The demands of the power quality industry require instruments to have excellent hardware and software integration, allowing for quick and easy access to the acquired information, which must then be available in a standard format.
The world is moving into the age of information. Computers have become a common item in many households and the World Wide Web permits quick and easy access to information in faraway places. This revolution, in which information is the currency, has greatly affected the realm of power quality instrumentation. The demands of the power quality industry require instruments to have excellent hardware and software integration, allowing for quick and easy access to the acquired information, which must then be available in a standard format. This article stresses the importance of integrating hardware and software essential for proper instrumentation.
Efforts continue by meter manufacturers to address the need for integration, but shortcomings persist. The meter discussed in this article is designed to overcome these problems:
-- Meters depend too much on personal computers for basic functionality.
-- Communication interfaces typically provide data access through only a few options, although technology has many to offer.
-- Configuration flexibility is limited and unable to acquire all the information relevant for the user for each monitoring location.
-- Meters have difficulty exporting to other standard software packages all the variables acquired and analysed.
An example of these shortcomings occurred when a university laboratory performed studies for an electrical utility. One researcher wanted to do further analysis on the resulting data. So, he wrote a macro for a communications package, but even then some of the data could not be extracted. Another example occurred during a meeting of the UIE (International Union of Electro-Heat). Manufacturers were demonstrating some flickermeters for members of the working group, and almost all the meters were under the control of portable computers. Today, meters are available that can perform all their functions in one package, without the need for an additional computer or additional software programming.
HARDWARE AND SOFTWARE INTEGRATION
Except for permanent installations, power quality professionals are looking for instruments that are flexible enough to perform studies under controlled environments (e.g., office buildings, control centers) or in adverse environments (e.g., manholes, electric poles). An instrument that cannot be set-up or used without a computer limits the type of installations. To overcome this problem, a power quality analyser needs to have a front panel graphic display and an easy-to-use functional keyboard, features that allow the user to configure the instrument on-site with no additional equipment. The floppy disk port, serial, parallel and Ethernet ports also allow users to download previously programmed set-ups into the instrument.
Software flexibility also refers to all other aspects of power analysis. With this flexibility, the user can configure the hardware platform to perform:
-- Power analysis such as rms values for voltage and current, energy consumption readings such as watts (W), reactive power (Vars), apparent power (VA), power factor (PF), demand (kWh and kVarh).
-- Harmonic analysis such as the total harmonic distortion (THD) and individual harmonics up to 50th order for voltage and current, plus their waveform.
-- Flicker analysis, a visual phenomenon (luminosity changes) produced by cyclical fluctuations of the line voltage. The measurement of this parameter can be used to assess the impact that an increasing load will have on the electrical network performance.
-- Transient analysis for voltage and current events with up to 16 different triggers available, plus logical triggering.
Flexibility in terms of recording information
Typically meters do not allow users to specify variable recording rates (other than the start and stop) for steady state measurements. For the meter described in this article, the recording rate is configurable. Although the sampling rate is very high, the user can determine how much data gets recorded. When all is running smoothly, it is possible that very little of the measured data will be actually saved and recorded. This gives the user freedom to determine the amount of information kept for further analysis (e.g., more information can be recorded in shorter time frames).
In the event of a slow recording rate, another method -- separate from the recording rate -- is needed to capture the unexpected anomaly. By using alarm management flags, the meter can detect whenever a particular electrical variable exceeds any user-set threshold independently of the recording rate. For the power analyser in this article, alarm management is independent of recording rates, giving users greater flexibility and control over two of the meter's more important functions.
Whether the trend recording of electrical variables is in wattmeter mode or harmonics mode, the instrument can detect the exact time and value of momentary violations of set thresholds. For example, Figure 1a shows voltage sags and swells in terms of percentage of user-set thresholds, captured in the alarm file (*.WAL), that do show up at all on the measurement file (*.WMS) because the recording rate is slow. The steady-state graph of the measurement file is shown in Figure 1b. The steady-state recording, set by the user to record data every ten seconds, may or may not capture these brief excursions, but having both modes of recording, the meter is able to save both types of information. The information obtained in the alarm files is also used to plot against tolerance curves such as the CBEMA curve. The same concept of using alarm thresholds applies to THD values or any individual harmonic order.
