14/1/98 Page 14 Issue H
7.3.5. Hot/Cold Ratio Setting
This setting should correspond to the amount of available thermal capacity for a motor running at
FLC in the Hot condition. This is set as a percentage of thermal capacity available in the cold
condition which is always 100%.
When the motor has been running for some time at full load current, the displayed value of Thermal
capacity will reach a steady state value SSTC%. This value depends on the HOT/COLD ratio setting
H/C% and corresponding values are given by the table below:-
H/C %
SSTC% - ± 1%
Amount Of Thermal
Capacity Available ± 1%
20 69 31
30 61 39
40 52 48
50 44 56
60 35 65
70 26 74
80 17 83
Table 3 - Steady State Thermal Capacities.
7.3.6. Thermal Overload Pre-Alarm Setting
When the running current exceeds the overload level, the thermal capacity will increase. When this
reaches the Thermal Pre-Alarm level, the output alarm Relay will operate.
7.3.7. Number of Starts per Hour.
The number of starts per hour the motor will make can be limited by the MPR3E5. The starting
energy is integrated on a time-basis separately from the thermal overload model. This parameter can
also be set to off in which case the number of starts is unlimited.
7.3.7.1. Start Time Detection
The start condition is detected as a rise in current from under 0.1 times to over 1.5 times I
N
. The start
time is calculated as the time from the rise to the average of the 3 line currents dropping to below
1.25 x I
N
.
Additionally, if auxiliary power is restored to the relay with more than approx 10% full load current
flowing then the relay assumes the running mode. This permits the relay to be unplugged and
plugged while on-line.
7.3.8. Start Inhibit Time
This sets the minimum time that must elapse before the motor can be restarted after previously
exceeding the pre-set number of starts. The total reset time can be longer than the setting because it
may include the integrated starts energy delay before the inhibit time delay is enabled.
7.3.9. Earth Fault Current
This setting specifies the pickup level of Earth Fault Current as a percentage of the Earth Fault relay
rating In.
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General