WHY THE FREQUENCY IS 50 HZ IN INDIA.CAN WE USE SOME OTHER
FREQUENCY.IF SO WHAT IS THE RANGE AND WHAT WILL BE THE
EFFECT IN PRESENT POWER SYSTEM IF WE CHANGE THE FREQUENCY
AS YOU SUGGEST ?
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Answer Posted / rakesh maurya
In India the electrical supply is based on 230 V Ac supply.
Countries that now use the 50 Hz frequency tend to use 230
V, and those that now use 60 Hz tend to use 120 V.
Unless specified by the manufacturer to operate on either 50
or 60 Hz, appliances may not operate efficiently or even
safely if used on other than the intended supply frequency
Reasons :
Several factors influence the choice of frequency in an AC
system. Lighting, motors, transformers, generators and
transmission lines all have characteristics which depend on
the power frequency.
The first applications of commercial electric power were
incandescent lighting and commutator-type electric motors.
Both devices operate well on DC, but DC cannot be easily
transmitted long distances at utilization voltage and also
cannot be easily changed in voltage.
With AC, transformers can be used to step down high
transmission voltages to lower utilization voltage. Since,
for a given power level, the dimensions of a transformer are
roughly inversely proportional to frequency, a system with
many transformers would be more economical at a higher
frequency.
If an incandescent lamp is operated off a low-frequency
current, the filament cools on each half-cycle of the
alternating current, leading to perceptible change in
brightness and flicker of the lamps; the effect is more
pronounced with arc lamps, and the later mercury-vapor and
fluorescent lamps.
Commutator-type motors do not operate well on high-frequency
AC since the rapid changes of current are opposed by the
inductance of the motor field; even today, although
commutator-type universal motors are common in household
appliances, they are universally of low ratings less than 1
kW. Once the induction motor had been developed, it was
found to work well on frequencies around 50 to 60 Hz but
with the materials available in the late 1800s would not
work well at a frequency of, say, 133 Hz. There is a fixed
relationship between the number of magnetic poles in the
induction motor field, the frequency of the alternating
current, and the rotation speed; so, a given standard speed
limits the choice of frequency (and the reverse).
Electric power transmission over long lines favors lower
frequencies. The effects of the distributed capacitance and
inductance of the line are less at low frequency.
Generators operated by slow-speed engines will produce lower
frequencies, for a given number of poles, than those
operated by, for example, a high-speed steam turbine. For
very slow prime mover speeds, it would be costly to build a
generator with enough poles to provide a high AC frequency.
As well, synchronizing two generators to the same speed was
found to be easier at lower speeds.
Generators can only be interconnected to operate in parallel
if they are of the same frequency and wave-shape. By
standardizing the frequency used, generators in a geographic
area can be interconnected, providing reliability and cost
savings.
Direct-current power was not entirely displaced by
alternating current and was useful in railway and
electrochemical processes. Prior to the development of
mercury arc valve rectifiers, rotary converters were used to
produce DC power from AC. Like other commutator-type
machines, these worked better with lower frequencies.
All of these factors interact and make selection of a power
frequency a matter of considerable importance. The best
frequency is a compromise between contradictory requirements.
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