Galloping is a high amplitude, low frequency, wind induced vibration on overhead power lines. It is caused by moderately strong, steady crosswind acting upon an asymmetrically iced conductor surface, creating periodic motion known as galloping. Severe galloping can cause flashovers due to phase-to-phase and phase-to ground wire contact resulting in a fault or subsequent outage. The increased movement of the conductor can also cause mechanical failure of the conductor, dampers, insulators or even the tower.
Mitigating the risk associated with galloping using Laki Power´s monitoring stations
To address the risks associated with galloping, Transmission System Operators (TSOs) have implemented Laki Power monitoring stations. These stations serve the purpose of monitoring various parameters such as ice accretion on power lines, conductor pitch and roll, ambient temperature, humidity wind speed, and wind direction. By continuously monitoring these factors, the grid operator can identify areas affected by icing, and get real-time information when a galloping event occurs. Additionally, the TSO can determine the type of ice present and calculate the ice load and therefore if the ice load becomes critical, they can dispatch crews to remove the ice buildup.
Furthermore, monitoring the conductor’s behavior over time and capturing galloping events provides valuable input for power line design. By studying the patterns of galloping and understanding the specific conditions that lead to such vibrations, engineers can make informed decisions on where to install dampers and how many are needed. This data-driven approach helps optimize the placement and number of dampers, enhancing the effectiveness of their deployment in mitigating galloping.
3-day galloping incident in east Iceland
Fljótdalslína 4 is a transmission line is located in east Iceland and lies from a substation in Fljótsdalur to the aluminum smelter in Reyðarfjörður. The total length of the power line is 52.9 km, and it lies through valleys and mountainous terrain. East of Iceland often experiences the most extreme weather conditions with heavy snow during winter and the warmest temperatures during summer. After the great storm of 2019, which caused power outages across Iceland, Landsnet, the Icelandic TSO installed Laki Power monitoring station on the FL4 power line next to a tower that failed during the storm. Two years after the great storm the Laki Power monitoring station captured a three-day galloping event which is described below.
December 19th 2022
On December 19th, a 1.5 cm ice wing formed on the conductor overnight. The wind direction was perpendicular to the power line and wind speed gradually increased as the morning progressed. At 11am the first oscillations were observed and recorded in the Laki Analytics software interface. As the day went on the wind speed surpassed 15 m/s and the galloping became more severe. Overnight the average wind speed was 17 m/s and wind direction perpendicular to the transmission line, indicating a continuation of the galloping through the night.
December 20th 2022
The morning of December 20th the wind speed remained above 15 m/s and ice wing diameter had increased to 3 cm. Once daylight broke, we saw extreme galloping of the phase wires. Around 11 in the morning the ice wing fell off the middle phase wire, leading to a decrease in oscillation for that particular phase. However, the left phase wire continued galloping and as the day went on the wind speed increased to 18 m/s and we observed large oscillations of the left phase wire and buildup of ice once again. Overnight, the average wind speed remained over 15 m/s with the wind direction perpendicular to the transmission line, indicating a continuation of the galloping through the night.
December 21st 2022
On the morning of December 21st, the ice wing on the conductor had further increased to 4 cm, while the wind speed remained around 15 m/s, with the wind direction perpendicular to the transmission line. Throughout the day the extreme galloping continued on the phase wires until midnight. Subsequently, the wind speed decreased and remained below 10 m/s. Despite the wind direction remaining perpendicular to the power line the wind speed was insufficient, leading to the end of the three-day galloping event. An overview of the galloping event recorded in the Laki Power Analytics Studio can be seen below.
Comparing the days before and after the galloping event
The following table outlines the distinctions between the days when galloping occurred and when it did not. The key factors considered are wind speed and ice accumulation on the conductor. On December 18th, there was no ice buildup on the conductor, and the wind speed was low. On December 22nd, although there was an ice wing on the conductor, the wind speed was insufficient for galloping to occur.
Dec. 18 | Dec. 19 | Dec. 20 | Dec. 21 | Dec. 22 | |
18.12 | 19.12 | 20.12 | 21.12 | 22.12 | |
Ice thickness [cm] | 0 | 1.5 | 4 | 3 | 4 |
Ice Type | - | Snow | Snow | Snow | Snow |
Ice Load [kg/m] | 0 | 4.1 | 5.4 | 4.7 | 5.1 |
Avg. wind speed [m/s] | 6.2 | 15.8 | 16.1 | 13.9 | 7.9 |
Wind Direction | N-NW | N | N | NW | N |
Avg. temp [°C] | -8.3 | -6.4 | -4.8 | -4.3 | -6.0 |
Avg. sag [m] | 2.9 | 2.8 | 3.1 | 2.9 | 2.8 |
Procedures after a galloping event
The galloping event did not cause any damage on Landsnet’s transmission line. Throughout the three-day galloping event, Landsnet effectively utilized the Laki Power user interface to actively monitor both the transmission line and prevailing weather conditions in real-time. A dedicated line crew remained on standby, ready to respond to any potential damage. Thanks to the combination of light ice load on the line and continuous monitoring by the Laki Power station, Landsnet was able to avoid dispatching a crew for damage assessment.
The key features on the LKX-201 that proved highly advantageous for Landsnet were the 4K optical camera system and the wind sensor. The wind sensor provided immediate data on wind speed and the angle at which the wind interacted with the power lines, indicating a sustained perpendicular wind for the duration of three days. Simultaneously, the camera system corroborated this information, confirming minimal icing on the lines and an absence of visible damage.
Even though the galloping did not result in a power outage, it is still advantageous to be aware of its occurrence and its specific location. Frequent galloping can impose additional stress on the equipment, potentially shortening its lifespan and necessitating more frequent inspections. Therefore, having this information allows for proactive measures to be taken, such as increased monitoring and maintenance, to mitigate the potential impacts of galloping on the infrastructure.
The Laki Power Monitoring stations provided us with invaluable real-time insights into the conditions of our transmission line during the challenging three-day galloping event. Using the precise data from the wind sensor, complemented by visual confirmations from the camera system, we transitioned from reactive to a proactive approach.
Þórarinn Bjarnason - Head of Grid O&M, Landsnet