{"id":645,"date":"2020-09-01T14:39:11","date_gmt":"2020-09-01T19:39:11","guid":{"rendered":"http:\/\/polywaterv2.wpengine.com\/?p=645"},"modified":"2025-05-19T16:06:35","modified_gmt":"2025-05-19T21:06:35","slug":"mapping-as-risk-and-cost-assessment-methodology","status":"publish","type":"post","link":"https:\/\/www.polywater.com\/en\/knowledge-hub\/mapping-as-risk-and-cost-assessment-methodology\/","title":{"rendered":"Mapping as Risk and Cost Assessment Methodology"},"content":{"rendered":"
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Abstract<\/strong><\/h2>\n

Generation, start-up and auxiliary transformers are typically designed for specific functions within an operating block in a power plant. \u00a0The planning, manufacture and installation of custom-designed power transformers can take many years to complete.\u00a0 Once in operation, the premature failure of these critical assets before their expected End of Life (EOL), can be devastating to the electric utility or industrial company owner. The mapping process aids in the proactive identification of those transformers which may create the most economic and performance risk. The process helps to identify remediation, conservation and conditioning actions which ensure that these critical assets function throughout their planned lifetime.<\/p>\n

Introduction<\/strong><\/h2>\n

Our article Mapping Transformer Populations<\/strong><\/a> focused on the use of the mapping process as a starting point to determine the appropriate remediation and conservation measures that your maintenance team needs to take to ensure a transformer block subjected to accelerated aging performs over the long-term. This article expands on mapping and risk assessment to identify the actions required to extend the operating lifetimes of transformers subjected to other forms of risk like design and random external risks.\u00a0 In cases of these risks, the mapping process generates different remediation and conservation strategies to ameliorate and control them. These strategies are then compared so that the option that best balances risks can be implemented with an evaluation of operational and financial considerations.\u00a0 We use a hypothetical example, based on typical field experience, to illustrate these concepts.<\/p>\n\n\n\n
Related Content: <\/strong>Mapping Transformer Populations<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Types of Risk<\/strong><\/h2>\n

A transformer block is a complex system.\u00a0 The transformers and auxiliary equipment that comprise an operating block are interconnected and must function as designed for the block to meet operational objectives over an extended period.\u00a0 The issues of accelerated aging and its effect on premature failure already have been addressed in previous articles.\u00a0\u00a0 A transformer block can also be at risk due to poor design and\/or workmanship which create functional weaknesses in a transformer. These, in turn, can cascade throughout the system to cause outages, fires or other system performance issues in the transformer block.\u00a0 Defects such as poor welded joints or defective head gasket sealing can increase risk of failure of an individual piece of equipment or the entire transformer block.\u00a0 \u00a0Random factors such as lightning strikes, natural disasters or short circuiting create another form of risk difficult to predict.<\/p>\n

The term End of Life (EOL) is commonly used to describe the time at which a transformer becomes inoperable.\u00a0 This term is imprecise as it does not convey the actions that can be taken to reduce the risks that most affect a transformer block.\u00a0 These actions could include oil reconditioning and monitoring in the case of accelerated aging or creating redundancy in the system to protect from the abrupt failure of critical assets.\u00a0 A useful term, used in this article, is remaining substance (RS), which conveys the concept of a valuable asset that can be consumed or conserved depending on how the risks are managed. The decline in RS is exponential if the appropriate measures are not proactively taken. \u00a0It is important to institute the remedial and\/or conservation measures early enough so RS can be preserved in good operating condition throughout the required operating lifetime of the transformer.\u00a0 Field experience suggests that once RS reaches 60%, the remaining operating life of the transformer is only six years.\u00a0 By taking proper and timely action to manage risk factors, the transformer\u2019s lifetime can be extended by another 10 to 15 years.\u00a0 The chart below depicts the trajectories of RS with and without conservation measures.<\/p>\n

\"\"<\/p>\n

Water content measurements under 2% to greater than 3% comprise a range from which accelerated aging is measured. Proper sealing design is one means to reduce the impact of O2<\/sub> on depolymerization.\u00a0 Partial degassing has proven to be an effective means to restore O2<\/sub> levels to 30% of its saturated values.<\/p>\n

