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Understanding Harmonics. Richard Molloy Technology Sales Manager, Power Quality. Agenda. Introduction Definition of ‘Power Quality’ Identification of power quality problems Harmonics – causes and effects Mitigation techniques Conclusion. The cost of poor power quality.

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understanding harmonics

Understanding Harmonics

Richard Molloy

Technology Sales Manager, Power Quality

agenda
Agenda
  • Introduction
  • Definition of ‘Power Quality’
  • Identification of power quality problems
  • Harmonics – causes and effects
  • Mitigation techniques
  • Conclusion
the cost of poor power quality
The cost of poor power quality
  • Cost of power quality problems to European industry & commerce is estimated at €10 billion per annum
  • Expenditure on preventative measures is less than 5% of this
definition of power quality
Source – Leonardo Power Quality InitiativeDefinition of Power Quality
  • ‘A supply that is always available, always within voltage and frequency tolerance, with a pure, noise free, sinusoidal wave shape’
how good is good enough
How good is good enough?
  • No definitive answer – entirely dependant on compatibility of equipment and supply
power standards
Power standards
  • Power standards are defined by the electricity regulator OFGEM
    • Standard EN 50 160
    • ‘Voltage characteristics of electricity supplied by public distribution systems’
en 50 160
Long term interruptions 10 to 50

Short term interruptions 30 to 1000

Dips 30 to 1000

Short-term over-voltage <1.5kV

Steady state voltage 230V +/- 10% for 95% of time

Voltage unbalance <2% for 95% of time

EN 50 160
en 50 1601
Total harmonic distortion </= 8% for 95% of time

Transient over-voltages Majority <6kV

Frequency 50Hz +/- 1% for 99.5% of time

Frequency 50Hz +/- 2% for 100% of time

EN 50 160
identification of problems
Identification of problems
  • Harmonic distortion
  • Voltage sags (‘dips’, ‘brownouts’)
  • Voltage swells (‘surges’)
  • Outages (‘power cuts’, ‘blackouts’)
  • Transient voltage surges (‘spikes’)
  • Earthing (‘grounding’)
  • Poor power factor
definition
Definition
  • Waveforms with frequencies that are multiples of the fundamental frequency (50Hz UK & Europe, 60Hz North America)
waveforms fundamental
Waveforms - Fundamental

Fundamental Wave, 50Hz

waveforms fundamental and 2nd harmonic
Waveforms – Fundamental and 2nd Harmonic

Fundamental Wave, 50Hz

2nd Harmonic, 100Hz

waveforms fundamental 2nd and 3rd harmonic
Waveforms - Fundamental, 2nd and 3rd harmonic

