برق. قدرت. کنترل. الکترونیک. مخابرات. تاسیسات.

دایره المعارف تاسیسات برق (اطلاعات عمومی برق)


Cooling and ventilation of electric motors (IC)

The surface cooling using flat ribs combined with a defined inner cooling circuit with shaft-mounted fan inside the motor ensure optimum motor utilization.

All rotating electrical machines generate heat as a result of the electrical and mechanical losses inside the machine. Losses are high during starting or dynamic braking. Also, losses usually increase with increased loading. Cooling is necessary to continuously transfer the heat to a cooling medium, such as the air. The different methods of cooling rotating machines are classified in the standards IEC 34.6 and AS 1359.21.

For AC induction motors, cooling air is usually circulated internally and externally by one or more fans mounted on the rotor shaft. To allow for operation of the machine in either direction of rotation, fans are usually of the bi-directional type and made of a strong plastic material, aluminum, or steel.

In addition, the external frames of the motor are usually provided with cooling ribs to increase the surface area for heat radiation.

The most common type of AC motor is the totally enclosed fan cooled (TEFC) motor, which is provided with an external forced cooling fan mounted on the non-drive end (NDE) of the shaft, with cooling ribs running axially along the outer surface of the motor frame. These are designed to keep the air flow close to the surface of the motor along its entire length, thus improving the cooling and self-cleaning of the ribs. An air-gap is usually left between the ribs and the fan cover for this purpose.

Internally, on smaller TEFC motors, the rotor end-rings are usually constructed with ribs to provide additional agitation of the internal air for even distribution of temperature and to allow the radiation of heat from the end shields and frame.
Special precautions need to be taken when standard TEFC induction motors are used with AC variable speed drives, powered by VVVF converters. For operation at speeds below the rated frequency of 50 Hz, the shaft mounted fan cooling efficiency is lost. For constant torque loads, it is sometimes necessary to install a separately powered forced cooling fan (IC 43) to maintain adequate cooling at low speeds. On the other hand, for prolonged operation at high speeds above 50 Hz, the shaft mounted fan works well but may make excessive noise. Again, it may be advisable to fit a separately powered cooling fan.

Larger rotating machines can have more elaborate cooling systems with heat exchangers.

The system used to describe the method of cooling is currently being changed by IEC, but the designation system currently in use is as follows:

  • A prefix comprising the letters IC (index of cooling)
  • A letter designating the cooling medium, this is omitted if only air is used
  • Two numerals which represent:
  1. The cooling circuit layout
  2. The way in which the power is supplied to the circulation of the cooling fluid, fan, no fan, separate forced ventilation, etc
Figure 1 - Designation of the most common methods of cooling


Designation system concerning methods of cooling refers to
Standard IEC 600 34-6
Example
IC 4 (A) 1 (A) 6
International Cooling
Circuit arrangement
0: Free circulation (open circuit)
4: Frame surface cooled
Primary coolant
A for air (omitted for simplified designation)
Method of movement of primary coolant
0: Free convection
1: Self-circulation
6: Machine-mounted independent component
Secondary coolant
A for air (omitted for simplified designation)
W for water
Method of movement of secondary coolant
0: Free convection
1: Self-circulation
6: Machine-mounted independent component
8: Relative displacement
ABB can deliver motors as below :
IC 410: Totally enclosed motor without fan
IC 411: Totally enclosed standard motor, frame surface cooled with fan
IC 416: Totally enclosed motor with auxiliary fan motor
IC 418: Totally enclosed motor, frame surface cooled without fan
IC 01: Open motors
IC 31W: Inlet and outlet pipe or duct circulated: water cooled
Note :
Motors without fan can deliver same output power provided installation are
according to IC 418.

صفحات جانبی

نظرسنجی

    لطفاً نظرات خود را درمورد وبلاگ با اینجانب در میان بگذارید.(iman.sariri@yahoo.com)نتایج تاکنون15000مفید و 125غیرمفید. با سپاس


  • آخرین پستها

آمار وبلاگ

  • کل بازدید :
  • تعداد نویسندگان :
  • تعداد کل پست ها :
  • آخرین بازدید :
  • آخرین بروز رسانی :