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SIMPRO-100
Motor Thermal Element
E
PRIM-2400C
209
E.5
Motor Running
Protection
Figure E.5
Motor Running Thermal Element With
Resistance and Trip Level Undefined
When the motor is running, it returns heat energy
to its surroundings through radiation, conduction,
convection, and, in some cases, using forced
cooling. The motor running thermal element
provides a path for that energy return through the
resistor R, in Figure E.5.
To determine the value of that resistor, recall that
the motor will reach an energy level representing
its rated operating temperature when 1 per unit of
positive sequence current flows in the motor for a
long time. Since the positive-sequence heat
factor K
1
, is 1 in the running model, and 1 per unit
of I
1
squared equals 1, the value of resistor R
equals the energy level representing the motor
rated operating temperature.
To determine the normal operating energy, recall
that many motor datasheets publish two locked
rotor trip times:
•
one longer time when the motor is started
from ambient temperature (referred to as Ta)
•
one shorter time when the motor is started
from operating temperature (To)
Figure E.6
Calculating the Normal Operating Energy
Using Locked Rotor Trip Times
Figure E.6 shows a graphical representation of
the problem and its solution. The motor normal
operating energy is the difference between the
ambient and operating temperature locked rotor
times, multiplied by locked rotor current squared.
For those motors that do not publish separate
locked rotor times, assume that the locked rotor
trip energy is approximately six times the
operating energy in the relation.
Equation E.8
The motor ratings allow the motor to be run
continuously at the motor service factor, thus the
service factor SF, is accounted for in the running
thermal element trip threshold. Figure E.7 shows
the final running thermal element.
Figure E.7
Motor Running Thermal Element
Summary of Contents for SIMPRO-100
Page 1: ...SIMPRO 100 Motor Protection Relay Instruction Manual Document No PRIM 2400C ...
Page 12: ...Contents SIMPRO 100 x PRIM 2400C ...
Page 16: ...Contents SIMPRO 100 xiv PRIM 2400C ...
Page 42: ...3 SIMPRO PC Software SIMPRO 100 40 PRIM 2400C ...
Page 100: ...6 ASCII Serial Port Operation SIMPRO 100 98 PRIM 2400C ...
Page 127: ...SIMPRO 100 Event Analysis 9 PRIM 2400C 125 Figure 9 2 Example SER Report ...
Page 136: ...10 Maintenance Troubleshooting SIMPRO 100 134 PRIM 2400C ...
Page 138: ...A Firmware Versions SIMPRO 100 136 PRIM 2400C ...
Page 206: ...D SIMPRO PC Compatibility Features SIMPRO 100 204 PRIM 2400C ...
Page 214: ...E Motor Thermal Element SIMPRO 100 212 PRIM 2400C ...
Page 230: ...F SIMPRO 100 Relay Settings Sheets SIMPRO 100 228 PRIM 2400C ...
Page 239: ......