Author(s):
Daniel Kaminský - ELCOM, a.s.
Petr Bilik - ELCOM, a.s.
Jiri Hula - ELCOM, a.s.
Why Are Power Quality Measurements Important?
Electricity is a product unlike any other and perhaps is the most essential raw material used by commerce and industry today. It is an unusual commodity because it is required as a continuous flow - it cannot be conveniently stored in quantity - and it cannot be subject to quality assurance checks before it is used. Electricity of poor quality, for example, can cause significant damages in production lines. Therefore, by monitoring power quality, it is possiblie to identify potential problems before they are big enough to create damages that all too often come with serious financial losses. Prevention, however, is relatively cheap and ranges from simple best-practice-design-considerations to global installations of monitoring and control equipment.
What Has to Be Measured?
A typical power quality analyzer analyses 3 voltages of power network to calculate voltage quality defined in international standards. Voltage quality is described by frequency, voltage level variation, flicker, three-phase system unbalance, harmonic spectra, total harmonic distortion and signaling voltages level. In some cases it is necessary to analyse the current signals along with the voltages. This allows analysis of current parameters and calculation of indirect quantities like active power, reactive power, energies and other quantities.
Figure 1. Electrical Energy Transmission with Power Quality Monitoring
Our power quality analyzer software and hardware suite is named ENA (ELCOM Network Analyzer) and represents a complex modular system for power quality monitoring according to actual international standards and other national-specific documents.
Considerations for Choosing the Development Platform
We chose to implement our system on the NI CompactRIO platform with C Series modules. In comparison to PC-based instruments, it is more compact, rugged, and smaller in size 3.4 x 7 x 3.5” (88 x 180 x 90mm H x W x D). It also has better temperature specifications (operating temperature -40°C to +70°C) as well as very low power consumption (approximately 8W). Furthermore the NI CompactRIO product family offers various form factors which we believed was important to be able to accommodate different customer and application needs.
From the variety of I/O modules we used the NI 9225 300V power measurement module for performing high-voltage measurements. The module is designed for measurements, such as line-to-neutral as well as line-to-line measurements of 110V power grids and line-to-neutral measurements of 240V power grids. For current measurements we use NI 9227. The NI 9225 and NI 9227 have simultaneously sampled channels at 50 kS/s for accurate three-phase power metering and power quality measurements such as flicker, harmonics and power factor. Alternatively we have designed voltage and current modules: EL9215U-R1 and EL9215I-R1 that are based on the NI 9215 module and use our signal conditioning electronics. These are embedded in 3 slots of a CompactRIO chassis.
For the software development environment we have used NI LabVIEW for all parts of the ENA software as the ease of use, portability and scalability of the solution was also very important. Several models of the CompactRIO power quality analyzers exist, which differ in CompactRIO models and the used input modules. ENA power quality analyzer firmware minimum requirements are 400MHz processor controller and chassis with 2M Gate FPGA.
The CompactRIO-based Power Quality Analyzer
The model name that we present here is ENA-450, but due to the scalability of the NI CompactRIO family and the portability of the LabVIEW code, we were able to implement the system in different form factors to accommodate various different application and customer specific needs. Besides the implementations based upon the fully flexible NI CompactRIO system (ENA450.EC), we have created turnkey solutions where we have deployed our application to:
- Integrated CompactRIO systems that combine a real-time processor and a reconfigurable field-programmable gate array (FPGA) within the same chassis (ENA450.EB, ENA450.NB)i
- NI Single-Board RIO systems that integrate the three core components of an NI CompactRIO system - real-time processor, field-programmable gate array (FPGA), and I/O - on a single printed circuit board (ENA460).
The analyzer capabilities are defined by instrument hardware and software. ENA power quality monitoring system contains a bundle of software applications for analyzer remote control, stored data analysis and for presenting power quality data across the Internet. The modular concept allows fulfilling all customer needs together with minimizing costs.
Measurement Capabilities
The firmware ENA-Node (see picture gallery) is running directly on the CompactRIO based ENA450 analyzer and provides a measurement service that handles all data acquisition, calculations and storing.
The ENA-Node contains several software modules running in parallel:
- FFT analyzer
- Vector analyzer
- Power Flow monitor
- Flickermeter
- EN50160 Voltage monitor
- Half-period RMS monitor
- Voltage Telegrams & Alarms
- Digital Inputs
All mentioned firmware modules are suited for 50Hz and 60Hz power system. Users can observe data on the instrument display and store them into the data files. All instruments are working with a sampling rate of 9.6kS/sec per channel. The sampling rate is synchronized with frequency of measured signals. Implemented algorithms follow the requirements of the actual power quality standards like IEC61000-4-30, IEC61000-4-15, and IEC61000-4-7.
