Study On Phase To Phase Fault Detection Method Based On Active Signal In Distribution System

For the domestic distribution system, it is allowed to continue operating for 1-2 hours when a phase to ground fault occurs for it is a Neutral ineffectively earthed system. The breaker is asked to trip out when a phase to phase fault occurs.For the most occasions, the faults occurring in the overhead lines are transient, such as lightning stoke. The lines return to normal after fault arc extinct. The breaker can reclose successfully. Faults like this are defined as transient fault. Another type of the faults is permanent, such as porcelain bottles breakdown. The fault keeps lines under short circuit and doesn’t disappear in a short time, so the breakers can’t reclose successfully. Faults like this are defined as permanent fault. For transient fault, it can resume power supply by reclosing the breaker. For permanent fault, the breaker can’t be reclosed successfully. When the breaker recloses under permanent, it would not only cause a serve short-circuit current rush to equipments but also make the breaker working condition worse. Therefore, it is significant to detect whether the fault has disappeared before reclosing the breaker. Professor Yaozhong GE proposes the adaptive reclosure method in 1990s.It is asked to detect the fault types before reclosing. The breaker is asked to reclose under transient fault and not reclose under permanent fault.This paper proposes a phase to phase fault detection method based on active signal in distribution.it can be used as distribution line adaptive reclosure method and line fault detection method under maintenance. It is designed to inject a transient voltage signal into the de-energized lines. Fault detection is completed by analyzing the voltage signal acquired at location breaker installed, so communication device is not needed. An inverter is used as exciting source. The thyristor in series with inverter is used to control the amplitude of voltage signal. As the thyristor firing angle can be adjusted within appropriate range, the voltage injecting into de-energized lines is also within appropriate range and can ensure to breakdown hidden faults to improve fault recognition rate. Fault types can be given by the degree of voltage leap at the time thyristor turning off and voltage amplitude at the moment before thyristor turning off under different faults finally. This paper proposes two means to detect faults by analyzing the voltage acquired at the breaker under different faults. And each of them is verified by theoretical analysis and simulation experiments. The simulation results reveals that the proposed fault detection method would not be affected by thyristor firing angle, motor speed decrease and fault resistance. It has a good engineering significance in fault detection.