A short circuit occurred in a transformer on 29 October 2021 on the Sleipner A facility in the North Sea, where Equinor is the operator.
Following the short circuit, fire pumps were activated because smoke was detected. One fire pump broke down during the course of events, with flame detection in fire-pump room.
During blowdown, flame detection also occurred on Sleipner T.
No personal injuries were suffered from the incident, but it caused material damage and had financial consequences:
- destroyed transformer
- destruction of flexible coupling and auxiliary hydraulic pump for fire pump B
- fire pump B out of action
- destroyed servomechanism for diesel supply shut-off valve to fire pump B
- loss of power supply to Sleipner B and Gudrun
- trip of Gina Krog
- consequent loss of production.
The PSA’s assessment is that neither the incident in the transformer room nor the subsequent breakdown in the fire-pump room had a major accident potential.
A larger fire could have broken out in the fire-pump room, but the PSA considers it unlikely that this would have escalated beyond the room.
An internal fault in the high-voltage winding is almost certainly the direct cause of the short circuit in the transformer. The direct cause of the incident in the fire-pump room is the failure of the flexible coupling installed in the shaft between the auxiliary hydraulic pump and the diesel engine for fire pump B.
The investigation found several underlying causes which could have been significant for the incident both with the transformer and in fire-pump room B.
Underlying causes for the transformer incident:
- design weaknesses and ageing
- organisational – Equinor has considered that it is not necessary to replace this type of transformer in the technical operating life programme, although the weakness was known.
Underlying causes of the fire pump breakdown:
- ageing of the rubber element and loss of flexibility in the coupling
- lack of preventive maintenance (PM)
- inadequate follow up of 2018 lessons-learnt report
- weaknesses in the system for sharing experience and learning lessons.
The investigation team has identified five nonconformities:
- system for experience-based knowledge and information
- barrier understanding and expertise
- selective disconnection in the event of a short circuit.
The investigation has identified serious breaches of the regulations, and Equinor has therefore been given the following order.
Pursuant to section 69 of the framework regulations on administrative decisions, see sections 45 and 47, paragraphs 1 and 2, of the activities regulations on maintenance and on maintenance programme, and sections 58 and 59a of the technical and operational regulations on maintenance and on maintenance programme, Equinor is ordered to ensure that failure modes related to flexible couplings attached to diesel-hydraulic fire pump packages are prevented systematically through maintenance programmes on offshore facilities and at land plants in Equinor where such equipment is present. See section 11.1.1 of the report.
The deadline for compliance with the order is 1 February 2023. We must be notified when the order has been complied with.