This subroutine provides an RMS quantity for a 3-phase, input voltage waveform by interpolated sampling. This subroutine operates in the same manner as that described for the [DGTL_RMS] Digital RMS Meter (1-Phase). The difference here is that the 3-phase voltage signal is converted to an equivalent 1-phase signal according to the following equation:
Where,
The output RMS signal is then determined in the same manner as described for the [DGTL_RMS] Digital RMS Meter (1-Phase).
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Subroutine Author(s): |
O. Nayak |
Nayak Corporation, 2002 |
SUBROUTINE DGTL_RMS3(NSAMI,SS,NA,NB,NC,FREQ,SCALE,INIT,OUTPUT)
Inputs:
|
Argument |
Type |
Dimension |
Description |
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NSAMI |
INTEGER |
1 |
The number of samples to be taken per cycle of fundamental frequency input FREQ. This input affects the number of storage locations used by this subroutine (see below). |
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SS |
INTEGER |
1 |
EMTDC subsystem number. |
|
NA,NB,NC |
INTEGER |
1 |
EMTDC node numbers representing the phases A, B and C at the measured bus point. |
|
FREQ |
REAL |
1 |
The fundamental frequency of the input 3-phase voltage based on NA,NB and NC [Hz]. |
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SCALE |
REAL |
1 |
A constant to scale the output value (ex. a per-unitizing base). This value is multiplied directly to the OUTPUT signal internally. |
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INIT |
REAL |
1 |
Initial output value (optional). The subroutine populates the entire buffer with this value at TIMEZERO [kV, L-L, RMS] |
Outputs:
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Argument |
Type |
Dimension |
Description |
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OUTPUT |
REAL |
1 |
Output RMS signal. If SCALE = 1.0, then this output will be in the same unit as the INPUT signal |
This function requires the following storage allocations per call (see #STORAGE Script Directive and STORx Arrays for more details):
#STORAGE INTEGER:2 REAL:<?> *See Note Below*
|
Address |
Description |
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|
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NSTORI + 0 |
The present sample number |
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NSTORI + 1 |
The adjusted number of samples per cycle (normally equal to NSAMI). See the Description above for more details. |
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NSTORF + 0 |
Sample period = 1 / FREQ*NSAMI. Minimum is the simulation time step DELT [s]. |
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NSTORF + 1 |
The time at which to take the next sample [s] |
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NSTORF + 2 |
Input from last time step |
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NSTORF + 3 |
Output from last time step |
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NSTORF + 4...4+NSAMI |
Buffered input array. Note that the quantities stored here are the squares of the inputs at each sample point. |
NOTE: The total number of REAL storage locations used is: REAL = 4 + <value of NSAMI>. It may actually be less than this, but this depends on what the subroutine decides is a valid number of samples, taking into account the input FREQ and the simulation time step DELT. Using the value of NSAMI is a safe choice. You may monitor the actual number of samples by accessing NSTORI + ? as indicated above.