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The Metering Function
Calculating Demand Values (Micrologic E)
Presentation
The Micrologic E trip unit calculates:
z The demand values of the phase and neutral currents
z The demand values of the total (active, reactive, and apparent) powers
For each demand value, the maximum demand value (peak) is stored in the memory.
The demand values are updated according to the type of window.
Definition
The demand value of a quantity can be called the:
z Average/mean value
z Demand
z Demand value (over an interval)
Example:
Current demand or current demand value, Power demand or power demand value.
The demand value should not be confused with the mean (which is an instantaneous value).
Example:
Mean current (or average current) Iavg = (I1 + I2 + I3)/3.
Calculation
Principle
The demand value of a quantity over a defined interval (metering window) is calculated according to 2
different models:
z Arithmetic demand value for the powers
z Quadratic demand value (thermal image) for the currents
Metering
Window
The specified time interval T is chosen according to 3 types of metering window:
z Fixed window
z Sliding window
z Synchronized window
Fixed Metering
Window
The duration of the fixed metering window can be specified from 5 to 60 minutes in steps of 1 minute.
5...60
mn mn
5...60
By default, the duration of the fixed metering window is set at 15 minutes.
At the end of each fixed metering window:
z The demand value over the metering window is calculated and updated.
z Calculation of a new demand value is initialized on a new metering window.
Sliding Metering
Window
The duration of the sliding metering window can be specified from 5 to 60 minutes in steps of 1 minute.
60 s
60 s
5...60
5...60mnmn
By default, the duration of the sliding metering window is set at 15 minutes.
At the end of each sliding metering window and then once a minute:
z The demand value over the metering window is calculated and updated.
z Calculation of a new demand value is initialized on a new metering window:
z By eliminating the contribution of the first minute of the previous metering window
z By adding the contribution of the current minute
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LV434104 06/2008