Understanding Power Quality Iiee Csc Ust

Understanding Power Quality February 7, 2007 University of Sta. Tomas

Marvin Ryan G. Bathan Power Quality Team Power Services / MERALCO

Objectives • 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

Objectives • 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

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

Power Quality Problem "Any power problem manifested in voltage, current, or frequency deviation that results in failure or mis-operation of utility or end-user equipment."

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PQ Problem Illustrated Failure

Normal

Failure

Power Quality Issues Power quality issues may be viewed from three different perspectives: 2 End-user 2 Utility 2 Equipment Manufacturer

PQ Problem Solution: A 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.

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MERALCO 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 Services

PQ Services

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PQ Services

PQ Services

C A S E S T U D Y

Voltage Sag Problem Voltage Unbalance Problem Transient Harmonics Interesting

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Background • 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 Diagram S1 R1 S2 R2 S3 R3

64% FLA

• Compressor - 230Vac, 3-phase,Voltage 60Hz Current Compressor S S S R R R L –L L –L L –L 1 44.8 44.1 43.5 46.7 41.0 75 48.0 FLA, 450 LRA • Contactors - 240 Vac, 1

2 3

31.5 39.7

2

35.2 39.7

3

34.6 38.0

1

31.5 36.7

2

35.9 40.0

3

35.2 37.9

1

2

228.3

2

3

232.8

3

1

228.3

Voltage Protection • Programmable Voltage Monitor • ±10% over and under voltage setpoint • 5% voltage unbalance setpoint

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Compressor 3 Inrush Current 80 Amperes. Loads running were the AHU and condenser.

180 Amperes. Represents the current drawn by the AHU, condenser, and compressor. 760 Amperes. Compressor #3 was started.

Compressor 1 Inrush Current 32 A

60 A

320 A

Compressor 1 Inrush Current

30 A 70 A

350 A

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RMS Voltage Variation V RM S A B (V)

RMS Voltage Profile

V RM S B C (V) V RM S CA (V)

275 265 Voltage

Transformer tap change.

Overvoltage incidents.

255 245 235 225 9/16/04 7:23

9/15/04 10:23

9/14/04 13:23

9/13/04 16:23

9/12/04 19:23

9/11/04 1:33

9/11/04 22:23

9/9/04 6:33

9/10/04 3:33

9/8/04 9:33

9/7/04 12:33

9/6/04 15:33

9/5/04 19:00

9/4/04 1:00

9/4/04 22:00

9/3/04 3:00

9/2/04 6:00

9/1/04 9:00

8/31/04 12:00

8/30/04 15:00

215

Date & Tim e

RMS Voltage Variation

Monitoring Site Compressor 3 Compressor 1

Minimum 95.67% 96.42%

Average 103.79% 101.80%

Maximum 112.31% 106.61%

Count 264 141

Voltage Unbalance

Minimum

Average

Maximum

Count

Compressor 3

Monitoring Site

0.08%

0.62%

1.09%

264

Compressor 1

0.16%

0.50%

0.98%

141

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Voltage & Current Harmonics • Maximum Voltage THD • Average Voltage THD

» »

• Maximum Current TDD • Average Current TDD

3.88% 2.06%

» 10.72% » 1.97%

Compressor Cycling Compressor 3 Number 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 Date

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

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

Compressor 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

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Causes of Intermittent Cycling

• • • •

Too sensitive Voltage protection Erratic operation of low pressure switch Insufficient refrigerant Closed suction service valve

Causes of Intermittent Cycling • Partially open discharge valve • Insufficient fluid flowing through the condenser • Presence of air in the system

Conclusion • 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.

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Recommendation

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

General PQ Evaluation Procedure Ξ Ξ Ξ Ξ Ξ

Problem Category Identification Power Measurements & Data Collection Solution Range Identification Solution Evaluation Optimum Solution

Solution Range Identification

   

Equipment Design/Specification Customer Systems Utility Distribution System Utility Transmission System

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Good Day! For your comments / suggestions / questions

MARVIN RYAN G. BATHAN [email protected] [email protected] 1622-3591

Voltage 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

Background

Customer business is lead recycling Customer complained of frequent breakdown of 3-phase motors

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Profile of Voltage Unbalance Voltage Unbalance Trend 9

Voltage Unbalance (%)

8 7 6 5 4 3 2 1

4:45

22:45

1:45

11:45

18:45

8:45

5:45

15:45

22:45

12:45

1:45

8:45

19:45

15:45

5:45

22:45

12:45

2:45

19:45

9:45

5:45

15:45

22:45

3:11

13:11

20:11

10:11

0

Time

Solution

Redistribution of single-phase welding machines

Voltage 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 motors Switching “on” of large loads Fault on either distribution, transmission, or generation systems

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Voltage Sag PerkinElmer Main - 6/3/2004 14:50:13.142 V RMS AB

V RMS BC

V RMS CA

460

• • • •

RMS Voltage (V)

450 440 430

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

420 410

0.000

0.025

0.050

0.075 Time (s)

0.100

0.125

EPRI/Electrotek

0.150 PQView®

Susceptibility Curve Information Technology Industry Council (ITIC) curve was developed to accurately reflect the performance of computertype equipment.

