TESTING SERVICES & EQUIPMENT
Testing solutions of a special kind: Integrated expert knowledge in the Protection Testing Library
Michael Albert of Omicron says that for protection engineers, the increasing complexity of modern protection devices represents a major challenge when preparing automated tests.
D
efining special distance and differential protection characteristics can turn out to
be particularly complex and time consuming. Omicron recognised this trend many years ago and since then has been offering optimised solutions in its Protection Testing Library (PTL).
Today, the PTL includes predefined and editable test templates for more than 270 types of protection devices and covers a comprehensive range of topics. Aside from overcurrent protection, distance protection and differential protection applications, it also includes machine protection (generator and motor). Furthermore, it offers solutions for testing grid disconnection protection devices for interconnection (including Q-U protection) or the recloser and sectionaliser controls used by many countries in distribution grids.
At Omicron, a team of protection experts is responsible for maintaining the library and ensures that it is kept up-to-date. The testing templates include test plans for all important protection functions and suitable XRIO converters.
The experts constantly face challenging tasks when developing new templates. At a glance, the logical structure of the user-friendly input masks used in the templates may appear to be based on simple background algorithms.
However, this would only be an assumption because they actually function at a high level of complexity. Being able to facilitate test solutions which can be adjusted to specific testing tasks and the test equipment at hand is precisely what makes the innovative functions of this library so useful. The following section uses three examples from the world of differential protection to help you learn more about these special functionalities.
1) T60 – Cubic Spline Interpolated Transformer Differential Tripping Characteristic
Differential protection characteristics can represent a major challenge to testers. For example, The GE Multilin T60 transformer differential protection employs an operating characteristic whose progression is determined by using a cubic spline interpolation. In the PTL template, these calculations are performed in the corresponding XRIO converter. Here, they are defined in such a way that the characteristic is displayed for all potential setting values in the differential protection test modules, making it easy to perform tests on a protection device such as this.
2) 7SD610 (7SD523) – Adaptive Tripping Operating Characteristic
Aside from complex mathematical algorithms, protection devices sometimes employ dynamic and adaptive methods with corresponding complexity for considering current conditions. For example, in Siemens’ 7SD610 line differential protection, the actual trigger characteristic is represented as a simple straight line.
(see f1, f2), strongly depend on the current level. With its graphic support, the ‘Advanced Differential’ testing module group of the Test Universe software facilitates efficient testing of differential protection relays. Due to its unique nature, the stabilisation characteristic for the 7SD610 is defined here in the PTL’s XRIO converter and shown with existing stabilisation quantities.
3) SEL 311L – Alpha Plane Current Differential Algorithm
Algorithms of phase comparison protection relays in particular are often very individual. Therefore, the solutions offered by protection device manufacturers vary accordingly. For example, the SEL 311L protection relay does not determine a differential current in a typical fashion with a protection trip being triggered when a threshold is exceeded. Instead, it continuously calculates the ratio of the complex currents at the two ends of the line. A plane, the so-called alpha plane, is then stretched over the real and imaginary part of this ratio.
The PTL provides optimum support for efficient testing. The template specially developed for the SEL 311L calculates test points automatically, whereby the automation approach employed is represented in a clear and comprehensible way.
A wealth of knowledge packaged into user-friendly solutions
Above: Testing 7SD610: display of the transformed characteristic in the ’differential operating characteristic’ testing module.
However, an exceptional type of stabilisation is defined for calculating IStab. Since the coefficients of the stabilisation formula also depend on the actual measured values here, this makes determining the test quantities significantly more difficult. Beside the measured line-end currents, the stabilisation formula also includes quantities that describe the transmission behaviour of the current transformer.
These properties and, in particular, the characteristic data of the current transformers
With the PTL, Omicron offers integrated expert knowledge in the form of pioneering and practical solutions for automated protective equipment testing. PTL users not only benefit from the extensive range of expertise, but also from the flexibility of the testing templates, which allow predefined approaches to be freely adjusted and extended to cater to individual requirements. In addition to this, the integrated XRIO converters can also be used independently in test plans.
Since the import masks used in the templates are based on the parameter setting software of the respective protective relay, this makes them especially easy to use.
www.omicron.at FOR MORE INFORMATION
rail technology magazine Apr/May 13 | 223
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