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Moving towards a Smart transmission grid

Conference: African Utility Week
Location: Cape Town, South Africa
Presenter: Tevfik Sezi
Abstract: Presented by Tevfik Sezi at African Utility Week

The introduction of IEC 61850 is a very important milestone in the history of power system protection and automation. It is the first world standard protocol for substation communication, enabling data exchange from Sensors to Intelligent Electronic Devices (IEDs), between the IEDs and from the IEDs to the substation controller with the same communication infrastructure. Its engineering tools define the complete substation, measurement, control and protection layout. Enabling world wide interoperability of protection relays and other IEDs of different vendors is a significant benefit for utility applications. At the same time, widely acceptance of fiber optic based Ethernet communication infrastructure reduces the risk of electromagnetic disturbances, while enabling high speed communication inside and between substations.

However, the introduction of IEC 61850 and the use of upcoming new Ethernet technologies seem to be the beginning of a series of technological changes, which will end in an evolutionary change of the protection and control practice of power systems.

Today, the time synchronization accuracy of 1ms is widely accepted in industrial plants, especially in manufacturing sites. Also in these fields, but especially in power automation and relaying applications, future high precision measurement algorithms require a time synchronization accuracy of less then 1µs.

Time synchronization of Intelligent Electronic Devices is provided today by a separate electrical or fiber optic infrastructure using IRIG-B or a 1pps (one puls per second) signal, for example DCF77. However, the new IEEE P1588 standard will establish the necessary accuracy directly over the existing Ethernet communication infrastructure. The task force HTF1 of IEEE Power System Relaying Committee PSRC is discussing the future implementation of IEEE P1588 in substation environment, providing this accuracy of less then 1 microsecond, utilizing only one master clock – preferably satellite receiver – connected to the same communication infrastructure.

The implementation of IEC 61850 – Process Bus will enable the integration of low power voltage and current transformers, fiber optic transducers and Rogowski coils into the same communication infrastructure, sending sampled data with precise time synchronization to the IEDs. This significant step will practically eliminate three major problems of the past – limited accuracy, limited dynamics and limited frequency range of the VTs and CTs.

Recently introduced Phasor Measurement Units (PMUs) meeting the C37.118 – 2005 standard enable precise measurement of voltage and current Phasors and the power system frequency with the same absolute time stamping capability of less then one microsecond.

These fundamental changes of communication, time synchronization and data acquisition technologies will enable a full range of new applications, which is the focus of this paper.

The first prototypes of Wide Area Monitoring Systems – WAMS with Phasor Data Processing Software and Phasor Measurement Units are being installed in various countries, mostly in areas with long lines and stability problems. The main focus is to monitor and understand the dynamic behavior of the power system.  With better understanding of inter area oscillations, voltage stability problems, reactive power shortages, load flow dynamics and other power system dynamics system operators expect improved solutions for the existing problems.

Wide Area Control Systems – WACS with Phasor Measurement Units and related software focus on the optimal control of power electronics in the power system like High Voltage Direct Current (HVDC) and Flexible AC Systems (FACTS) to increase system stability.

Today, System Integrity Protection Schemes – SIPS are mostly event based systems to identify system instabilities, for example caused by load and generation unbalance. They are planned with offline simulation studies and implemented with fixed response schemes.

With the introduction of PMUs and central computers with flexible logic and Phasor processing capabilities, these systems will be replaced by the response based SIPS. In long term, their implementation may impact and change the power system operation practice significantly due to the capability of early detecting of system instabilities.

The authors will also discuss other topics like remote backup protection, intelligent load shedding, power system loadability limits, state estimation and state measurement under the influence of the upcoming technologies.