Tech Insights

Traveling Wave Monitoring of Transmission Lines Promises Ease, Accuracy

May 22, 2024 by Liam Critchley

Researchers have developed an online monitoring system to locate transmission line disturbances. This method requires less information and provides more accurate results.

Electrical power needs are becoming increasingly complex, so the advanced monitoring approaches offered by smart grids are becoming more important in today’s energy systems. This is particularly true for transmission lines, which are crucial in grid operations but often difficult to maintain and monitor due to their length and remote locations.

Grid operators have used many monitoring systems to detect fast dynamic events in transmission lines, such as traveling waves. These systems have so far been applied to a range of temporary events along transmission lines, including faults, lightning strikes, and partial discharges.

A commonly used transmission line monitoring approach is to measure the propagation of traveling waves along transmission lines. However, most traveling wave methods require prior knowledge of the transmission line's wave propagation characteristics. This propagation value changes throughout the transmission line, so working with these static values can cause major errors. 

A European research team has been working to overcome these errors by using an online method to localize transmission line events. Their method may be more informative and efficient than previous systems.

 

Smart grid monitoring.

Smart grid monitoring. Image used courtesy of National Renewable Energy Laboratory

 

The Problem With Current Traveling Wave Methods

Transmission line disturbances—including faults, short-circuiting, and opening/closing of the line—can generate an overvoltage or an overcurrent. This manifests as a traveling wave, which propagates from the disturbance source to either the line’s end or termination, such as a substation. Once the traveling wave hits a line section end, the medium the wave is traveling through changes. Part of the wave is reflected, and part is transmitted.

The traveling waves are also subjected to attenuation (i.e., a drop in magnitude) and distortion (changing the wave's shape). These are caused by energy losses within the wave brought about by resistance, leakage, and corona discharge along the transmission line.

 

Measuring traveling waves on transmission lines

Measuring traveling waves on transmission lines. Image used courtesy of the authors

 

Traveling wave detection methods use numerous measurement devices, known as single-terminal, double-terminal, and multi-terminal systems, based on the number of devices used. These methods detect incident and reflected waves. However, detecting the reflected waves requires a high resolution because the waves’ attenuation means the propagation times are no longer comparable to the incident waves.

Most methods determine the traveling wave’s arrival time by processing the time and assigning a timestamp to it. The difference in timestamps enables grid operators to determine the wave’s location. However, many methods require prior information about the wave’s propagation velocity, frequency-dependent velocity, and propagation length to calibrate the calculations and determine the traveling wave's location.

Many analyses contain significant errors because the medium the wave passes through changes over time. Additionally, any changes in overhead line operating conditions, soil moisture, and temperature in underground cables can affect the wave characteristics and give different-than-expected property results. Switching towards an online method for localizing events could help overcome some of these errors and provide a more robust monitoring program.

 

Online Methods Address Traveling Wave Measurement Challenges

Researchers from Jožef Stefan Institute and the University of Ljubljana in Slovenia investigated ways to account for propagation length changes and improve the disturbance event localization. The online method determines the frequency-dependent wave propagation characteristics of the wavelet transform (decomposition of a signal) to simultaneously deduce the frequency-dependent properties and location of the traveling wave.

Most other methods require two measurements and a velocity or wave propagation length setting. By comparison, this new method requires three traveling wave measurements with no settings. Without needing prior data, it eliminates a major source of error in traveling wave event localization. It provides better insights into the transmission line’s condition in real time rather than after the event.

 

Model of researchers’ proposed method

Model of researchers’ proposed method. Image used courtesy of the authors

 

The researchers tested the method for accuracy using the IEEE 39-bus system with extensions specific to electromagnetic transient-type simulations. The extra information required to simulate the transmission environment included transmission line geometry, conductor types, line lengths, and details about loads, grid transformers, and generators. The method was tested under various conditions, considering different grid locations, line lengths, line characteristics, event types, event locations, and noise conditions. In most cases, the localization error was below 0.1%.

The method for localizing line disturbances can be used with single- and double-terminal measurements requiring reflected waves and multi-terminal setups needing only incident waves to provide a measurement.

 

Three-Measurement Approach

Unlike other methods, this approach can determine the wave propagation characteristics during operation, whereas many other newly developed methods require the lines to be shut for analysis. The method is not affected by medium changes in the transmission line. It also considers the traveling waves’ dispersion, whereas other methods only consider this indirectly at regions where bigger errors occur, such as line ends. 

The three-measurement approach significantly reduces the error associated with reflected waves. Since the method uses real-time monitoring and does not require prior knowledge of line characteristics, accurately pinpointing transmission line disturbances is a huge advantage for ensuring that the transmission line is still running optimally after it has experienced a disturbance or environmental event.