By Satish Mohanram, Technical Marketing Manager, NI India
Power system disturbances can be the result of various system events, transmission congestions, and fluctuations in renewable energy sources. In order to make the Grid smarter a better understanding of these disturbances is needed and this will enable us to detect the system events before they result in failures. Synchro-phasor systems are used for this purpose.
A Synchrophasor system is a wide deployment of Phasor Measurement Units (PMU) and dedicated high-speed communication to collect and deliver synchronized high-speed grid condition data along with analytics and other advanced on-line dynamic security assessment and control applications. This will improve real-time situational awareness and decision support tools to enhance system reliability. Synchrophasor measurements can also be used to improve component and system models for both on-line and off-line network analysis to assess system security and adequacy to withstand expected contingencies. But to realize this great potential, each interconnection must deploy a highly reliable, secure and robust synchrophasor data measurement and collection system and develop a suite of validated, highly available, robust and trustworthy analytical applications.
This article discusses the technologies that are involved in making the Phasor Measurement unit, which is meant to build a robust data measurement and collection system. It also highlights some of the initial deployments in India and around the world that are seen to be the next generation of the Smart Grids.
Phasor Measurements units are precisely time-synchronized, high-speed, measurement units that monitor the current and voltage waveforms (sinusoids) in the grid and convert them into a Phasor representation through high-end computation and securely transmit the same to a centralized server.
Figure 1: Phasors representation of Grid Power
In short, PMUs measure voltage, current and frequency and calculate phasors, and this suite of time- synchronized grid condition data is called phasor data.Each phasor measurement is time- stamped against Global Positioning System universal time; when a phasor measurement is time- stamped, it is called a synchrophasor. This allows measurements taken by PMUs in different locations or by different owners to be synchronized and time-aligned, then combined to provide a precise, comprehensive view of an entire region or interconnection. PMUs sample at speeds of 25 to 50 observations per second, compared to conventional monitoring technologies (such as SCADA) that measure once every two to four seconds and sometimes even once every 5 minutes. Synchrophasors will enable interconnection-wide views of grid stress and dynamics to better maintain and protect grid reliability.
Phasor Measurement system can be categorized into a cyber-physical system that has the following characteristics
1. High end computation capabilities
2. Parallel processing
3. Modular Expandable I/O channels
4. Rugged field worthy
5. Field Upgradeable
6. Real-time 24×7 operation.
National Instruments addresses this with the Graphical System Design approach of bringing commercially-off-the-shelf hardware that is powerful, modular, rigged and reconfigurable with powerful software like LabVIEW with the Electrical power toolkit that has these advanced capabilities. The architecture of the CompactRIO product series fits best for this requirement.
Figure 2: System architecture of the Compact Reconfigurable I/O
A Real-time processor that runs a very deterministic real-time operating system connected to an FPGA( Field Programmable Gate Array) that can do concurrent high speed operations defined in Software finally connected to the I/Os that can connect to the CT/PTs to measure current and voltages precisely at high speeds. The modular nature of this platform enables addition of the GPS Time stamping module as well.
Figure 3: NI PMU
Rugged Hardware that can withstand upto 50G of Shock, capable of operating from -40 to 70 Degree Centigrade. The system runs the most advanced computational algorithms to calculate the phasors and this high processing capability allows for the best in class measurement accuracy. The high speed I/Os that are interfaced with the FPGA enables parallel processing and hence maintains the measurement performance even when the number of channels is increased. Hence the performance of the system built on the above architecture has the following characteristics.
• Multichannel synchrophasors, expandable up to 32 channels
• Data transfer configurable up to 240 messages per second
• Data packages based on IEEE C37.118
• Multiple protocol TCP/IP, DNP3, Modbus RTU, IEC-60870
• High fidelity ADCs with 24-bits of resolution
• Dual-Ethernet, serial ports and digital communication
• PMU and power quality algorithms in one unit
• Up to 1000 samples/cycle(at 50Hz)
• Rugged design: -40 to 70oC
National Instruments with its partners has successfully deployed these units in WRLDC and SRLDC and the results of the same are available in the report published by the Power Grid in the following location.
http://www.nrldc.in/docs/documents/Other Documents/Synchrophasors Initiative in India_June 2012.pdf
The benefits of using PMU technology enable utilities to proactively plan and prevent deviations in the delivery of energy. The NI PMU is designed to meet requirements for accuracy, reliability, interoperability; extreme environmental conditions suitable for substation or pole mount and advanced algorithms for event and system analysis.