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How does an Overhead Line Fault Passage Indicator work?

Fault Passage Indicator

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Could you imagine an hour without electricity? Even today, towns and villages in rural areas have to go hours or even days without electricity because of simple problems like a branch falling on a power line. These distribution lines travel hundreds of kilometers through forests or hilly areas where it’s extremely difficult to find faults when they occur. But, in recent years, a simple product has been solving this problem. The fault passage indicator.

In this blog, we will dive into Overhead Line Fault Passage Indicators. By the end, you will have a clear understanding of what a Fault Passage Indicator is, how it functions, its features, and the different types available in the market. At Axis, we’ve been manufacturing products for Low and Medium Voltage Distribution Lines for over 30 years. Our products are approved by more than 80 utilities across India, Africa, and globally.


What is an Overhead Line Fault Passage Indicator?

Quite simply – It’s a device designed to detect and indicate faults in an electrical distribution network.

Fault detection

These indicators work by noticing changes in the current flowing through a power line. If there is a fault on the line, like a short circuit or overcurrent, it increases the current level (which can lead to a fire). The FPI picks up on this change and sends a signal back to the monitoring to show a fault and its approximate location. It monitors the system all day, every day, helping to eliminate downtime by quickly identifying the fault location.

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    Need for Fault Passage Indicator

    Need of FPI

    Electrical networks, being exposed to the outdoors, face nature’s challenges throughout the year.  Lightning, heavy rain, dust, and even local wildlife can make these systems prone to developing faults over time. When faults occur, it can impact large numbers of end users, including both households and industrial areas, leading to dissatisfaction and financial losses for the local utility.

    Without a fault indicator, Utilities and Operations & Maintenance firms rely on a standard practice where several technicians walk or drive the length of the line to pinpoint the fault’s location. This task becomes especially challenging with insulated cables, where cables are grouped together, requiring technicians to lower the line to locate the fault. The difficulty increases if the fault happens at night or in densely forested or hilly areas.

    The development of FPIs has been driven by the need to reduce revenue losses for utilities and lower the operations and maintenance costs associated with fault detection. Installed in overhead electrical lines, these indicators offer utilities a solution to quickly identify the location of a fault through visual or remote signals.

    How does a Fault Passage Indicator work?

    One Fault Passage Indicator is attached to each phase of the circuit. This setup allows utilities to monitor currents and detect faults in each phase effectively. By installing FPIs at regular intervals along the line, these devices will spot faults by observing the electromagnetic field around the conductor. The distance between the FPI’s depends on local conditions and financial considerations – they can be as low as a few hundred metres to as high as a few kilometres.

    When a fault occurs, the conductor’s magnetic field spikes due to a surge of high current flowing through, which then drops to zero as the circuit breaker trips. The FPI senses this abrupt change and triggers an alert. This alert is triggered locally at the site when a non-communicable type FPI is used and remotely at the SCADA Centre in the case of a communicable type FPI.

    The illustration below provides a basic topology of a communicable system.


    Fault Passage Indicator


    Communicable & Non-communicable Type

    First, the non-communicable type. This type signals an alarm directly on-site with an ultra-bright red LED flashing. It distinguishes between permanent faults, transient faults, and low battery voltage with three unique blinking LEDs. Earth faults trigger two different light signals, providing clear notifications for various issues. These indicators are ideal for areas where lines are easily accessible and can be quickly inspected via a nearby road. In this case, the process of locating faults relies entirely on visual signals from the indicators.

    Next, the communicable type of FPIs. These not only alarm on-site but also transmit data to the SCADA center via the Data Collection Unit over GSM/GPRS networks. Communicable FPIs are effective in all kinds of terrain because it is not defendant only on visual inspection. The operations and maintenance team has a clear indication on the location of the fault and does not need to waste time on finding it.


    Advantages of Fault Passage Indicator

    The main aim of an Overhead Line Fault Passage Indicator is to reduce the physical efforts needed to identify the faults & that occur in distribution networks. There is a significant reduction in the time, effort and manpower required for identifying faults. In conclusion, these indicators are helpful in reducing downtime by quickly identifying the fault location. I hope this blog has given you a clear understanding of Fault Passage Indicators.

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