Energy giants Scottish and Southern Energy are continuing their investigations into one of the largest power cuts ever to hit Scotland.
Engineers have been concentrating their efforts on a 55-mile stretch of cable line between Moray and the south of Inverness.
An SSE spokesman said: “Engineers have completed aerial and ground inspections of around 90km of overhead power lines between Blackhillock and Knocknagael substations following the rare and unexpected power failure in the north of Scotland which briefly affected 205,000 homes lateon Wednesday evening.
“Although no obvious damage has been found to date, our teams will continue their technical analysis and close up inspections of equipment in the area over the coming days and weeks if necessary.
“However, early indications point to what is known as a ‘transient’ fault which although leaves no obvious damage to a power line, will cause a brief interruption and is usually caused by an object striking the line.
“Examples could include debris, lightning, birds or a failure within a specific piece of equipment.”
He added: “Although our network is reliable 99.9% of the time there are occasions when a fault may occur.”
He added: “When it does we will always restore power as safely and as quickly as possible while keeping customers updated on our progress.
“We would like to thank customers once again for their patience and apologise for any inconvenience caused while we restored electricity supplies to affected households safely.”
First Minister Alex Salmond has chaired “pow-wow” emergency meetings of the Scottish Government Resilience Committee (SGoRR) following the blackout.
He was given an update on the work being undertaken by Scottish and Southern Energy Power Distribution (SSEPD) to identify the cause of the power outage.
A Government spokesman said: “SSEPD confirmed they have now visually inspected some 90km of lines where the fault is believed to have occurred.
“This was carried out by helicopter and by staff on the ground but as yet no visible damage or signs of the fault have been identified.
“SSEPD informed the First Minister that the fault was transient (i.e. non-damaging to the lines) as the system came back on line with no issues.
“Such faults can be caused by foreign objects striking the lines such as debris in windy weather, lightning strike, pollution or equipment failures.
“The First Minister also took the opportunity to praise the hard work of all involved in getting the power back on last night, including those keeping customers informed.
“The First Minister also received updates from Police Scotland, Transport Scotland and the NHS and was assured that all emergency procedures worked well. He also thanked them for the role they played.”
The blackout affected street lights and train services, while shops and bars were forced to shut early as they were plunged into darkenss.
Radio services monitoring the shipping distress channel were also affected for a short period, while mobile phone masts stopped transmitting.
Highland league football matches were abandoned as floodlights went out.
Questions continued to be asked as to why a fault on a relatively small section of power line could knock out an entire region of Scotland.
Scottish Hydro Electric Power Distribution said: “In terms of the scale of the interruption of supplies, this would have been caused by safety equipment acting as a circuit-breaker to safeguard the network.
“Our investigation is ongoing.”
The outages first struck shortly after 8.30pm on Wednesday, affecting homes in Inverness, Moray, Caithness, Sutherland, Orkney and the Western Isles.
Within two hours the number of those affected had reduced to around 95,000. By 12.30am on Thursday all power had been fully restored across the region.