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2. Overview. What is Power Quality?What are some power quality concerns?What are Harmonics and what causes them?What effects do Poor PQ and Harmonics have on a building power system and components?How can Power Quality and Harmonics Issues be mitigated?Questions. 3. What is Power Quality?. Can

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## Power Quality and Harmonics: Causes, Effects and Remediation Techniques Carol Gowan Chad Loomis, PE

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**1. **1 Power Quality and Harmonics:Causes, Effects and Remediation Techniques Carol Gowan Chad Loomis, PE Cornell University PDC 12/13/2006 Electrical Design Section

**2. **2 Overview What is Power Quality?
What are some power quality concerns?
What are Harmonics and what causes them?
What effects do Poor PQ and Harmonics have on a building power system and components?
How can Power Quality and Harmonics Issues be mitigated?
Questions

**3. **3 What is Power Quality? Can be defined as:
“Any power problem manifested in
voltage,
current,
or frequency deviations
that results in failure or misoperation of customer equipment”

**4. **4 What are general classes of power quality problems per IEC? Conducted low-frequency phenomena
Signal systems (power line carrier)
Voltage fluctuations (flicker)
Voltage dips and interruptions
Voltage Imbalance (unbalance)
Power frequency variations
Induced low-frequency voltages
DC in ac networks
Harmonics, interharmonics
Radiated low-frequency phenomena
Magnetic and Electric Fields

**5. **5 Categories and Characteristics of Power System Electromagnetic Phenomena (IEC)

**6. **6 Voltage Fluctuations withinCornell’s Utility Distribution Transients – very quick < 1 cycle
Normal cause is lightning strike
No lights flicker
Cornell Utilities employs lightning arrestors at substations and at primary switches located at each building electric service equipment
End users need to purchase/install TVSS equipment to further clamp the voltage spike.

**7. **7
Sags / Swells
Voltage imbalance lasting from 3-20 cycles
Typical cause ? NYSEG switching on the incoming 115kV transmission line
Lights flickering are indicative of this fault
Utilities does not protect for this condition

**8. **8 Long term voltage fluctuations
As load increases, voltage drops (and vice versa)
Cornell Utilities compensates the long-duration voltage variations through the use of automatic load tap changers at the Maple Ave. substation
System voltage tolerance limits are set in ANSI C84.1. The Cornell system voltages are designed to always operate in the range ‘A’ limits (108 – 126V)
* refer to IEEE 141-1993

**9. **9
Harmonic Distortion
Typically generated within a facility, not a distribution issue
Utilities does not protect for this condition

**10. **10 CBEMA curve for susceptibility of 120V Computer Equipment Computer Business Equipment Manufacturers Association
Early 1980’s CBEMA designed the curve to point out ways in which system reliability could be provided for electronic equipment

**11. **11 ITIC curve for susceptibility of 120V Computer Equipment Information Technology Industry Council
This derivation was developed to show a curve that more accurately reflects the performance of typical single-phase, 60-Hz computers and their peripherals

**12. **12 Computer Equipment Disturbance Table(Dranetz-BMI Field handbook for PQ Analysis)

**13. **13 What are NOT proper descriptors of power quality problems per IEC? Blackout
Blink
Brownout
Bump
Clean Ground
Clean Power
Dirty Ground
Dirty Power

**14. **14 What are the causes of most trouble tickets issued for computer problems at Cornell? Internally (building area specific) induced problems
Shared neutrals
Overloaded circuits (breakers tripping)
Poorly or improperly grounded circuits
Note there are VERY minimal utility / delivery issues (we are very fortunate here at Cornell!)
Handful of harmonic issues in the last 20 yrs, but harmonics are becoming a larger concern with more sophisticated systems and buildings.

**15. **15 What Are Harmonics? “A component frequency of a harmonic motion of an electromagnetic wave that is an integral multiple of the fundamental frequency”
US fundamental frequency is 60 Hertz
3rd Harmonic is 3 x 60Hz or 180Hz
5th Harmonic is 5 x 60Hz or 300Hz, etc.

**16. **16 What Causes Harmonics?
Non-Linear Loads
Current is not proportional to the applied voltage

**17. **17 Linear loads and current waveforms.
Pure resistance, inductance, and capacitance are all linear.
What that means:
If a sine wave voltage of a certain magnitude is placed across a circuit containing pure resistance, the current in the circuit follows Ohm's Law: I = E ÷ R.
So, for a specific value of ohms, the relationship of volts and amperes is a straight line. The current will always be a sine wave of the same frequency.
Linear Loads include Incandescent lighting, heating loads, and motors Linear vs. Non-linear loads and current waveforms

**18. **18 Linear vs. Non-linear loads and current waveforms Nonlinear loads and current waveforms.
Solid state electronics is based on the use of semiconductors. These materials are totally different in that their response to voltage is not a straight line.
What this means:
With a nonlinear load, you cannot easily predict the relationship between voltage and current — unless you have an exact curve for each device. With equipment containing many solid-state devices, such an approach is impossible.
Nonlinear loads are switched on for only part of the cycle, as in a thyristor-controlled circuit, or pulsed, as in a controlled-rectifier circuit.

