Power Quality Monitoring for Utility Power Grids
As the Chinese economy grows, there is an increased adoption of nonlinear loads such as electric railways, arc furnaces and frequency converters that are creating detrimental consequences to the electric supply system and resulting in the creation of serious power quality problems like harmonics, unbalances, flickers and voltage transients. The rise in power quality problems bring unpredictable effects to the stability of the power system and affect the normal operations of countless enterprises with power-sensitive production facilities.
Being one kind of commodity, the quality of electricity supply has become a mutual concern between utility companies and power consumers. For power suppliers, their quality of power supply can be evaluated by testing their ability to satisfy the requirements and expectations of power consumers. In other words, power suppliers must provide power in a way that satisfies the customers' actual operational needs. On this basis, it is necessary for power suppliers to first understand their own supply capability before committing themselves to an agreement to provide the kind of power required by the customers. To achieve this, power suppliers need to setup power quality monitoring systems (PQMS) that allow them to not only do real-time monitoring of their supply systems but also to capture PQ events and then subsequently perform statistical analysis in order to determine their real capability. The PQMS should provide the following functions:
¡ñ Monitor power quality of the entire power supply network based on nationally and internationally recognized PQ standards and generate PQ reports that provide meaningful benchmark for the supply system.
¡ñ Monitor the influence of power consumers' loadings on the quality of the power supply by recording and locating the sources of PQ pollution so that any PQ problems can be effectively and appropriately handled to the satisfaction of suppliers and consumers alike.
¡ñ Analyze the stability of power supply network based on the PQ data collected in order to improve the quality of the supply network on a gradual basis.
PQMS for county, city and district level electricity supply network
A typical PQMS for county, city and district level electricity supply network consists of two layers. The lower layer includes power quality monitoring devices installed at the substations or power distribution rooms. The upper layer is the PQMS software located inside the utility company's central control room. The PQMS consists of a database server, a data collection and processing server, a WEB server and several application servers. The upper and lower layers communicate with each other using different communications technologies such as Ethernet networks, telephone modems, RS485 networks, GPRS/CDMA modems or other wireless communications means.
The power quality monitoring devices, such as CET's PMC-580 PQ monitor, are typically deployed at the critical feeders and transformers of the various voltage-level substations such as 6kV, 10kV, 35kV, 66kV, 110kV, 220kV and 330kV.
The PQMS, such as CET's PQSys Power Quality Analysis and Management Software, supports a distributed and modular architecture where different modules such as the database module, the data collection and processing module and the WEB module can be integrated in a single server or dispersedly deployed on different servers over an enterprise network. CET's PQSys supports different Windows Operating Systems such as Windows 2000 Server, Windows XP and Windows 2003 Server and widely used commercial databases such as MS SQL Server and Oracle SQL Server.
PQMS for provincial and regional power grids
A typical PQMS for provincial and regional power grid consists of three layers. The first layer is the PQ monitoring devices installed in every substation or power distribution room of the provincial or regional electricity supply network. The second layer is the PQMS system deployed within the central control room of the county, city and district utility's company. The third layer is PQMS software deployed at the central control room of the provincial and regional power research institutes or utility companies.
¡ñ CET's PMC-580 advanced PQ monitor provides a maximum sampling rate of 1024 points/cycle, capable of providing different functionalities such as voltage sags/swells and transients capture, setpoint eventing, harmonics energy metering, and various I/O capabilities. It also provides a rich set of accurate data for power quality analysis and management.
¡ñ CET's PQSys Software can generate power quality reports, complying with national power quality standards, which provide a clear picture of the level of power quality that the power supplier is capable of providing. It can provide information on the statistical distribution of various PQ indicators within the electricity supply network. The PQSys Software also provides advanced reporting features such as automatic report generation, report exporting and sharing via emails or web pages, and report printing. Customized reporting is also supported which will satisfy basically any user requirements for PQ reports and minimize the workload of PQ engineers.
¡ñ CET's PQSys Software is capable of providing PQ statistical analysis and assessment over a map, showing an overview of the distribution of PQ indicators geographically based on the installed locations of the PQ monitors. This function is very powerful as it is able to show the propagation of transient PQ events geographically, enhancing the understanding, the analysis and the location of certain faults. This geographical view of PQ events and statistics also enables the users to appreciate much more intuitively regarding the distribution and dissemination of power quality events and as a result significantly reducing the PQ analysis workload.
¡ñ CET's PQSys is able to enhance the power quality analysis and reasoning by correlating SOE events against certain incidents such as the explosion of capacitors and switching errors, providing high pragmatic values.
¡ñ CET's PQSys is a WEB-based software, making it extremely easy for users to access and analyze PQ information, reducing the learning curve as well as operational cost, thus increasing the value and effectiveness of PQ management for the customers.