1

Understanding Power Understanding Power

QualityQuality

February 7, 2007

University of Sta. Tomas

Marvin Ryan G. Bathan

Power Quality Team

Power Services / MERALCO

ObjectivesObjectives

• To understand the concept of EMC and what specifically becomes a power quality problem

• To establish collaboration among involved parties in dealing with PQ problems

ObjectivesObjectives

• To have a common understanding of power quality and its attendant terminology

• To be acquainted with the typical causes and solutions to specific power quality problem

2

Power QualityPower Quality

Power Quality - the quality of the voltage, including its frequency and the resulting current that are measured in the Grid, Distribution System, or any User System

Quality?Quality?

Quality is a relative term

Power Quality is relative to the sensitivity of a device, equipment, or system

Power Quality ProblemPower Quality Problem

"Any power problem manifested involtage, current, or frequency deviation that results in failure or mis-operation of

utility or end-user equipment."

3

PQ Problem IllustratedPQ Problem Illustrated

NormalNormal

Failure

Failure

Power Quality IssuesPower Quality Issues

Power quality issues may be viewed

from three different perspectives:

2 End-user

2 Utility2 Equipment Manufacturer

PQ Problem Solution: PQ Problem Solution:

A joint effortA joint effort

• Solution to PQ problems is not the responsibility of only one party.

• The solution is a concerted effort between the power supplier, the electricity user, and equipment manufacturer.

4

MERALCO Power Quality TeamMERALCO Power Quality Team

Profile:

PEE – 1

REE – 5

RME – 1

MBA – 1

Trainings:

Attended various PQ conferences/trainings here and abroad

Seminars conducted:

Regular speaker in PQ seminars and lectures

PQ ServicesPQ Services

PQ ServicesPQ Services

5

PQ ServicesPQ Services

PQ ServicesPQ Services

Voltage Sag ProblemVoltage Sag Problem

Voltage Unbalance ProblemVoltage Unbalance Problem

TransientTransient

HarmonicsHarmonics

InterestingInteresting

CC

AA

SS

EE

SS

TT

UU

DD

YY

6

BackgroundBackground

• series of compressor breakdowns

• 5 replacements since the installation of their 3 compressors

• Refrigeration experts says that the power supply caused the breakdown

• Customer requested for technical assistance in characterizing their power supply

Simplified Schematic DiagramSimplified Schematic Diagram

S1

S2

S3

R1

R2

R3

• Compressor - 230Vac, 3-phase, 60Hz

• Contactors - 240 Vac, 75 FLA, 450 LRA

Current Voltage

Compressor S1 S2 S3 R1 R2 R3 L1 –L2 L2 –L3 L3 –L1

1 44.8 44.1 43.5 46.7 41.0 48.0

2 31.5 35.2 34.6 31.5 35.9 35.2

3 39.7 39.7 38.0 36.7 40.0 37.9

228.3 232.8 228.3

64% FLA

Voltage ProtectionVoltage Protection

• Programmable Voltage Monitor

• ±10% over and under voltage set-point

• 5% voltage unbalance set-point

7

Compressor 3 Inrush Compressor 3 Inrush

CurrentCurrent

760 Amperes.

Compressor #3 was

started.

180 Amperes.

Represents the

current drawn by

the AHU,

condenser, and

compressor.

80 Amperes.

Loads running

were the AHU

and condenser.

Compressor 1 Inrush Compressor 1 Inrush

CurrentCurrent

32 A

320 A

60 A

Compressor 1 Inrush Compressor 1 Inrush

CurrentCurrent

30 A

350 A

70 A

8

RMS Voltage VariationRMS Voltage Variation

RMS Voltage Profile

215

225

235

245

255

265

275

8/3

0/0

4 1

5:0

0

8/3

1/0

4 1

2:0

0

9/1

/04 9

:00

9/2

/04 6

:00

9/3

/04 3

:00

9/4

/04 1

:00

9/4

/04 2

2:0

0

9/5

/04 1

9:0

0

9/6

/04 1

5:3

3

9/7

/04 1

2:3

3

9/8

/04 9

:33

9/9

/04 6

:33

9/1

0/0

4 3

:33

9/1

1/0

4 1

:33

9/1

1/0

4 2

2:2

3

9/1

2/0

4 1

9:2

3

9/1

3/0

4 1

6:2

3

9/1

4/0

4 1

3:2

3

9/1

5/0

4 1

0:2

3

9/1

6/0

4 7

:23

Date & Time

Vo

ltag

e

V RM S AB (V)

V RM S BC (V)

V RM S CA (V)

Transformer tap

change.Overvoltage

incidents.

