In the power module, there are several system configurations available. The most common ones are 1-phase and 3-phase star and 3-phase delta connections. 2-phase is used with special motors and also in some applications 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.
Firstly, the line frequency must be set. In the public grids the frequencies are 50 Hz for Europe and 60 Hz in the USA (please make sure that the correct frequency is set for the region where the measurement will take place). There are also other line frequencies available (16,7 Hz, 25 Hz, 400 Hz, 800 Hz) for special applications. For inverter measurements “variable frequency” must 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 very high accuracy (mHz) but is also very CPU intensive (CPU power). For optimal performance, it’s recommended to set a range (start and end frequency) where the fundamental frequency could be via the “Exact frequency settings”. For example, when measuring an inverter driven motor and it is known the fundamental frequency is no higher than 200 Hz it is recommended to add an end frequency a little higher than the known frequency for example at 250 Hz.
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, external signal or an arbitrary channel can be selected.
Arbitrary channel uses filters for better and more stable frequency determination. For all different types of frequency sources, it is possible to select the channel which should be used for the frequency calculation. If there are more than one power module, it is possible to synchronize the modules with arbitrary channels. (E.g. by selecting one phase out of another power module)
As seen in the following image of an inverter measurement, the voltage (green) isn’t a sinusoidal waveform any more. It has become a packet of pulses. In this case, if voltage is selected as the frequency source there is a chance that the determination might be faulty. On the other hand, the current waveform (orange) has a nice stable sinusoidal form and should then be selected as the frequency source as this will yield much better results. The oscilloscope function in the DEWESoft software is extremely helpful in analyzing the signals for frequency source determination.
Number of cycles
In this option, the number of cycles for the power calculation can be set as shown in the image below on the left-hand side. As standard, this value is 10 periods for 50 Hz measurements and 12 periods for 60 Hz applications (required in 61000-4-30). In the drop-down list only 10 and 12 cycles are selectable, but any arbitrary number up to 999 can be entered into the field, the lowest number of periods is 5. For all other applications, if there is a need for faster values the “period values” functionality can be used, ensure that this function is enabled by clicking in the small box, it is activated when there is a tick in the box as seen in the image on the right-hand side.
The entry of the nominal voltage is important if you want to calculate the Flicker values. For other measurements the voltage should be set to at least an approximate voltage of the measurement. 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
In the drop-down list 120 V and 230 V is available, but it is possible to enter any arbitrary voltage that is required for the measurement in the nominal voltage field.
Calculation sample rate
The calculation sampling 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 all the configurations have been done, the channel list will show which parameters will be calculated by the DEWESoft X software:
The power module calculates many parameters. Most of the time not all these parameters are needed for the current application. In this case it is possible to deselect some of the unneeded parameters. This will reduce the data file sizes (The size of the reduction relies strongly on the number of deselected parameters but also on the parameter calculation intensity as these also differ).
The vector scope functionality in the power module depicts a fast overview of all voltage and current channels that are connected to the power module and if they are connected correctly to the measurement device.
The bottom right of the vector scope depicts what the voltages and currents should look like. If a voltage or current has been connected incorrectly the hardware connections don’t have to be changed, this can be corrected in the Dewesoft X software using the wiring schematics. In addition to the correct positioning of the phases, it is also possible to verify that the current transducers have been connected correctly. Should this not be the case, it can also simply be changed within the software, in the analog set-up using the scaling option just click on the “±” to change the polarity.
Multiple power modules
In the Dewesoft X software multiple power modules can be created. This means that power can be measured at multiple points completely synchronous. In the math library the power modules can be further refined, for example the efficiency can be calculated automatically (see efficiency calculation). This is also very helpful when measuring multi-phase motors (6-12 phases). Just click on the + next to the already active power modules to add another one.
Harmonics, THD, Flicker, Flicker emission, Rapid voltage changes, Background harmonics
These features will be described in the Power quality course in the PRO training.
Period values are needed to perform a detailed analysis of electrical equipment (e.g. analyzing behavior 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 as well as 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
Period values are not corrected in amplitude and phase as is the case for the other power calculations in the power module.
Considering the period values for the symmetrical components (for more details please see the Power Quality Pro training) there are more than 50 parameters available.