Application Guide - NP900 Series
286 (504
)
A996A
Below is presented the formula for three phase reactive power (Q) calculation when line-
to-neutral voltages are available:
Q
L1
= U
L1
× I
L1
sin
φ
Where,
Q
L2
= U
L2
× I
L2
sin
φ
UL1…UL3 = Line to neutral voltage
Q
L3
= U
L3
× I
L3
sin
φ
IL1…IL3 = Phase current
Q = Q
L1
+ Q
L2
+ Q
L3
φ
= Angle difference between voltage and current
In case the line to line voltages are measured and zero sequence voltage is not measured
and known the three phase power calculation is based on Aaron’s theorem:
Q = U
23
× I
L1
sin(30-
φ
) + U
31
× I
L2
sin(30 +
φ
)
Outputs of the function are Start Trip and Blocked signals. Setting parameters are static
inputs for the function which are changed only by user input in the setup phase of the
function. Under excitation function utilizes total of eight separate setting groups which can
be selected from one common source.
The operational logic consists of input magnitude processing, threshold comparator, two
block signal check, time delay characteristics and output processing.
Inputs for the function are the operating mode selections, setting parameters and
measured and pre-processed power magnitudes and binary input signals. Function
outputs START, TRIP and BLOCKED signals which can be used for direct IO controlling
and also for user logic programming. The function registers its operation into 12 last time-
stamped registers and also generates general time stamped ON/OFF events to the
common event buffer from each of the three output signal. In instant operating mode the
function outputs START and TRIP events simultaneously with equivalent time stamp.
Time stamp resolution is 1ms. Function provides also cumulative counters for START,
TRIP and BLOCKED events.
In the following figure is presented the simplified function block diagram of the UEX
function.
