Automation is it

The challenges for protection testing have evolved on the same scale, Omicron says

Inasmuch as the reliability of electricity generation, transmission and distribution is hinged on the quality of protection system, engineers have to master the complexity of modern equipment. This will minimise the risk of malfunctioning relays, whose thorough commissioning and routine testing must be undertaken by experts or companies with a proven track record in the field.

Increasing the productivity of experts through automation may also help sustain the quality of protection equipment and, eventually, the entire power system. This move is ideal in today’s environment, where trends like liberalisation of the electricity market and privatisation of utilities put the relay commissioning, routine testing and protection engineering departments under pressure to cut costs.

“Automation can save the relay experts’ time, allowing them to concentrate on solving and analysing actual failures during the power system operation or relay commissioning and maintenance,” says a paper prepared by Omicron, a global electronics firm providing innovative solutions for primary and secondary testing. Also, automation can raise the bar for both a system’s efficiency and quality, as it increases the depth of testing in a shorter period.

Titled “Efficient Testing of Modern Protection IEDs”, the paper was written by Dr Fred Steinhauser, Production Manager of Substation Communication Issues at Omicron Electronics in Austria; the company’s head of product management in the field of testing solutions for protection and measurement systems, Boris Bastigkeit, and Thomas Schossig, Product Manager for Substation Communication and Protection Testing Products.

PROTECTION DEVICES

IEDs, or intelligent electronic devices, are actually protection equipment with integrated additional functions, such as transient recorder, SCADA (supervisory control and data acquisition) functions, interfaces, process bus, fault locator and control functions, amongst other things. The standard IEC 61850, a new communication protocol, keeps track of this development and emphasises it by using the term “IEDs” instead of protection devices.

The integration of additional functions is one of the factors contributing to the complexity of modern-day protection devices, the Omicron paper says. It also cites multifunctional protection relays, shorter lifecycle of devices, greater variety of interfaces and the need to update the software that handles algorithms.

Finding ways to manage these parameters brings experts and professionals to define a standard setting for a standard application. This is usually the case as only a very small amount of parameters is set to configure the relay to protect certain equipment. “This standard setting often is defined in connection with the acceptance test by the standardisation group of the utility,” the paper says.

STANDARDISED PARAMETERS

The standardisation work, which is usually done in a laboratory, allows field engineers not to touch the standardised parameters anymore when applying the relays to the local conditions. This means reducing the complexity of IEDs, which now have a limited amount of varied but relevant parameters. In most cases, however, the standardisation process inside a utility’s laboratory does not stop there. Utilities have started to create test plans in connection with the settings’ standardisation process.

Once a standardised process is achieved, the next step is “test automation”, which focuses on creating a step-by-step, comprehensible test of all the important functions of an IED. Test strategies must consider such factors as firmware bugs, unmonitored hardware, human errors, changes in network topology and changes in the configuration of IED data.

A set of guidelines shall then be drawn up based on automatic test plans – linking the test steps to the relay settings, for instance – test modules, GOOSE possibilities, easy adaptation of standard test plans and trouble-shooting tools, amongst other things.

A GOOSE – generic object substation event – is used to exchange data between IEDs, and is a part of IEC 61850, which, besides describing the communication between IEDs and SCADA functions, also addresses many tasks inside a substation.

IMPROPER ANALYSES

Measuring a GOOSE performance is a challenge, the paper points out, as there are occasional reports of failed applications due to insufficient performance. Most of these problems, however, have stemmed from non-recommended usage or improper analyses of the applicability of devices. “One problem is the lack of performance specifications, which would facilitate the assessment of a device in a distinct application,” it says.

It cites a number of specifications that can help a system integrator assess a device well, such as measuring a round-trip time to obtain a conservative estimate for the GOOSE performance. In this process a GOOSE is sent out from a test set to a device under test (DUT), which then sends the GOOSE back to the test set at the soonest time possible.

Time synchronisation is also important in well functioning protection system, as performance figures have been pushed into the sub-millisecond range. This means the need for a tighter control over the behaviour of IEDs, particularly for test sets. And this requires a dedicated hardware controlled by carefully coded real-time software, for reliable performance and accuracy of measurements.

All of this shows that the challenges for protection testing have evolved on the same scale, as single-function electromechanical relays graduated to multifunctional numerical relays with protocol interfaces. “Modern test systems master the complexity with a high-degree of automation,” the Omicron paper says. “Accurate test signal generation and versatile testing functions allow testing of sophisticated protection algorithms.”