Tuesday, May 22, 2012

LOCKED ROTOR CURRENT OF A MOTOR


LOCKED ROTOR CURRENT OF A MOTOR
The Locked Rotor Torque or Starting Torque is the torque the electrical motor develop when its starts at rest or zero speed. The magnitude of the Locked rotor current is determined by motor horsepower and design characteristics. Normally it will be 6 to 7 times of the Motor full Load current.
Normally Motor Name plate contains KVA code or Design Letter.
We can calculate the Locked Rotor Current Using the following Formula
Single Phase = (577 x HP x KVA/HP)/V
Three Phase= (1000  x HP x KVA/HP)/V
Find KVA/HP using the Following chart
CODE
LETTER
KVA/HP
RANGE
CODE
LETTER
KVA/HP
RANGE
A
0.00 – 3.14
J
7.10 – 7.99
B
3.15 – 3.54
K
8.00 – 8.99
C
3.55 – 3.99
L
9.00 – 9.99
D
4.00 – 4.49
M
10.00 – 11.19
E
4.50 – 4.99
N
11.20 – 11.49
F
5.00 – 5.59
O
12.50 – 13.99
G
5.60 – 6.29
R
14.00 – 15.99
H
6.30 – 7.09



Example:
Motor Name plate indicates phase 3,300 HP,4160 Volts,KVA Code G
LRC will be
(577 X 300 X 5.60)/4160 to (577 X 300 X 6.29)/4160
=232.02 to 261.73 Amps
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10 comments:

  1. warm Greeting




    Have you been thinking about the power sources and the tiles whom use blocks
    I wanted to thank you for this great read!! I definitely enjoyed every little bit of it and I have you bookmarked to check out the new stuff you post.







    Single Phase Motor

    ReplyDelete
  2. Hi your example calc states phase as 3 but you have used the value 577 as for single...therefor 403A to 453A would be the answer ?

    ReplyDelete
  3. This is a wonderful article, So much info given in it, These type of articles keeps the users interest in the website, keep on sharing more... good luck.

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  4. the relation is (kva/hp × hp × 1000/root(3)×volt)

    ReplyDelete
  5. the relation for calculating the locked rotor current for three phase motors is LRC=(kva/hp × hp ×1000 / root(3) × v(line voltage).

    ReplyDelete
  6. what is the full meaning of Kva

    ReplyDelete
  7. YOU HAVE SINGLE (SHOULD BE 1000) AND THREE (SHOULD BE 577) PH SWITCHED

    ReplyDelete
  8. You can find more information on Instrumentation here

    Website: www.InstrumentationTools.com

    Thanks,
    Bharadwaj

    ReplyDelete
  9. Okay guys your help needed:

    Q) A 4000kW 6.6kV 50Hz MOTOR with Torque load is 5 times the rated load.
    I need its Locked Rotor/Starting Current as well as full load current to arrange a well-sized power system sufficient for its operation.

    ReplyDelete