The software analyses three voltage signals up to 300V rms and the instant value of three currents of power networks to calculate various quantities like: RMS values, frequency, harmonic spectra, total harmonic distortion, flicker, three-phase system unbalance, active power, reactive power, energies and many other quantities. Currents as outputs of current transformers (1A/5A) can be measured directly by using the NI 9227 current module or the ELCOM EL9215I-R1 current module connected indirectly by current clamps.
Figure 2. ENA450 wiring diagram – how to connect to power lines
List of measured quantities:
| Voltage |
Current |
Power |
Energy |
Voltage evaluated according EN50160 |
| RMS (200ms & half period) |
RMS (200ms & half period) |
Power factor |
Active energy total |
RMS |
| THD |
THD |
Cosine |
Active energy fundamental (1st harmonic) |
THD |
|
Harmonic (1-50th)
|
Harmonic (1-50th) |
Active power total |
Reactive energy total |
Harmonics (1-25th) |
|
Interharmonic (0.5 – 49,5th)
|
Interharmonic (0.5 – 49,5th) |
Active power harmonic (1-50th) |
Reactive energy fundamental (1st harmonic) |
Unbalance |
|
DC part
|
DC Part
|
Reactive power total |
Apparent energy total |
Frequency |
|
Unbalance
|
|
Reactive power harmonic (1-50th) |
Active energy positive |
Signaling voltages |
| Short time flicker Pst, long time flicker Plt |
|
|
Active energy negative |
|
| |
|
Apparent power total |
Reactive energy inductive |
|
| |
|
Apparent power harmonic (1-50th) |
Reactive energy capacitive |
|
User Interface for Instrument Control, Data Management and Reporting
The easy to use user interface ENA-Touch is a graphical user interface for the ENA measurement service. All instrument control, data presentation and measurement configurations are operated through this application. To display measured quantities it allows easy and well arranged configuration and measured data presentations. There are two types of visualization panels: some panels have fixed set of quantities in tables,some panels have fixed sets of quantities in tables, and some panels have a user-defined set of quantities to display while enabling numerous ways to present data: tables, frequency domain graphs, scope, vectorscope and statistical results for power quality. ENA-Touch user interface is optimized for control by touch screen display and can be used also on Ultra Mobile PC with resolution 800x480. ENA-Touch can control ENA-Node remotely by using TCP/IP protocol over Ethernet. Simultaneously with all on-line data presentations, the system allows the user to store data for off-line analysis as well. The calculated quantities are aggregated in time, and some data are statistically evaluated before storing. The data is stored periodically with defined time intervals, while event-based data is stored just when the event appears.
With ENA-Report stored data can be analyzed comfortably off-line and besides that it can be used for report generation too.
Distributed Power Quality Monitoring with ENA
Distributed monitoring systems can be built using several ENA450 analyzers. The data in the distributed system can be replicated to MS-SQL or ORACLE database for central storage and off-line analysis.
Conclusion
The main advantage of the described power quality monitoring system is its high-performance, flexibility and small size. Using the C-Series modules with built-in signal conditioning, and implementing the powerful and user-friendly solution, dramatically simplifies the software maintenance and further development without impact on the current solution. In case of any updates or changes to the standards, the instrument features can be updated quickly and the system stays up to date. Due to the open solution the existing system can be easily integrated with other systems, as the communication protocols can be adjusted in accordance with customer needs or integration into existing SCADA systems. The open hardware architecture makes it possible to add new DIO for monitoring and controlling as well as modules for wireless communication via GPS or GSM.
The flexibility of NI CompactRIO and NI LabVIEW also allowed us to implement a complete PMU analyzer (Phase Measurement Unit) in the matter of weeks. It allows precise evaluation of the synchrophasors in accordance with the IEEE C37.118-2005 standard. We are currently working on integrating the PMU analyzer with the power quality analyzer, ENA450, into one single instrument.
Author Information:
Daniel Kaminský
ELCOM, a.s.
Division of Virtual Instrumentation, Technologická 374/6
Ostrava - Pustkovec 708 00
Czech Republic
Tel: +420 558 279 913
Fax: +420 558 279 901
Print
PDF
