Power Quality Analyzer Based on CompactRIO

The main goal of this article is to implement a power quality analyzer that contains a complete set of instruments that can perform all necessary power-related measurements and can implement parallel processing on a small hardware system running a real-time operating system. In addition, the scalability of the system must also be taken into account, mainly in order to comply with the latest IEC and EN standards when designing measurements and data processing operations.

Figure 1 Schematic diagram of power transmission with power quality monitoring function

What is the quantity to be measured?

Voltage quality is defined by the following parameters: frequency, voltage level variation, flicker, three-phase system unbalance, harmonic spectrum, total harmonic distortion and signal voltage level. In special cases, the current signal needs to be analyzed together with the voltage. This allows the analysis of current-related parameters and the calculation of some indirect parameters.

A typical power quality analyzer collects and analyzes three voltages in the power grid and calculates the voltage quality according to international standards. Why

is power quality measurement important?

Electricity is unusual in that it must be received and used continuously, it is not easy to store large amounts of electricity, and it is not easy to check its quality before use. The cost of preventive work is relatively low at this time, and engineers have everything from optimizing system operation processes to the overall installation of monitoring and control equipment. If the

power quality is poor, it may cause significant damage to the production line. Therefore, by monitoring the power quality, we can find potential problems before the system is damaged and cause serious financial losses.

Our power quality analysis software and hardware package is named ENA, which is a comprehensive modular system for power quality monitoring.

Power Quality Analyzer Based on CompactRIO The

model shown in this article is the ENA450 power quality analyzer, but due to the scalability of the NI CompactRIO product family and system and the portability of LabVIEW code, the system can be adjusted to different sizes to meet various applications and customer specific needs.
In addition to being based on the fully flexible NI CompactRIO system (ENA450.EC), this article also creates two other overall solutions that can deploy applications to: "Integrated CompactRIO System (ENA450.EB, ENA450.NB);" or Single-Board RIO (ENA460) system.

The performance of the power quality analyzer is determined by the instrument hardware and software. The ENA power quality monitoring system includes a series of software applications that can be used for remote control of the analyzer, analysis of stored data, and publishing power quality data via the Internet.

How to choose a development platform

Compared with traditional computer-based instruments, C Series modules enable systems that are more compact, rugged, and smaller in size. Moreover, the NI CompactRIO series of products can also provide us with a variety of different size specifications, which can quickly adapt to the needs of different customers and different applications.
This article selected the NI9225300V power measurement module designed for power grid measurement from the rich C series I/O modules for high voltage measurement. This module can measure the phase voltage and line voltage of the 110V power grid and the phase voltage of the 240V power grid. For current measurement, we used the NI9227. It also has better temperature specifications (operating temperature range between -40°C and +70°C) and very low power consumption (about 8 watts).
The NI9225 power quality analyzer and the NI9227 power quality analyzer can achieve synchronous sampling at a sampling rate of 50k samples/second, which can achieve accurate three-phase power measurement and power quality measurement. This article also designed special voltage and current modules for selection: EL9215U-R1 and EL9215I-R1, both of which are based on the NI9215 module design and embedded with our signal conditioning electronics. They occupy three slots and can be integrated into a CompactRIO chassis. The minimum requirements for the ENA power quality analyzer firmware are a controller with a 400MHz processor and a chassis with a 2M field programmable gate array (GateFPGA).

Measurement capabilities

The firmware ENA-Node includes several software modules that run in parallel:
"FFT analyzer
" Vector analyzer
"Current monitor
" Flicker meter
"EN50160 voltage monitor
" Half-cycle RMS monitor
"Voltage alarm and alarm
" Digital input Figure 2 ENA450 wiring diagram – how to connect to the power line The software will analyze the three voltage signals of the power grid (up to 300Vrms) and the three current instantaneous values ​​in order to calculate various variables of the power grid: RMS value, frequency, harmonic spectrum, total harmonic distortion, flicker, three-phase system unbalance, active power, reactive power, energy and many other variables. All the above firmware modules are suitable for 50Hz and 60Hz power systems. All instruments work at a sampling rate of 9.6kS/sec/channel. The current output of the current transducer (1A/5A) can be measured directly by using the NI 9227 current module or by connecting to the ELCOMEL 9215I-R1 current module via a current clamp. The sampling rate is synchronized with the frequency of the measured signal. The implemented algorithm complies with the provisions of the power quality standards such as IEC61000-4-30, IEC61000-4-15 and IEC61000-4-7. List of measurable variables User interface for instrument control, data management and reporting All instrument control, data display and measurement configuration are performed through the ENA-Touch user interface. It can be easily and properly configured and the measured data is displayed in order to display the measured values. At the same time, since all online data are displayed, the system also allows data to be stored for offline analysis. The calculated variables can be accumulated in time and some data are statistically evaluated before storage. Data is stored periodically according to a specified time interval, and some event-based data is stored only when an event occurs. The ENA-Touch user interface is optimized for control and can be displayed using a touch screen and can also be used on ultra-mobile PCs with a resolution of 800x480. ENA-Touch can remotely control the ENA-Node via the Internet TCP/IP protocol. There are two types of visualization panels: some panels display fixed values ​​in a table, and some panels can support multiple methods of displaying data (such as tables, frequency domain diagrams, charts, vector diagrams and power quality statistics) to display user-defined values. The stored data can be easily analyzed offline and reports can be generated using ENA-Report. Conclusion Due to the openness of the solution, the existing system can be easily combined with other systems, and the communication protocol can be adapted to customer needs or integrated into the user's existing SCADA system. By using C series modules with built-in signal conditioning, a powerful and user-friendly solution can be achieved, which can greatly simplify software maintenance and further development. The open hardware architecture allows the user to add new DIOs for monitoring and control, or add communication modules for GPS or GSM wireless communication. The main advantages of this power quality monitoring system are high performance, good flexibility and small size.