What is the Difference between Megger and
contact resistance meter?
Megger is maily used to measure very high resistance like insulation resistance of a cable, to test the continuity of a conductor, identification of the phase sequence etc. where as contact resistance
meter used to measure low resistance like relays , contactors.
What is the use of connecting the
capacitor bank in series with the power transmission lines ?
we connect capacitor bank in series to improve the
voltage profile at the load end, in transmission line there is considerable
voltage drop along the transmission line due to impedance of the line. so
in order to bring the voltage at the load terminals within its limits i.e (+ or
- (6%) ) of the
rated terminal voltage the capacitor bank is used in series.
What is Diversity factor in
electrical installations?
Diversity factor is the ratio of the sum of the
individual maximum demands of the various subdivisions of a system, or part of
a system, to the maximum demand of the whole system, or part of the system,
under consideration. Diversity factor is usually more than one.
Why the motor field rheostat is kept
in minimum position while armature rheostat at maximum position?
In motors at the time of starting the armature
resistance is introduced to reduce the high starting current and the field
resistance is kept minimum to have high starting torque.
Why humming sound occurred
in HT transmission line?
This sound is coming due to ionization (breakdown of
air into charged particles) of air around transmission conductor. This effect
is called as Corona
effect, and it is considered as power loss.
what is rated speed?
At the time of motor taking normal current (rated
current) the speed of the motor is called rated speed. It is a speed at which
any system take small current and give maximum efficiency.
What is difference between
grounding and earthing?
Grounding means connecting the neutral point of the
load to the ground to carry the residual current in case of unbalanced
conditions through the neutral to the ground whereas earthing is done in an
electric equipment in order to protect he equipment in occurrence of fault in
the system.
Why should be the frequency
is 50 hz only why not others like 45, 95, 56 or anything , why should we
maintain the frequency constant if so why it is only 50 ?
We can have the frequency at any frequency you
like, but than you must also make your own motors, transformers or any other
equipment you want to use.We maintain the frequency at 50hz or 60hz cos the
world maintains a standard at 50 /60 hz and the equipment's are are made to
operate at these frequency.
Why transformer rating in KVA instead of KW?
Any device is rated depending on losses of the machine. In a transformer the
losses are iron losses which depends on voltage and copper losses which depends
on current so there are no losses which depend on power factor hence
transformer is rated in KVA.
There are 2 losses in transformer. One is copper loss which depends on
current and the other is iron loss which depends on voltage. These two factors
are not affected by the power factor. This is why transformers are rated in KVA
and not KW. Single phase KVA = Amps x Volts/1000. Single phase KW = Amps x
Volts x pf/1000. 3 phase KVA = Amps x Volts x 1.73/1000. 3 phase KW = Amps x
Volts x 1.73 x pf/1000
There are two type of losses in transformer is that ohmic losses and
core losses . ohmic losses due to transformer current and core losses due to
transformer voltage. these losses are due to transformer voltage and current.
and these losses not depends on load ie kw that's the way its rating in kva..
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