The role of the arc suppression coil connected to the neutral ground
Publisher: Administrator Release time: 2019-7-24
Single-phase ground faults have the highest probability of accidents in power systems. When a single-phase metal grounding occurs in a neutral point ungrounded system, the voltage to ground of the non-grounded phase will rise to the line voltage, and the neutral point voltage will rise to the phase voltage. Considering the three-phase lines, cables, power distribution devices, and other capacitors to ground, the fault current is the sum of non-fault compatible currents. The magnitude of this ground current is related to the system voltage and line length. If this current reaches a certain value, intermittent or stable arcs will form. Stable arcs can burn equipment or expand from a single-phase grounded arc to a two-phase or three-phase arc short. Intermittent arcs that are extinguished and reignited periodically will cause strong oscillations of electromagnetic energy, produce intermittent arc-ground overvoltages, endanger the weak links in the network, and may even cause breakdown. When the grounding capacitor current in the neutral-point ungrounded system exceeds the allowable value, in order to reduce the capacitor current at the grounding point and form a condition of self-extinguishing at the fault point to avoid the harm caused by the stable arc and gap arc, The point of contact is grounded through the arc suppression coil. The arc suppression coil is essentially an adjustable inductance coil with an air gap in the iron core. From a structural point of view, it is generally a single-phase type. Figure 5-7 is a schematic diagram of its principle. The arc suppression coil is connected between the neutral point and the ground, and its volt-ampere characteristics are close to linear. Under normal circumstances, the neutral point and the ground have the same potential, and no current flows through the arc suppression coil. When a single-phase ground fault occurs, the neutral point voltage rises. Under this voltage, an inductive current will be generated on the arc suppression coil, which is opposite to the direction of the capacitive current flowing through the fault point. If the inductance size (turns) of the inductor coil is appropriately selected, the inductive current of the arc suppression coil and the capacitive current of the non-fault phase can basically cancel each other, so that the capacitive current of the ground point is limited to the allowable range, which is beneficial to the ground arc Off.