Sampled Values

Author: Stefan Meier, ABB Power Systems, Switzerland

A combination of these vital technologies was used in the world’s first commercial implementation of IEC 61850-9-2 LE to refurbish a substation that was first commissioned in 1999.

The commissioning of a series of six outdoor substations with process bus and NCIT technology began in 1999. The mixed technology, or “hybrid” substations supplied to the Australian utility, Powerlink Queensland, were based on an intelligent plug-and-switch system. Electronic modules integrated into the drives of the circuit breaker, disconnector and earthing switch of the system’s modules could communicate using a proprietary optical process bus.
Furthermore, the modules were equipped with non-conventional sensors for voltage and current measurements, also connected to the process bus.

A process bus is the communication network between primary equipment (such as instrument transformers) and secondary equipment (such as protection and control IEDs) of a substation automation system. This optical communication network is used to transmit analog data (such as current and voltage measurements). The network can also be used to transmit binary data (such as the switchgear’s position indications) and trip-and-close commands (to operate the circuit breakers and disconnectors), but this is not part of the described process bus implementations.

In today’s conventional substations, this information is exchanged through extensive parallel copper cabling. The use of fiber-optic networks not only eliminates vast parts of the copper cabling lowering the installation and commissioning time and decreasing the risk of connection errors, it also increases operational safety by isolating the primary from the secondary process (Figure 2).

The sensor families are based on redundant sets of Rogowsky coils for current measurement and two independent capacitive dividers for voltage measurement. Designed for single-phase encapsulated GIS, the enhanced NCITs cover nominal voltages ranging from 170 kV to 550 kV and nominal currents up to 4,000 A. The combined current and voltage sensors feature very high accuracy and linearity throughout the entire measuring range, supporting protection as well as revenue metering applications. Software-configurable ratios support efficient design of the switchgear, independent of CT and VT calculations. Configurable current ratings enable future adaptation of CT ratios without needing to replace CT cores or to open gas compartments.
The redundant measuring path is complemented by two independent, ruggedized sensor electronics, the secondary converters. As it contains no oil, this equipment is both environmentally friendly and extremely safe.

The fully redundant design of the sensors (including the associated electronics) permits application of two completely independent and parallel protection systems, boosting the availability of the secondary system. As sensor electronics can be replaced independently and without requiring a shutdown of the entire protection system, repair activities require less time and, because no live parts need to be handled, these activities are also much safer (See Figure 1).

More than 300 such electronic sensors were installed in Powerlink’s substations. Notably, in more than 14 years of service, none of the primary converters ever failed. Based on experience values, the mean time between failures (MTBF) of the sensor electronics is estimated to be around 300 years. This demonstrates the extreme reliability and high availability of the sensors, even under the very demanding environmental conditions of the Australian climate.






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