Interested to Buy Any Domain ? << Click Here >> for more details...
why do we use star-delta starter. what is its need?
- 6 Answers
- 49659 Views
- I also Faced
- E-Mail Answers
Answer Posted / 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 |
Post New Answer View All Answers
I want to replace the 3 KW DC motor with AC motor so what should be the rating of AC motor? Details Of DC motor to be changed with AC are - Kw - 3, Vf - 310, If - 0.15, Va - 400, Ia - 13, RPM - 2400
why is the conservator tank painted white on the transformer
What is the diff. between single compression and double compression gland
1.what is difference between ATS & STS main use. 2.what is difference between ACB& VCB With symobles,and main partes, manimum range. 3.How many types of relays and main function.
Control wiring of a dol starter for forward and backward
Why do not we prefer non conventional sources of energy to conventional sources?
why Lightening Arrester Probe sharp at Top of telecom tower.
Dear All, I am new in construction company , my boss ask a question at time of interview , If we have 60MW generation and Single Power Transformer step-up we have. if CMR 50/60MVA , ONAN, ONAF respectively , is it sufficient or not ? for that much power to transfer,
what is frequency response?
why we are using earth pit in sub stations.?
54 Comments Alok and Bhanu play the following min-max game. Given the expression N = 38 + X*(Y – Z) where X, Y and Z are variables representing single digits (0 to 9), Alok would like to maximize N while Bhanu would like to minimize it. Towards this end, Alok chooses a single digit number and Bhanu substitutes this for a variable of her choice (X, Y or Z). Alok then chooses the next value and Bhanu, the variable to substitute the value. Finally Alok proposes the value for the remaining variable. Assuming both play to their optimal strategies, the value of N at the end of the game would be?
sir, 3phase induction motor takes different pf and different KW in three phase while running,explain reason
why we use 630mm single core cable for transformer secondary side and why two neutral cable
how we calculate torque ? how we improve it ?where torque will either motor or generator ?
Scott connection is used for A 3-phase to 2-phase conversion B to achieve higher effciency C to save copper D to reduce harmonics
