Views:227 Author:Site Editor Publish Time: 2021-04-27 Origin:Site
The cable fault indicator is an important equipment that can intelligently judge, detect and locate power grid operation faults according to the changes in current and voltage in the power grid. It is usually installed in the power transmission network and is mainly used to monitor and detect possible short circuits and single phase grounding faults in the power network. When a short circuit occurs in the power network, the current value in the line suddenly changes, and the fault current at this time passing the fault indicator will trigger the indicator's flop, and the non-fault current will not affect its normal display. Today we take a detailed look at the working principle of the power fault indicator.
There are two types of faults that are most likely to occur in power network transmission, they are inter-phase short circuit and single-phase grounding. Therefore, the power line fault indicator is also designed according to these two faults. Phase-to-phase short circuit refers to the contact between two or three phases of the transmission line, causing the occurrence of line short-circuit fault. When a short circuit occurs between phases, the instantaneous current in the line suddenly increases and a current jump is formed. The ground fault indicator sets the current mutation value inside. If the current change exceeds the set value, the earth fault indicator will display corresponding fault signal.
For the judgment basis and principle of single-phase grounding, the zero-sequence current amplitude method is the most commonly used, that is, collecting temporary current, voltage and other data values in the distribution network where the neutral point is not directly grounded, and then adopting the steady-state zero sequence fundamental waves or higher harmonics of current and voltage to calculate and analyze the collected data to determine the current and voltage values in the line. If it is a fault current, it will display a flop, otherwise the fault current indicator will not change.
The working principle of the fault path indicator is that when a short circuit fault occurs in the line, the short circuit fault indicator obtains a fault current, and the display screen of the indicator will change from white to red (or glow). It has the characteristics of accurate action and strong anti-interference ability. The signal is not affected by lines, inrush current, high-order harmonics, current fluctuations, and especially the bypass of cable distributed capacitors.
The fault section is easy to find. The fault circuit indicator is directly installed on the distribution line, and the fault section can be easily found by whether the two adjacent indicators operate or not.
Automatic or manual reset: The indicator automatically returns to the normal position from the fault state after the action according to the factory-set reset time. It can also be reset manually according to user needs.
When installing, it is necessary to check whether it is opened in the original state and separate the shell from the metal device. Unscrew the screw, clip the metal piece to the cable, clip the shell and the metal piece together, tighten the screw to fix the indicator on the cable.
Short circuit detection: Detect the cable line current and set a threshold value. After the set value is exceeded and the specified delay is reached, the action will be turned over to indicate which phase has a short circuit fault.
Alarm indication of short-circuit current: The short circuit indicator detects the current in the power supply line at all times. When its value reaches or exceeds the short circuit starting current, the short-circuit detection processor sends out a signal and the indicator flops.
Automatic reset: After the indicator is displayed, if there is no manual reset within the set time, the indicator will automatically reset.