Start Date: 2017
A cable trench in a substation caught fire, causing serious disruption to the client company’s power distribution infrastructure. An investigation was called to identify the cause of the fire and report on the likelihood of future recurrence.
The client’s challenge was to source and work with a reliable subject matter expert with extensive laboratory testing facilities and comprehensive technical knowledge to: investigate the joints and cables present in the trench, advise whether the cables were correctly specified and assess each cable to determine whether or not they required replacement.
RINA Asset Integrity Team received selected samples from the scene of the fire in readiness for extensive examination and testing. We examined failed and un-failed cable joints and advised on the future life expectancy of 28 types of cable including; Cross Linked Polyethylene (XLPE), fluid fi lled and paper insulated cables (PILC).
More in detail, failed and unfailed joints were stripped down, examined in detail and subjected to microscopy, tensile testing and bimetallic weld examination.
XLPE cable samples were examined using: Fourier Transform Infra-Red spectroscopy; Oxidation Induction Time and Thermal History using Differential Scanning Calorimetry; Tensile testing before and after ageing and transparentisation.
The lead microstructure of PILC and fluid filled cables was investigated using Scanning Electron Microscopy and the moisture content, degree of polymerisation and the extent of waxing and embrittlement of the insulating paper were determined.
A detailed report was provided to give confidence in the resilience of the distribution network to prevent future recurrence.
We established that the transition joints between XLPE and PILC cables were the cause of the fi re and the XLPE, PILC and fluid f lled cables all had significant remnant life and therefore they did not need immediate replacement. The risk of further failures of the existing cable network was advised as being low.