RMS Voltage VariationRMS Voltage Variation

Monitoring Site Minimum Average Maximum Count

Compressor 3 95.67% 103.79% 112.31% 264

Compressor 1 96.42% 101.80% 106.61% 141

Voltage UnbalanceVoltage Unbalance

Monitoring Site Minimum Average Maximum Count

Compressor 3 0.08% 0.62% 1.09% 264

Compressor 1 0.16% 0.50% 0.98% 141

9

Voltage & Current HarmonicsVoltage & Current Harmonics

• Maximum Voltage THD » 3.88%

• Average Voltage THD » 2.06%

• Maximum Current TDD » 10.72%

• Average Current TDD » 1.97%

Compressor CyclingCompressor Cycling

Compressor 3

DateNumber of

Starts

30-Aug-04* 6

31-Aug-04 20

1-Sep-04 20

2-Sep-04 4

3-Sep-04 1

4-Sep-04 1

5-Sep-04 0

6-Sep-04 1

7-Sep-04 2

8-Sep-04 1

9-Sep-04 3

10-Sep-04** 2

*Started at 3:30 PM **Ended at 3:48 PM

The number of start and stops the compressor makes could be greaterthat those listed in the table!

Compressor CyclingCompressor Cycling

Compressor 1

Date Number of Starts

10-Sep-04* 7

11-Sep-04 10

12-Sep-04 0

13-Sep-04 30

14-Sep-04 35

15-Sep-04 31

16-Sep-04** 18

*Started at 3:48 PM **Ended at 1:08 PM

10

Causes of Intermittent CyclingCauses of Intermittent Cycling

• Too sensitive Voltage protection

• Erratic operation of low pressure switch

• Insufficient refrigerant

• Closed suction service valve

Causes of Intermittent CyclingCauses of Intermittent Cycling

• Partially open discharge valve

• Insufficient fluid flowing through the

condenser

• Presence of air in the system

ConclusionConclusion

• Power supply characteristics conforms

with the PDC recommended limits and therefore could not have caused the compressor breakdowns.

• It is the intermittent cycling of the compressors that lead to its premature failure.

11

RecommendationRecommendation

Coordinate closely with your supplier to address the intermittent cycling of the

compressors.

General PQ Evaluation General PQ Evaluation

ProcedureProcedure

Ξ Problem Category Identification

Ξ Power Measurements & Data Collection

Ξ Solution Range Identification

Ξ Solution Evaluation

Ξ Optimum Solution

Solution Range IdentificationSolution Range Identification

� Equipment Design/Specification

� Customer Systems

� Utility Distribution System

� Utility Transmission System

12

Good Day!Good Day!

For your comments / suggestions / questionsFor your comments / suggestions / questions

MARVIN RYAN G. BATHANMARVIN RYAN G. BATHAN

powerservices.powerquality@meralco.com.phmavinrya@yahoo.com

1622-3591

Voltage UnbalanceVoltage Unbalance

Maximum deviation from the average of the three-phase voltages divided by the average of the three-phase voltages, usually expressed in percent

t

•Unbalanced distribution of single phase loads•Unstable system neutral•One-phase out power supply

BackgroundBackground

Customer business is lead recycling

Customer complained of frequent breakdown of 3-phase motors

13

Profile of Voltage UnbalanceProfile of Voltage UnbalanceVoltage Unbalance Trend

0

1

2

3

4

5

6

7

8

9

10:1

1

3:1

1

20:1

1

13:1

1

5:4

5

22:4

5

15:4

5

9:4

5

2:4

5

19:4

5

12:4

5

5:4

5

22:4

5

15:4

5

8:4

5

1:4

5

19:4

5

12:4

5

5:4

5

22:4

5

15:4

5

8:4

5

1:4

5

18:4

5

11:4

5

4:4

5

22:4

5

Time

Vo

ltage U

nb

ala

nce (%

)

SolutionSolution

Redistribution of single-phase welding machines

Voltage SagVoltage Sag

A decrease in RMS voltage between 10% to 90% of the nominal value for duration from half cycle to 1 minute

1 minute

or less

Starting of electric motorsSwitching “on” of large loadsFault on either distribution, transmission, or generation systems

14

Voltage SagVoltage Sag

410

420

430

440

450

460

0.000 0.025 0.050 0.075 0.100 0.125 0.150

PerkinElmer Main - 6/3/2004 14:50:13.142

EPRI/Electrotek PQView®

RM

S V

olta

ge

(V

)

Time (s)

V RMS AB V RMS BC V RMS CA

• Nominal Voltage: 460V• Magnitude: 88.41%• Duration: 4 cycles• Cause: Fault on the

adjacent substation

Susceptibility Susceptibility

CurveCurve

Information Technology Industry Council (ITIC) curve was developed to accurately reflect the performance of computer-type equipment.

