Harmonic Measurement –

VFD Load w/ Line Reactor

Volt, Amp Measurement of Phase A Harmonic Measurement of Current

Harmonic Measurement –

VFD w/ Harmonic Filter

Effects of Harmonics

• Current Harmonics create Voltage Distortion

• One of the major effects is to increase the current in a system

• Component Overheating. Motors, Generators, Transformers, wires will experience additional losses resulting in additional heat.

• Power Factor Capacitor issues, resonance, additional loading.

• Voltage Flat Topping

• Increased Utility current requirement.

For troubleshooting:

• Check the harmonics present

• Check for the levels of the harmonics

• Look for recognizable patterns

Harmonics Troubleshooting

Effect of distortion on test tools

Both Clamp Meter’s are calibrated and functioning

correctly

59.2 A 40.5 A

Distortion Effect

True RMS Measurement

True RMS / Harmonics

A True RMS meter calculates the effective

heating value of the distorted waveform.

This will include all harmonics.

“RMS” stands for root-mean-square.

Crest Factor = Peak Value / RMS Value

For a Sinewave, Crest Factor = 1.414

RMS

Peak

Peak value = 2.9 X RMS Value.

Crest Factor = 2.9

Crest Factor

RMS vs Average Sensing

• True-RMS versus Average Sensing

Crest Factor = Peak Value / RMS Value

Sinewave = 1.414

Square wave = 1

• Professional Multimeters usually rated at CF <3

• High Quality units rated at CF of 6

• Power Quality Analyzer CF >11

C.F. = 1.43 C.F. = 2.39 C.F. = 4.68

More on Crest Factor

Power Factor Measurement

Screen Shots from a Fluke 43 Single Phase and a Fluke 434 Three Phase analyzer

Two Power Factors

• System with no Harmonic content

True Power (W), P

Reactive power (VAr), Q

Cos φ (DPF) : True power/Apparent Power (fundamental)

DPF = Displacement Power Factor

Apparent power (VA), S

Power Factor, no Harmonics

28

HARMONIC

Current

Ireact

Ireal

Ifund

Itotal

Iharm

(in phase with

line-to-neutral

voltage, VLN)

REACTIVE

Current

Q

P

S1

S

D

x-axis

y-axis

z-axis

REAL

Current

222 DQPS

What is the Power Factor

of a Non-Linear load?

Linear Load Power Factor Non-Linear Load Power Factor

No Current Distortion Includes the Effect of Current Distortion

PF = Watts/VA

or phase angle between

voltage and current

What about the Power Factor?

Power Factor with Harmonics

Total Power Factor = 𝑷𝑭 = 𝑷/𝑺, (includes Harmonics)

Cos φ (DPF) = 𝑷𝑭𝟏 = 𝑷/𝑺𝟏 = cos (angle between 𝑷 and 𝐒1 )

DPF = Displacement Power Factor (fundamental) Distortion Power Factor = 𝑷𝑭𝑫 = 𝑺𝟏/𝑺

Screen Shots from a Fluke 43 Single Phase and a Fluke 434 Three Phase analyser

Two Power Factors !

Power Factor Measurement

31

• High energy, short term deviations or changes

from desired voltage level

• Unwanted electrical energy in AC power lines or

communication lines (a potential seeking a

pathway to ground)

• High voltages spikes

What are Transients?

32

Any switching that creates a spark

From outside the facility Lightning strike

Utility grid switching

Within the facility Motors

Large starters

Power factor correction capacitor banks

Air circuit breakers

Any inductive load as it switches on and off

80%

20%

80% Transients are created from inside the facility

How are Transients Generated?

Power Factor Correction Capacitor Switching Transient

Peak Value approx. 1100 V.

PFC Capacitor Switching - LV

“Noisy” Voltage Waveform

Measurements

1. Volts, Amps & Frequency

2. Power

3. Harmonics

4. Transients

5. Sags & Swells

6. Unbalance

7. Flicker

8. Inrush

9. Temperature

PQ Measurements & Equipment

Using a Power Quality Analyzer

View all of the main parameters at point of connection

Graphical as well as numeric display can help highlight potential problems

Scope

Vector

Trend

1) Volts, Amps & Frequency

• Typical power

measurement information

• Shows the sides of the

triangle

2) Power & PF Measurement

3) Harmonic Measurement

• Cause….. interference

• Difficult to capture

• Modern power quality analyzers purpose built for the job

• Envelope trigger

• Accurate real time stamping is essential

240V

+X%

- X%

4) Transient Measurement

• Recording of upstream and downstream sags & swells can

indicate loads causing problems

Upstream Sag Downstream Sag

5) Sags & Swells

• The phase diagram gives a

quick indication of phase

relationships and balance

• In this example voltage

unbalance is very small, but

current unbalance is nearly

19%.

6) Unbalance

greater than 1 means that most people will perceive flicker in an incandescent

7) Flicker Measurements

• A reading greater than 1 means that

most people will perceive flicker in an

incandescent bulb

• Measurement

– Pst (1 min): Short-term flicker over 1

minute

– Pst: Short-term flicker over 10

minutes

– Plt: Long-term flicker over 2 hours

• Inrush Current Measurement

– Momentary peak of current

during switch on.

– Current clamps can capture

peak reading

– Analyzers can give time

measurement

Screen Shot of a PQA showing start-up current generated by a cooling system

Three Phase Inrush Measurement

8) Inrush

• Many power quality problems initially result in an

increase in temperature of components,

connectors, cables and machinery

• Infra red non contact measurement is the ideal

way to locate this type of problem

Temperature

Fluke Equipment on Show Floor

To view Fluke Test Equipment visit Booth 303

Related Presentations:

PQ01 – Harmonic Solutions for VFD’s

PQ02 - Power Quality and Monitoring with iSense/iGrid/DySC & Surge/Sag/Transient Protection

Fluke Meters Booth 604

Rockwell Power Quality Solutions area SA1

46

Power Quality

Questions?

For questions or additional information please contact:

Mark Skoyen

Werner Electric

715-855-0584

mskoyen@wernerelec.com