What is the kva code of a motor

[rizwan]

Hi

 

The kva code is mentioned on the name plate of almost all the motors. What is it ?

Is it to be used to calcute the short circuit current of the motor ? If so how can we calculate the short circuit current from the kva code?

 

Thanks for any reply.

 

Rizwan.

[marke]

Hello rizwan

 

I expect that you are referring to the KVA rating of the motor which is the KVA rating at full load where the KVA is volts time amps/1000. In the case of three phase voltage, you take the line to line voltage times root 3.

 

This does not give you the Locked Rotr Current of the motor which is a different matter.

The Locked rotor current of a motor is tyupically in the range of 550% - 900% of the rated current of the motor, but varies from motor to motor. It is usually quote on the motor datasheets.

 

Best regards,

[jOmega]

Hello Rizwan.

 

To answer your questions, I would refer you to the Cowern Paper on "Locked Rotor Code Letters and Reduced Voltage Starting Methods" (see http://www.motorsanddrives.com/cowern/motorterms6.html

 

from which the following is taken:

 

" When AC motors are started with full voltage (Across-the-Line Starting), 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 or LRA) is determined by motor horsepower and design characteristics. To define inrush characteristics and present them in a simplified form, code letters are used. Code letters group motors depending on the range of inrush values and express the inrush in terms of KVA (Kilovolt Amperes). By using the Kilovolt ampere basis, a single letter can be used to define both the low and high voltage inrush values on dual voltage motors."

 

"The code letter designations and their values appear in Table I."

(SEE ATTACHMENT)

 

"To determine starting inrush amperes from the code letter, the code letter value (usually the mid-range value is adequate), horsepower and rated operating voltage are inserted in the appropriate equation. The equation to be used is determined by whether the motor is single or three phase.

 

INRUSH AMPERES(SINGLE PHASE MOTORS)

= ((CODE LETTER VALUE) X HP X 1000)/(RATED VOLTAGE)

 

INRUSH AMPERES(THREE PHASE MOTORS)

= ((CODE LETTER VALUE) X HP X 577)/(RATED VOLTAGE)

 

The following simplified equations for three phase motors will give approximate results for 3 phase motors rated for 200, 230, 460 or 575 volts:

 

200 volts LRA = Code Letter Value x HP x 2.9

230 volts LRA = Code Letter Value x HP x 2.5

460 volts LRA = Code Letter Value x HP x 1.25

575 volts LRA = Code Letter Value x HP x 1.0 "

 

If you have further questions regarding this subject, please post them and we will try to answer them for you.

 

Kind regards,

jΩ

[rizwan]

 

 

 

 

Hello Rizwan.

 

To answer your questions, I would refer you to the Cowern Paper on "Locked Rotor Code Letters and Reduced Voltage Starting Methods" (see http://www.motorsanddrives.com/cowern/motorterms6.html

 

from which the following is taken:

 

" When AC motors are started with full voltage (Across-the-Line Starting), 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 or LRA) is determined by motor horsepower and design characteristics. To define inrush characteristics and present them in a simplified form, code letters are used. Code letters group motors depending on the range of inrush values and express the inrush in terms of KVA (Kilovolt Amperes). By using the Kilovolt ampere basis, a single letter can be used to define both the low and high voltage inrush values on dual voltage motors."

 

"The code letter designations and their values appear in Table I."

(SEE ATTACHMENT)

 

"To determine starting inrush amperes from the code letter, the code letter value (usually the mid-range value is adequate), horsepower and rated operating voltage are inserted in the appropriate equation. The equation to be used is determined by whether the motor is single or three phase.

 

INRUSH AMPERES(SINGLE PHASE MOTORS)

= ((CODE LETTER VALUE) X HP X 1000)/(RATED VOLTAGE)

 

INRUSH AMPERES(THREE PHASE MOTORS)

= ((CODE LETTER VALUE) X HP X 577)/(RATED VOLTAGE)

 

The following simplified equations for three phase motors will give approximate results for 3 phase motors rated for 200, 230, 460 or 575 volts:

 

200 volts LRA = Code Letter Value x HP x 2.9

230 volts LRA = Code Letter Value x HP x 2.5

460 volts LRA = Code Letter Value x HP x 1.25

575 volts LRA = Code Letter Value x HP x 1.0 "

 

If you have further questions regarding this subject, please post them and we will try to answer them for you.

 

Kind regards,

jΩ

 

[rizwan]

Dear J omega,

 

Thak you very much for such a nice reply.

 

Regards.

Rizwan.