Digital Current Measurement Element for Operation During Current Transformer Severe Saturation

Abstract

The development and implementation of a digital current measurement element for proper operation during current transformer (CT) magnetic core severe saturation are considered. CT transient performance is often accompanied by primary current transformation to secondary one with great errors. In this case the secondary CT current which is an input signal of the digital measurement element differs from the ideally transformed CT current both in shape and magnitude. This causes impermissible signal settling time at the standard digital measurement element output. As a result, main requirements to the protection devices such as reliability and fast operation are violated, that in some cases makes the high-speed protection device ineffective. To solve this problem, it is proposed to form the output signal of the digital current measurement element in depending on the input signal total harmonic distortion (THD) coefficient value. Moreover, it is worthwhile to form the output signal so that for a low CT saturation conditions this output signal slightly differs from the secondary current RMS value, and for a severe CT saturation conditions it exceeds this value. Digital current measurement element model has been developed and implemented in the MatLab-Simulink environment using the following blocks: a digital filter block responsible for the input signal fundamental frequency component magnitude calculation; a digital filter block responsible for the input signal RMS value calculation; and, also, a standard blocks for basic mathematical calculations needed for proper functioning of the proposed measurement element. The functional testing of the proposed digital current measurement element model was carried out using the signal, that was similar in form to the waveform of the secondary current of the severe saturated CT. The tests that had been performed confirmed that the proposed digital current measurement element in comparison with the standard current measurement element ensures stable functioning and enhanced operation time during transients.

Formation of Orthogonal Components of Input Currents in Microprocessor Protections of Electrical Equipment

“…В структуре указанной модели содержатся энергосистема, трехфазная группа ТТ, нагрузка, блок КЗ, а также модели элементов, обеспечивающих реализацию описанного выше метода получения ОС входных токов [10]. Моделирование функциональных блоков и элементов цифровой структуры выполнено с использованием методов и правил, изложенных в [11][12][13][14].…”

Orthogonal Components Forming of the Microprocessor-Based Protection Input Signals

“…В структуру указанной модели входят энергосистема, трехфазная группа трансформаторов тока и трансформатор напряжения, нагрузка, блок короткого замыкания, а также модели элементов, обеспечивающие реализацию алгоритма получения ОС [7,8]. Моделирование блоков и элементов цифровой структуры выполнено с применением методов и правил, использовавшихся в [9][10][11].…”