Faulty electrical connection causes a series of building fires in Lieksa

The Finnish Safety and Chemicals Agency (Tukes) has investigated an accident which took place in Lieksa on 18 December 2021, and in which a faulty connection in a substation caused several building fires. The accident investigation report is now available on the Tukes website.

The chain of events leading to the accident in the electricity distribution network started during maintenance carried out on 30 November 2021. An unexpected fault was detected at the 110/20 kV substation that supplies electricity to the accident location, as a result of which the busbar interruption carried out for maintenance could not be returned to the normal connection state as planned. Due to the unexpected fault, a replacement connection had to be planned for the switchgear.

During winter, snowfall is heavy in the distribution network area where the accident site is located. On Saturday 18 December 2021, a tree fell onto the open 20 kV wire from outside the transmission line corridor due to packed snow, resulting in a network fault. The incorrect and dangerous connection made during maintenance, combined with the wire damaged by the fallen tree, caused a series of building fires and the risk of an electrical accident over a large area.

In the chain of events, the fault protection coordination of the substation’s 20 kV outputs and the operation of the switchgear were not in compliance with their specifications due to the incorrect connection. Significant safety functions were inoperable during the fault, and the extended hazardous operation was not detected in network control.

According to the investigation, the risk assessment and the connection decision made regarding safe operation during the unexpected change were based on insufficient information, resulting in an incorrect assumption that the fault protection would operate as required in the operating situation.

The information produced by the electricity network control system on safety-related alarms and status data changes being received as a single non-prioritised list, based on which control room employees cannot easily identify the measures required for making deductions and solutions related to the operation of the network, was regarded as another key factor leading to the accident. 

Recommendations for preventing similar accidents

1. A case-specific safety assessment of fault protection based on sufficiently detailed information must always be an integral part of various network connection situations and changes caused by the network structure. Connections must be planned following the written procedure for preparing a connection programme established in the industry when carrying out activities in the high-voltage system.

2. The Electrical Safety Act requires that electrical equipment to be operated so that it does not present any hazard to people’s life or health or property. The network holder must therefore have appropriate procedures in place to monitor the safety of network operations and react immediately to any faults while maintaining safety.  

Alarms forwarded to the control room must clearly indicate their significance for safety.

3. Switchgear systems with different types of structure and of different ages are used at substations. To operate electrical equipment safely, it must be ensured and verified that up-to-date documentation is always available, indicating equipment-specific safety connections and permitted connection situations.

4. Regarding substation safety systems, including the modernisation of existing substations and any changes in protection, protection technology that is independently safe regardless of the operator’s activities should be preferred.
 

"Network and industry companies should assess their activities relative to the attached recommendations and ensure that their documents on electrical safety and protection are sufficient and up to date,” says Janne Kinnunen, Head of Unit at Tukes.

More information:

Juha-Pekka Törmälä, Senior Officer, tel. +358 (0)29 5052 217
Janne Kinnunen, Head of Unit, tel. +358 (0)29 5052 188
email format: [email protected]

Appendix:

Investigation report (in Finnish)

PowerPoint presentation of an accident investigation (in Finnish)