Western Power Distribution (WPD) said its engineers signed off at 06:30 GMT after working overnight to fix faults.

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Mrs Morgan called on PPL Corporation, which owns WPD, to join forces with Cardiff council to help secure the site's future.

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Western Power Distribution (WPD) is testing the Static VAr Compensator for Distribution Networks (D-SVC), which is described as "a very clever box".

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Road access to the site of a new electricity substation is narrow so Western Power Distribution (WPD) agreed the alternative method of transport.

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It is believed that WPD plans to keep the SWALEC electricity distribution system and pass on Welsh Water to the English company United Utilities.

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Severn Trent claims that WPD, the winner of the four-month takeover battle, plans to contract out some of Hyder's water services to United Utilities.

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The National Assembly for Wales - which has opposed WPD's bid all along over job relocation fears - said it was now prepared for "constructive talks".

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If the trials of the grey box prove successful, it will allow new renewable energy plants such as the farm in Roscrow to connect without the need for expensive grid reinforcement, said Roger Hey of WPD's Future Networks team.

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