Answer / guest

DOL-Direct on line Starter, here the starting current will
be 6 times of full load current. A bimetallic thermal
overload relay provides protection against the over load.
There will be no reduction of starting torque during
starting.

Star Delta Starter:In order to limit the starting current
of motors this method is followed. Initially motor windings
are connected in star configuration. The applied voltage
across the winding is reduced 1/1.73 times of rated voltage
due to reduced the voltage current also reduced. Once the
motor reaches the rated speed windings are connected in
Delta. There is 66% reduction in starting toque

Auto Transformer Starters:
In this method windings of the motor is permanently
connected in delta. Reduced starting current is achieved by
applying reduced voltage by means of an auto transformer
while starting, The tapping of auto transformer will be
60%,70%,80% after attaining full speed of the auto
transformer is bypass from the circuit and full system
voltage is applied to the winding, there is a proportional
reduction in starting torque depending upon the taping
selected.

Soft Starter :
Soft starters are Thyristor Drives The rms value of
theapplied voltage is reduced by controlling the firing
angle of power Thyristor. The achieving the full speed
Thyristor conducts in full. Here the starting voltage can
be varied from Zero to maximum value and the motor starting
is vary smooth. Similarly soft-stop facility is also
available therby the motor can be stopped by gradually
reducing the speed.

VFD or VSD:
In VFDs the 50Hz AC is rectified into DC and again inverted
as variable frequency supply , the variable frequency is
achieved by thyristor controlled inverter.
the frequency can be varied from 0-200% This makes speed
contol possible in squrrel cage induction motor. At maximum
frequency the voltage will be eaual to maximum supply
voltage

Answer / vinod

dol--direct online starter.a contactor is connected across
the phase during the start.here the current will be more

VSD--VARIABLE SPEED DRIVE--they are actually used for speed
control.in some places they are used for starting
purpose,because the acleration can be programmed

s/s: they are made up of thyristors.each block prosuces a
modulated step by step input

a/t--they are also called as variac.the voltage can be
increased gradually through a cap.

In PFI plant one stage capacitor connection is directly connected(with out megnetic contact controll). but why?

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HOW TO TEST THE SODIUM VAPOR AND MERCURY VAPOR LAMP ?

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if a motor has 1500rpm then what will its HP?

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i need to now what will be the cable size to the following load, transformer to distribution panel distance 110m, load 1000kw, voltage 400v, pf 0.85, permissible voltage drop 2.0%, overhead line, atmospheric temperature 35 degree c.

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During the main stator winding insulation testing (phase to ground)of 11kv alternator (Lerysomer) i found 0 and resistance with multimeter and found 20 killo ohm while the power cables are connected both end (Generator & VCB). In VCB PT (Potential transformer) are connected. Please any body explain that method of insulation is correct or not? also describe of PT connections

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How phase displacement change in the over current relay coils.

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what is the means of dedicate earthing?

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bit confused - am i correct in thinking that to determine line to line voltage in a star config 110v 3 phase 4 wire distribution system i would use a voltmeter? I have a circuit configured as an unbalanced load, consisting of three incandescent lamps (1x40w, 1x60w, 1x100w - all 110v rated)connected in a star configuration to a 110v 3 phase 4 wire distribution system. I want to find out what types of meters i would use to obtain: a) each line to line voltage b) the line to neutral voltage across each load c) current flowing in each line and load d) current flowing in the neutral conductor e) power supplied to the loads im assuming i would be using ammeters in series along each line and voltmeters in parallel across each line to neutral? Also how could i predict these meter readings before taking them and with which formulae? Any help would be greatly appreciated A.

1 Answers  

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