<p>It is presented a method of controlling a magnitude of an electrical parameter in a power system by means of a high voltage electron tube. The method comprises the steps of measuring (S1) the magnitude of the electrical parameter; generating (S2) a control signal based on the magnitude of the electrical parameter and on a reference magnitude of the electrical parameter;and switching (S3) the high voltage electron tube by means of the control signal such that the reference magnitude of the electrical parameter is essentially obtained. It is also presented a control arrangement and a power system.</p>
