How Do High-voltage Series Reactors Suppress Inrush Current During Switching On Using Their Inductive Characteristics?

High voltage series reactor utilizes their inductive characteristics to effectively suppress the excitation inrush current. Their core principle is based on inductance resistance to sudden changes in current. Here's a breakdown:
I. Inductive Characteristics: resistance to sudden current changes.
ii. Mathematical Expression of Inrush Current Limitation
The multiple (K) of the excitation inrush current is closely related to the inductive reactance (XL) and capacitance (XC) of the reactor.
This means that by serializing a standard reactor of 6%, the inrush current can be limited from 100 times the rated current to approximately 5 times, greatly reducing the impact on capacitors and switching equipment.
III. Selection of Reactance Ratio and Effect of Inrush Current Constraint
The reactance ratio (K%) is the ratio of the inductance of the series reactor to that the capacitor capacitor. Its selection directly affects the inrush current limiting effect:
Low reactance ratio (0.1%~1%): Suitable for low harmonic content of the grid, the main purpose of which is to limit inrush. In this case, the active power loss of the reactor is low, the size is small, the floor area is small and it is easy to install in capacitor banks. For example, the use a 0.5% reactance ratio can limit the inrush to 15 times the rated current.
Standard reactance ratio (6%): applies to most industrial and urban substations, effectively limiting inrush to approximately 5 times while avoiding harmonic amplification (e.g. 5 times harmonic).
High reactance (12%~13%): Suitable for high harmonic content in power grid. The characteristic harmonics are suppressed by adjusting the capacitor bank group and reactor to form a partial resonant circuit.
IV. INTRODUCTION Reactor protection of capacitors and systems
Protective Capacitor: Inrush can cause great mechanical and thermal stress that potentially damaging capacitor plates, fuses or wiring. Series reactors extends capacitor life by limiting the excitation inrush current.
Protective switchgear: Inrush current can lead to circuit breaker contact erosion or contactor re-breakdown, resulting in operational overvoltages. Reactor reduces damage to switching equipment by reducing inrush current amplitude.
Suppression of Harmonic Amplification: Reactors and capacitor banks form LC filter circuit that resonate at specific harmonic frequencies, prevent harmonic currents from flowing into the power grid or nearby equipment, and improve power quality.
V. Precautions measures in practical application
Reactor linearity: To avoid harmonic amplification, the voltammetry of a series reactors should be as linear as possible to ensure a stable inductive reactance under different currents.
Reactor capacity matching: reactor capacity capacity must be selected based on the rated current of the capacitor bank and the short-circuit circuit capacity of the system, so as not to reduce the reduced limiting effect or increase the cost of the capacity too much.
Installation location: Reactor is usually serialized on the circuit breaker side or neutral side of the capacitor bank. Ensure safe connections and good ventilation to prevent local overheating.