Electrical Testing

21st Century Facilities

• Facility Owners face tough challenges

– 24 X 7 reliability needed

– Non linear loads cause harmonics

• VFD

• Computers

– Switching transients disrupt operations

– Less customer support from Utilities

– Pressure to hold energy costs down

– Compressed schedules for expanding facilities

– Effect of EMF on computers and equipment

– How to expand facilities to meet customer needs cost

effectively

– Harsh environments

Formula For Successful Facilities

• Facility Planning and Scheduling

• Engineering Design

• Quality Installation

• Acceptance Testing

• Regular and Complete Maintenance

– Preventative Maintenance Testing

Testing for All Phases of Facility

Improvements

• Load analysis for facility improvements

• Trouble shooting and correction of problems

• Acceptance Testing for New Projects

• Switchboards and/or Switchgear

• Circuit Breakers

• Preventative Maintenance

• Forensic Testing

Testing – Load Analysis

• Measuring existing loads with portable test equipment

– 120V to 480V, 0 – 3000 Amps

– Recorded values

– Volts - Power Factor

– Amps - KVA

– KW - KVAR

– Measure harmonic distortion

– THD - Voltage & Current

– Individual harmonics

• Measure loads for emergency generator sizing

• Motor starting studies

CURRENT Trend Monitoring

48

54.75

61.5

68.25

75

48

54.75

61.5

68.25

75

10:50 AM 11:00 AM 11:10 AM 11:20 AM 11:30 AM 11:40 AM 11:50 AM

11/5/01 10:50:00 AM to 11/5/01 11:50:00 AM

IAvg

IA

IB

IC

Trend Plot For Device: 3 Phase Current

Testing – Acceptance Testing

• Equipment Acceptance Testing

– Medium Voltage

– Transformers

– Switchgear

– Cables

– PFC

– Air Switches

– SF6 Circuit Breakers

– Below 600V

– Switchboards and Switchgear

– Motor Control Centers

– Generator Load Testing

Acceptance Testing Cont’d.

• Short Circuit and Coordination Studies

– Short Circuit Study verifies overcurrent protective

devices meet requirement for interrupting available fault

current.

– Coordination Study graphically shows how overcurrent

protective devices coordinate to have the CB closest to

the fault open.

• Ground Resistance Testing

– 3 Point Fall of Potential Method

• Ground Fault Interruption Testing – Required by NEC

Transformer Testing

Oil Filled Transformers

• On Line, no shutdown

• Excellent analytical technique developed by IEEE to

evaluate condition of transformer

• IEEE/ANSI C57 Distribution, Power and Regulating

Transformers. C57.104 is the Standard for Interpretation.

• NFPA 70B

– Section 7-2.81 Oil Tests

– Section 7-2.9.4 Dissolved Gas Analysis

Transformer Testing Cont.’d

• Mineral Oil is complex hydrocarbon molecular compound

– At normal conditions it is very stable

– Heat, corona and arcing break molecule down to sub

elements (combustible gases) (H2, CH4, etc.)

– Analysis of dissolved combustible gases gives the

condition of the transformer.

– Trending of gases is very helpful in the analysis.

• DGA is one of the best ways to monitor the condition of the

transformer and help the Owner plan repairs or

replacements.

Infrared Thermography Scan

• Heat is the enemy for electrical equipment

• Heat breaks down electrical insulation

• 10° C Rule = ½ life

• Infrared thermography scanning

– Looks at thermal image of switchgear, busbars,

connections, cables, etc.

– Hot spots and irregularities are discovered by trained

technicians

– Problem areas can be corrected before they cause

shutdowns or cause fires.

• Scanning Saves Equipment

– Technician scanning is much faster that tightening all bolts.

– Cannot see some circuit breaker problems without IR.

– Early detection and correction = preventative maintenance.

Infrared Thermography Scan

95.8°F

148 .5°F

100

110

120

130

140

SP01

SP02

Spot 1 Temperature 154.7°F

Spot 2 Temperature 93.9°F

Spot 1 Rise over Spot 2 60.84°F

Ambient Temperature 68.0°F

Circuit Breaker Testing

• Contact Resistance

– Results vary with size and construction of circuit breaker

• less than 100 microhms for medium voltage

– Contact resistance exposes problems not detectable with

IR when there is little load current.

• Insulation Resistance

– Phase to ground

– Phase to phase

• Functionality Tests

– Close, Open

– Trip

– Kirk key interlocks, etc.

Circuit Breaker Testing Cont’d.

• Overcurrent Trip Point Calibration and Testing

– Secondary Injection Testing

– Electronic CB test sets for accurate testing

• Square D

• Cutler Hammer

• GE

• Siemens

• New Circuit Breakers with on-board secondary injection testing

• Cutler Hammer 1150 Trip Unit

Cable Testing

– Medium Voltage (> 600 Volts)

• New Cables

– Insulation resistance testing using hi pot at

manufacturer’s recommended values

– NETA use Table 10.6 of Acceptance Testing Specs.

– Leakage current should be <10 micro Amps for new

cables.

• Existing Cables

– Watch out! – Be careful what voltage you use on old

cables.

– Conservative approach

• RMS X Square Root of 2 = Peak voltage

• Use peak value as DC value

Relay Testing

• Relays are typically used on medium voltage systems

– Older electro mechanical style relays (typical single phase)

– Newer models–microprocessor based, 1 Phase + 3 Phase

– Incorporate metering and relay tripping.

