Document 241237

What is Power Quality?
Power Quality (PQ) is a generic term applied to a
wide variety of electromagnetic phenomena in the
electrical power system.
Quite often the term PQ is associated with specific
problems with equipment or system for example
equipment damage, data problem or loss,
equipment malfunction or complete system failure.
The duration of these phenomena ranges from a
few nanoseconds (e.g., transients) to a few
milliseconds (e.g., voltage sags) to steady-state
disturbances (harmonic distortions and voltage
Why is Power Quality becoming a BIG issue
amongst industrial customers?
It is important to note that PQ has been an intrinsic
feature of the electrical power systems since the
earliest times.
Yet in recent decades PQ has become an
increasingly troublesome disturbance, giving rise to
inconvenience and even considerable economic
Categories of Power Quality Events
Voltage Sags, Swells, Transients, Harmonics,
Flickers, Notches, Noises & Unbalance are common
names given to all PQ events (IEC 61000-2-1).
All these PQ events are termed as electromagnetic
disturbances (ED) that form the electromagnetic
environment (EE) for all electrical equipment/
device (IEC 61000-2-4/12).
What is voltage sag (dip)?
The reason is due to the fact that some modern
electricity utilization equipment, either in its own
design or because of control features incorporated
in it, has become more sensitive to PQ events.
The sensitivity to such voltage deviations varies
from one piece of equipment to another, what may
be considered poor PQ to one device may be
perfectly acceptable PQ to another.
Voltage sag (dip) is a short duration voltage
variation and is caused by motor starting, heaters in
printers and copiers cycling, as well as faults in the
power system. Sags often cause lights to dim or
flicker and computer equipment to lock up or lose
There is therefore a need for an increased
awareness of the phenomenon among the
suppliers and users of electricity and the
manufacturers of equipment using electricity.
Technical definitions of Power Quality
Power Quality (PQ) is the concept of powering and
grounding sensitive equipment in a manner that is
suitable to the operation of that equipment (IEEE
Std.1100 & IEEE Std.1159).
According to IEEE Std. 1000 & IEC 60364-4-44,
voltage sensitive equipment requires full protection
against all voltage disturbances.
What is the impact of Power Quality?
PQ affects the reliable operation of computers and
computer-based equipment, which are now so
Often more important than the physical effect on
the equipment is the loss of productivity resulting
from computer equipment failure, mis-calculations
and downtime.
According to the Electric Power Research Institute
(EPRI) from USA, voltage sags are the number one
PQ problem for semiconductor industries and other
voltage sensitive industries.
Electromagnetic Compatibility (EMC)
Power Quality (PQ) is also defined as conducted
electromagnetic disturbances present in electrical
supply network in the frequency range from 0 to 9
kHz. These conducted disturbances make up the
electromagnetic environment (EE) for sensitive
electrical device (IEC 61000-2-1)
EMC highlights the requirement of a device to work
satisfactorily in the existing electromagnetic
environment (EE). To ensure several electrical
devices can function together, they shall not emit
electromagnetic disturbances (emission) and on the
other hand must be able to withstand a certain
level of electromagnetic disturbances (immunity).
compatible with the electromagnetic environment
(EE) of the electrical power system.
For existing equipment, EMC compliance tests must
be performed to verify non compliance. Mitigating
measures must then be implemented to improve
electromagnetic disturbances (ED).
TNB efforts in managing PQ/EMC
Every year, TNB organizes FREE awareness
programs on PQ/EMC for Prime Customers at all
states. TNB has also standardized an internal
procedure (ENGR 750-31) to response to all
complaints regarding PQ/EMC from Prime
How to handle PQ/EMC issues
PQ/EMC problem occurs in every electrical power
system around the world. International standard
bodies e.g. IEEE (US), SEMI (US) and IEC (Europe)
are producing documents on PQ/EMC guidelines
and standards as reference to the power utilities,
equipment manufacturers and equipment users.
TNB also provides technical consultancy on
PQ/EMC mitigation. The technical consultancy
program comprises of three subprograms:•
Technical assessment
Voltage immunity test (voltage sags)
Proposal on mitigation measures to improve
For further information on PQ/ EMC please
According to the EPRI, as much as 80% of PQ/EMC
problems relate to inadequate design for electrical
wiring or grounding requirement.
The best way to avoid PQ/EMC problem is by
ensuring all new equipments to be installed are
Asset Management Department (AMD)
Distribution Division TNB
Wisma TNB, Jalan Timur, Petaling Jaya
46200, Selangor, MALAYSIA
Tel : 603-7967 9000
Fax : 603-7960 0360
Understanding Power Quality
& Electromagnetic Compatibility