Toshiba GR-200 Series Instruction Manual page 348

where
t
I
I
AOL
Ip
τ
s
Ln
In Equation (2.28-5), cold curves are special versions of the hot curves where Ip is zero, catering
for the situation where a cold system is switched onto an immediate overload.
Figure 2.28-8.a shows the cold state where an overload has been switched onto a previously
un-loaded system. Figure 2.28-8.b shows the hot state where an overload is switched onto a
system that has previously been loaded to 90% of its capacity. The figures are in conformity
with the IEC 60255-149 curves, and these curves are drawn in a range of settings of the time
constant ( ).
s
a.Thermal Curves (Cold Curve - no prior load)
When the motor status is stop status, the stator thermal state can be shown by Equation
(2.28-7):
time to operate for a constant overload current of I (minutes)
motor current (amperes)
allowable overload current (amperes) of the stator, defined by the setting
[Mot-THM]
the pre-motor current (amperes)
thermal time constant (minutes), defined by the setting [T-Mot-THM]
natural logarithm
Figure 2.28-8 Thermal curves
- 329 -
b. Thermal Curves (Hot Curve - 90% prior load))
6F2T0200 (0.15)

100
50
20
10
5
1
GRE200 (1,2)