4
Settings Calculation
SIMPRO-100
46 PRIM-2400C
Example: Thermal Element Rating Method
Setting
A 4160 V, 600 HP motor is to be protected
using the SIMPRO-100 Relay Thermal
Element Rating Method. The motor data
sheet includes the following information.
Rated Horsepower (HP) = 600 HP
Rated Voltage (V) = 4160 V
Rated Full Load Current (A) = 62.1 A
Rated Locked Rotor Amps (A) = 382.5 A
Safe Stall Time at 100% Volts
Cold = 21 seconds
Hot = 16 seconds
Service Factor = 1.2
Phase current transformers having 80:5
ratios are selected for the application. The
SIMPRO-100 Relay settings for the
application are calculated as shown below.
Current Transformer Ratio (CTR) =
80/5 = 16
CT Secondary Rating (ITAP) = 5
Full Load Amps (FLA) = 62.1/16 =
3.88 A secondary
Service Factory (SF) = 1.2
Locked Rotor Amps (LRA) = 382.5/16 =
23.9 A secondary
Hot Locked Rotor Time (LRTHOT) =
16 seconds
Cold Locked Rotor Time (LRTCOLD) =
21 seconds
The Locked Rotor Trip Time Dial setting reduces
or extends the allowed accelerating time under
locked rotor conditions. You can always safely set
this value equal to 1.00. If you know that the
driven load will always accelerate in less than the
rated locked rotor time, you may wish to use a
Locked Rotor Trip Time Dial less than 1.00 to
provide a faster trip in locked rotor conditions. Do
not set the Locked Rotor Trip Time Dial setting
greater than 1.00, except in an emergency to
allow a start with a longer than normal
accelerating time.
Example: Locked Rotor Trip Time Dial
Setting Calculation
In a particular application, a motor with a
10 second hot locked rotor time always
starts in 5 seconds.
Setting the Locked Rotor Trip Time Dial
setting equal to 0.75 causes the relay to trip
in 7.5 seconds under locked rotor
conditions. This setting allows ample time
for the motor to start, but does not subject
the motor to the full 10 seconds of locked
rotor current if a locked rotor start attempt
takes place.
Continue calculating the balance of thermal
element settings with Section 4.4.1.4, page 53.
4.4.1.2 Thermal Element GENERIC
Setting Method
Table 4.7 Thermal Element Configuration Settings,
Setting Method = GENERIC
For simple, yet thorough motor protection, you
may elect to use one of the 45 available standard
motor overload/locked rotor curves. Set the motor
rated Full Load Amps and Service Factor, then
select the desired curve from Figure 4.2,
page 48. Be sure that the standard curve you
select trips in a time less than or equal to the
motor rated locked rotor time at locked rotor
current. Each increase in the curve number yields
a 2.5 second increase in the curve thermal limit
Setting Prompt
Setting
Range
Setting Name =
Example Setting
Setting Method
Rating,
Generic, User
SETMETH = GENERIC
Full Load Amps
2.50 – 8.00 A
ITAP = 5 A
FLA = 5.00
0.50 – 1.60 A FLA = 1.00
Service Factor 1.00 – 1.50 SF = 1.15
Curve Number 1 – 45 CURVE = 1
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