GE M60 Instruction Manual page 260

5.6 GROUPED ELEMENTS
• START INHIBIT TCU MARGIN: This setting prevents starting of a motor if there is insufficient thermal capacity avail-
able for a successful start. The motor start inhibit logic algorithm is defined by
MOTOR START INHIBIT MARGIN
is tripped by thermal protection (TCU = 100%). After being asserted, the
new motor start is permitted when TC
5
where TCU is the thermal capacity level when the
start
mal capacity level when
To calculate the thermal lockout time for the case when
values are to be applied to the above equation: TCU
If the motor is tripped or stopped by a means other than thermal protection (TCU < 100%), the
operand is not asserted and a new start is permitted. There is a potential risk in this situation to trip out
INHIBIT
NOTE
the motor by thermal protection during the new start.
If
MOTOR START INHIBIT MARGIN
motor is tripped by thermal protection (TCU = 100%) or tripped/stopped by any other reason (TCU < 100%).
Each time motor is tripped/stopped by a means other than thermal protection (TCU < 100%) the available thermal
capacity (100% – TCU) is evaluated and compared to the TC required for starting the motor. If the available thermal
capacity is not sufficient to perform new motor start, then the
mal capacity required for starting the motor (TCU
where TCU
margin
cessful motor starts. The relay monitors motor starting and captures the TCU for each successful start. The largest
value from the last five (5) starts is used in the start inhibit calculation.
In this case, the
MOTOR START INHIBIT
To calculate the thermal lockout time for the case when the
following TCU values are to be applied:
TCU
TCU
5-122
100
Hot/Cold = 0.85
80
Rated Temperature=130°C
Insulation Rating=155°C
60
40
20
RTD Bias Minimum
0
–50 0
Figure 5–53: RTD BIAS CURVE
is set to "0", the
MOTOR START INHIBIT
decays to a level of 15%. The thermal lockout time is calculated as follows.
used
TCU
end
MOTOR START INHIBIT
is greater than "0", the
TCU TCU
=
onStart maxStart
is the relay setpoint, and TC
maxStart
operand resets when TCU decays to the level satisfying the following equation:

≤
TCU 100% TCU
–

TC accumulated from the moment the motor was stopped
=
start

100% TCU
= –

end maxStart
M60 Motor Protection System
RTD Bias Maximum
RTD Bias Center Point
50 100 150 200
Maximum Stator RTD Temperature
808721A1.CDR
FlexLogic™ operand is asserted only when motor
MOTOR START INHIBIT
T τ ⁄
–
×
TCU e
=
start
MOTOR START INHIBIT
operand is reset, and τ is the
MOTOR START INHIBIT MARGIN
= 100% and TCU
start end
MOTOR START INHIBIT
MOTOR START INHIBIT
) is defined from the following equation:
onStart
TCU 100%
+
 
margin
× ----------------------------------------------- -
 
100%
is the maximum thermal capacity value from the last five suc-
TCU 100%
+

margin
× ----------------------------------------------- -

maxStart
100%
MOTOR START INHIBIT MARGIN
TCU
  
margin
× 1 ------------------------- -
+
  
100%
5 SETTINGS
250
MOTOR START INHIBIT MARGIN
operand resets and a
operand is asserted, TCU
end
COOL TIME CONSTANT STOPPED
is set to "0", the following TCU
= 15%.
MOTOR START
operand will be asserted either when
operand will be asserted. The ther-
setting is greater than "0", the
setpoint. If
(EQ 5.20)
is the ther-
setpoint.
(EQ 5.21)
(EQ 5.22)
(EQ 5.23)
GE Multilin