The NSW government announced the deal to sell the backbone of the nation's electricity network, Transgrid, to a consortium of local and offshore buyers on Tuesday.

It will now move to sell half of Ausgrid and Endeavour Energy, which distributes electricity to households and businesses in Sydney, Newcastle and Wollongong. The Ausgrid sale is expected to be concluded by mid-2016.

All up the NSW power network assets are expected to fetch more than $20 billion over the next 18 months.

"It was encouraging to see the level of global interest in these assets," one bidder said Wednesday, with investor interest remaining "at high levels".

The NSW Premier described the outcome as "stunning" and it follows the sale in 2013 of Port Botany for $5.07 billion which has prompted other deals including the Victorian government putting the much larger Port of Melbourne on the block. That deal is expected to raise well over $6 billion.

There were four bidding consortiums for Transgrid with the successful group composed of Canadian pension fund Caisse de depot et placement du Quebec (CDCQ) with 24.99 per cent, Hastings (20.02 per cent), the Abu Dhabi Investment Authority (19.99 per cent), Kuwait Investment Authority (19.99 per cent) with the remaining 15.01 per cent held by Spark Infrastructure, which is listed on the ASX.

There were four bidders, which all had Foreign Investment Board (FIRB) approval although most attention had focused on the China State Grid consortium with Macquarie Investment funds given the links of the Chinese company to the Chinese government.

Sources close to the losing consortium indicated they had been outbid by a sizeable margin, signalling political concerns were not at play with the final decision.

Operationally, Spark's expertise in running networks in Victoria and South Australia – Powercor, CitiPower and SA Networks, it has a 49 per cent stake in each – is central to the consortium's bid.

"In mid-2014, we engaged with Spark to lead a 'mini-UN consortium' realising Spark's expertise with controlling and operating networks in Victoria and South Australia," a spokesman for Hastings said.

"We wanted a lead partner who we could work together with," given its experience in working assets of existing networks harder.

Signalling its lead position, Spark will initially have two board seats on Transgrid while the other consortium members will have just one, with Spark chief Rick Francis to chair the company, at least initially.

Following heavy investment over the past decade, Transgrid has the youngest electricity network in the country which will reduce its spending in the future, although it intends to ramp up its spending in its non-regulated businesses.

The winning bid was close to 1.5 times the $6.4 billion-rated asset base of Transgrid after taking the stamp duty component of the price into account.

A particular attraction was the non-regulated businesses of Transgrid, primarily its power connections arm which links wind farms, large solar farms and the like to the electricity grid, along with its fibre-optic communications network, with both earmarked for expansion.

The partners are putting in $4.89 billion of equity and borrowing $5.5 billion, with Spark seeking to raise $405 million from shareholders.

The consortium opted for much higher equity upfront to reduce the leverage, in a bid to reduce the volatility of the investment, a consortium spokesman said.

With the NSW government likely to raise more than $20 billion from the sale of the a large part of the NSW electricity network, this compares with the $22 billion raised by the Victorian government from the sale of its entire electricity business in the 1990s as it sought to stave off bankruptcy.