Module 8
Power Quality
Troubleshooting with Handheld Test Tools
PQ Troubleshooting Modules
Modules contained in this resource:
• Section 1: Receptacle and branch circuit
• Section 2: Service panel
• Section 3: Transformer
• Section 4: Motor and drive
• Section 5: Commercial lighting
PQ Troubleshooting Philosophy
• Start at the scene of the crime
• Examine the victim (the load)
PQ Troubleshooting: Bottom-up
• Example: High harmonics everywhere
• Load location
• Problem location, most likely causes
• Monitoring issues
PQ Troubleshooting:
Getting Started
• Make a simplified “as-built” one-line
• Do a walk-around
• Interview witnesses
Power Distribution System
2. Distribution Transformer
Branch circuit and
receptacle measurements
• Line-neutral voltage
• Neutral-ground voltage
• Transients, sags, swells, and outages
• Ground loops and noise
• Performance wiring
Receptacle Line to Neutral Voltage
Source Impedance (Z)
Receptacle Flat-topped Voltage
N-G Voltage Measures Loading
N-G Voltage & Shared Neutrals
Transients
• Causes
• Effects
• Protection
Transients and Power Supplies
Capturing Transients – Single Phase
Capturing Transients –
Three Phase
120V Receptacle Sag Incidence
120V Receptacle Trending
Voltage Event Recorders
Voltage Event Recorder: Details
ITC Curve
Electrical Signal-to-Noise Ratio
Sources of Noise: Ground Loops
Coupled CM Noise
Branch Circuit Solutions:
Performance Wiring
Branch Circuit Summary
• Bottom-up troubleshooting
• Measurements
• Solutions
Power Quality Troubleshooting:
Panel
Feeder Current
Feeder Phase Balance
Neutral Current
Neutral current
180 Hz waveform
40.57A
3rd Harmonic
Feeder N-G Voltage
Three-phase measurements
Isolating Source of Disturbance
Load Side N-G Bonds
Service Panel Solutions
PQ Troubleshooting:
Panel Summary
• Inspection
• Measurements
• Solutions
Power Quality Troubleshooting:
Transformer
Transformer kVA, Balanced Load
For a balanced load:
kVATOTAL= kVA PHASE-PHASE (1.73)
Transformer kVA, Unbalanced Load
For an unbalanced load:
kVATOTAL= kVA1 + kVA2 + kVA3
Transformer Harmonic Spectrum
• Typical current harmonics:
• Single-phase loads:
3rd harmonic
• three-phase loads:
5th and 7th
• Beware of resonance
Voltage Harmonics, THD
Current Harmonics, TDD
Understanding TDD Specs
Comparing THD and TDD
Transformer Derating Curve
Transformer Derating and CF
Transformer Solutions: K-Factor
• A measure of the heating effects of harmonics
• Read at transformer not at load
Separately Derived System
Transformer as SDS
• Secondary is source
• Lower source impedance
• Electrical isolation
• Ground reference
Correct Grounding of SDS
Transformer Grounding
Bubble Principle
Transformers, Summary
• Measurements
• Inspections
• Solutions
Lightning Protection
Surge Protection
Three Levels:
• Surge Arrestors
• Surge Suppressors (TVSS)
• Point of Use
PQ Troubleshooting:
Motors and Drives
• Voltage unbalance
• Voltage %THD
• Current unbalance,
single phasing
• Loading
• Inrush current
• Power Factor
Voltage Balance on 3-Ø Motors
Motors: Voltage Distortion
Motors: Current Unbalance
and Loading
• Measure current unbalance
• Measure loading
Motors: Inrush Current
What is Power Factor?
Power Triangle
Total Power Factor (PF)
Power Factor Correction
PF Measurement:
2-Wattmeter Method
PF – Three phase analyzer method
PF Measurement:
Grounded-Y Method
Correct PF to Reduce the Utility Bill
• Kilowatt hours
• Peak demand
• Power factor
• Total kVA
AC Adjustable Speed Drives
• ASDs benefit power system
• ASDs as victim loads
• ASDs and notching
Capacitors Attract Harmonic Currents
Capacitors and System Resonance
DPF and Harmonics Mitigation
Power System
Resonance Solutions
• Capacitors
• Filters
• Drives
• Drive leads
Motors and Drives: Summary
• Measurements
• Solutions
Commercial Lighting
• Power (kW)
• Power Factor
• Harmonic distortion
• Voltage stability