The evolutionary pattern of power demand has made it imperative for suppliers to ensure uninterrupted and high quality power supply to consumers. This mandates a quick response to various undesirable situations such as service interruptions and outages produced by equipment failures or natural calamities. Reliable supply and competitive prices are some of the concerns that consumers usually have. In such a scenario, access to high quality real-time information becomes very important.
Consequently, in recent times, power utilities across the world have started placing greater emphasis on real-time information to enhance system reliability and ensure better asset management, and operations and maintenance. Utilities have automated their systems to provide a quick response to real-time events with pre-specified actions to maintain uninterrupted power service. With regard to substations, which are an important component of the transmission and distribution infrastructure, the development of substation automation systems primarily enables an electric utility to remotely monitor, control and coordinate the components installed in the substation.
Earlier, automation efforts involved the installation of remote terminal units (RTUs) in substations and numerous hardwired connections. The contact points were connected for monitoring relay and switch status and analog transducers were deployed for metering purposes. But soon, the cumbersome collection of auxiliary relays and hardwired logic was replaced by programmable logic controllers (PLCs). However, with further advances in digital electronics and communications technology, intelligent RTUs were introduced. These allowed utilities’ supervisory control and data acquisition (SCADA) system to communicate directly with the various intelligent electronic devices (IEDs) deployed in a substation.
An IED is any device that incorporates one or more processors with the capability to receive or send data/control from or to an external source (for example electronic multifunction meters, digital relays and controllers). It consists of various protection controls, and metering and monitoring devices, which are implemented using a microprocessor-based technology. It includes microprocessor-based protective relays, metering devices, PLCs, digital fault recorders, circuit breaker monitors, power quality meters, etc. The deployment of IEDs helps utilities to improve reliability, gain operational efficiencies and enable asset management programmes, including predictive maintenance, life extensions and improved planning.
IEDs facilitate the exchange of both operational and non-operational data. Operational data or SCADA data consists of instantaneous values of power systems’ analog and status points such as volts, amps, MW, MVAR, circuit breaker status and switch position. Such data is time critical and is used to monitor and control the power system. However, non-operational data consists of files and waveforms, for example, event summaries, oscillographic event reports and sequential event records, in addition to SCADA-like points that have a logical state or a numerical value.
In substations, IEDs are most widely used for monitoring and protective relaying. As protective relays, they perform the essential processing of analog data such as currents and voltages. Analog or digital filtering techniques are applied to obtain the fundamental components of current and voltage wave forms. These are further processed for protective relaying functions. The main advantage of IEDs is their multifunction relaying property. An IED-based multifunctional protective relay consists of sequence component filters, which help generate the positive, negative and zero sequence currents and/or voltages used in different protection schemes. These devices provide real-time monitoring and form the basis of substation intelligence.
However, with a variety of IEDs deployed at substations, several problems crop up. The most important problem pertains to the lack of data verification, both analog and digital, which can lead to serious errors in substation operations. The understanding of the current status of substation equipment (such as circuit breakers), load flows, location and type of faults can be difficult with unmatched data sets. This in turn can affect the capability of operators to monitor and control substation operations. The second pressing issue is the inability of operators to efficiently extract the required information. This can be mainly attributed to the large quantities of data originating from IEDs. Manual retrieving and processing of such a huge quantum of data is time-consuming and many utilities do not have adequate resources to perform the function effectively. As such, much of the recorded data may not be analysed in a timely manner, thereby underutilising the monitoring advantage of IEDs.
Going forward, there is a need to better understand the functionalities of the emerging IEDs and their performance characteristics. The new functions are expected to provide more automated means of handling data and making related controlled decisions, and hence may require different approaches to database and user interface solutions.