Induction motor class 3

[pamungkas]

I read an handbook about squirrel cage motor class. I am confusing with the explanation about class A, B,C and D induction motor. Could anybody explain to me the difference between them. Suppose I design a system with motor drived by VSD, should I consider this class?

Thanks you.

rgds,

pamungkas

 

[dbaird]

Goto:

http://www.manufacturing.net/ctl/article/CA188249?pubdate=12/1/1999

David Baird
mrbaird@hotmail.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[electricpete]

"Class" usually refers to insulation system temperature rating: A, B, F, H... and motor design limited to the associated temperature rises.

The letters A, B, C, D might more likely correspond to the NEMA design letters which define the torque speed characterstics.

 

[jbartos]

Suggestion: There is one more NEMA Motor Design Letter, namely 'E'.
Motor nameplate also includes NEMA Code Letters the are closely linked to Locked-Rotor Current. See NFPA 70-2002 National Electrical Code

Table 430.7(B) Locked-Rotor Indicating Code Letters
Code Letter
Kilovolt-Amperes per
Horsepower with Locked
Rotor
A 0- 3.14
B 3.15 – 3.54
C 3.55 – 3.99
D 4.0 – 4.49
E 4.5 – 4.99
F 5.0 – 5.59
G 5.6 – 6.29
H 6.3 – 7.09
J 7.1 – 7.99
K 8.0 – 8.99
L 9.0 – 9.99
M 10.0 – 11.19
N 11.2 – 12.49
P 12.5 – 13.99
R 14.0 – 15.99
S 16.0 – 17.99
T 18.0 – 19.99
U 20.0 – 22.39
V 22.4 and up

 

[jbartos]

Suggestion to pamungkas (Electrical) Dec 4, 2003 marked ///\\I read an handbook about squirrel cage motor class. I am confusing with the explanation about class A, B,C and D induction motor. Could anybody explain to me the difference between them. Suppose I design a system with motor drived by VSD, should I consider this class?
///Assuming that the letters stand for the NEMA Design Letters, then they should be considered during a motor-VSD integration.\\\

 

[jOmega]

JB:

Joseph... you state that the NEMA design letters should be consideed during a motor-VSD integration.....

But you neglect to tell us how they should be considered.

Would it not have been more helpful to state exactly how they should be considered....

Perhaps you'd care to enlighten us ...

Thank you

j

&#937

 

[jbartos]

Suggestion to the previous posting: I just mentioned an eng-tip. The detailed elaboration is another topic. Actually, the request of this nature is supposed to come from the originator of this posting not from you. So, if you do not know things, originate another thread. In the meantime, visit:

http://search.netscape.com/ns/boomf...+%2B+%22a%22&clickedItemURN=http%3A%2F%2F

http://www.cleanrivers-pdx.org%2Fte...anual/Adobe%2520Acrobat/Section16150_2003.pdf

for:
3.3.7 Motors for Variable Frequency Drive
and notice the motor - drive requirements. Also, check specification data sheets of VFDs.
Visit

http://search.netscape.com/ns/boomf...+%22drive%22&clickedItemURN=http%3A%2F%2F

http://www.ecmweb.com%2Far%2Felectr.../www.ecmweb.com/ar/electric_applying_new_nec/

for:
By contrast, the Design E version of the same motor must have a nominal efficiency of 95.4 % and a minimum efficiency of 94.5 %, an appreciable improvement. In October of 1997, the federal energy efficiency legislation becomes effective and requires that replacement motors meet at least the minimum energy efficiency standards required for the "energy efficient" marking. Although this doesn't necessarily mean a Design E motor, such motors may often end up as the ones specified because of their greater efficiency. Be very careful, because often such motors cannot be used as horsepower-for-horsepower replacements. Even if the torque characteristics of the replacement motor will drive the load, as shown in subsequent portions of this article, the controller and the disconnect may not be able to handle the new motor.
\\\

 

[pamungkas]

The book that I read is based on NEMA. But at our plan, the motor drive is SIEMENS manufactured. At the name plate The motor type is xxx-xxx-Z, means non-NEMA standards. It seems them motor is using DIN standards (IMB3 types of construction).
This motor is operated in fixed speed (50 Hz) and DoL starting. In order to increase its utilization, we'll plan to operate in 2 mode for the future, 50 Hz and 25 Hz (in creep speed). Should I replace the motor or just add the appropriate VSD? note:
Motor spec:
3300 V Y 0.85 pf 405A
50 Hz 1475 rpm IMB3
104 A S Rotor IP55
480 kW 720 V
May someone told me the meaning of: S rotor 720 V 405A? Are these parameters same as lock rotor in NEMA?

Thanks for advanced!!

 

[edison123]

Yours seems to be a slipring (wound rotor) motor. S rotor values are rotor open circuit voltage of 720 volts and rotor current on short circuit and under full load of 405 Amps. For VFD operation, you may have permanently short the rotor winding (with or without brushes). VFD at 3.3 KV may be mite expensive.

 

[panelman]

i looked a similar project a few years ago...then it was cheaper to install a 3.3 to 415 transformer and buy a new motor to go with an LV drive than it was to get a 3.3 drive

 

[jbartos]

Suggestion: Notice that insulation systems shall be classified as follows:
Nema Class A = 105degC, 65degC rise over ambient 40degC
Nema Class B = 130degC, 90degC rise over ambient 40degC
Nema Class F = 155degC, 115degC rise over ambient 40degC
Nema Class H = 180degC, 140degC rise over ambient 40degC
if the letter D is missing in here, then the Nema motor design letters A,B,C,D and missing E are more appropriate interpretation of the original posting.

 

[GordS]

Design A and B motors are similar in torque-speed characteristics in that they have a starting torque about 100-150% of rated and a breakdown torque of about 200-250% near rated speed. (Design A tends to have greater starting current than Design B). Design C motors have a starting torque of about 200-250% and a breakdown torque of about 200-250% near rated speed. Design D motors have a starting torque equal to breakdown torque - ie torque is highest at zero speed and slowly drops as the motor speeds up.

The motor design does have an impact on VFD operation. For example, Design D has a high rotor resistance in order to shift the breakdown torque away from rated speed towards zero speed. This resistance generates more heat due to the harmonics impressed upon the motor due to the VFD. So there is a greater impact on motor life if the motor is design D vs Design B. Generally, Design C and D are not as well suited as Design B motors.

 

[pamungkas]

Thanks all for your advice and ideas. I'll consider VSD 3.3 kV and lower voltage VSD (i.e add transformer). Thank you for enlighten me in motor induction class.
-pamungkas-

 

[mtchufi]

Just 1% words,
You can check this URL:

http://www.sea.siemens.com/step/pdfs/acm_2.pdf

hope you 'll find what u need.
Mtchufi,bekasi

 

[jbartos]

Comment on jOmega (Electrical) Dec 5, 2003 marked ///\\JB:

Joseph... you state that the NEMA design letters should be consideed during a motor-VSD integration.....

But you neglect to tell us how they should be considered.

Would it not have been more helpful to state exactly how they should be considered....

Perhaps you'd care to enlighten us ...

Thank you
///Please, may I inquire where is the eng-tip? I do not see it anywhere in your posting? What is this posting worth?\\