How often do disturbances occur in the main grid, and what causes them?
In recent years, there have been 300–350 disturbances in the main grid annually. The majority are transient and require little action to be taken. Natural phenomena and weather conditions cause most of the disturbances: thunder, wind, snow burdens, supercooled water, and birds colliding with transmission lines. Disturbances happen throughout the year.
How quickly are faults noticed and rectified?
If there is a disturbance in the main grid, the control centre notices straight away. Most disturbances clear themselves thanks to the auto-reclosure function in relay protection, but sometimes we send a team to check the location. This is one way of preventing larger problems from occurring. Patrols are sent out to check transient faults on a random basis. For example, if there has been a thunderstorm, it is obvious what caused the disturbance, but during the winter, there may be snow that needs to be cleared from transmission lines. Approximately ten per cent of all disturbances require a patrol team to check the location. The time it takes to clear a fault can vary dramatically. It can take up to a week to repair a fallen tower. Permanent faults are rare.
What technology is used to locate faults and disturbances?
Fingrid uses a location technique to discover the exact location of a fault. Substations have disturbance records and travelling wave meters. The travelling wave meters send a timestamp to the main application, which calculates the location of the fault based on the difference between the timestamps, the length of the line, and the velocity of the travelling wave in the line. The control centre receives an email if the travelling wave meter has obtained a true value from both ends of the transmission line. Disturbance recording begins when a circuit breaker opens, meaning that the power line is not energised. The control centre receives a record, and we interpret the data to obtain variables such as the voltage and current, as well as the duration of the fault.
How accurately are faults located?
Travelling wave meters can trace a fault to the correct tower in almost every case, for a precision of approximately 250 metres. The control centre receives information on the location (the number of kilometres from the start point) within a few minutes of a fault arising. If the travelling wave meter does not provide a value, the estimated location of the fault is less accurate, and the potential range is a few kilometres.
What role do people play in locating faults?
Control centre employees quickly form situational awareness based on the information generated by the systems. Experience in analysing faults helps to identify the locations of faults more precisely. We send customers and Fingrid employees an email or text message notification immediately after the fault. Dedicated transmission line specialists have been appointed to coordinate fault clearance in different areas.