Also, the user can configure alarm management to enable the recorder to record only when alarms exceed their thresholds (e.g., exception recording). Instead of recording everything for the entire length of the study, the data is recorded only when an anomalous situation occurs (e.g., sags, swells, brownouts, low power factor, energy consumption abnormally high, harmonic levels violating the standard emission limits). Typically, users desire the maximum information possible during an alarm situation, thus the recorder is programmed to its fastest rate during these anomalous conditions. When the value in alarm falls back to within the specified threshold, the meter stops recording (although it continues to make measurements). Figure 2a shows four out-of-limits events, and Figure 2.b shows how the voltage recording started and stopped when the voltage fell below 110V or went above 130V (Note: the meter adds in extra readings immediately before and after the alarm period, to ensure nothing unusual is missed.) When no alarm conditions were active, the recorder was inactive. A typical use of this capability is to examine motor start-up currents. This application demands fast recording rates for short periods of time.
Platform expandability and reusability
A power quality meter should be based in an open hardware and software platform that can easily be expandable via software or with minimum hardware modifications. Such an approach will leave the door open for future improvements in the product, thereby increasing the lifecycle of the instrument. For example, initially a user may need an instrument that only performs consumption analysis and nothing else. But later the need to measure flicker and harmonics may arise. The meter we refer to in this article was used to perform only the typical power quality measurements (e.g., steady-state measurements, transients), and within the space of three months, users had the possibility of also measuring flicker with the same instrument with no hardware modifications (only a firmware upgrade was required).
SOFTWARE CONTROL, DATA ACCESS AND TRANSPORTABILITY
Users of power quality meters need the flexibility to access the acquired data and transfer it to different media to create reports, share the data with other parties, store in databases and perform extra off-line analyses. Alternative ports for data download give users the flexibility to access and transfer data (i.e., to a computer or printer via standard communication ports, or downloading to floppy disks). The ability to transfer data to a standard format creates data that is portable, allowing many other people to have access to it. For a truly flexible design like the one discussed so far, the hardware should interface with the software via either the standard parallel or serial communications port. Also, remote control and data transfer should be possible via modem or Ethernet.
Hardware set-up and monitoring via software
Software users can configure the hardware off-line, query the configuration of the hardware remotely and upload a new set-up. Figure 3, shows a steady state configuration panel. Since there is a unified philosophy for measurements, the main set-up elements (miscellaneous parameters for configuration of each mode, alarm management set-up, and the recorder set-up) are conceptually similar for both wattmeter and harmonic analyser modes.
Figure 4 illustrates the parameter set-up for the recorder. The recorder set-up window is similar for both harmonic and wattmeter measurements. The user specifies what type of information should be recorded, and the mode of recording: normal, on presence of an alarm condition (e.g., exception recording) or when an external input is activated. The user can determine the recording rate desired or can enable recordings to start and stop at particular times.
With the software, a real-time viewer is an additional feature provided to monitor the instrument remotely for wattmeter and harmonic analyser mode.
Data transportability, analysis and automatic report generation
Meter manufacturers should provide users with an easy to use analysis environment that will help them highlight the relevant aspects of an event. Figure 5 shows a typical motor start-up. The voltage phase to phase experiences a drop with the inrush current. The capacity to transfer the acquired data into standard ASCII CSV (comma separated variable) format extends the analysis capabilities of the instrument into other software packages such as ExcelT or MATLABT. Figure 6 shows the very same data plotted with ExcelT.
Raw wattmeter data can be used off-line for many reasons, such as specifying VAR compensation banks for industrial sites. Harmonic data can be used to design filters if any resonance conditions are produced by reactive compensation. Calculation of K-factor can be done with the information obtained from the harmonic analyses. These are only some examples of the wide range of analysis that can be performed once data is transferred to ASCII CSV.
Automatic, semiautomatic, and manual report generation (depending on the user request) that produce RTF formatted files that can be read by any popular word processor are provided by the supporting analysis software that comes with the instrument.
Conclusion
A truly flexible power analysis instrument is needed to meet the demands of users facing information overload. The solution lies in the proper integration of hardware and software that perform the following:
- Easily to configure the meter with or without computer.
- Adjust recording rates, modes of recording and alarm management criteria.
- Use alternate ports to extract data and send it to a variety of media
- Communicate remotely with the meter.
- Incorporating the acquired data in reports automatically, semiautomatically or manually.
- Export the variables to a standard ASCII file format for off-line analysis. ET
Juan Pineda is Manager, Technical Support for CPM Leading Edge Technologies Inc.