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

Voltage 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”

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Monitoring Results Parameter

Minimum

Average

Maximum

Limits

Comment

105.83%

±10%

Within Recommended Limits

2.50%

5%

Within Recommended Limits

13.59%

5%

Outside Recommended Limits

1.85%

2.5%

Within Recommended Limits

Vab – 102.37% RMS Voltage

99.83%

Vbc – 103.32% Vca – 101.15%

Voltage Harmonic Distortion Current Total Demand Distortion

Vab – 1.16% 0.31%

Vbc – 1.20% Vca – 1.18% Vab – 3.63%

0.66%

Vbc – 4.37% Vca – 3.94%

Voltage Unbalance

0.38%

1.02%

Voltage Sags Date

Time

Magnitude

Duration

Coincident Data

Effect on Customer

7/26/05

18:36

38.75%

9 cyc

7/26/05

18:40

36.67%

8 cyc

7/26/05

18:41

34.79%

9 cyc

7/26/05

18:42

36.12%

7 cyc

Equipment Failure

Shutdown

7/30/05

13:27

87.67%

2 cyc

Transient

7/31/05

12:51

82.86%

3 cyc

NPC 230kV

7/31/05

12:51

88.77%

2 cyc

line trip

8/1/05

18:33

88.32%

4 cyc

Lightning

8/2/05

16:46

71.39%

5 cyc

Transient

8/6/05

16:48

88.02%

13 cyc

Transient

8/11/05

10:23

70.11%

4 cyc

8/15/05

11:00

81.87%

1 cyc

No data

8/17/05

14:10

69.09%

5 cyc

Transient

8/17/05

14:10

89.41%

1 cyc

Transient

No data

Shutdown Shutdown

Findings / 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

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Customer Facility • High rise residential building • 2 - 53 story buildings with 396 semifurnished units • each unit is equipped with two refrigerators and two freezers (personal-size)

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

Monitoring Equipment

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Monitoring Results

Phase AB, BC and CA RMS Voltage Chart

245

244

242

240

240

238

236

Volt

235

234

230

232

230

225

228

226

15:35:00

9:35:00

7:35:00

13:35:00

11:35:00

5:35:00

3:35:00

1:35:00

23:35:00

21:35:00

19:35:00

17:35:00

9:35:00

15:35:00

13:35:00

7:35:00

11:35:00

5:35:00

3:35:00

1:35:00

23:35:00

21:35:00

19:35:00

17:35:00

9:35:00

15:35:00

13:35:00

7:35:00

11:35:00

5:35:00

3:35:00

1:35:00

23:35:00

21:35:00

19:35:00

17:35:00

224 15:35:00

220

Time

4 days monitoring

Monitoring Results Nominal Voltage: 230V

VAB Maximum

238.4

Minimum

227.0 (-1.3%)

VBC

VCA 242.7 239.9 (+5.52%) 229.6

231.1

Most 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

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Recommendations • 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? Increasing Cost

Utility Solution

Over-all Protection Inside Plant

3

4

Control Protection

2

Equipment Specification

1 Controls Motors Other Loads

Think about it….

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End of Presentation Good day!

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

Background • 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.

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Single Line Diagram

Requirements for evaluation

• Magnitude of harmonic currents • Equivalent circuit model

Current TDD Measured using Dranetz-BMI 7100 PQ Node Ch ann el IT D D A IT D D B IT D D C

A v e ra g e 1 7 .8 5 % 1 7 .1 7 % 1 8 .0 8 %

M a x im u m 2 5 .2 1 % 2 3 .8 7 % 2 4 .2 0 %

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Harmonic Current Statistical Summary of Current TDD and Harmonics

CP05 Average CP95

25.00%

% of Base Current

20.00%

15.00%

10.00%

5.00%

25

23

21

19

17

15

13

9

11

7

5

3

TDD

0.00%

TDD and Individual Harm onics PQView ®

Equivalent Circuit • Equivalent circuit for nth harmonic frequency

• Equivalent circuit for fundamental frequency

Variable Definitions • XT0 - tx impedance at fund. freq. ω 0, 0.0649 pu • XS0 - source impedance at fund. freq. ω 0, 0.021189 pu • XC0 - capacitor impedance at fund. Freq. ω 0, 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

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Resonant Frequency • Determine hr

I Ch

Let,

     − h2 X S0   X    C0   = Ih  1 − h 2  X S 0    X    C0   

1 − hr 2

X S0 =0 X C0

Which results to

hr =

XC0 X S0

=

1.94 = 9.57 .021189

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

I Ch

2    −h   hr2  = I 2  h  1 −  h     h2     r 

  h    hr  VCh = jX S I h  2   1 −  h     h2     r 

   h      hr  Vh = jI h  hX T 0 + X S  2    h   1−      h2       r   

Effect of Resonance Equations for equivalent circuit for fundamental frequency

VCh =

− XC0 X S 0 − XC0

I Ch =

1. 0 X S0 − X C0

Vh =

− XC0 X S 0 − X C0

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Harmonic Current & Voltage Magnitude h 1 3 5 7 9 11 13 15 17 19 21 23 25

Ih -1.00000* 0.02760 0.20403 0.05450 0.01023 0.03950 0.01907 0.01060 0.04940 0.03610 0.01393 0.01300 0.00753

Ic -0.51011* -0.00301 -0.07664 -0.06275 -0.07852 0.16233 0.04161 0.01787 0.07231 0.04837 0.01758 0.01572 0.00883

Vc Vh -0.95038* -0.92472* 0.17814 0.00732 2.72252 0.09594 1.59227 0.04215 1.54958 0.02290 -2.62120 -0.00043 -0.56850 0.00988 -0.21164 0.00801 -0.75549 0.04625 -0.45215 0.03958 -0.14873 0.01737 -0.12141 0.01808 -0.06271 0.01154

Effective voltage across the capacitor will reach as high as 460% of nominal voltage!

Recommendation 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.

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