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Wind turbine controllers are generally designed for grid connected operation. Under certain grid conditions such as islanding of offshore wind farms following HVDC converter blocking, voltage and frequency of the island remains uncontrolled. Measurements in real wind farms show that the voltage in this situation can rise to unacceptably high values. In this paper the performance of the well-known...
This paper presents measurement and simulation results in offshore wind farms following blocking of the HVDC converter used for connecting the wind farm to the main onshore grid. It is shown that the voltage will rise by approximately 30% within 50–100 ms in the ensuing island operation. The process is superimposed by transients caused by short but repetitive periods of saturation of the transformer...
Up till now inductive voltage transformers are only suitable for measuring harmonics if high measurement errors are acceptable. However, as monitoring frequency harmonics becomes more important, the design of inductive voltage transformers needs to be changed in a way to increase its frequency range. The poles and zero points of the frequency response of voltage transformers can be compensated by...
Inductive voltage transformers in the electrical grid are normally used for frequencies of 50/60 Hz. This is reasonable, because they have natural frequencies which lie considerable above 50/60 Hz. On a 20 kV voltage transformer the first natural resonance is about 5 kHz which obviates a dependable measurement of harmonics up to 9 kHz. However, as the measurement of harmonics becomes more important,...
Increasing load and the growing proportion of injected power from distributed energy generation lead to higher loading of distribution grids. Without suitable improvements like e. g. additional cables or substations, violations of voltage constraints in low voltage distribution grids have to be expected. A further alternative is represented by on-load tap-changers (OLTC) which are combined with distribution...
In many cases, the increasing load and the growing proportion of injected power from distributed energy generation results in the violation of voltage constraints in low voltage distribution grid. As an alternative to additional cables or substations, the application of distribution transformers equipped with on-load tap-changers (OLTC) is under development. This paper presents their benefits, and...
To increase the linear frequency range of inductive medium voltage transformers, the calculation of its frequency response will be the first step. For this several capacitances have to be known, such as the layer, the ground and the front part capacitances. For the calculation of these three most important parasitic capacitances mathematical models based on measurements of medium voltage transformers...
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