EXPERIENCE OF FERRORESONANCE PHENOMENA IN TAMIL NADU (INDIA) GRID UNDER SINGLE PHASE OPERATING CONDITION

摘要

Ferroresonance is an oscillation of a charge trapped in a circuit that contains capacitor and nonlinear inductor. This oscillation is characterized by highly distorted voltage and current wave shapes. The non-linear inductor normally works as a linear device, but is forced to operate outside its normal linear range under ferroresonance. The non-linearity is generally due to the saturation of iron; hence the ferroresonance. This complex non-linear phenomenon that can generate severe overvoltage in a power network. At times the operation of the grid with intentional single phasing arrangement (in three phase network) may lead to a situation wherein the connected equipment and line insulation suffer serious damages. Under such conditions, the system exhibit ferroresonance or nonlinear dynamic phenomena. The sustained ferroresonance of a transformer requires a continuous transfer of power from one or more energized conductors that are capacitively coupled to the de-energized conductor that remains connected to the transformer. This non-linear phenomenon experienced in Tamil Nadu (India) grid on one such occasion is presented in this paper. Due to non-linearities, time domain simulation seems to be the only reliable approach to predict the severity of a ferroresonance and to verify the effectiveness of countermeasures. So the simulation tool Electromagnetic Transient Program is used to understand how ferroesonance starts and how it becomes sustained. This simulated overvoltage value is compared with actual field results. The remedial measures are also described to avoid the above condition.