Transcript SMJE 2103

SMJE 2103
Power Quality, Reliability and
Availability
Power quality, reliability and
availability
Topics discussion
1) Power performance
2) Quality, Reliability, Availability
3) Type of PQ problems
4) Solutions
Power Performance
• Due to advance power system loads (ASD, PLC,
EEL), costumers need very high power quality
instead of modernization of the system.
• PQ is focusing on clean voltage waveform, but
due to scheduled and unscheduled
disturbances, generated voltage is on signal
interferences.
• Both parties should responsible for preventing
the problems by respecting respective rules.
Quality, Reliability, Availability
• PQ – Any electric supply condition that causes
appliances to malfunction (CP). A PQ problem
might be perceived as noncompliance with
various standards (UP).
• PR – Primarily concerned with all aspect of
customer interruptions, including sustained (>
few minute) and momentary (< few minute)
interruptions.
• PA – The percentage of time a voltage source is
interrupted.
Type of PQ problem
D. A decrease of the normal voltage level between 10 to 90% of the
nominal rms voltage at the power frequency for durations of 0.5
cycle to 1 minute
C. Fault on the transmission or distribution network. Faults in
consumer’s installation. Connection of heavy loads and start-up of
large motor.
Co. Malfunction of infor technology equipment, namely microprbased control system (PCs. PLCs , ASDs , etc) that may lead to a
process stoppage. Tripping of contactors and electro relays.
Disconnection and loss of efficiency in electrical rotating machine.
Type of PQ problem
D. Total interruption of electrical supply for duration from few
ms to one or two seconds.
C. Mainly due to the opening and automatic reclose of
protection devices to decommission a faulty section of the
network. The main fault causes are insulation failure,
lightning and insulator flashover.
Co. Tripping of protection devices, loss of information and
malfunction of data processing equipment. Stoppage of
sensitive equipment such as PC, PLC, ASD, if they are not
prepared to deal with this condition.
Type of PQ problem
D. Total interruption of electrical supply for
duration greater than 1 to 2 seconds.
C. Equipment failure in the power system
network, storms and objects (trees, cars, etc)
striking lines or poles, fire, human error, bad
coordination or failure of protection devices.
Co. Stoppage of all equipment.
Type of PQ problem
D. Very fast variation of the voltage value for durations
from a several ms to few ms. These variations may
reach thousands of volts, even in low voltage.
C. Lightning, switching of lines or power factor correction
capacitors, disconnection of heavy loads.
Co. Destruction of components (electronics equip) and of
insulation materials, data processing error or data loss,
electromagnetic interference.
Type of PQ problem
D. Momentary increase of the voltage at the power frequency,
outside the normal tolerance, with duration of more than one
cycle and typically less than a few seconds.
C. Start/stop of heavy loads, badly dimensioned power sources,
badly regulated transformers (mainly during off-peak hours)
Co. Data loss, flickering of lighting and screens, stoppage or
damage of sensitive equipment, if the voltage values are too
high.
Type of PQ problem
D. Voltage or current waveform assume non-sinusoidal shape. The
waveform corresponds to the sum of different sinewaves with
different magnitude and phase. Having frequency that are multiples
of power-system frequency.
C. Classic sources: electric machine working above the knee of the
magnetization curve (magnetic saturation), arc furnaces, welding
machines, rectifiers and DC brush motors. Modern source: all nonlinear loads, such as ASDs, data processing equip.
Co. Increased probability in occurrence of resonance, neutral overload
in 3-phase system, overheating of all cables and equipment, loss of
efficiency in electric machines, electromagnetic interference with
communication system, errors in measures when using average
reading meters, nuisance tripping of thermal protections.
Type of PQ problem
D. Oscillation of voltage value, amplitude modulated by a
signal with frequency of 0 to 30Hz.
C. Arc furnaces, frequent start/stop of electric motors
(elevator), oscillating loads.
Co. Most of them are common to under-voltages. The
most perceptible problem is flickering of lighting and
screens, giving the impression of unsteadiness of visual
perception.
Type of PQ problem
D. Superimposing of high frequency signals on the waveform
of the power system frequency.
C. Electromagnetic interferences provoked by Hertzian waves
such microwaves, television diffusion, and radiation due to
welding machines, arc furnaces, and electronic equipment.
Improper grounding may also be a cause.
Co. Disturbances on sensitive electronic equipment, usually
not destructive. May cause data loss and data processing
errors.
Type of PQ problem
D. A voltage variation in a three-phase system in which the
three voltage magnitudes or the phase angle differences
between them are not equal.
C. Large single-phase loads (induction furnaces, traction
loads), incorrect distribution of all single-phase loads by the
three phases of the system (this may be also due to a fault).
Co. Unbalanced system imply the existence of a negative
sequence that is harmful to all three-phase loads. The most
affected loads are three-phase induction machines.
Solution
Solution
(Grid Adequacy)
• Many PQ problem have origin in transmission
and distribution grid.
• Adequate planning and maintenance is
essential to minimize the occurrence of PQ
problem.
Solution
(Distributed Resources – ESS)
• It has potential to provide increased power
reliability.
• Most practical in electrochemical battery
instead of flywheels, super-capacitors and
superconducting magnetic energy due to low
price.
Flywheels
A supercapacitors provides power during
short duration interruptions or voltage sag
SMES
Due to the high inductance, off switch, magnetic coil behaves
as a current source. SMES systems are large and generally
used short duration, such as utility switching events
Solution
(Distributed Resources – DG)
• As a back-up generator to assure energy
supply to critical loads during sustained
outages.
• Also, can be used for load management
purposed to decrease the peak demand.
Solution
(Enhanced Interface Devices)
• Dynamic Voltage Restorer (DVR) – voltage source
connected in series with the load to kept
approximately constant voltage by using Tx.
• Transient Voltage Surge Suppressors (TVSS) – to
damp the transient before it reaches the load.
• Constant Voltage Transformer (CVT) – to mitigate
the effect of voltage sag and transient.
• Noise Filters – to avoid unwanted frequency
current or voltage by using a combination of
capacitors and inductances.
Solution
(Enhanced Interface Devices)
• Isolation Transformer – to isolate sensitive loads
from transients and noise deriving from the main.
The Tx has a grounded shield made of
nonmagnetic foil located between the primary
and secondary.
• Static VAR Compensators – it use a combination
of capacitors and reactors to regulate the voltage
quickly.
• Harmonic Filters – it is used to reduce
undesirable harmonics.
Solution
(Develop Codes and Standard)
• The utilities have to provide some measures to
consumers for the purpose of regulating the
minimum PQ problem level and the immunity
level that equipment should have to operate
properly when the power supplied is within the
standard.
• Such the CBEMA curve – the standard specifies
the minimum withstanding capability of
computer equipment to voltage sag, microinterruptions and overvoltage.
Solution
(Make End use Devices Less Sensitive)
• Adding a capacitor with a larger capacity to
power supplies.
• Using cables with larger neutral conductors.
• Derating transformers.
• Adjusting under-voltage relays.