Wayne J. Chatterton

An update on silicone transformer fluid: specification, manufacturing, maintenance and end of life options

Silicone transformer fluid has been used in liquid transformers for over 25 years now. There are well over 100,000 silicone fluid filled transformers in operation around the world in network, secondary unit substation, medium power, three phase pad mount distribution and specialty applications. This paper will review recent developments related to the use of the fluid including application testing, manufacturing issues, maintenance procedures, and end of life options. Emphasis is on recent progress within the IEEE Transformers Committee on Dissolved Gas Analysis for silicone filled transformers, a review of environmental characteristics of silicone fluids, and practices of reuse and recycling the fluid.

Environmental and life cycle considerations for distribution and small power transformer selection and specification

A superficial review of power transformer options frequently leads to the conclusion that a standard dry-type transformer is more environmentally responsible alternative than a liquid transformer. However the differences in lifetime losses represent real differences in environmental costs as well as energy costs. This paper equates the losses to various environmental costs, and presents a life cycle economic model to help evaluate total lifetime owning costs in monetary terms. The cost components include the initial costs of the transformer itself, directly related equipment and installation costs, operating costs including power losses and maintenance and end of life costs related to decommissioning, salvage value or disposal cost. Less quantifiable factors such as audible noise, physical size and reliability are also be compared for dry-type transformers and their liquid counterparts. Finally, electrical insulating fluids commonly used in these transformers are compared in terms of economic, environmental and safety factors. Economic factors include the initial fluid cost, maintenance and disposal cost or salvage value. Environmental properties such as biodegradation, BOD, fate and effects and environmental regulations are discussed. Safety aspects, including transportation and workplace exposure regulations, are compared, and fire properties including ignition resistance, heat loading, smoke generation and combustion toxicity are detailed.

Chemical treatment of URD cables

Cable rejuvenation fluids have been safely injected into cables for more than 20 years. This process increases the dielectric strength of the cable and removes the water trees plaguing older polyethylene cables. The increased dielectric strength and the removal of water trees leads to a considerable increase in the remaining life of the cable. This paper first looks at the early stages of the injection process. A look at how long it takes the fluid to move from the conductor into the PE insulation is calculated. Next, the basic chemistry of the water tree filling and fluid oligomerization is addressed. The resultant fluid is then tracked by diffusion in the polyethylene to give an estimate of how long the fluid stays in the insulation. This can give a cable owner comfort in the length of time the cable should maintain in reliable service. This cable is looked at from the start of injection to the end of its useful life.

Rejuvenation of Insulation in Aged Power Cables

Three short cases studies will be documented to highlight the efficacy of silicone rejuvenation technology. The first is a 115 kV class transmission cable from Duke Power, the second will be a 3 phase, 1000 kcmil, 260 mil, 1973 vintage feeder circuit from Dominion Power and the third case will be a 500 kcmil, 1968 vintage Cu, 175 mil XLPE, 15 kV cable that was one of the first treated cables at Dow Corning Corporation. The progress over the years and the great success of silicone cable rejuvenation were discussed.

Extruded cable reliability- life estimation and life extension

The reliability of distribution class cable systems installed in utilities can be significantly improved by employing cost effective strategies offered by innovative technologies. This will provide a better engineering tool to prioritize the capital expenditure. The on line condition assessment technology offers a non invasive, non destructive approach, which will assist the user to establish a predictive maintenance program in a proactive manner. The technique is particularly applicable for identifying the type of defects that cause aging and loss of life in system components. The rejuvenation technology extends the operating life of aged extruded cables commonly used in distribution systems. It is based on a well proven silicone fluid injection process, which is successfully employed in distribution systems all over the world.

How Cables Fail-the Myths and Fundamentals to Ensuring Long Cable Life

“How do cables fail?” is a loaded question. The mechanisms by which many cables fail are presumed unknown due to the catastrophic failure site being un-diagnosable post failure. There are many myths regarding the phenomena of what causes a cable to fail. The expected life of cables is also a hotly debated topic. “Cables last 40 years” is the common mantra most asset managers live by. There are many other myths as well such as “Water trees fail cables” and “Electrical trees have very short lives”. These myths will be discussed and debunked. An understanding of what really causes cables to fail will be described allowing the asset manager to make corrective actions prior to having an unplanned failure. Key cable issue fundamentals will be presented that need to be understood to help promote a long cable life. Proper cable system partial discharge (PD) assessment is very important in helping to ensure long cable life. Statistically significant supporting data will be presented. Assess first, then act on the findings to guarantee a long cable life.

MV CABLE LIFE CYCLE MANAGEMENT

A reliable MV cable network is vital for the petro-chemical industry. Outages can result in losses of revenue. A prudent life-cycle management maintains network reliability in a cost-effective way. Most cable test technology providers are not able to determine cable condition according to the manufacturer’s quality control standards, thus resulting in unreliable cable condition results. These methods risk huge financial loss due to process interruption or unnecessary replacement costs. Nowadays it is possible to evaluate MV cables according to manufacturer’s factory standards. Assessment based on 50Hz/60Hz testing voltage per the standard’s requirements is possible. Partial discharges (PD) can now be measured with a superior sensitivity in the field, measuring values as low as 5pC as specified by the manufacturers. This makes it possible to establish an effective condition based life-cycle management program. When planned and executed properly, management can save millions of Euros in loss of production due to unplanned outages. This also provides a cost-effective alternative to costly unnecessary cable replacement.

Lightning protection for aged cable systems — Problems with water trees

The injection of a silicone dielectric fluid in to cables to treat the water trees has been practiced for more than 25 years. Lightning protection combined with silicone fluid injection is a unique way to protect critical aged circuits. These circuits are more susceptible to damage as the water trees decrease the impulse strength of the cable. The review of cable rejuvenation and the factors necessary for protecting aged cables will be discussed.

Options for cables post diagnostic testing

It is good engineering practice to routinely test the electrical components and critical cables located within your system. Once testing is complete, it is prudent to develop a plan to address concerns identified from the electrical assessment. This presentation will briefly address electrical system testing followed by options available to the cable reliability engineer for correcting issues identified via the testing. On-line diagnostic testing, testing while the system is energized, will be discussed. The cables and components can grade from Level 1, where there is no system degradation and hence the system requires no maintenance, up to a Level 5, where the component or cable system is highly degraded and immediate action is required. Cables that test in the middle or below (level 4 to 1) do not have to be replaced as modern and proven technology allows for specialized silicone fluid injection to rejuvenate the dielectric strength of the cables insulation. Removing the water and filling the water trees in the insulation increases the dielectric strength of the cable and will lengthen the remaining life of the cable by many years. A critical look at cable replacement versus cable rejuvenation will be discussed.