It is generally applicable to other equipment containing solid-state devices.

Voltage Sag ProblemVoltage Sag Problem

• Mall somewhere in the north

• 3 transformers, 1.5MVA each, 34.5kV / 230V

• Mall tenants are complaining of power “fluctuations” that causes equipment

shutdown

• Mall pumps and fans shutdown on power “fluctuations”

15

Monitoring ResultsMonitoring Results

Within

RecommendedLimits

2.5% 1.85%1.02%0.38%Voltage Unbalance

Vca – 3.94%

5%13.59%Vbc – 4.37%0.66%Outside

RecommendedLimits

Vab – 3.63%Current Total DemandDistortion

Vca – 1.18%

5%2.50%Vbc – 1.20%0.31%

WithinRecommended

Limits

Vab – 1.16%Voltage

HarmonicDistortion

Vca – 101.15%

±10%105.83%Vbc – 103.32%99.83%RMS VoltageWithin

RecommendedLimits

Vab – 102.37%

CommentLimitsMaximumAverageMinimumParameter

Voltage SagsVoltage Sags

Transient1 cyc89.41%14:108/17/05

Transient5 cyc69.09%14:108/17/05

No data1 cyc81.87%11:008/15/05

ShutdownNo data4 cyc70.11%10:238/11/05

Transient13 cyc88.02%16:488/6/05

ShutdownTransient5 cyc71.39%16:468/2/05

Lightning4 cyc88.32%18:338/1/05

line trip2 cyc88.77%12:517/31/05

NPC 230kV3 cyc82.86%12:517/31/05

Transient2 cyc87.67%13:277/30/05

7 cyc36.12%18:427/26/05

9 cyc34.79%18:417/26/05

8 cyc36.67%18:407/26/05ShutdownEquipment Failure

9 cyc38.75%18:367/26/05

Effect on

Customer

Coincident DataDurationMagnitudeTimeDate

Findings / RecommendationFindings / Recommendation

• Voltage regulation, unbalance, and voltage harmonics are within prescribed limits

• Adjust the -5% under-voltage relay setting to -10% and include 1 sec delay

• Holding coils could be installed to increase voltage sag ride-through

• Reduce ITDD levels to within limit

16

Customer FacilityCustomer Facility

• High rise residential building

• 2 - 53 story buildings with 396 semi-furnished units

• each unit is equipped with two refrigerators and two freezers

(personal-size)

Supplier InvestigationSupplier Investigation

“Cause of motor-compressor failure is due to low voltage”

Monitoring EquipmentMonitoring Equipment

17

Monitoring ResultsMonitoring ResultsPhase AB, BC and CA RMS Voltage Chart

220

225

230

235

240

245

15:3

5:0

0

17:3

5:0

0

19:3

5:0

0

21:3

5:0

0

23:3

5:0

0

1:3

5:0

0

3:3

5:0

0

5:3

5:0

0

7:3

5:0

0

9:3

5:0

0

11:3

5:0

0

13:3

5:0

0

15:3

5:0

0

17:3

5:0

0

19:3

5:0

0

21:3

5:0

0

23:3

5:0

0

1:3

5:0

0

3:3

5:0

0

5:3

5:0

0

7:3

5:0

0

9:3

5:0

0

11:3

5:0

0

13:3

5:0

0

15:3

5:0

0

17:3

5:0

0

19:3

5:0

0

21:3

5:0

0

23:3

5:0

0

1:3

5:0

0

3:3

5:0

0

5:3

5:0

0

7:3

5:0

0

9:3

5:0

0

11:3

5:0

0

13:3

5:0

0

15:3

5:0

0

Time

Volt

224

226

228

230

232

234

236

238

240

242

244

4 days monitoring

Monitoring ResultsMonitoring Results

VAB VBC VCA

Maximum 238.4 239.9242.7

(+5.52%)

Minimum227.0

(-1.3%)229.6 231.1

Nominal Voltage: 230V

Most Probable CauseMost Probable Cause

• Voltage sags and short duration interruptions can contribute to the degradation and eventually failure of the motors.

• If the motor-compressors were running prior to an interruption, large inrush current will be imposed on the motor winding as it tries to restart when power is restored.

