Introduction to Power Quality

Power Quality, Reliability and Management

What is a Power Quality Problem ? “ Any occurrence manifested in voltage, current, or frequency deviations that results in failure or mis-operation of end-use equipment.” Dictionary

What does that mean? It’s dependant on your susceptibility. Given the quality of supply do I have to worry about problems with my equipment or systems?

Typical Financial Loss Per Event Source: The Cost of Power Quality, Copper Development Association, March, 2001 Industry Typical Loss Financial $6,000,000/event Semi-conductor mfg. $3,800,000/event Computer operations $750,000/event Telecommunications $30,000/minute Data processing $10,000/minute Steel/heavy mfg. $300,000/event Plastics $10,000-15,000/event

Sources Of Power Problems
Referenced at the utility PCC (point of common coupling)
Utility
lightning, PF correction caps, faults, switching
impact from other customers
Internal to the facility
individual load characteristics, motors, ASDs
computers, microprocessors
wiring
changing loads
Typically, 70% of all PQ events are generated within the facility

Types Of Power Quality Disturbances (per IEEE 1159)
Transients
RMS Variations
Short Duration Variations
Long Duration Variations
Sustained
Waveform Distortion
DC Offset
Harmonics
Interharmonics
Notching
Voltage Fluctuations
Power Frequency Variations

Types of Power Quality Problems

What is a Transient?
Momentary (& undesirable) high frequency sub-cycle “event”
Usually measured in microseconds
May also be called a Spike, Surge or Impulse
Characteristics of a Transient:
Rise time (dv/dt)
Ring frequency
Point-on-wave
Multiple zero crossings
Magnitude

Transients -200 -100 0 100 200 Unipolar Positive Negative Notching Oscillatory Multiple Zero Crossings Bipolar

A transient power quality event has occurred on DataNode H09_5530. The event occurred at 10-16-2001 05:03:36 on phase A. Characteristics were Mag = 478.V (1.22pu), Max Deviation (Peak-to-Peak) = 271.V (0.69pu), Dur = 0.006 s (0.35 cyc.), Frequency = 1,568. Hz, Category = 3 Upstream Capacitor Switching

Possible Causes • PF cap energization • Lightning • Loose connection • Load or source switching • RF burst  Possible Effects • Data corruption • Equipment damage • Data transmission errors • Intermittent equipment operation • Reduced equipment life • Irreproducible problems Transients

What is an RMS Variation? (longer duration events)
A change in the RMS voltage. Typically 16 ms (1 cycle) or longer
Reduction in voltage: Sag or Interruption
Increase in voltage: Swell

RMS Voltage Variations 100 -100 0 Sag Swell Interruption

Motor Starting

IEEE1159 Characterizations (RMS Variations)
Instantaneous (0.5 - 30 cycles)
Sag (0.1 - 0.9 pu)
Swell (1.1 - 1.8 pu)
Momentary (30 cycles - 3 sec)
Interruption (< 0.1 pu, 0.5 cycles - 3s)
Sag
Swell
Temporary (3 sec - 1 minute)
Long Duration (beyond 1 minute)

What is Directivity?
Where the problem originated referenced to the point being monitored (where the instrument is)
Typically referred to as “Upstream” or “Downstream”
Upstream
Source side . Originated from the source of supply (can be utility)
Downstream
Load side . Originated from a load
Helps you identify where the problem is and what actions to take.

Case Study – Major Financial Institution (Benefits of Learning Directivity)
Problem – Utility Sag
Damaged elevator controls
No UPS alarms (2 static, 1 rotary)
No reported problems with critical systems
02/19/2002 00:29:29.26 PM Module Input Temporary Sag Rms Voltage AB Mag = 366.V (0.76pu), Dur = 3.300 s, Category = 2, Upstream Sag 02/19/2002 00:29:29.26 SYSA Input Temporary Sag Rms Voltage AB Mag = 353.V (0.73pu), Dur = 3.300 s, Category = 2, Upstream Sag 02/19/2002 00:29:29.26 SYSB Input Temporary Sag Rms Voltage AB Mag = 372.V (0.78pu), Dur = 3.300 s, Category = 2, Upstream Sag

Utility Sag Utility Supply RMS Trend Utility Supply Waveforms

Corresponding UPS Swell Utility Supply UPS Output UPS Swell

Conclusion
Utility sags damaged elevator controls
Corresponding UPS Swell coincident with utility return to normal
Cause of swell being investigated by manufacturer
Possible effects of swells”
Damaged power supplies and other devices
Without monitoring, the customer would be unaware of the UPS problem. The next time, the damage could be worse

PQ Rule #1
For a source generated Sag, the current usually decreases or goes to zero

August 14, 2003 Blackout: Long Duration Interruption

PQ Rule #2
For a load generated Sag, the current usually increases significantly.

