CCS WattNode WNA-1P-240-FT10, User Manual

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30 Operation
Whenever a new demand peak occurs, the peak demand value and
nvoPeakDemT
are updated.
nvoPeakDemT
is a SNVT_time_stamp that records the time at which the peak demand occurred, as this
can sometime affect billing, and may be useful in monitoring applications as well.
When the peak demand is zeroed, the output value will be zero until the next demand interval or
subinterval is completed. Since the peak demand may be used for billing, the time when it is zeroed is
recorded in
nvoPkDemResetT
. This records the start of the peak demand measurement period and allows
tampering to be detected. If the billing agent reads and resets the peak demand on January 31st at
10:30AM, then
nvoPkDemResetT will contain that date and time. If an unauthorized person resets the peak
demand before the next scheduled meter reading, say February 2nd, then the billing agent can detect this
because
nvoPkDemResetT
will contain February 2nd instead of January 31st. For best billing security, use
authentication as described in section 3.3.1 Authentication .
4.4.4 Demand Alarms
The demand measurement object supports two levels of alarms for high demand. Since demand updates
occur infrequently, there are no timers to delay the alarms, and no support for hysteresis in the demand
alarms. Whenever a demand measurement is made, the new value is compared to each of the two alarm
levels and if either of the alarm levels has been exceeded, then an alarm is reported with the
nvoAlarm
variable. If the demand is below the two alarm levels, then the absence of an alarm is reported. All demand
alarms set the
nvoAlarm field object_id to 3 (Demand Object) to indicate the source of the alarm.
The demand alarm configuration variables,
nciDemHiLim1
and
nciDemHiLim2
, use the SNVT_power_f
type, which ranges from 0 to 1.0e38 W.
nciDemHiLim1
should be set to a lower level than
nciDemHiLim2
, which is a higher priority alarm. Alarms tripped by
nciDemHiLim1
are set to a priority of
1, while alarms tripped by nciDemHiLim2 are set to a priority of 2 (higher priority). To disable either of
the demand alarms, set the configuration variables to the maximum value of 1.0e38 W.
4.4.5 Load Control
The WattNode supports a load shedding feature. If the demand exceeds nciDemHiLim2 , then the
SNVT_switch type variable nvoLoadControl is set to OFF. This network variable can be used to control
some load that may be turned off to save power during periods of high demand.
nvoLoadControl
goes back
to ON when the demand falls below
nciDemHiLim1
. This allows some hysteresis to prevent rapid cycling
of the load.