What Is a Fault Indicator?

Fault indicator refers to a device installed on power lines (overhead lines, cables and busbars) to indicate fault current. Most fault indicators can only identify and indicate a short-circuit fault by detecting the characteristics of the short-circuit current. ^[1]

A fault indicator is an electromagnetic induction device that can reflect a fault sign (red card) when a short-circuit current passes. Install this fault indicator along the power distribution line. Once a fault occurs in the line and a short-circuit current flows, the fault indicator will act and the red flag of the fault indicator will appear. Then patrol along the line, the fault indicators on the power source to the fault point before the red card appear, the fault indicator after the fault point does not show a red card, you can judge, the fault point will be the last red card point and the first non-red card point behind between. ^[2]

1. According to the application object, the fault indicator can be divided into three types: overhead type, cable type and panel type.

The overhead fault indicator sensor and display (indication) are integrated in a unit and mechanically fixed to the overhead line (including bare conductors and insulated conductors). The overhead fault indicator generally consists of three phase sequence fault indicators. And can be loaded and unloaded with electricity, no false alarms during loading and unloading.

The cable type fault indicator sensor and display (indication) are integrated in a unit, and are mechanically fixed to the cable line (busbar). They are usually installed on power distribution equipment such as cable branch boxes, ring network cabinets, and switch cabinets. Consists of three phase sequence fault indicators and a zero sequence fault indicator.

The panel type fault indicator is composed of a sensor and a display unit. Usually, the indicator of the display unit is embedded in the operation panel of the ring network cabinet or the switch cabinet. The sensor and the silicon display unit communicate by optical fiber or wireless. Reliable insulation.

2. According to whether the communication function fault indicator is divided into local type fault indicator and communication fault indicator.

The local fault indicator detects a line fault and a local flop or flash alarm. It does not have the communication function, and the fault search still requires manual intervention.

The communication fault indicator 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 on the spot or flash the alarm, but also transmit the fault information to the communication through a short distance wireless method Device, the communication device then 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 telesignal functions, and report the telemetry information and state quantities such as switch opening and closing, energy storage and so on to the master station.

3. According to the function of 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. The principle is to detect the fault by using the sudden change of the current when the line fails and the power failure of the line. According to the characteristics at the time of short circuit, measure the current sudden change and duration in the line by electromagnetic induction method to judge the fault. Therefore, it is a fault detection device that adapts to load current changes and is only related to the short-circuit current component at the time of the fault. Its comprehensive criteria can greatly reduce the possibility of misoperation.

The single-phase ground fault indicator can be used to indicate a single-phase ground fault. The principle is to determine 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-circuiting are comprehensively considered. ^[3]

(1) Fault indication: When the line is running normally, it will display white, and the window will turn red when a fault occurs.

(2) On-line operation: directly installed on the power line, it can run outdoors for a long time without power maintenance.

(3) Automatic reset: When a short-circuit fault occurs on the line, it will start timing and reset automatically according to the selected reset time.

(4) Different types: there are overhead type, cable type, busbar type, etc.

(5) Live loading and unloading: When the line is running normally, it can be installed and removed with power on (except busbar type).

The fault indicator technology itself is very mature. It is often used in medium and low voltage switch cabinets. The earliest simple mechanical type has now developed into a mechatronic type.

1) The outgoing line of the substation is used to judge whether the short circuit fault is inside or outside the station.

2) Long line segmentation, indicating the section where the short-circuit fault is located.

3) High-voltage user entrance for judging user failure.

4) Installed at the connection between the cable and the overhead line, indicating whether the fault is in the cable section.

5) Incoming and outgoing lines of the ring network cabinet or cable branch box, to judge the faulty section and faulty feeder line. ^[2]