Fault indicator refers to a device installed on power lines (overhead lines, cables and busbars) to indicate fault current. Most fault indicators can only distinguish and indicate short-circuit faults by detecting the characteristics of short-circuit current.
1. Introduction of fault indicators
The fault indicator is an electromagnetic induction device that can reflect a fault sign (red card) when a short-circuit current passes through it. Install this fault indicator along the distribution line. Once the line fails and the short-circuit current flows, the fault indicator will act, and the red card of the fault sign will appear. Then patrol along the line, the fault indicators from the power supply side to the fault point all show red cards, and the fault indicators after the fault point do not show red cards, so it can be judged that the fault point is between the last red card point and the first non-red card point after the fault point between.
Fault indicators usually include current and voltage detection, fault discrimination, fault indicator drive, fault status indication and signal output, and automatic delay reset control.
Fault indicators are generally installed on overhead lines, overhead cables or buried cables, and switchgear busbars, so it detects voltage by detecting the potential gradient of the electric field in space, and detects line current by electromagnetic induction.
2. Classification of fault indicators
2.1 According to the application object, fault indicators can be divided into three types: overhead type, cable type and panel type.
The overhead type fault indicator sensor and display (indication) part are integrated in one unit, which is mechanically fixed to the overhead line (including bare wires and insulated wires). The overhead type fault indicator generally consists of three phase sequence fault indicators. And it can be loaded and unloaded with electricity, and there will be no false alarm during the loading and unloading process.
The cable type fault indicator sensor and display (indication) part are integrated in one unit, fixed on the cable line (busbar) by mechanical means, usually installed on the power distribution equipment such as cable branch box, ring network cabinet, switch cabinet, etc. It consists of three phase sequence fault indicators and one zero sequence fault indicator.
The panel-type fault indicator is composed of a sensor and a display unit. Usually, the display unit is embedded on the operation panel of the ring network cabinet and the switch cabinet. The sensor and the silicon display unit communicate with each other by optical fiber or wireless. Reliable insulation between.
2.2 According to whether there is a communication function, the fault indicator is divided into an in-situ type fault indicator and a communication fault indicator.
The on-site fault indicator detects a line fault and flips a card or flashes an alarm on the spot. It does not have a communication function, and manual intervention is still required for fault finding.
The fault indicator with communication is composed of a fault indicator and a communication device (also known as a concentrator). When the fault indicator detects a line fault, it can not only flip the card or flash an alarm on the spot, but also transmit the fault information to the communication device through a short-distance wireless method. device, and the communication device sends the fault information to the master station through the wireless public network or optical fiber. The communication fault indicator can also be equipped with telemetry and remote signaling functions, and report telemetry information, switch opening and closing, energy storage and other status quantities to the master station.
2.3 According to the functions realized by the fault indicator, it can be divided into short-circuit fault indicator, single-phase ground fault indicator and ground and short-circuit fault indicator.
Short-circuit fault indicator (also known as two-in-one fault indicator) is a device used to indicate the flow of short-circuit fault current. Its principle is to use the current positive mutation and the power failure of the line to detect the fault when the line fails. According to the characteristics of the short circuit, the fault is judged by measuring the sudden change and duration of the current in the line by means of electromagnetic induction. Therefore, it is a fault detection device that adapts to load current changes and is only related to the short-circuit current component during faults. Its criterion is relatively comprehensive, which can greatly reduce the possibility of misoperation.
The single-phase ground fault indicator can be used to indicate a single-phase ground fault. Its principle is to judge whether a ground fault has occurred on the line through the ground detection principle.
In the design of the ground short-circuit fault indicator, the characteristics of the transmission line during grounding and short circuit are considered comprehensively.
3. Function of fault indicator
3.1 Fault indication: When the line is running normally, it will display white, and the window will turn red when a fault occurs.
3.2 On-line operation: It is directly installed on the power line, and can run outdoors with electricity for a long time without manual maintenance.
3.3 Automatic reset: When a short-circuit fault occurs in the line, it will start timing, and it will automatically reset according to the selected reset time.
3.4 Different types: overhead type, cable type, busbar type, etc.
3.5 Live loading and unloading: When the line is in normal operation, it can be installed and disassembled live (except busbar type).
The technology of the fault indicator itself is very mature. It is often used in medium and low voltage switch cabinets. It was originally a simple mechanical type, and now it has developed into a mechanical and electronic type.
4. Installation position of fault indicator
4.1 Substation outgoing line is used to judge whether the short-circuit fault is inside or outside the station.
4.2 Long line section, indicating the section where the short circuit fault is located.
4.3 High voltage user entrance, used to judge user faults.
4.4 Installed at the connection between the cable and the overhead line, indicating whether the fault is in the cable section.
4.5 For the incoming and outgoing lines of the ring network cabinet or cable branch box, determine the faulty section and the faulty feeder line.