Page 35 - Industrial Power Engineering and Applications Handbook

111 6 Industrial Power Engineering and Applications Handbook
100 Effect of cooling water inlet temperature
For large motors, which use water as the secondary coolant
80 in a closed circuit, the temperature of the cooling air, i.e.
of the primary coolant, varies with the temperature of
the cooling water inlet temperature and its rate of flow.
For the performance of the motor output, this primary
.- coolant, temperature has the same significance as the
t 6o
ambient temperature for an air-cooled motor. The motor
40 output is unaffected by the ambient temperature. For
0
'D such motors the output graph is shown in Figure 1.13 at
2 different coolant temperatures and altitudes. The rating
F
ij 20 at 25°C inlet water temperature for water-cooled machines
8 is the same as for air-cooled machines at an ambient
Ambient temperature ("C) -
temperature of 40°C.
0
40 50 60 70 80 90 100 D Effect of altitude
Motors are designed for an altitude up to 1000 m from
Figure 1.1 1 Derating curve for higher ambient temperatures
for insulation class E or B mean sea level, according to IEC 60034-1. At higher
altitudes, cooling reduces due to lower atmospheric
pressure and should be compensated as for higher ambient
100
temperature. It is estimated, that for every 100 m above
1000 m, the cooling is affected to the extent of 1% and
the required output must be enhanced accordingly. Table
80
1.8 shows temperature rise restrictions for different
altitudes above 1000 m and the corresponding deratings
- 160 based on Table 1.7. With these values, a graph is also
drawn in Figure 1.14, from which the derating for
9 intermediate values can also be ascertained.
40
s? Note A slightly higher derating for higher-speed motors, 1500
F r.p.m. and above, is required in view of the cooling which in higher-
\
speed motors will be affected more than in lower-speed motors.
8 20
% Temperature rise ("C) -
IIIIIIIIIIIIIIIIIIIIIIII IIO]
0 tIII!IIII!'II'!IIII!ItII 1
60
80
40
20
Figure 1.12 Derating curve for temperature rise restriction
(drawn for class E insulation)
Total permissible temperature for class B,40 + 80 = 120°C
End temperature required 50 + 60 = 110°C
Note If the manufacturer can ascertain that a 100 h.p. frame
has a reserve capacity such that at full load the temperature
rise will not go beyond 60°C, the derating as calculated below
will not be necessary.
If the machine is derated for a 60°C temperature rise above
4OoC, then the total temperature the motor would attain will
be 100OC. In this case, even if the ambient temperature rises
to 50°C (the temperature rise remaining the same) the total
temperature the motor will attain will be; "V I Cooling water inlet ternperatue ("C) -
10 20 30 40
= 50" + 60" = 110°C as desired
Therefore, derating the machine only for limiting the tem- (1) Altitude up to -1000 m
perature rise to 60°C will be adequate. (2) Altitude above 1000-1500 m
Derating from Table 1.7 for restricting the temperature rise (3) Altitude above 1500-2000 m
to 60°C is 84%. (4) Altitude above 2000-2500 m
(5) Altitude above 2500-3000 m
e
:. h.p. required = - 119 h.p.
100 '
I
Figure 1.13 Effect of the cooling water inlet temperature on
0.84 . '
The next nearest size to this is a 125 h.p. motor. output, at different altitudes