When Selecting a Motor, How to Decide Between an Ht or LT Motor?

Generally, the end Client's installation and standards will dictate the choice. An HT motor will be generally a bit smaller than an LT one of the same rating, as there will be less copper in it owing to it operating at lower currents.

Power consumption is strongly related to the mechanical torque presented to the motor and the rotational speed, which is the same for the rotating equipment connected to it irrespective of motor voltage selection.

Control gear considerations need to be embraced also.

Generally, the forum does not get involved in <...costly...> considerations as these vary with location, specific installation and currency exchange rates. Further, the use of previously-enjoyed equipment can eliminate some of the options available in the vacuum of an unconstrained environment.

"Horses for courses".

If in doubt, consult a qualified local Electrical Engineer.

You could go either way, depends on the setup....this really requires an electrical engineer on site to evaluate all the variables...

http://www.lmpforum.com/forum/topic/2512-advantages-of-using-ht-motors66kva33kva-vs-lt-motors440v/

Back in the mid 70's, a consultant I worked for did an extensive study of the costs to purchase, install and operate medium voltage motors, including distribution system considerations. The study determined that the cost breakpoint was at 250 horsepower. This is supported in the US by the availability and cost of starting equipment above NEMA Size 5. Not so easy to come by, and it is not cheap to maintain.

This study was for new installations, so determined the design of the entire plant. For an existing installation, usually the determining factor is the availability of the higher voltage, a simple cost estimate for a single motor install. All of your evaluation parameters are valid, but can be widely different for each individual case. Also you need to consider the ability of the owning facility to operate and maintain the alternate voltage equipment.

One question to ask with HT is what are you calling HT for it has many different voltage levels ascribed to HT? 1.1KV, 3.3KV, 6.6KV, 11KV are all voltage rating I have seen used for motor supplies.

Do you have the HV transformer supply at the nominated voltage?

Do you have the HT cabling to connect from the transformer to the switchgear?

Do you have the switchgear and the isolation which has to be designed for the higher voltage? Will you use Vacuum Contactors, low volume oil circuit breakers or whatever for the disconnect device. You need to have mechanical interlocks on the disconnect and the means of earthing.

Do you have procedures to maintain and safely work on the HV supply and suitable isolation processes and trained personnel.

I have worked on 415V motors up to 355 KW so the KW rating of the motor would not be a problem it is just thet they were fed with paralleled cables of suitable rating.

1. Selection criteria depends upon so many things such as availability of distribution voltage, capital cost vs running cost ,voltage drop etc. however in general it is advisable to go with hv motor above 200 kw.

2. Hv motor will be more efficient.

3. Hv motor is costly.

4. Not sure for pf

5. More maintenance for LV motors.

6. Hv breaker is more than 2 times costlier in India

7. HV cable size and number of runs will be much less when compared to lv so you will save in cable if you hv motor

8. Hv motor

9. Yes. For high starting torque, you may require slip ring induction motors with LRS or you can get high torque using vfd suitable for this purpose.

10. 200 kw and above.

I personally prefer hv motors above 180 kw however if there's a issue in getting hv supply, you can use lv motors with vfd. For mill duty better to use mv slip ring induction motors .