91
6
F
2
S
0
8
5
0
is switched onto a system that has previously been loaded to 90% of its capacity.
Thermal Curves (Cold Curve - no
prior load)
0.01
0.1
1
10
100
1000
1
10
Overload Current (Multiple of I
AOL
)
Operate Ti
m
e
(m
inutes)
Thermal Curves (Hot Curve - 90%
prior load)
0.001
0.01
0.1
1
10
100
1000
1
10
Overload Current (Multiple of I
AOL
)
O
p
erate Ti
me (mi
nutes)
Figure 2.8.1
Thermal Curves
Scheme Logic
Figure 2.8.2 shows the scheme logic of the thermal overload protection.
The thermal overload element THM has independent thresholds for alarm and trip, and outputs
alarm signal THM ALARM and trip signal THM TRIP. The alarming threshold level is set as a
percentage of the tripping threshold.
The alarming and tripping can be disabled by the scheme switches [THMAL] and [THMT]
respectively or binary input signals THMA BLOCK and THM BLOCK.
T
A
THM
&
THM ALARM
+
"ON"
[THMAL]
+
"ON"
[THMT]
THM TRIP
&
&
&
1
THMA_BLOCK
1593
1
THM_BLOCK
1594
367
363
416
417
Figure 2.8.2
Thermal Overload Protection Scheme Logic
τ
100
50
20
10
5
2
1
τ
100
50
20
10
5
2
1
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Summary of Contents for GRL100-701B
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