Rockwell Automation 193 193-5.0: Bulletin 913/592 SMP-3 Solid-State Overload Relay - Manual (Page 51)

Chapter 4 – Functional Description
4-3
SMP-3 PROTECTION FEATURES
The SMP-3 overload relay provides four primary forms of
motor protection: Overload, Phase Loss, Ground Fault, and
Jam/Stall Protection.
Overload Protection
Overload protection is an embedded feature of the SMP-3
overload relay. The SMP-3 overload relay provides overload
protection by monitoring the maximum phase of motor current,
and then using that data to calculate the overload’s thermal
capacity utilized. The SMP-3 overload relay will trip on an
overload fault (F2) if the following condition exists:
% Thermal Capacity Utilized (%TCU) > 100%
Trip Class. The SMP-3 overload relay offers adjustable trip
class settings of 10, 15, 20, and 30 (See Chapter 3 for “Setting
the Trip Class” instructions). The time it takes for the SMP-3
overload relay to reach 100% TCU, at a specific over-current
level, is dependent upon this trip class setting.
Typically, the trip class number (10, 15, 20, or 30) defines the
maximum time in seconds in which the overload relay will trip
when carrying 600% of rated current. For the SMP-3 overload
relay, the rated current is 1.2 times the full load current (FLC)
set with the eight FLC DIP switches.
Trip Curves. The following figures illustrate the SMP-3 over-
load relay’s time-current characteristics for each trip class.
Figure 4.1 SMP-3 Trip Curves – Class 10
0.1
1.0
10.0
100.0
1000.0
1 10
Multiples of Full Load Current
2 3 9 8 7 6 5 4
Approximate T
rip
T
ime
(sec.)
Approximate trip time
for 3-phase balanced condi-
tion from cold start.
Approximate trip time
for 3-phase balanced condi-
tion from hot start.