Table of Contents
Advertisement
Accumulated demand can be checked for maximum demand allowed to trigger a
setpoint at the moment when the actual demand has exceeded the predefined
threshold and prior to the end of the demand interval, when only the new maximum
demand value will be calculated.
Predicted sliding window demand is a predicted value that a sliding window
demand will reach at the end of the present demand interval, assuming the
instantaneous power load will not change. Predicted demand is updated as new
instantaneous power is measured, and reflects changes in power load as they occur.
It is calculated as average on the prior calculated set of partial block interval
demands (N-1, assuming N = number of demand intervals in the sliding window),
and on the predicted value for the present demand interval that is extrapolated to its
end, considering power integrated from the beginning of the interval and
instantaneous power being measured.
Due to extrapolation, predicted sliding window demand is very sensitive to the
duration of the interval over which extrapolation is made. The predicted demand
deviation might be slightly increased near the beginning of the demand interval
where a base for extrapolation is too small.
In the event that sliding demand window comprises a solitary demand period (N =
1), the prediction will be made at any moment considering only present accumulated
demand and measured instantaneous power .
4.3.6 Demand Interval Measurement
For the demand period measurements, one of two time references can be used: the
instrument' s internal timer, or external time synchronization source giving a timing
pulse at the start of each demand interval.
Volt/Ampere Demand Interval
For the volt and ampere demand calculations, demand interval measurements use
internal timer as a reference. The demand period is defined directly by the user from
1 to 1800 seconds. The demand interval duration and the number of demand
intervals are calculated by the instrument from the billing demand period. The
maximum number of entries in the demand window is 30. Up to a 30 second billing
interval, voltage and current demands are updated each second, assuming a one
second partial demand interval. Update time will then be increased proportionally to
the expansion of the demand period.
Operation Techniques
61
Advertisement
Table of Contents
