What is the purpose of a 'reactor' in a substation and how is its health assessed?

A reactor, also known as an inductor, is a device used in substations to provide inductive reactance. Its primary purpose is to limit or control current flow in specific situations. Different types of reactors serve different functions. Shunt reactors are connected in parallel with transmission lines or busbars to compensate for capacitive charging current, which is especially important in long transmission lines. This helps to prevent voltage rise under light load conditions. Series reactors are connected in series with transmission lines or equipment to limit short-circuit currents, protecting equipment from damage during faults. They can also be used to limit inrush currents when energizing transformers or capacitor banks. Neutral grounding reactors are connected between the neutral point of a transformer or generator and ground to limit ground fault currents. This helps to reduce stress on equipment during ground faults and improve system protection. Assessing the health of a reactor involves several key activities. Visual inspection checks for signs of physical damage, such as cracked insulators, oil leaks (for oil-filled reactors), or corroded connections. Insulation resistance testing (Megger) measures the insulation resistance between the windings and ground. A low insulation resistance indicates insulation degradation. Inductance measurement measures the inductance of the reactor. A significant change in inductance indicates a problem with the winding or core. Winding resistance measurement measures the resistance of the reactor windings. A high winding resistance indicates a problem with the winding conductors or connections. Frequency response analysis (FRA) is a technique used to detect winding deformation or core damage. It involves measuring the reactor's impedance over a range of frequencies and comparing the results to baseline data. Dissolved Gas Analysis (DGA) is used for oil-filled reactors to detect the presence of dissolved gases in the oil, which can indicate overheating or insulation breakdown. Infrared thermography detects hotspots, which can indicate overheating or insulation problems. Vibration monitoring detects unusual vibrations, which can indicate mechanical problems. Periodic testing using specialized test equipment is also performed to verify the reactor's performance. The results of these tests are compared to baseline data and manufacturer specifications to determine the reactor's condition. Therefore, regular assessment of reactor health is essential for maintaining the reliability and safety of substations.