POWER QUALITY
-- Bhanu Bhushan -<a3bhanu@gmail.com>
June, 2011
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• How close is the supply voltage waveform
to sinusoidal, and how close are the supply
voltage and frequency to the rated ?
• What Power Quality do we actually have ?
What Power Quality do we really need ?
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POWER QUALITY
in a wider, Indian perspective
GRID - Level
& CONSUMER - Level
1) SUPPLY CONTINUITY
2) FREQUENCY
3) VOLTAGE
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SUPPLY INTERRUPTIONS
a) LOAD - SHEDDING due to own or others’
over-drawal : Maximize generation, and
allow over-drawal, as long as grid can
sustain it, and it is paid for.
b) LOAD - SHEDDING to curtail over-loading
or under-voltage : If too frequent, ask for
system augmentation, additional capacitors.
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c) TRIPPING due to a fault or equipment
failure : Minimize outage duration,
: Reliable protection, Auto-reclosing,
: Ask for building redundancies.
FREQUENCY : covered in another session.
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VOLTAGE PROBLEMS
• HIGH / LOW : Can be corrected by
transformer tap-changing and reactive
compensation : shunt / series capacitors,
reactors, SVC, MVAR generation change.
• SWELLS & SAGS, SPIKES & DIPS,
FLICKER : Caused by switching on / off
of large loads, capacitor banks, electric
furnaces, welding machines.
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• PHASE UNBALANCE : Caused by single
- phase or unbalanced loads (e.g. railway
traction), pole - discrepancy, break in a
phase (conductor snapping), break in
neutral, hanging faults, non-transposition.
• WAVE FORM DISTORTIONS
(HARMONICS and DC offset) : caused by
HVDC, SVC, FACTS, Converters, UPS,
power / speed controllers, computers,
TVs, chargers, printers, tube-lights, CFLs,
fan regulators, electronic ballasts,
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communication equipment, arc furnaces,
welding, railway traction, etc.
Circuit breaker and isolator operation
(switching transients), L.A., transformer
magnetizing current inrush, lightning,
Faults and their clearance, insulator flashover, corona, faulty grounding.
Adverse effects : Over-heating & noise,
resonance, telephone interference, hum,
capacitor failure, mal-operation of control
device and medical equipment.
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POSSIBLE SOLUTIONS : Circuit
segregation, harmonic filters, U.P.S.
DAMPING by synchronous and induction
machines.
A use of harmonics: Harmonic restraint in
transformer differential relays.
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Simple examples around us :
• Ceiling fan regulators
• Tube lights
• Lap-tops & peripherals
• Domestic inverters
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Ceiling fans -- 1- ph Induction motors,
shaded - pole or split - winding, inverted.
Fan regulators -- 3 different types:
i) Choke : weighty, costly, low PF
ii) Resistor : energy loss, heating
iii) Electronic : voltage and current
distortions, harmful on both sides.
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Supply voltage and fan current, regulated by old
resistance type regulator, at full-speed
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Supply voltage and fan current, regulated by old
resistance type regulator, at low speed
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Fan current, regulated by electronic regulator,
at full speed
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Fan current, regulated by electronic regulator,
at low speed
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Harmonics in fan current, at low speed,
with electronic regulator
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Voltage wave form, after electronic regulator
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Harmonics in fan voltage, at low speed
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Tube lights : non-linear discharge lamps.
Smoothening & PF improvement by choke
and capacitor. Not a serious problem.
Electronic ballasts : V & I distortions ?
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Tube light current waveform
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Lap-tops & peripherals : AC / DC adapters
draw non-sinusoidal current.
Domestic inverters : Battery charging
current is always non-sinusoidal.
INDUSTRIAL U.P.S.
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Voltage Wave form – UPS output
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Harmonics in UPS output voltage
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IEEE Standard 519 - 1992
Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems
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