why do we use star-delta starter. what is its need?
Answers were Sorted based on User's Feedback
Answer / guest
TO DECREASE STARTING CURRENT AND TO IMPROVE STARTING TORQUE IN
INDUCTION MOTOR
Is This Answer Correct ? | 67 Yes | 11 No |
Answer / riyash mohamed
first of all the basic principle of a starter to use in a motor is to limit the starting current,different starters were used depending upon the watts,this star delta is used above 5kw,
when the starter is connected to a motor ,to prevent it from high starting current it will be connected in star connection after certain second it will be switched to delta for running the motor
Is This Answer Correct ? | 32 Yes | 12 No |
Answer / d.ramesh classes
Technical explanation
When the windings of a 3-phase motor are connected in STAR:
the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service lines in DELTA.
the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA.
so, because of the Power Law V [in volts] x I [in amps] = P [in watts],
the total output power when the motor is connected in STAR is:
PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3)] = PD x (1/3) [one third of the power in DELTA]
where:
VL is the line-to-line voltage of the incoming 3-phase power service
ID is the line current drawn in DELTA
PS is the total power the motor can produce when running in STAR
PD is the total power it can produce when running in DELTA.
by D.RAMESH CLASSES
Is This Answer Correct ? | 19 Yes | 8 No |
Answer / sduhakar
We use star to delta bcoz it can reduce the motor current carrying capacity up to 1/3 times. For DOL stater it's starting current and running is same
Is This Answer Correct ? | 19 Yes | 11 No |
Answer / james allan
Star Delta starters make use of the way current flows in
Star and Delta. In Star Line current = phase current and in
Delta line current =1.73 phase current. During starting it
is also accepted the the current drawn can me as high as 6
times the motor rated current for a short period. When
starting a motor the load needs to be accelarted from rest
to speed and thus requires massive torque. Torque is
directly proportional to the current (which is also
determines the stregth of the magnetic field in the poles
that grab hold of the rotor to drag it along). When
starting in star your line current will equal the phase
current. This means that line current at start will be 1.73
times less than startig the motor in Delta. Power of the
motor stays the same as the voltage in star reduces by a
factor of 1.73. However current through windings generates
heat so you do not want the high current constantly in the
windings as this equates to heat losses by the square of
the current multiplied by the resisitance (Actually it
should be impededance Z which takes induction and
capacitance in the motor into account. Once the load is
accelarated, it does not require as much torque to keep
rotating at its speed so requires less current. At this
point the motor switches over to delta. The phase voltage
ups by a factor of 1.73 and the current reduces by a factor
of 1.73 thus the power consumed is constant. less current
in the windings means less heat losses. Star delta does not
affect the spead of an induction motor. A motor sunning in
star runs at the same speed as a motor running in delta.
Speed of an induction motor is detemined by the frequence
from te supply 50Hz or 60Hz, and the number of poles in the
motor. This is fixed. Only frequency drives can control the
speed iin an induction motor.
Is This Answer Correct ? | 8 Yes | 7 No |
Answer / yogesh
in star-delta starter the starting current is reduced . Its about 1.5 to 3 times the full load . in DOL starter, it will be 6 to 7 times . Its because the starting current taken is just the one single phase current(R or B or Y)( phase current = line current) . thats why star-delta is used in HT motors .
Is This Answer Correct ? | 10 Yes | 14 No |
What is the difference between Static and servo controlled voltage stablizer?
if only one generator is running in droop mode parrallel with grid and suddenly grid breaker off what will happen? It will trip o/u freq or stay as it is? (urgent)
In India the supply voltage is 230 volt A.C. During the negative half cycle phase becomes neutral and neutral become phase? or what will happen during negative half cycle? how the electrons flow during positive and negative half cycle?
how to select a capacitor, i mean we use 3.5 mico ferad cap for a celling fan,but how to select a cap for 1h.p motor,etc.........
Which system use dc to dc high voltage gain A. Solar system B. Battery backup
if the field circuit of a d.c. shunt motor running without load gets opened, then the motor will
what is the difference between a hooter and a mcp
why do we need a 4th wire in 3phase 3wire transmission line
If two hack saw blades, seperated by 1mm thick paper,are connected across 230volts, and immersed in water,then they start getting heat. This is fact,i dont know how they get heated.Blades are not directly connected together. Please if anybody knows the fact ,revert back to me
The SFC of an engine is 0.25 kg/kW hr. when the fuel used has a calorific value of 36000 kJ/kg. the thermal efficiency of the engine is
What is frantic effect?
redundant connection in contactor?