By Jonathan Tolentino and Jonathan Colao
Population growth, technological advancements, rising quality of life expectations, and global demand for energy are increasing rapidly. Smart grid systems offer an efficient solution to support these energy demands and are essential to decarbonize electricity,[i] aligning with the Net Zero Emissions by 2050 (NZE) Scenario.[ii]
This two-part discussion will cover the problem of traveling waves within transmission lines and how to achieve a system-efficient fault diagnosis. First, informed by the challenges of a traditional grid system, we will highlight the growing demand for fault location systems using traveling waves in smart grids. In the next post, readers will learn how bandwidth, throughput, and multi-channel simultaneous sampling ADCs enable optimized fault location of fast transient signals.
Transmission lines traverse multiple places. When a fault happens, disturbance within the transmission line is induced, and many variables could be the cause. Trees, storms, animals, sabotage, line degradation, and breakdowns can introduce faults, leading to downtime of transmission lines.
Two common faults within the transmission line are series faults and shunt faults.[iii]
Series faults, also known as open circuit faults, can be associated with failure of single or multiple conductors from join failure of overhead lines, failure of a circuit breaker, and aging conductors.
A shunt fault, or short circuit fault, can occur when lightning strikes the transmission line. This induces a voltage and current into the power system, the magnitude of which depends on the current waveform and impedances of the path.[iv]
Both types of faults cause system fluctuations or instability, resulting in traveling waves.
Series faults and shunt faults can cause transient signals to propagate down the transmission line as traveling waves (TWs), moving at nearly light-speed.[v] Any disturbance caused by any fault in the power line may cause changes in the utility frequency. Power system faults can occur due to insulation failure.
Power line utility frequency is around 50Hz or 60Hz, depending on the region. Faults introduce disturbance, inducing an impulse or fast transient signal that will propagate along with this frequency. The impulse occurs for only a short duration, microseconds or milliseconds at most, but during that time the signal is traveling at frequencies between 2kHz and 10MHz.v
Figure 1. The traveling wave
Traveling waves propagate from the fault point towards the terminals and return. Initially, the current is supplied locally from the charge stored in the line capacitance. At this moment, a remote observer measuring at the line terminal (substation) cannot detect that the fault has happened.
The first indication of the fault reaches the observer only when the wave head of the traveling wave itself reaches the observer's location. The time required for propagation and return are important parameters for estimating the fault location.
A smart grid is an electricity network that uses digital and advanced technologies to monitor and control the flow of electricity from various generation sources, ensuring it meets the changing demands of end users. Compared to traditional grid systems, the smart grid is expected to be more efficient, stable, and flexible.[vi]
According to the Electric Power Research Institute (EPRI), the smart grid enables rapid diagnosis and solutions to events that degrade power quality, such as line faults.vi This can address a significant troubleshooting inefficiency and cost of a traditional grid system: The need to dispatch crews to find and repair a fault, resulting in a longer downtime of the grid system.
Figure 2. Conventional way of troubleshooting fault within transmission line
Lightning can occur thousands of times in a single night. It happens in a flash, and the strikes are unpredictable. Capturing fault information enables faster fault location and power line inspection, allowing shorter downtime for repair.
Modern TW fault locators in smart grid systems use precise timing synchronization to compare the TW arrival time at one or both terminals. Only by perfectly synchronizing the fault-locating devices can you capture TW arrival times with the same time reference. A satellite-synchronized clock (GPS) or direct point-to-point fiber-optic channel between devices can provide the level of synchronization required.[vii]
There are two methods of fault location: Single-ended and double-ended.
The single-ended method measures the time difference between the first arrived wave and successive reflections. Accuracy can be a challenge of using this method, since reflections can arrive from the fault location, from the remote terminal, or from behind the local terminal.vii
The double-ended method[viii] overcomes this challenge by installing a TW location device at both terminal ends, Ta and Tb, and measuring the traveling wave propagation time.vii That’s the time difference between the first wave head captured at terminals A and B, along with line length and the velocity of propagation of the TW. The transmission diagram in Fig. 3 shows the basic principle of the double-ended method.
Figure 3. Traveling wave fault location using double-ended method
Once the TW locator has collected timing data from both terminals, it can use the following equation to calculate the distance from Terminal A to the fault.vii Alternatively, one could calculate the distance between Terminal B and the fault point.
Where:
Figure 4. Troubleshooting efficiency using traveling wave fault location
As stated in the previous section, fault impulses occur within a short period and have a very wide frequency range that must be captured. The next post will explore signal chain elements needed for an efficient solution to locate faults and address the challenge of traveling waves.
[i] “Executive summary – Electricity Grids and Secure Energy Transitions – Analysis.” IEA, Oct. 2023.
[ii] “Smart grids.” IEA, July 2023.
[iii] “Overhead Power Lines Faults (Causes and Solutions).” Electrical4u online, Aug. 2022.
[iv] Lorenzo Mari. “Understanding the Interaction between Lightning and Power Transmission Lines.” EE Power, Nov. 2021.
[v] Marx, Stephen et al. “Traveling Wave Fault Location in Protective Relays: Design, Testing, and Results.” Bonneville Power Administration, University of Idaho, & Schweitzer Engineering Laboratories, Inc., 2013.
[vi] Rihan, Mohd. “Applications and Requirements of Smart Grid.” Springer, Nov. 2018.
[vii] “Use Of Travelling Waves Principle In Protection System And Related Automations.” ENTSOE, April 2021.
[viii] Jing, Liuming et al. “A VMD-Based Double-Ended Traveling Wave Fault Location Method for Distribution Networks.” Springer Nature Link, March 2024.