Fundamental Wave, 50Hz

2nd Harmonic, 100Hz

3rd Harmonic, 150 Hz

causes of harmonics
Causes of harmonics
  • Harmonic currents are caused by the use of non-linear loads:
    • Switched mode power supplies
    • HF fluorescent ballasts
    • Compact fluorescent lamps
    • Inverters
      • Variable frequency drives
      • UPS systems
effects of harmonics
Effects of harmonics
  • Erroneous operation of control systems
  • Excessive heating in rotating machines
  • Overloading of transformers
  • Overloading of switchgear and cables
  • Nuisance tripping of circuit breakers
effects of harmonics1
Effects of harmonics
  • Overloading of capacitors
  • Damage to sensitive electronic equipment
  • Excessive currents in neutral conductor
effects of triple n harmonics
Effects of Triple-N harmonics
  • Triple-N harmonics are odd multiples of 3 times fundamental frequency, i.e., 3rd, 9th, 15th etc.
  • They are all in phase and sum in the neutral conductor
  • Switched Mode Power Supplies (SMPS) produce a lot of 3rd harmonic - this is especially problematic in commercial buildings due to the vast number of computers, office equipment etc.
effects of triple n harmonics2
Effects of Triple-N harmonics
  • A 3-phase star connected system with a balanced linear load has no current flowing in the neutral
  • Where a lot of 3rd (or other triple-N) harmonics are present, neutral currents can be considerably in excess of phase currents
  • This causes overheating of neutral conductors. Note these may only be 50% rated in older buildings
  • Neutrals do not normally have over-current protection
limits on harmonic distortion
Limits on Harmonic Distortion
  • Harmonic currents flowing back to the supply cause harmonic voltage distortion due to the supply impedance
  • Governed by Engineering Recommendation G5/4
  • Title : ‘Limits for Harmonics in the U.K. Electricity Supply System’.
  • Guidance ONLY
mitigation measures
Mitigation measures
  • Neutral up-sizing
  • Passive filters
  • Active harmonic conditioners
  • Transformer based solutions
neutral up sizing
Neutral up-sizing
  • All neutrals in the system, including switchgear etc., must be rated for the neutral current as well as phase currents
  • A 4 or 5 core 3 phase cable is rated for current flowing in the phase conductors only. Current in the neutral can cause overheating of the cable
  • Above 7th harmonic (350 Hz), skin effect should be considered
  • Cables should be de-rated in accordance with IEC 60364-5-523 / BS 7671 (Appendix 4)
passive filters
Passive filters
  • Capacitor and reactor combination
  • Tuned to specific frequency
  • Requires higher voltage capacitors
  • Designed for a fixed system requirement
avoiding resonance with pfc capacitors
Avoiding resonance with PFC capacitors
  • Calculate the Resonant Frequency
effect of adding reactors
Effect of adding reactors

Current flowing into supply in A

Series Reactor Tuned to the frequency shown below

filters
Single Frequency Filter

Double Tuned Filter

2nd Order High Pass Filter

Filters

|z|

f (Hz)

|z|

f (Hz)

|z|

f (Hz)

active harmonic conditioner
Active harmonic conditioner
  • Harmonic current compensation, 2nd to 25th
  • Harmonic neutral current compensation
  • Global or selective harmonic current compensation
  • Site adjustable compensation parameters
ahc points of connection
AHC points of connection

INCOMING SUPPLY

SUB BOARD 1

SUB BOARD 2

DIS BOARD

DIS BOARD

ahc points of connection1
AHC points of connection

INCOMING SUPPLY

SUB BOARD 1

SUB BOARD 2

AHC GLOBAL

DIS BOARD

DIS BOARD

ahc points of connection2
AHC points of connection

INCOMING SUPPLY

SUB BOARD 1

SUB BOARD 2

AHC GLOBAL

DIS BOARD

AHC PARTIAL

DIS BOARD

ahc points of connection3
AHC points of connection

INCOMING SUPPLY

SUB BOARD 1

SUB BOARD 2

AHC GLOBAL

DIS BOARD

AHC PARTIAL

AHC LOCAL

DIS BOARD

ahc advantages
AHC advantages
  • Continued guaranteed effective harmonic compensation
  • Easy to use and install
  • Auto configures
  • NOT susceptible to harmonic overload
  • Expandable
  • Compatible with electric generators
  • Connected anywhere
transformer based solutions
Transformer based solutions
  • 3rd Harmonic rejection transformers
  • Phase shifting transformers
  • Isolation or harmonic suppression transformers
conclusions1
Conclusions
  • As more electronic equipment is used in industry and commerce, harmonics have become a major power quality problem – more harmonics are generated, and more equipment is adversely affected by these harmonics
  • A combination of good design practice and effective harmonic mitigation measures is required
conclusions2
Conclusions
  • The power quality required will be dependant upon the equipment to be operated at any given location
  • A holistic approach to power quality is required – one solution is unlikely to address all the problems – a combination of equipment will be required to achieve the quality required.
power quality measurement
Power quality measurement
  • Most power quality problems can be measured or monitored – if you suspect a problem, we can conduct a PQ survey to identify:
    • Harmonic distortion
    • Transient voltage disturbance
    • Power factor
    • Load survey
    • Unbalance
    • Flicker