Troubleshooting with Waveform Simulations Using an AC Power Supply
Reproducing High-Voltage Three-Phase AC Waveforms Observed Onsite
On-site equipment malfunction is a common occurrence. Malfunctions have a variety of causes, including common mode or differential (normal) mode noise across power supply lines and power fluctuation. When equipment does malfunction, the first response should be to log the output waveforms of the power supply lines on site, enable you to view the waveform while investigating the cause of the malfunction. However, as malfunctions tend to manifest themselves sporadically or irregularly, it is often making it impossible to identify the cause of the malfunction and implement a solution on site. In such cases, there will be times when you need to take the voltage waveform data you recorded on site back to the lab with you and then use an AC power supply to generate an identical waveform so that you can reproduce or simulate the symptoms.
Here, I will describe a method for reproducing a voltage waveform observed on site using a Kikusui power supply (of the PCR-LE series). While this article assumes a three-phase AC system, the approach is basically the same for single phase and three-wire single-phase systems─you just have fewer phases to deal with.
1. Principle of Operation of PCR-LE Series AC Generation System
The PCR-LE is not only able to generate AC output, but the it also has power line simulators with built-in arbitrary waveform generators. Using this features, the user is able to emulate commercial power supplies, as well as allowing the user to create arbitrary power supply waveforms easily.
As shown in Figure 1, the waveform generation system used by the PCR-LE series' built-in arbitrary waveform generator has 64 waveform banks, each of which stores one cycle of waveform data. These function selects waveform data and repeatedly performs digital to analog conversion at the selected frequency to generate alternating current. By default, the waveform bank is set to waveform zero (sine wave) and generates sinusoidal AC. Users wishing to output arbitrary waveforms are able to import up to 63 user-defined (arbitrary) waveforms into the waveform bank, then select the desired waveform from the waveform bank to be output. A variety of waveforms is thus able to be generated.
In a three-phase system, a separate waveform generation system is provided for each of the phases (U, V, and W). Therefore, in order to output an arbitrary waveform, the user needs to input the selected waveform into the waveform bank for each of the respective phases. The PCR-LE series AC power supply can be used to reproduce waveforms observed on site by recording the voltage waveforms in question on site, storing them in the waveform bank, and then using the power supply to output them.
To generate waveforms, you will need:
Wavy for PCR-LE (SD011-PCR-LE) sequencing software (Kikusui Electronics)*1
A three-phase system comprising three PCR-LE series power supplies (Kikusui Electronics)*2
The recorded waveform data (the waveforms for each of the phases)
*1: Any of the SD012-PCR-LE, SD019-PCR-LE, or the SD-020-PCR-LE can be used.
*2: The multi-output PCR-LE2 can also be used.
3. Requirements for Recording Voltage Waveforms
An oscilloscope capable of recording waveform data in CSV format is used to measure and log voltage. The outputs of the PCR-LE series supplies are connected in the Y configuration. Because line voltage is the composite of the phase voltages in question, you need to record the waveforms of all phase voltages. Note that a recording of line voltage cannot be used to generate the waveform.
The data logged by the oscilloscope must be no greater than 10,000 data points in length, so check the length of the data record before commencing recording. Data records over than 10,000 data points long can be compressed down to 10,000 data points or less by using an oscilloscope utility or similar tool.
4. Uploading Voltage Waveforms Recorded on Site to the Waveform Bank
Voltage waveforms recorded on site are uploaded to the waveform bank in accordance with the steps set forth in Figure 2.
(1) Converting Waveform Data into a Format Readable by Wavy
As shown in Figure 3, the CSV data from the oscilloscope contains superfluous information. We remove this using Excel to leave only the necessary data, as shown in Figure 4, and record it as a .csv file.
(2) Inputting Data into Wavy for Scaling into an Arbitrary Waveform Format that Can be Uploaded to the Waveform Bank
Step 1: Run Wavy for PCR-LE.
Step 2: Select Sequence → Create/Edit (A) Arbitrary Waveform to launch the arbitrary waveform window.
Step 3: Select “Arbitrary” from amongst the types of user-defined waveform available.
Step 4: Click “Upload”, and then select the data file (csv file) recorded earlier to upload the data.
Step 5: A window for converting text data will be displayed. Select the start and end points of a single cycle of the required data, and click “Convert”. When you are finished, you can return to the Arbitrary Waveform screen by selecting “Back”. You now have a single cycle of necessary data. As it should display in the window, the arbitrary waveform, in a format that can be saved in the waveform bank and scaled both vertically and horizontally.
(3) Saving Arbitrary Waveform Data
Selecting “Save” at the top of the Arbitrary Waveform window, the waveform is saved as an .arb file. By default the files are saved in the “Arbitrary Waveforms Folder” at the bottom of the Tools →Preferences menu, however users may also change the directory.
(4) Uploading Arbitrary Waveform Data to PCR-LE Waveform Bank
In the Waveform Bank section of the Arbitrary Waveform window, select the destination waveform number (waveform bank number) and the destination phase, and click “Upload”. For a three-phase waveform, you need to upload the same waveform number (waveform bank number) to each of the phases. This means you need to upload the data three times (Fig 5). The uploaded waveforms can be reviewed by going to Display→ Wave View →Wave Image.
5. Using PCR-LE Series Power Supply to Output Waveforms Saved in the Waveform Bank
Figure 6 shows a system that uses PCR-LE series AC power supplies to recreate a three-phase AC waveform recorded on site.
To output the desired waveform from stored waveform bank data, in Wavy for PCR-LE, go to “Tools” and select “Direct Control”, then specify voltage and frequency. This Direct Control window also allows you to set the phase angle, and monitor voltage, current, power, and other attributes of each phase (Fig 7).
Figure 8 shows an actual waveform recreated by a PCR-LE series power supply based on waveform data recorded onsite. This graph shows line voltages.
Other Kikusui Electronics products capable of simulating real waveforms include the PBZ series of high speed bipolar power supplies and the PLZ-5W series of electronic loads. Any of these devices allows data to be recorded on site and reproduced using the process described here. Should you interested for a demonstration, feel free to contact Kikusui directly or through Kikusui local partners.
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