Page 43 - Industrial Power Engineering and Applications Handbook

1/24 Industrial Power Engineering and Applications Handbook
Table 1.11 Types of Protection against ingress of water For gases Air - A
Freon - F
Second Type of protection Hydrogen - H
characteristic Nitrogen - N
number Carbon dioxide - C
For liquids Water - W
No special protection Oil - U
Dripping water (vertically falling droplets) will
have no harmful effect. 3 The letter is then followed by a number, describing
Droplets of water falling at any angle up to 15" the method to circulate the coolant as in column 3 of
from the vertical will have no harmful effect. Table 1.12.
Water falling as a spray at an angle equal to or 4 Another letter and a number are added after the above
smaller than 60" from the vertical will have no to describe the secondary cooling system.
harmful effect.
Water splashed under stated conditions against
the machine from any direction will have no Example
harmful effect. I C 3 A l W 6
Water injected under stated conditions through a
nozzle against the machine from any direction
will have no harmful effect. Coding arrangement
Water from heavy seas will not enter the machine as in column 1, Table 1.12
in a harmful quantity.
Ingress of water in the machine immersed in Primary cooling system
water under stated conditions of pressure and Method of circulating the
time will not be possible in a harmful quantity. coolant as in column 3 of
Ingress of water into the machine immersed in Table 1.12
water under specified pressure and for an
indefinite time will not be possible in a harmful Secondary cooling system 1
quantity.
J I

Depending upon its size, a machine may adopt more
1.16 Cooling systems in large than one cooling system, with separate systems for the
stator and the rotor and sometimes even for bearings. To
motors define the cooling system of such a machine, each system
must be separately described. For more details refer to
The cooling system in large motors becomes vital, as IEC 60034-6.
one fan cannot cover the entire length of the motor body The following are some of the more prevalent systems
or cool the inside bulk of the motor windings. Now a for totally enclosed large machines:
more judicious design is required for adequate cooling
to eliminate any hot spots in the rotor, stator or the Tube Ventilated Self Cooled (TV)
Closed Air Circuit Water Cooled (CACW)
overhangs of the stator windings and bearings etc. There Closed Air Circuit Air Cooled (CACA)
are many cooling systems adopted by various rnanu-
facturers, depending upon the size of the machine and The above cooling systems will generally comprise
the heat generated in various parts during full-load the following:
continuous running. The cooling system may be self-
ventilated, closed circuit, not requiring any external source 1 Tube ventilation In this system cooling tubes which
to augment the cooling system, or a forced cooling system, work as heat exchangers are welded between the core
employing an external source, to basically work as heat packet and the outer frame and are open only to the
exchangers to dissipate the heat. Thus, there may be a atmosphere. See to Figures 1.20 (a)-(c). One fan inside
variety of cooling systems to cool a large machine. the stator, mounted on the rotor shaft, transfers the
IEC 60034-6 has specified a number of probable cooling internal hot air through the tube walls which form the
systems, as adopted by various manufacturers. The more internal closed cooling circuit. A second fan mounted
commonly used practices are shown in Table 1.12. outside at the NDE blows out the internal hot air of
According to this specification any cooling system may the tubes to the atmosphere and replaces it with fresh
be expressed by the letters IC (international cooling) cool air from the other side. This forms a separate
followed by external cooling circuit.
2 ClosedAir Circuit Water Cooled (CACW) The motor's
1 A number to indicate the arrangement of the cooling interior hot air forms one part of the closed air circuit
circuit as in column 1 of Table 1.12. that is circulated by the motor's internal fans. A separate
2 Each cooling circuit is then identified for the primary heat exchanger is mounted on top of the motor as the
cooling medium by a letter A, H or W etc. which cooling water circuit. This forms the second cooling
specifies the coolant as noted below: circuit.