Fault Detection And Positioning Principle

1. Short-Circuit Detection Principle And Positioning 

When the phase-to-phase short circuit occurs in the power distribution line, it will flow very large current between the substation and the fault point, the relay protection device will start protection and the line will trip. Therefore, the short-circuit fault criterion has four conditions:

(1) The line is with electricity

(2) The line appears mutations  It ≥ 200A   It is mutational volume of current start, which can be adjusted according to the actual line

(3) Large current duration time  0.02s ≤ △ T ≤ 3s   △ T is the current mutation time

(4) Power outage of line

The above four conditions should be satisfied at the same time; after detection of the line at the location, it appears short circuit fault.

When a short-circuit fault occurs on the line, the short-circuit fault indicator senses the fault current, and the display window of the indicator changes from white to red (or from non-light to light). According to the 2# line B-phase indicators 2, 5, 8 and 3# line C-phase indicators 3, 6, 9 turnover( or light) and the 11,12 indicator does not turnover (or does not light), the fault point could be determined promptly as D point.

2. Earthing Detection Principle And Positioning

The principle of asymmetric current method to monitor the earth fault is as shown below:

Asymmetric current is composed by the three vacuum switches K1, K2, K3 , high voltage diode and current limiting resistors, with the three vacuum switches connected to line A, B, C three-phase. When the earth fault occurs somewhere on the line, the PT zero-sequence voltage of the substation rises, the earthing phase-earth voltage decreases, the non-fault phase-earth voltage rises, the asymmetrical current source controller controls the corresponding switches to get into action, and make the single-direction characteristic current flow over the fault line, but the other non-faulty lines have no characteristic current flowing through it, the fault detection devices installed on the line and the substation can detect the faulty line and the position after detecting the signal, so as to realize the earthing line selection and positioning.

According to the 2# line C-phase indicators 3, 6, 9 turnover( or light) and the 12 indicato does not turnover (or does not light),  The earthing fault point could be determined as D point.