Flicker

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Flicker

• John Outram
• Outram Research Ltd
• Bosham,West Sussex (44) 1243 573050
• johnoutram_at_aol.com, www.outramresearch.co.uk

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Outram Research Ltd PM7000
PM2000
PM1000
SCOUT
PM3000
PM6000
PRONTO
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Flicker

• What is it?
• Is it important?
• How is it caused?
• Relevant Standards
• How is it measured?
• Can we do anything about it?
• Examples

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Flicker What is it?

• A perceptible change in light intensity
• Generally caused by small fluctuations in voltage
  
• Rarely harmful to electronic equipment
• Nuisance - causing annoying, noticeable changes
  in lighting levels

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Is it important?

• Yes!
• Second most common Power Quality problem
• As well as being irritating -
• Can cause Migraines,
• Bring on epileptic fits

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Its effect depends on

• how often and how regularly the voltage
  fluctuates,
• if rapid, the frequency of the flickering
• how much of a voltage change occurs,
• ambient light levels.

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and also on

• The kind of light
• Incandescent
• Fluorescent
• HID - high intensity discharge
• The gain factor of the lamp

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Flicker - Early History

• 1891 Power Distribution Frequency chosen to
  prevent visible Flicker.
• 1921 Early research into human response (lt 10
  Hz)
• 1925 GE Flicker Curve from the 1921 research.
  
• 1937 - Comprehensive study on human perception of
  flicker, validates GE Curve
• 1950s Fluorescent lights introduced concern
  of strobe effects.
• 1964 - Modified GE Flicker Curve gt IEEE Standard

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Organisations feeding IEC

• UIE - The Union Internationale dElectrotherme,
• CIGRE - Conférence Internationale des Grands
  Réseaux Electriques à Haute Tension
• CIRED - Congress International des Reseaux
  Electriques de Distribution
• Significant cross fertilisation from BSI

Nov 2, 2005
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More recent history

• 1980s IEC working groups, leading to
• 1993 - EN60868 Flickermeter, Evaluation of
  Flicker
• 1994 - 61000-3-3 Flicker limits for low voltage
  eqpt lt 16A
• 1994 - 61000-3-5 Flicker limits for LV eqpt gt 16A
• 1996 - 61000-3-7 Flicker limits MV HV systems
  (1kV to 230kV)
• 1995 - EN50160 Public Supply Voltage
  characteristics
• 1998 - IEC 61000-4-15 Flickermeter
• 2005 - IEEE 1453 Flickermeter - as IEC61000-4-15
  with extensions

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Flicker Evaluation on a product(61000-3-3 lt 16A)
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Flicker - Terminology

• Pu - Unit of perception. The average person
  just about sees 1.0 pu
• Pst - Short term flicker perceptibility. The
  average person borders on irritation for a level
  of 1.0
• Measured over a short period, normally 10 minutes
• Plt - Long term flicker perceptibility. Same
  scale as Pst
• Measured over longer period, typ. 2 hours (12 Pst
  intervals)
• Acceptable level is lower than for Pst
• Pfs Instantaneous Flicker Sensation

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Flicker
Nov 2, 2005
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Flicker - causes

• Electric arc furnaces
• Induction motors w/high inrush currents (high
  efficiency AC units)
• Arc-welders, spot-welders
• Wind turbine generators
• Ovens
• Malfunctioning power electronics
• Any large-draw varying load!

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Flicker - Impact

• Worse closer you are to offensive load
• Worse on weak (high impedance) systems
• Larger offensive loads cause more flicker
• Made worse by
• High gain factor lighting
• Lower-inertia lighting
• Dimmers (maybe)

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Flicker
Typical Working Levels on the Network lt 0.1 Pst
is rare.
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Pst evaluation for multiple motor starts
Nov 2, 2005
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IEC Flickermeter
Nov 2, 2005
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PM7000 ltRanger PQ
products, measurement options
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Statistical processor
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Flicker final calculations used in IEC model
P0.1 is flicker level exceeded for 0.1 of the
time, etc.
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IEC Flickermeter
Nov 2, 2005
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Plt calculation when?
Nov 2, 2005
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Mitigation

• Depends on the source of the problem
• Good News!!
• 90 of problems are neutral related, or involve
  poor joints, and some are just unfortunate
  configurations

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Mitigation

• Not so good news
• 10 are serious, and probably expensive, caused
  by heavy industrial plant
• Change feed to offending plant
• Run new feed to sensitive site
• Invest in distribution infrastructure

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S C Electric Company

• STATCOM Static Synchronous Compensator
• Adaptive VAR Compensator (Switched capacitor - ½
  cycle response)

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American Superconductor

• SuperVAR Dynamic Synchronous Condenser
• Flicker mitigation Steel mills, mines, arc
  furnaces.
• Reactive compensation, Dynamic Power Factor
  correction

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Best Characteristics

• Response time 1/4 cycle, though switches can
  operate faster
• Reactive power range up to /- 150Mvar
• Shunt connection at 450V to 400kV
• Minimal harmonics, no special filtering

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Example 1 - Oops!
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Oops!
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Oops!
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Example 2 - Significance of Rate
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Example 3
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High Flicker levels not obvious from Voltage
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Diagnose from Instantaneous Flicker and Current
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Pfs Current unrelated
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2 mins after midnight
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Zoomed to 2 secs
½ cycle of 6 Hz Nearly worst case
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Flicker

• John Outram
• Outram Research Ltd
• www.outramresearch.co.uk

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