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
Trend Plot For Device: 3 Phase Current
IAvg
75
75
68.25
68.25
61.5
61.5
54.75
54.75
IA
IB
48
10:50 AM
48
11:00 AM
11:10 AM
11:20 AM
11:30 AM
11:40 AM
11/5/01 10:50:00 AM to 11/5/01 11:50:00 AM
11:50 AM
IC
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
– Section 7-2.9.4
Oil Tests
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
148.5°F
140
SP02
SP01
130
120
110
100
95.8°F
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
Model 7100
350.0V
RMS Sag Disturbance
Three Phase Wye
340.0A
Vc
Ic
175.0V
170.0A
0.0V
0.00ns
M SWBD
Channel
Voltage
0.0A
5.83 ms/div
116.67ms
11/22/01 07:57:32.98 AM
Y1
Y2
Delta
285.185
205.967
79.218
Channel Y1
Current 277.037
Y2
200.082
Delta
76.955
X2
Delta
Time
X1
Main SWBD Voltage Sag on Phase C-N
Model 7100
500.0V
Impulse Disturbance
Three Phase Wye
640.0A
Vc
0.0V
-500.0V
0.00ns
M SWBD
0.0A
-640.0A
2.50 ms/div
50.00ms
11/22/01 07:57:32.98 AM
Main SWBD Utility Capacitor
Switching Transient – Phase B-N
Model 7100
500.0V
Impulse Disturbance
Three Phase Wye
2.1KA
Vb
0.0V
-500.0V
0.00ns
M SWBD
0.0A
-2.1KA
2.50 ms/div
50.00ms
12/03/01 09:48:07.93 AM
Utility Capacitor
Switching Transient Phase B-N
Model 7100
550.0V
Impulse Disturbance
Three Phase Wye
2.3KA
Vb
0.0V
0.0A
-550.0V
0.00ns
M SWBD
-2.3KA
2.50 ms/div
50.00ms
12/03/01 11:43:11.90 AM
Channel Y1
Voltage -56.584
Y2
-377.984
Delta
321.399
Channel
Y1
Y2
Delta
Time
X1
X2
Delta
Panel NEH1 Power Source
Switching Transient – Phase A-N
Model 7100
650.0V
0.0V
-650.0V
0.00ns
Pnl NEH1
Impulse Disturbance
Three Phase Wye
575.0A
Va
0.0A
-575.0A
2.50 ms/div
50.00ms
01/03/02 02:00:54.74 PM
Panel NEH1 Power Source
Switching – Phase B-N
Model 7100
700.0V
Impulse Disturbance
Three Phase Wye
570.0A
Vb
0.0V
-700.0V
0.00ns
Pnl NEH1
0.0A
-570.0A
2.50 ms/div
50.00ms
01/03/02 02:48:29.37 PM
Harmonic Distortion – Voltage Waveform
Model 7100
200.0V
Snapshot WaveformThree Phase
50.0A
Wye
Va
0.0V
-200.0V
0.00ns
PDU PnlD
1.0%
0.0A
-50.0A
833.33
16.67ms
us/div 01/17/02 01:06:45.97
PM
0.5%
0.0%
60Hz
2940Hz
Distortion: thd=1.41% Odd=1.36%
Harmonic Distortion - Current
Model 7100
200.0V
Snapshot WaveformThree Phase
50.0A
Wye
Ia
0.0V
0.0A
-200.0V
0.00ns
PDU PnlD
32.0%
-50.0A
833.33
16.67ms
us/div 01/17/02 01:06:45.97
PM
16.0%
0.0%
60Hz
Distortion: thd=42.34% Odd=42.19%
2940Hz
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!