• Results to over-heating and additional motor stress

18

RecommendationsRecommendations

• Installation of time delay switch. This will provide ample time for pressure equalization in the compressor and thus lower the motor load.

• Installation of a thermal protector on the motor-compressor. This will prevent burning of the motor winding due to overloading / overheating.

What is the best solution?What is the best solution?

1

3

EquipmentSpecification

ControlProtection

Over-all

ProtectionInsidePlant

4

Utility

Solution

Increasing Cost

Controls

Motors

Other Loads

2

Think about it….Think about it….

19

End of PresentationEnd of Presentation

Good day!

BackgroundBackground

An electrical service contractor offered Company X installation of additional capacitor banks to improve pf and avail of the pf discount

• Several days after the installation of the new capacitor banks, the existing old capacitor bank failed.

• The electrical service contractor sought the help of MERLACO PQ Team to determine the feasibility of installing a 1800 kVar capacitor at the high voltage feeder in place of the existing capacitor banks.

BackgroundBackground

20

Single Line DiagramSingle Line Diagram

Requirements for Requirements for

evaluationevaluation

• Magnitude of harmonic currents

• Equivalent circuit model

Channel Average Max im um

ITDD A 17.85% 25 .21%

ITDD B 17.17% 23 .87%

ITDD C 18.08% 24 .20%

Current TDDCurrent TDD

Measured using Dranetz-BMI 7100 PQ Node

21

Harmonic CurrentHarmonic Current

Statistical Summary of Current TDD and Harmonics

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

TD

D 3 5 7 9

11

13

15

17

19

21

23

25

TDD and Individual Harmonics

% o

f B

as

e C

urr

en

t

CP05

Average

CP95

PQView®

• Equivalent circuit for nth harmonic frequency

• Equivalent circuit for fundamental frequency

Equivalent CircuitEquivalent Circuit

• XT0 - tx impedance at fund. freq. ω0, 0.0649 pu

• XS0 - source impedance at fund. freq. ω0, 0.021189 pu

• XC0 - capacitor impedance at fund. Freq. ω0, 1.94 pu

• VCh - hth harmonic component of voltage across the

capacitor

• Vh - hth harmonic component of the voltage at

transformer secondary

• Ich - hth harmonic component of the current through

the capacitor

• Ih - hth harmonic current generated by the load

Variable DefinitionsVariable Definitions

22

• Determine hr

Let,

Which results to

h

C

S

C

S

Ch I

X

Xh

X

Xh

I

−

−

=

0

02

0

02

1

012

=−

C0

S0r

X

Xh

57.9021189.

94.1

0

0===

S

Cr

X

Xh

Resonant FrequencyResonant Frequency

Determine the effect of resonance to the capacitor current and voltage, and the load voltage

h

r

rCh I

h

h

h

h

I

−

−

=

2

2

2

2

1

−

=

2

2

1r

rhSCh

h

h

h

h

IjXV

−

+=

2

20

1r

rSThh

h

h

h

h

XhXjIV

Effect of ResonanceEffect of Resonance

Equations for equivalent

circuit for fundamental

frequency

00

0.1

CS

ChXX

I−

=

00

0

CS

CCh

XX

XV

−

−=

00

0

CS

Ch

XX

XV

−

−=

Effect of ResonanceEffect of Resonance

23

h Ih Ic Vc Vh

1 -1.00000* -0.51011* -0.95038* -0.92472*

3 0.02760 -0.00301 0.17814 0.00732

5 0.20403 -0.07664 2.72252 0.09594

7 0.05450 -0.06275 1.59227 0.04215

9 0.01023 -0.07852 1.54958 0.02290

11 0.03950 0.16233 -2.62120 -0.00043

13 0.01907 0.04161 -0.56850 0.00988

15 0.01060 0.01787 -0.21164 0.00801

17 0.04940 0.07231 -0.75549 0.04625

19 0.03610 0.04837 -0.45215 0.03958

21 0.01393 0.01758 -0.14873 0.01737

23 0.01300 0.01572 -0.12141 0.01808

25 0.00753 0.00883 -0.06271 0.01154

Effective voltage across the capacitor will

reach as high as 460% of nominal voltage!

Harmonic Current & Voltage Harmonic Current & Voltage

MagnitudeMagnitude

RecommendationRecommendation

Installation of the capacitor at the high

voltage feeder should be complemented with preventive measure/s to prevent harmonic resonance. This could be

through:

– installation of reactors at the capacitor for harmonic de-tuning or

– filtering of the harmonics at the harmonic generating load.