Air cooled v Water Cooled Motor

[BRIS]

we have 2.5 MW pumps (13.8 Kv) that have been specified with air cooled motors. The client has now instructed that the motors shall be water cooled. This is a desert environment - air temperature 25 to 50 degree C, water temp 25 to 60 degree C.

I would be interested to know what the pros and cons are for water V air cooling?.

 

[wolf39]

BRIS:

If properly designed, both cooling modes would work satisfactorily. However, I would stick to the air-cooled version. The max. water temperature is higher than the max. ambient air temperature. In your case the resulting max. cooling air temperatures of a motor equipped with water/air coolers can be expected to be 65 to 70 degrees C as a minimum.

Water/air coolers have to be maintained and may leak.

Air-cooled motors have to be equipped with effective filters.

Regards

Wolf

http://www.hydropower-consult.com

 

[BRIS]

Wolf39 - thanks for your reply - water is desal water hence temperature will be high for most of the year, whereas ambient air temp is a maximum only during summer. Obviously the design has to be based on maximum temperature but I would expect service life will increase if average normal operating temperature is lower than peak maximum design temperature.

I should add that I am hydraulic/civil and I am raising this question for my own interest. Similar size pumps I have been involved with have been air cooled and I understood that the client decided on air cooling from a maintenance view point.

 

[wolf39]

BRIS:

You are quite right. Lower temperatures do increase service life of winding insulation considerably.

For the water/air-cooled motor and a cooling air inlet temperature of 70 degrees C, for instance, the permissible temperature rise is 20 Kelvin less than for the air-cooled version. This would result in a more expensive motor. The price of water/air coolers has to be added as well. Maintenance is another important factor, as you pointed out already.

Regards

Wolf

http://www.hydropower-consult.com

 

[macmckim]

Pro's & Con's in desert environments: TEAAC versus TEWAC

TEWAC (water cooled)
- Noise level is substantially lower than TEAAC design
- typical cooling water temp is 25C, but have seen designs
up to 35C using two or three radiators
- Radiators can be offer with double walled piping. Need
water analysis to determine best cooling tube material.
- lead detection system required

TEAAC (Totally Enclosed)
- Noise level is higher than a water cooled machine
- Can be designed for high ambient area's - IE 55 to 60C
- Motor frame can be double walled for solar heat protection
if motor is outside in the sun
- Motor frame size are larger than a water cooled machine
- Motor frame size are sized larger for high ambient areas
- typically lower maintanance than water cooled machine.

 

[BRIS]

Thanks for the response - I think I understand - if we use the product water which is blended desalinated water typically at about 60 degree C - then air cooling is probably better. If we are to use water cooling then we should have an independent cooling water circulation and a cooling plant for that water.

 

[rmw]

To say what Wolf said but differently, with TEWAC you have 2 approaches to ambient; ambient to water, water to motor internal circuit air.

With air cooling you have only one approach to ambient to deal with and your motor should run cooler overall with the air cooling.

Another reason you might need to consider TEWAC is if there is anything in the atmosphere that the motor has to operate in that would be detrimental to motor operation, such as being near a source of atmospheric pollution that attacks motor internal metals.

rmw

 

[rasevskii]

In the desert environment, and that the motors are likely outdoors, if open circuit air cooled, as said, air pollution can be a serious problem. Particularly sandstorms, if they ever happen where you are, would be ruinous.

I was once involved in service for an open circuit cooled motor of 8 MVA of modern design, in a cement mill, the cooling passages in the unit were largly blocked by dust after only a only about a year's operation. In the same plant there were old open-frame, induction motors, put in around 1918 still running happily. They just blew them out with compressed air hoses, without even stopping the motor.

The new unit had to be stopped, numerous covers and shrouds removed, and the internals laboriously cleaned by hand...

rasevskii

 

[wolf39]

rasevskii:

Good point, but as I've mentioned out three days ago already: Effective filters are to be provided for an air-cooled motor.

A closed circuit cooling would be the answer in case heavy air pollution cannot be ruled out at site. Instead of using water/air coolers the motor could be equipped with an air/air exchange system mounted on top of the motor housing. It would consist of a box with a number of pipes through which the ambient air is blown by an auxiliary fan. The secondary side air flow is provided for by the motor shaft fan itself. Compared with the conventional air-cooled version with filters, the air/air cooled motor would run hotter, of course.

Regards

Wolf

http://www.hydropower-consult.com

 

[rasevskii]

For the open-circuit air cooled solution, using filters, a differential pressure gauge with an alarm contact, such as a Magnehelic gauge, should be specified. In the O & M environment that usually pertains in the desert (Middle East?) the filters won`t otherwise be changed until the motor gets too hot. You are specifying RTD winding and bearing temperature detectors, it is assumed. Absolutely essential.

regards, rasevskii

 

[BRIS]

in pump station installations in Kuwait the air cooled motors draw in air from the pump hall, but facing each air intake is a large sand trap louver and filter in the outside pump hall. Air is extracted at roof level by extract fans. Pump hall under negative air pressure.

For the project I am now involved in the designer originally proposed air handling units forcing air from outside into each motor with louvered outlets from the pump hall - i.e pump hall under positive pressure


as noted the client has now instructed that the motors shall be water cooled. I had assumed that the water cooling would be obtained by taping into the process water, but from the comments above I see that the water cooling will need to be a separate cooling system.

This leads me to think that since we can adequately filter the air, air cooling is probably the better option.