Introduction to Qualitrol’s Travelling Wave Fault Locator

Transmission line trips happen…often.

The number of outage hours that utility customers experience in a year can vary depending on several factors, including the size and location of the utility, the age and condition of its infrastructure, and the frequency and severity of weather events.

This also has an economic impact. In 2021 the DOE estimated that outages are costing the U.S. economy up to $209 billion annually. A similar story can be told in many other countries across the world.

The increase in outages is down to 3 major factors.

  1. Renewables are adding more complexity to the network.

The U.S. currently has about 200,000 miles of high-voltage transmission (HVT). Achieving 100 percent renewables would require doubling these transmission lines.

  1. The climate is changing.

From 2003 to 2012, weather-related outages around the world have doubled.  High winds, hurricanes, wildfires are all to blame.

  1. The Grid is aging.

Some of the oldest power lines across the world date back to the 1880s, and most of today’s grid was built in the 1950s and 1960s with a 50-year life expectancy.

Trips have massive implications for customers and utilities.

Utility customers in USA experienced 1.33 billion outage hours in 2020. This is an increase of 73% from roughly 770 million in 2019.

Transmission line outages can cost utilities approx.  $100k-$200k per hour depending on geography. With an average unplanned outage lasting 2-4 hours the cost to a utility is significant.

In addition, according to NERC’s 2020 State of Reliability report 50% of analyzed events over the last 5 years did not yield a definitive root cause.

This also has an economic impact. In 2021 the DOE estimated that outages are costing the U.S. economy up to $209 billion annually. A similar story can be told in many other countries across the world.

Travelling Wave Fault Locator from Qualitrol helps reduce outage times and costs.

Historically finding the location of a fault on a power line was done by protection relays and fault recorders using a technique called “Impedance based distance to a fault”. This is where a fault record taken from the relay or fault recorder was analyzed.

A fault would generally last several milliseconds before the protection system kicked in and cleared the fault. During this time the voltage would dip and the current would rise. By using the value of the voltage and current at the time of the fault it would be possible to calculate the impedance at this moment in time.

Assuming all this impedance is caused by the cable and the cable manufacturer provides the impedance per unit length it is then possible to calculate how much cable is in play and therefore how far it is to the fault location.

However, this method is fraught with errors. If the fault is caused by a high impedance object such as a tree, this would create extra impedance to the ground, therefore, invalidating the impedance calculation and causing errors in the distance to the fault. Other factors also come into play such as incorrect line parameters, mutual coupling, unstable fault arc, etc. These cause inaccuracies that could put a distance to fault calculation out by 1-15% of the overall line length.

If we imagine a 100km line that is an error between 1k and 15km. In addition: –

  • Data gathering and analysis is dependent on expert engineers.
  • It takes approximately 7+ years to become proficient in fault analysis.
  • Utilities are suffering from a brain-drain as expert engineers retire.
  • An average sized utility experiences 70-100 trips per year and these go on develop into 3-5 permanent outage.

Therefore, a more accurate and simplified fault location method is necessary to reduce manpower, reduce time searching, reduce downtime, and identifying trouble spots that can go on to cause further outages.

Qualitrol’s travelling wave fault locator is a one stop shop for identifying the location of a fault. It uses a different technique to locate faults in power transmission lines. When a fault occurs in a transmission line, it creates a disturbance that travels along the line in the form of a wave. By measuring the time it takes for the wave to travel from one end of the line to the other it is possible to determine the location of the fault.

This technique relies on precise time-synchronized measurements of the voltage and current signals at both ends of the transmission line. Qualitrols travelling wave fault locator has the ability to time tag the arriving travelling wave to a precision of 100 nanoseconds. This allows for a distance to fault accuracy to within one tower span no matter what the line length is. All the factors that affect the impedance distance to fault no longer apply. The measurements are automatically performed at Qualitrols iQ+ master station software. Figure 1 gives a graphical representation of the double ended travelling wave fault location technique.

Fig 1 Double ended travelling wave fault location technique.

Double ended travelling wave fault location technique.The same iQ+ master station software can be configured to execute several automated tasks including scheduled polling, device health monitoring and email notifications. Automating tasks standardises the process and reduce the variation across the business. Figure 2 gives a flavour of some of the automated tasks available including downloading data from the device on the network and emailing associates with distance to fault results.

Fig 2 Automated tasks.

Visualising the fault location results.

Once the relevant data is automatically gathered and processed and an accurate distance to fault is obtained the software lists all the fault location results in the main screen in chronological order. A user can focus in on one disturbance by double clicking the time tag and opening up the waveforms from each end of the line.

Figure 3 Listing power system disturbances.

The software goes one step further and presents the fault location in a GIS system. This can be Qualitrols own GIS or can also be integrated with a utilities existing GIS.

Visualizing fault locations on a map with satellite imagery can identify local terrain and infrastructure helping get crucial information to the patrol team in the search for faults.

Displaying historical incipient faults on a map where clusters are formed in the same location can also help identify weak points on the transmission line and allow corrective action before the issue leads to a permanent outage. Figure 4 shows the single line diagrams overlayed on a Qualitrols GIS system. This can be access via a button on the iQ+ software.

Fig 4 Displaying the results in GIS


Qualitrol has been at the forefront of the grid monitoring industry for 30 years shipping to 50-60 different utilities per year across 20-25 different countries. Qualitrol has been at the cutting edge of innovation during this time with a number of world first including

  • Worlds first digitized fault record (1982 BEN)
  • Worlds first slow scan recording (1984 IDM+)
  • Worlds first travelling wave fault locator (1999 TWS)
  • Worlds first truly multi function monitoring device (2013 IDM+)

Qualitrol are now on their 7th generation fault locator with 30 years’ experience in the field.  With an install base of over 3000 fault locators across more than 25 countries in every continent of the world Qualitrol continue to lead the field in providing fast accurate distance to fault results.

Automating the task from fault to result ensures the correct information gets to the appropriate resource within minutes of a disturbance potentially eliminating 15-30 minutes per disturbance analysis.

Reducing the time a patrol team gets to a fault location by 0.5-hours can save an average sized utility approximately $516k/per year for 100 trips and 5 outages.


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