In the power module, there are several system configurations available. The most common are 1-phase and 3-phase star or delta. 2-phase is used with special motors or also in some parts of the grid. The Aron and V configuration are basically star or delta configuration but measuring only 2 currents instead of 3 (see 3-phase measurement). Special configurations like 6-, 7-, 9- or 12 phase motor measurement can be done with multiple single phase systems and adding up the power values in the Math library.
At the next step, the line frequency has to be set. With standard grid measurements, the frequency of 50 Hz (e.g. Europe) or 60 Hz (e.g. USA) has to be set. There are also other line frequencies available (16,7 Hz, 400 Hz, 800 Hz) for special applications. For inverter measurements “variable frequency” has to be selected. The “variable frequency” setting searches automatically for the fundamental frequency in the signal via an FFT algorithm (highest peak). This algorithm calculates the frequency with high accuracy (mHz) but is also very CPU intensive (CPU power). For optimal performance, it’s recommended to set a range (start and the end frequency) where the fundamental frequency can be via the “Exact frequency settings”. For example if you're measuring an inverter driven motor and you know that the fundamental frequency is never higher than 200 Hz, it’s recommended to set the end frequency to 250 Hz for example.
When measuring high power, it could be useful to change the output unit to a higher unit. Available are Watt, Kilowatt and Megawatt.
A special functionality in the power module is the selection of the frequency source. As a source, the voltage, the current or an external signal can be selected. As you can see in the next picture of an inverter measurement, the voltage (green) isn't a sinusoidal waveform any more. It’s a packet of pulses. If you select the voltage as the frequency source the frequency determination can be faulty. The waveform of the current is a lot more sinusoidal and should be selected as a frequency source to get correct results. The oscilloscope functionality in Dewesoft is very helpful for analysing the signal.
Number of cycles
In this option, the number of cycles for the power calculation can be set. As standard, this value is 10 periods for 50 Hz measurements and 12 periods for 60 Hz applications (required in 61000-4-30). The lower level for the number of periods is 5. For all applications, if you need faster values the “period values” functionality can be used.
The entry of the nominal voltage is important if you want to calculate the Flicker. Also for other measurements the voltage should be set to at least an approximate voltage. If this value is set very high (e.g. measuring inverter with 20 V output and the nominal voltage is selected to 400V) the frequency determination can fail.
- 230 V - line to earth voltage for star configuration
- 400 V - line to line voltage for delta configuration
The calculation rate in the power module is like a sample rate divider for the power calculations. At high sampling rate (>100 kHz) this is often necessary due to performance problems (CPU power at the limit). So just select the calculation rate you need for your measurement. If you store all data in the full sampling rate (always fast) you also can calculate the power in the full calculation rate via the post-processing functionality.
Typical calculation rate:
- grid measurement - 10 to 20 kHz
- wind, renewable, etc. - 50 kHz
- inverter measurement - 100 kHz or more
After doing the configurations, you see in the channel list which parameters are calculated by Dewesoft:
The power module calculates a lot of parameters. Most of the time there are a lot of parameters calculated which are not necessary for a certain application. In this case, you can deselect in the channel list all the channels you do not want to store. So you can reduce your data file sizes.
The vector scope functionality in the power module gives a fast overview if all voltage and current channels are connected correctly to the measurement device.
In the bottom right of the vector scope, you see how the voltages and currents should look like. If you connected a voltage or a current incorrectly you don’t have to change the hardware connection, you just can correct this in the wiring schematics. Additionally to the correct position of the phase you also see if you have connected the current transducers in the right direction. If there is one connected wrong you again can simple edit this in the software the analog setup via the scaling by adding a minus.
Multiple power modules
In Dewesoft X you can create multiple power modules. So you can measure the power at multiple points completely synchronous. Via the math library you can further process the data of the power modules and for example automatically calculate the efficiency (see efficiency calculation).
Harmonics, THD, Flicker, Flicker emission, Rapid voltage, Background harmonics
These features will be described in the Power quality course on PRO training.
Period values are needed for detailed analysis of electrical equipment (e.g. analysing behaviour at faults or switching processes) and for fault recording (as a trigger argument). The period values are calculated for voltages, currents, active, reactive, apparent power, power factor and other parameters.
The period values can be calculated with a definable overlap (up to 99%) and for a definable number of periods (up to 4). Using an overlap of 99% at a 50 Hz measurement you can calculate the power values for every 0,2 ms. That’s a unique feature of Dewesoft.
Overlap: 25%, 50%, 75%, 90%, 95%, 99%
Periods: 1/2, 1, 2, 4
The period values are not corrected in amplitude and phase as it is done for the other power calculations in the power module.
Considering also the period values for the symmetrical components (see more details in Power Quality Pro training) there are more than 50 parameters available.