Evolution of Protection Relays From Alstom

������ ���������� ������� ��������� Since 1962, it has been Alstom’s endeavor to provide the most advanced protection solutions for electrical grid. The evolution of protective relays begins with the electromechanical relays. Over the past decade it upgraded from electromechanical to solid state technologies to predominate use of microprocessors and microcontrollers. To see this we can observe the timeline of technology advancement for relays 1900 to 1963: Electromechanical Relays 1963 to 1972: Static Relays 1972 to 1980: Digital Relays 1980 to 1990… Numerical Numerical Relays Electromechanical Relays: These relays were the earliest forms of relay used for the protection of power systems, and they date back around 100 years. They work on the principle of a mechanical force operating a relay contact in response to a stimulus. The mechanical force is generated through current flow in one or more windings on a magnetic core or cores, hence the term electromechanical relay. The main advantage of such relays is that they provide galvanic isolation between the inputs and outputs in a simple, cheap and reliable form. Therefore these relays are still used for simple on/off switching functions where the output contacts carry substantial currents. Static Relays: The term ‘static’ implies that the relay has no moving parts. This is not strictly the case for a static relay, as the output contacts are still generally attracted armature relays. In a protection relay, the term ‘static’ refers to the absence of moving parts to create the relay characteristic. Their design is based on the use of analogue electronic devices instead of coils and magnets to create the relay characteristic. Early versions used discrete devices such as transistors and diodes with resistors, capacitors and inductors. However, advances in electronics enabled the use of linear and digital integrated circuits in later versions for signal processing and implementation of logic functions.

Digital Relays: Digital protection relays introduced a step change in technology. Microprocessors and microcontrollers replaced analogue circuits used in static relays to implement relay functions. Early examples were introduced around 1980 and with improvements in processing capacity is still current technology for many relay applications. However, such technology could be completely superseded by numerical relays. Compared to static relays, digital relays use analogue to digital conversion of all measured quantities and use a microprocessor to implement the protection algorithm. The microprocessor may use a counting technique or use Discrete Fourier Transforms (DFT) to implement the algorithm. However, these microprocessors have limited processing capacity and associated memory compared to numerical relays. Numerical Relays: The distinction between digital and numerical relays is particular to Protection. Numerical relays are natural developments of digital relays due to advances in technology. They use one or more digital signal processors (DSP) optimized for real time signal processing, running the mathematical algorithms for the protection functions. For faster real time processing and more detailed analysis of waveforms, several DSPs can be run in parallel. Many functions previously implemented in separate items of hardware can then be included in a single item. Relay Operating System Software: The software provided is commonly organized into a series of tasks operating in real time. An essential component is the Real Time Operating System (RTOS) which ensures that the other tasks are executed when required, in the correct priority. Other software depends on the function of the relay, but can be generalized as follows: System services software – this is comparable with the BIOS of an ordinary PC and controls the low• level I/O for the relay such as drivers for the relay hardware and boot-up sequence. HMI interface software – this is the high level software for communicating with a user on the front • panel controls or through a data link to another computer to store data such as settings or event records. Application software – this is the software that defines the protection function of the relay • Auxiliary functions – software to implement other features in the relay, often structured as a series of • modules to reflect the options offered by the manufacturer.

Relay Application Software: The relevant software algorithm is then applied. Firstly the quantities of interest are determined from the information in the data samples. This is often done using a Discrete Fourier Transform (DFT) and the result is magnitude and phase information for the selected quantity. This calculation is repeated for all of the quantities of interest. The quantities can then be compared with the relay characteristic, and a decision made in terms of the following: Value above setting – start timers, etc. • Timer expired – action alarm/trip • Value returned below setting – reset timers, etc. • Value below setting – do nothing • Value still above setting – increment timer, etc. • Numerical Relays & Software: The 40 series platform, incorporating a full complement of utility, generation and industrial-focused models is the principal building block of Alstom Grid’s offer, hosting the wide variety of protection, control, measurement, monitoring and communication functions demanded. The versatile hardware allows deployment with confidence and the PC tool, S1 Agile, makes for easy configuration, application and management of the installed base. Numerous integrated communication protocols allow easy interfacing to substation control or SCADA systems. From simple wired serial buses, to Ethernet station and process bus architectures with IEC 61850 - MiCOM Alstom protection has the solution. Programmable scheme logic Powerful logic available in the 40 series relays allows the user to customise the protection and control functions of the relay. It is also used to program the functionality of the opto-isolated inputs, relay outputs, LED and user alarms.

Disturbance records The internal disturbance recorder will record the sampled values of all analogue input variables such as phase currents and voltages where applicable during a fault. Oscillographic analysis can be performed using the S1 Agile PC tool which will provide the means to quickly analyse analogue and digital signals on the same time scale for convenience.

Relay Configuration Software: MiCOM S1 Agile is the truly universal IED engineering toolsuite. No-longer are separate tools required for redundant Ethernet configuration, phasor measurement unit commissioning, Busbar scheme operational dashboards, programmable curve profiles or automatic disturbance record extraction – all applications are embedded.