Echo Electric Motors

Reference Locked Rotor Code Le ers & Reduced Voltage Star ng Methods When AC motors are started with full voltage (across-the-line star ng), they draw line amperage 300% to 600% greater than their full load running current. The magnitude of the "inrush current" (also called locked rotor amps of LRA) is determined by motor horsepower and design characteris cs. To define inrush characteris cs and present them in a simplified form, code le ers are used. Code le ers group motors depending on the range of inrush values and express the inrush in terms of kVA (kilovolt amps). By using the kilovolt ampere basis, a single le er can be used to define both the low and high voltage inrush values on dual voltage motors.

The code le er designa ons and their values appear in Table 1.

Table 1 Code Le er

Approximate Mid-Range Value

Approximate Mid-Range Value

kVA / HP Range 9.0 - 10.0 10.0 - 11.2 11.2 - 12.5 12.5 - 14.0 14.0 - 16.0 16.0 - 18.0 18.0 - 20.0 20.0 - 22.4

kVA / HP Range 0.00 - 3.15 3.15 - 3.55 3.55 - 4.0

Code Le er

A B C D

1.6 3.3 3.8 4.3 4.7 5.3 5.9 6.7 7.5 8.5

L

9.5

M

10.6 11.8 13.2 15.0 17.0 19.0 21.2

N P R S T U V

4.0 - 4.5 4.5 - 5.0 5.0 - 5.6 5.6 - 6.3 6.3 - 7.1 7.1 - 8.0 8.0 - 9.0

E F

G H

J

22.4 - and up

K

To determine star ng inrush amperes from the code le er, the code le er value (usually the mid-range value is adequate), horsepower and rated opera ng voltage are inserted in the appropriate equa on. The equa on to be used is determined by whether the motor is single or three-phase.

Inrush amperes (single-phase motors)

(Code le er value) x HP x 1000 Rated voltage

=

Inrush amperes (three-phase motors)

(Code le er value) x HP x 577 Rated voltage

=

The following simplified equa ons for three-phase motors will give approximate results for three-phase motors rated for 200, 230, 460 or 575 volts.

200 volts LRA = (Code le er value) x HP x 2.9 230 volts LRA = (Code le er value) x HP x 2.5 460 volts LRA = (Code le er value) x HP x 1.25 575 volts LRA = (Code le er value) x HP x 1.0

X

X

X

©2017 ABB. Technical Papers, Cowern Papers 9AKK107303

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