– Programmable on site

– Fault analysis logging for retrieval

• Short Circuit and Coordination Studies

– At least 50% of facilities are not coordinated

• Poor maintenance

• Poor installation

Power Quality - Today’s Perspective

• The quality of power 30 years ago was not much of an issue

– Linear Devices

• Today many devices disrupt and corrupt the quality of the

power

– Utility Side

• Voltage Sags

• Impulses

• Transient Disturbances

• Loss of One Phase

• Over voltage

Power Quality – Today’s Perspective

– Customer Side

• Switch mode power supplies (non-linear device)

– Harmonic Distortion

– Overloaded neutrals

– Transformer heating

• SCR (non-linear device)

• Loose wiring

• Large motor starting

PQ Testing

• Power Quality Analyzer – 3 phase microprocessor based

analyzer that samples the voltage waveform 128 times per

second. We set thresholds for voltages. By exceeding the

thresholds, the machine is activated to record the “events”

as they occur.

• Harmonic testing and analysis

– Measure voltage and current THD

– Analyze individual harmonic values

• Engineering investigation of problem and surrounding

power distribution system by power quality engineer.

Main Switchboard Voltage Sag

340.0A

170.0A

0.0A

350.0V

175.0V

0.0V

5.83 ms/div 0.00ns 116.67ms

RMS Sag Disturbance Model 7100

M SWBD 11/22/01 07:57:32.98 AM

Three Phase Wye

Vc Ic

Channel Y1 Y2 Delta

Channel Y1 Y2 Delta

Time X1 X2 Delta

Voltage 285.185 205.967 79.218

Current 277.037 200.082 76.955

Main SWBD Voltage Sag on Phase C-N

640.0A

0.0A

-640.0A

500.0V

0.0V

-500.0V

2.50 ms/div 0.00ns 50.00ms

Impulse Disturbance Model 7100

M SWBD 11/22/01 07:57:32.98 AM

Three Phase Wye

Vc

Main SWBD Utility Capacitor

Switching Transient – Phase B-N

2.1KA

0.0A

-2.1KA

500.0V

0.0V

-500.0V

2.50 ms/div 0.00ns 50.00ms

Impulse Disturbance Model 7100

M SWBD 12/03/01 09:48:07.93 AM

Three Phase Wye

Vb

Utility Capacitor

Switching Transient Phase B-N

2.3KA

0.0A

-2.3KA

550.0V

0.0V

-550.0V

2.50 ms/div 0.00ns 50.00ms

Impulse Disturbance Model 7100

M SWBD 12/03/01 11:43:11.90 AM

Three Phase Wye

Vb

Channel Y1 Y2 Delta

Channel Y1 Y2 Delta

Time X1 X2 Delta

Voltage -56.584 -377.984 321.399

Panel NEH1 Power Source

Switching Transient – Phase A-N

575.0A

0.0A

-575.0A

650.0V

0.0V

-650.0V

2.50 ms/div 0.00ns 50.00ms

Impulse Disturbance Model 7100

Pnl NEH1 01/03/02 02:00:54.74 PM

Three Phase Wye

Va

Panel NEH1 Power Source

Switching – Phase B-N

570.0A

0.0A

-570.0A

700.0V

0.0V

-700.0V

2.50 ms/div 0.00ns 50.00ms

Impulse Disturbance Model 7100

Pnl NEH1 01/03/02 02:48:29.37 PM

Three Phase Wye

Vb

Harmonic Distortion – Voltage Waveform

50.0A

0.0A

-50.0A

200.0V

0.0V

-200.0V 833.33 us/div

0.00ns 16.67ms

Snapshot Waveform Model 7100

PDU PnlD 01/17/02 01:06:45.97 PM

Three Phase Wye

0.0%

0.5%

1.0%

60Hz 2940Hz

Va

Distortion: thd=1.41% Odd=1.36%

Harmonic Distortion - Current

50.0A

0.0A

-50.0A

200.0V

0.0V

-200.0V 833.33 us/div

0.00ns 16.67ms

Snapshot Waveform Model 7100

PDU PnlD 01/17/02 01:06:45.97 PM

Three Phase Wye

0.0%

16.0%

32.0%

60Hz 2940Hz

Ia

Distortion: thd=42.34% Odd=42.19%

How Do You Spot PQ Problems?

• Variable speed drives trip off line more than usual.

• Computer data errors that cannot be explained by hardware or

software

• Lights flicker (not in a storm).

• Equipment power supplies have burned or damaged boards.

• Transformers overheating.

• Circuit breaker nuisance tripping.

• Motors overheating or failing easily.

• Voltages vary significantly from loose wiring.

• Computer screens wave or are disrupted.

Power Quality and Facility

Maintenance Are Related

• Loose connections are one of the leading power quality

problems

• Lack of coordination of overcurrent protection devices can

cause blackouts that could have been avoided.

– Coordination Study

– Short Circuit Study

• Preventative Maintenance

– Infrared thermography scan – looks for hot spots

– Transformer Testing

– Oil Quality

– Dissolved Gas Analysis

– Cable Testing

– Test Circuit Breakers

– Switchgear Maintenance

Conclusion

• Facilities today face tough problems:

– Harsh environments

– Power Quality Problems

– Need for 24/7 Reliability

– Compressed schedules

• A successful 21st Century Facility needs four solid legs to

stand on:

– Engineering Design

– Quality Installation

– Maintenance

– Testing

Conclusion Cont’d.

• Excellent resources and standards from IEEE, NETA and

NFPA for Testing and Maintenance

• A proper test is worth a thousand opinions. The right test

equipment and experience will aid the Design Engineer in

ensuring success for the Customer.

Call IETC at 717-252-4730 for a quote today!