CEA7 CONTROL UNIT ALARMS | PAGE 46
EXAMPLE CALCULATION OF THE IDMT CURVE TIME CONSTANT (T)
For a genset current (I) with a value of 110% of the nominal value, the desired
tripping time (td) is 1 hour (3,600 seconds).
From the IDMT curve equation, we obtain the time constant:
For a genset current value of 110% of In, the value is set to the ratio
Therefore, the value of the time constant for a trip time of 3,600 sec for a current
110% of the nominal is established as:
HIGH TEMPERATURE PT100 PROBE 5 TO 8. REQUIRES CCPT100 PROBES
EXPANSION
The CEA7 control unit’s high temperature alarm for PT100 probes 5 to 8 is
associated to the analogue inputs for PT100 temperature of the analogue input
expansion. The high temperature alarm for PT100 probes 5 to 8 is activated
when a temperature value above the programmed limit (Thresholds table,
parameters 52-55) is detected or when the probe is detected as not connected.
Detection of the high temperature alarm for PT100 probes 5 to 8 is set by default
(Alarms table, parameter 183, 186, 189 and 192) to be activated: Never.
A high temperature alarm for PT100 probes 5 to 8 can be associated a debounce
time (Alarms table, parameters 184, 187, 190 and 193) during which it must be
detected that the water temperature is above the limit set (Thresholds table,
parameters 52 to 55).
The high temperature alarm for PT100 probes 1 to 4 is set by default (Alarms
table, parameters 185, 188, 191 and 194) to perform no action (warning).
IDMT ALARM
The CEM7 control unit’s IDMT alarm is associated to the measurement of the
genset current. The alarm detection time (td) ts the curve given by the formula:
where the time constant parameter T is dened in seconds (Times table,
parameter 34, default value 36 seconds) and a percentage of the maximum
overload current of genset I (Thresholds table, parameter 51, default value
200%). With these default values, the base of dened times is equal to one hour
for a circulating current corresponding to 110% of the genset’s overload threshold
(Thresholds table, parameter 7).
The purpose of the IDMT alarm is to avoid heating as a result of the ow of
current in the installation components (contactors, cables etc.). Therefore, the
trip time of the alarm is a function of the current owing where a higher current in
the genset corresponds to a shorter alarm trip time. In addition, this condition
implies that the IDMT alarm can trip repeatedly in less time than is established
(Times table, parameter 34) as a result of not being given sufcient cooling time
when the genset current is below the overload current threshold.
The cooling time is determined by the formula:
Detection of the IDMT alarm is set by default (Alarms table, parameter 180) to
be activated: Never.
Once an IDMT alarm has been generated, the genset current must be less than
the nominal current dened by the IDMT curve (Thresholds table, parameter 51)
for a programmable interval of time (debounce) (Alarms table, parameter 181).
The genset power alarm is set by default (Alarms table, parameter 182) to
perform no action (warning).
Value 0 for the time constant (Times table, parameter 34) or nominal current
(Thresholds table, parameter 51) of the IDMT curve disable the management of
this alarm.
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