 Possible Causes • Sudden change in load current • Fault on feeder • Fault on parallel feeder • Motor start • Undersized distribution system Possible Effects • Process interruption • Data loss • Data transmission errors • PLC or computer misoperation • Damaged product • Motor failure RMS Voltage Variations Causes and Effects

Common RMS Voltage Variations
Visualization methods using power monitoring instrumentation
Sampled data
Recorded Waveforms
Magnitude vs. Time
Timelines
Magnitude vs. Event Duration
CBEMA (IEEE 446)
ITIC
3-D Mag-Dur
Equipment susceptibility curves
Custom curves that represent that specific device

IEEE 446 - 1995 Limits (CBEMA)

Information Technology Industry Council (ITIC) Curve

Another Perspective – 3D Mag-Dur Histogram

( Laser Printer Heating Cycle)
Case Study

Voltage Timeline Vl-n= 120 --> 108 45 seconds

SAG when heater turns on V l-n I load

Overlay Voltage & Current - Heater turning on

An integer multiple of the fundamental frequency Fundamental (1 st harmonic) = 60hz 2 nd = 120hz 3 rd = 180hz 4 th = 240hz 5 th = 300hz … What is a harmonic?

Linear Voltage / Current No Harmonic Content voltage current

Non-Linear Voltage / Current Harmonic Content voltage current

When should I be concerned about Harmonics?
Harmonics are typically considered a problem when they are always present…Steady state distortion that is continuously occurring.
Although any waveform can have harmonics we are typically concerned with the cumulative effects of continual harmonic distortion on the power system

How are harmonics measured?
Individual Harmonics
2, 3, 4, 5, 6…50+
Fourier Transform, FFT, DFT
Total Harmonic Distortion (THD)
Ratio, expressed as % of sum of all harmonics to:
Fundamental (THD)
Total RMS
Load Current (I TDD only)
Interharmonics
Content between integer harmonics
Required for new IEC standards (IEC 61000-4-30)

Harmonic Spectrum

PQ Rule #3
Even harmonics typically do not appear in a properly operating power system .
Symmetry
Positive & Negative halves the same: Only odd harmonics.
If they are different: Even & Odd harmonics

What are Triplen Harmonics?
Harmonics who’s order is a multiple of 3
3, 6, 9, …
Why should I be concerned about Triplen Harmonics?
Triplen Harmonics add in the neutral.

Additive Triplen Harmonics

Harmonics (sustained) Possible Effects • Overload of neutral conductors • Overload of power sources • Low power factor • Reduced ride-through Possible Causes • Rectified inputs of power supplies • Non-symmetrical current • Intermittent electrical noise from loose connections 

( Laser Printer Heating Cycle)
Continued…
Case Study

Current Waveform - heater on

HARMONIC DISTORTION - heater on Ithd = 5% Harmonics V l-n Harmonics I load Vthd = 2.8%

Current With Printer Idle

Harmonic Distortion - Idle Ithd = 140% Harmonics V l-n Harmonics I load Vthd = 3.1%

Review of What We Just Saw
Nearly Sinusoidal Current
Low Voltage Harmonic Distortion (4%)
Voltage and Current In-phase
Power Factor Near One
Flat-topping of Voltage when Idle
Corresponds with Current Pulse

Other PQ Concerns (defined in IEEE 1159)
Frequency
Frequency different from the ideal 50/60hz
Frequency not synchronized with the grid
Unbalance
Deviation from the average 3 phase voltage (IEEE)
Voltage Fluctuations (Flicker)
Small changes to the magnitude of the voltage
Visual perception. Effects on lights

How Many Can You Find?

Monitoring Approaches and Tools
Handheld/Portable
(Reactive) Vs. Permanently Installed (Proactive)

Reactive Monitoring
After the fact - Reactive
Forensic approach
Problem Solving, Hopefully you’ll find it!
Portable instrumentation typically used

Proactive Monitoring
Permanently installed monitoring systems
Anticipate the future, On-Line when trouble occurs
Monitor system dynamics
Preventive Maintenance, Trending, identify
equipment deterioration
Power Quality and Flow

Monitoring Solutions From Dranetz-BMI Portable/Handheld Permanently Installed Get the right tool for the job!

Capabilities Handheld Family

PowerXplorer PX5 PowerGuide 4400 New Products!

8 Channels
4 Differential Voltage, AC/DC
4 Current, AC/DC
256 Samples Per Cycle
50/60HZ, 16/20HZ (railroad)
Harmonics to the 63 rd
Flicker
Low Freq Transients (up to 5KHZ)
Medium Freq Transients (5-10KHZ)
Ethernet, USB, serial commun.
PowerGuide 4400 Color touch screen Unique annunciator

Applications
Inrush
Fault Recorder
Motor Testing
Power Studies
System Commissioning/compatibility
Telecommunications
General Troubleshooting
Compliance
PowerGuide 4400

Advanced Power Quality Analysis
Includes all PowerGuide 4400 Features
High Speed (658/8800 like) Digitized Transients
Advanced Power Analysis
IEEE1459
PX5-400 – 400HZ Option
PowerXplorer PX-5

Applications
All PowerGuide 4400 Plus…
Medical Diagnostic Equipment
Advanced PQ Surveys
400HZ Aircraft, Naval, Military
Utility Surveys
Any 658 or 8800 application
PowerXplorer PX-5

Data to ... ... Information to ... ... Answers Advanced Visualization

Thank You! Questions? Dranetz-BMI 1000 New Durham Rd. Edison, NJ 08818 1800-372-6832 www.dranetz-bmi.com

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Introduction to Power Quality

by Steve Johnson

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