**19. **19 Effect of harmonics on waveform

**20. **20 What do harmonics do? Harmonics are carried through the system from the source and can nearly double the amount of current on the neutral conductor in three phase four wire distribution systems.
Distorted currents from harmonic-producing loads also distort the voltage as they pass through the system impedence. Therefore, a distorted voltage can be presented to other end users on the system.
Overall electrical system and power quality is affected by the introduction of harmonics.

**21. **21 Sources of Harmonics Solid State Electronic Devices which contain a poor power supply
Computers (PCs/CPUs)
Laser Printers
Copy Machines
*Solid State UPS Units
Solid State Devices (Fluorescent lighting ballasts)
**Rectifiers (AC-DC Converters ? VFDs)
Welding Units
Arc Furnaces

**22. **22 What are the order of typical harmonics generated by non-linear loads?

**23. **23 Effects of Harmonics Distorted Voltage
Overheated Transformers and Motors
Increases Hysteresis (magnetization) losses in steel and iron cores of transformers, motor and magnetic trip units of circuit breakers (Equipment inefficiencies and overheating)
Heating of Neutral Conductors
Skin Effect ? Increased amount of current flowing on the outside of conductors (overheating)
Low Voltage at End Loads
High Neutral to Ground Voltages at End Loads

**24. **24 Effects of Harmonics (cont) Operation Problems of Relays and Circuit Breakers
Thermal/Magnetic Trip Circuit Breakers
Fuses & bimetal strips respond to True RMS
Harmonic currents increase eddy current losses in the core steel of the metallic strip.
This causes an OVERprotection situation… Increased losses generate additional heat, this effect the thermal trip of the unit.
Electronic Trip Circuit Breakers
Magnitude and phase angle(s) of harmonic current(s) in relationship to the fundamental current can cause:
Overprotection when: Peak current sensing > True RMS
Underprotection when: Peak current sensing < True RMS
Changing power system loads will vary the magnitude and phase angle, resulting in inaccurate and unpredictable sensing units and overload protection

**25. **25 Effects of Harmonics (cont) Communication Problems
If sharing common parallel path, potential for harmonics to have inductive coupling effect on unshielded cabling
Current Measurement Problems (distorted waveform)
Unreliable Operation of Electronic Equipment
Mis-operation of electronic equipment that measures frequency or uses the zero crossing point of a sine wave.
Control of Speed and Voltage Problems on Emergency Generators (supplying power)
Capacitor Bank Application Problems (heating)
Computer (PC/CPU) data errors / data loss
Affects power supplies and sensitive electronics

**26. **26 How can Harmonics be Reduced? Isolate harmonic loads on separate circuits (with or without harmonic filters)
Harmonic mitigating transformers
Phase shifting (zig-zag) transformers
Used to cancel out specific harmonics by making one voltage circuit 180 degrees out-of-phase
Filter capacitor backs

**27. **27 How can Harmonics be Reduced? For VFD and UPS specifically:
Line Reactors
K-Rated / Drive Isolation Transformers
Harmonic Mitigating / Phase Shifting Transformers
12, 18 or 24 pulse Converters
Passive parallel / series tuned Filters
Active Filters

**28. **28 How can Harmonics be Reduced? PROPER GROUNDING
Neutral to ground conductor connection at one location; at main panel or transformer secondary
When neutral is connected to ground at multiple locations, interference can occur with sensitive electronic devices.
Run power and control conductors in separate raceways
Sensitive loads should not share neutral and ground conductors.
Avoid using conduit as the ground return path, run dedicated ground wire with circuit conductors
Refer to IEEE Std 1100-1992 (Emerald Book)

**29. **29 Computer Equipment Grounding TOP ? Radial or “daisy chain” grounding Although Code compliant per NEC, small differences in potential can cause unintended ground loops
BOTTOM ? Best method for grounding is via dedicated equipment grounding conductors back to the source

**30. **30 IEEE Defined Harmonic Current Limits

**31. **31 Voltage Limit /HarmonicsEvaluation Procedure

**32. **32 Questions?
Thank You!
Cornell Planning, Design & Construction
Carol Gowan 254-1457 cag57@cornell.edu
Chad Loomis 255-8039 cel36@cornell.edu

**33. **33 Simplified Distribution System Diagram

**34. **34 Simplified Distribution System Diagram

**35. **35 Simplified Distribution System Diagram

**36. **36 Simplified Distribution System Diagram

**37. **37 Simplified Distribution System Diagram

**38. **38 Simplified Distribution System Diagram

**39. **39 Simplified Distribution System Diagram

**40. **40 Simplified Distribution System Diagram

**41. **41 Simplified Distribution System Diagram

**42. **42 Simplified Distribution System Diagram

**43. **43 Simplified Distribution System Diagram

**44. **44 Typical PQ Evaluation Process

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