1- Frequency
distortions/fluctuating
A frequency variation involves variation in frequency above or below the normally stable utility frequency of 50 or 60 Hz
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OLTC MEANS ON LOAD TAP CHANGER
A frequency variation involves variation in frequency above or below the normally stable utility frequency of 50 or 60 Hz
Cause
·
Start-up or shutdown of very
large item of consumer equipment, e.g. motor
·
Unstable frequency power sources
Effect
·
Miss operation, data loss, system
crashes and damage to equipment and motor
·
For certain kinds of motor load,
such as in textile mills, tight control of frequency is essential
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2- Voltage dip /
sag or swell
Any short-term (half cycle to 3
seconds) decrease (sag) or increase (swell) in voltage
Cause
·
Start-up or shutdown of very
large item of consumer equipment, e.g. motor
·
Short circuits (faults)
·
Utility equipment failure or
utility switching
Effect
·
Memory loss, data errors, dim or
bright lights, shrinking display screens, equipment
·
Shutdown
·
Motors stalling or stopping and
decreased motor life
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3- Flicker
Flicker is a periodically
repeated voltage fluctuation
= Impression of unsteadiness of visual
sensation induced by a light stimulus, the luminance or spectral distribution
of which fluctuates with time.
Cause
·
Intermittent loads
·
Motor starting
·
Welding plants
Effect
Changes in the luminance of lamps
can result in the visual phenomenon called flicker on people, disturbing
concentration, causing headaches, etc.
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4- Transient
A transient is a
sudden change in voltage up to several thousand volts. It may be of the
impulsive or oscillatory type (also termed impulse, surge, or spike)
Cause
·
Utility switching operations,
starting and stopping heavy equipment, elevators, welding equipment static
discharges, and lightning
Effect
·
Processing errors
·
Data loss
·
Lock-up of sensitive equipment
· Burned circuit boards
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5- Harmonic
Distortion is alteration of the
pure sine wave due to non-linear loads on the power supply
Cause
·
Non-linear loads
Effect
·
Harmonic distortion causes
motors, transformers, and wiring to overheat
·
Improper operation of breakers,
relays, or fuses
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6- Inter-harmonics
It consists of non-integer orders
of the fundamental frequency.
Cause
·
This is generated by a
voltage/current waveform distortion caused by an electronic frequency
converter, cycle converter, Scherbius system, inductive motor, welder or arc
furnace, etc.,
Effect
·
Cause damage, malfunction or
deterioration of equipment due to the zero-cross shift of the voltage waveform.
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7-
Power factor
The conventional explanation of
power factor assumes a pure sine wave of volt and current, this is
associated with a system have not any
power semiconductor component.
In this case (pure sine wave) the power factor
is defined as the ratio of active power (watt) to the apparent power
(volt-ampere)
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8
K- factor
·
K-factor is a weighting of the
harmonic load currents according to their effects on transformer heating.
·
When a non-linear load is
supplied from a transformer, it is sometimes necessary to derate the
transformer capacity to avoid overheating and subsequent insulation failure.
·
The reason for this is that the
increased eddy currents caused by the harmonics increase transformer losses and
thus generate additional heat.
·
The K-Factor is used by
transformer manufacturers and their customers to adjust the load rating as a
function of the harmonic currents caused by the load(s).
·
Generally, only substation
transformer manufacturers specify K-factor load de-rating for their products.
·
From the customer’s viewpoint,
K-factor must be established in order to calculate the size of the transformer
that is needed. In other words, if a company with many offices were to install
poor quality electronic ballasts having a poor K-factor, a larger transformer
would be needed than is apparent from the overall power consumption
calculation.
·
The K-factor is a number derived
from a numerical calculation based on the summation of harmonic currents
generated by the non-linear load.
K-factor transformers are designed to reduce the
heating effects of harmonic currents created by loads like those in the table
below. The K-factor rating is an index of the transformer's ability to
withstand harmonic content while operating within the temperature limits of its
insulating system.
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9-
Crest Factor
·
Crest factor is the ratio of the
Peak value of a sinusoidal waveform to its RMS value.
·
Crest factor indicates the level
of peaking which an instrument can handle without measurement errors.
·
For a perfect sine wave the crest
factor would be 1.414. This relates to the Peak amplitude that an instrument
can measure accurately.
·
Typical crest factor ratings are
from 2.0 to 6.0. The higher the factor, the more capable the instrument of
measuring a complex waveform correctly.
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10 - Instrumentation
· Is defined “the art and science of measurement and control".
· instruments are devices, which are used to measure attributes of physical systems. The variable measured can include practically any measurable variable related to the physical sciences. These variables commonly include ( Pressure, Flow, Temperature, Level, Density, Radiation, Current, Voltage, Inductance, capacitance, frequency, chemical composition, chemical properties, various physical properties, etc )
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11- The different between earth and ground
Grounding:
The NEC, National Electrical Code defines a ground as: A conducting connection, whether
intentional or accidental, between an electrical circuit or equipment and the point that has the reference voltage
· Is defined “the art and science of measurement and control".
· instruments are devices, which are used to measure attributes of physical systems. The variable measured can include practically any measurable variable related to the physical sciences. These variables commonly include ( Pressure, Flow, Temperature, Level, Density, Radiation, Current, Voltage, Inductance, capacitance, frequency, chemical composition, chemical properties, various physical properties, etc )
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Grounding:
The NEC, National Electrical Code defines a ground as: A conducting connection, whether
intentional or accidental, between an electrical circuit or equipment and the point that has the reference voltage
Earthing :
Connection with The conductive mass of the earth, whose electric potential at any point is conventionally taken as equal to zero. (In some countries the term "ground" is used instead of "earth.")
Neutral
is the return bath of current that make the circuit is a complete circuit and allow to the electricity to follow .
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12- OLTC
The
function of OLTC is to change the voltage level
of secondary side of transformer according to change in load to meet the
requirement and to keep the voltage constant WITHIN THE LIMITS
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