26
Operation
Power
Hi
Lo - HystLo
Hi + HystHi
Hi - HystHi
Lo + HystLo
Lo
Normal Operation - No alarms
Note: all alarm level variable names
have the prefix 'nciPowLim' left off.
High power alarm SET
High power alarm CLEARED
Low power alarm CLEARED
Low power alarm SET
Alarm Levels
Alarm Actions
Figure 4.4: Power Alarm Levels
All power alarms set the
nvoAlarm
field
object_id
to 2 (Power Object) to indicate the source of the alarm.
As a result of measurement and processing delays, a power alarm may not be reported for up to 10 seconds
after the onset of the alarm power level.
4.3.3 Power Alarm Example
As an example, suppose we are monitoring the power consumption of a cooling pump motor. Its normal
power consumption is 20 kW. If its consumption goes up to 25 kW, then we want to warn that it may need
service and may start overheating. Since the cooling pump is essential, we also want an alarm if the power
falls below 10 kW to indicate that the pump may no longer be performing its cooling duty.
We set
nciPowLimHi
to detect the 25 kW (25,000 W) level alarm. Suppose we don’t want the alarm
turning on and off too frequently when the power is near 25 kW. First, we set the hysteresis; by setting
nciPowLimHystHi
to 1000 W, we change the alarm so that it does not come on until 26 kW, and does not
turn off until 24 kW. Then if we want to prevent brief surges from tripping the alarm, we change
nciPowAlmSetT
to 20 seconds. This adds the requirement that 26 kW be exceeded for 20 seconds before
the high power alarm is set. This also affects the low power alarm, so the value chosen may be a
compromise.
Then, we use
nciPowLimLo
to detect the low power alarm. For this alarm we use hysteresis in conjunction
with the tripping delay configured for the high level power alarm. We want the alarm to be set whenever
the power falls below 10 kW, and be cleared whenever the power exceeds 14 kW. To achieve this, we set
nciPowLimHystLo
to 2 kW (2,000 W), and
nciPowLimLo
to 12 kW (12,000 W).
