TRANSMISSION AND DISTRIBUTION

Installation of Lightning Surge Arresters Helps Control Outages at Newfoundland and Labrador Hydro

Newfoundland and Labrador Hydro owns and operates facilities for the generation, transformation and distribution of electricity to utility, industrial and residential customers in the Province of Newfoundland.

Two of Newfoundland and Labrador Hydro's 230 kV transmission lines, TL202 and TL206, extend approximately 141 km from its major hydro electric plant at Bay D'Espoir to the Sunnyside Terminal Station. They are on separate towers, sharing the same right-of-way and spaced about 40 meters apart (center-to-center). These lines are the major transmission facilities and major source of power servicing a large portion of the power system load for the Avalon Peninsula, which includes the City of St. Johns, and surrounding vicinity.

The lines are of a lattice steel (guyed and self-supporting towers) construction and are unshielded (i.e. there is no overhead ground wire), making them particularly susceptible to lightning-caused flashovers. Both lines have experienced approximately 10 simultaneous double circuit faults along with 77 single circuit faults as a result of lightning strikes within the last 25 years. These double circuit faults are presumed to be due to large magnitude lightning currents that flashover not only the stricken circuit, but also cause a backflash of the parallel circuit due to its close proximity and grounding.

As a result of studies conducted by an external consultant, the installation of lightning surge arresters was recommended as a means to mitigate these outages and decrease the double circuit simultaneous outage rates that have plagued these lines. The Hubbell/Ohio Brass Protecta*LiteĻ Arrester System proved to be the answer to some very difficult questions and required results.

The required results are as follows:

• The installation of such an application must be carried out so as not to compromise the present daily operations and reliability of the line.
• A rate of one (1) double circuit outage in every 35 years is sought through the use of station class varistor blocks -- 60 mm in diameter.
• The lightning arresters are to be fitted to one of the line's structures only -- TL206.

The upgrade of TL206 represented a significant technical challenge in order to meet the long-term performance improvements required. The Hubbell Team, including Hubbell Canada Inc., The Ohio Brass Company, Harris & Roome and various consultants tracked this project with great interest through various stages of investigation and analysis. The project had also been scheduled on a fast track basis requiring delivery of complete arrester assemblies in order to facilitate an April installation. The actual timeline proceeded as follows:

• The first phase of the project spanned a period from February 2000 until May 2000, which included the tender review, award of project in March 2000, supply of complete arrester assemblies in April 2000 and installation completion by the first week of May 2000.
• The first phase of installation included 50 per cent of the arrester assemblies that amounted to 560 assemblies.
• The second phase included the timeline from November 2000 to March 2001.

The initial feedback concluded that the line had not experienced any outages through the first lightning season.