Type 1 Failures<\/strong>-Age related degradation of electro-mechanical assemblies such as bushings, OLTCs and of solid insulation can contribute to transformer block failure.\u00a0 The risks caused by accelerated aging are quantified in the mapping process through DGA and transformer fluid testing.\u00a0 These testing procedures provide indications of the level of depolymerization of the solid insulation in the transformer as it cannot be measured directly.\u00a0 The level and rate of exposure of cellulose to aging accelerators such as high temperature, moisture, oxygen (O2<\/sub>) and acids are the starting points to this process.\u00a0 These influence the physical and electrical properties of the transformer and influence the rate of accelerated aging.<\/p>\n

Type 1 risks are accurately determined with today\u2019s increased sophistication of test methodologies and technologies.\u00a0 Once the effects of the accelerators are quantified, measures to conserve the cellulose insulation can be undertaken to extend the lifetime of the transformer.\u00a0 These measures include gas monitoring and oil regeneration. \u00a0If managed properly, Type 1 risks can be controlled to slow age related degradation and EOL of a transformer. It is important to understand that even when the proper actions are taken, the transformer will continue to age but at a slower rate than otherwise.\u00a0 This means that the probability of failure from type 1 risks increases with time.<\/p>\n

Type 2 Failures<\/strong>– Inadequate design or poor construction of a transformer often cause sudden EOL conditions. The inadequate design of a transformer\u2019s cooling system creates overheating, which in turn contributes to accelerated aging and a higher probability of premature failure. Poor workmanship on welding joints results in gateways for oil leakage or the ingress of moisture and atmospheric gases into the transformer, which again cause accelerated aging leading to premature failure. Type 2 risks can develop when the poor design or poor-quality workmanship of a new transformer causes the premature failure of the transformer, resulting in significant lost revenue and repair\/replacement costs. Understanding how the new equipment reacts to actual field conditions when connected to existing equipment in the block takes time.<\/p>\n

The probability of Type 2 failures begins at a high level, but with time, it declines as the transformer is checked and adjustments are made to optimize its performance.\u00a0 Proper vetting can take years before the probability of failure reaches normal levels.<\/p>\n

Type 3 Failures<\/strong>-External influences such as lightning or short-circuits often generate sudden and catastrophic transformer failures. The risk from a lightning strike is unquantifiable due to the uncertainty of the timing and severity of the strike. However, the short circuit of a third-party grid or station transformer also can create this type of risk. Type 3 risk is uncontrollable and random. Type 3 risks are incorporated into the mapping process by focusing on the transformers, which are most exposed to this uncertainty.<\/p>\n

The uncertainty surrounding Type 3 failures makes them difficult to predict.\u00a0 As such, the cost in the event of a Type 3 failure, is often used as a proxy for the risk. These measures include lost revenue from a loss of power production over some period or the cost of buying power on the open market.\u00a0 Type 3 risk does not increase or decrease over time and can be thought of as a uniform probability distribution over the lifetime of the block. Type 3 failures are especially dangerous when they affect weakened assets which cause a cascade of outages to other units in the block.<\/p>\n\n\n\n
Related Content: <\/strong>Transformer Leak Repair Story from Polywater\u00ae<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Reasons for Mapping<\/strong><\/h2>\n

All transformers are exposed to various risks.\u00a0 They age over time causing premature failure. Their poor design can create functional weaknesses, which are only detected when operating over time. Random weather or grid related risks can cause complete transformer block shutdown. The mapping process described in this article is used to identify the risk to which a transformer block is exposed and what actions are needed to counteract the negative impact they have on performance. The process also considers the objectives of the plant owner which may include timing of plant shutdown or operating extensions, financial or safety goals. \u00a0If not maintained properly, the original financial justification of the transformer and functional block in which it operates may not be reached.\u00a0 The final outcome of the mapping process is to provide multiple options that the plant owner can select based on an acceptable level of risk and required economic commitment.<\/p>\n

The Mapping Process<\/strong><\/h2>\n

The mapping process consists of eight steps.\u00a0 Each step builds on the next resulting in the evaluation of different long-term replacement, remediation and conservation actions that can be taken to reduce the risks of EOL. These action plans identify their associated costs and risks to enable the transformer block operator to select the actions best suited to meet the objectives of the plant.<\/p>\n

The steps in the mapping process will be described using the following scenario:<\/p>\n

Scenario Description<\/strong><\/h3>\n

In order to ensure that the transformers in a combined heat & power plant (CHP) would operate until its planned shutdown in six years, a preservation plan was developed for the plant. The initial phase of this plan was to regenerate insulating fluid for high voltage, start-up and station supply transformers.\u00a0 One year after the start of the preservation plan, the second phase of conditioning and conservation actions to one of the Generation Step Up Units (GSU) began when a transportable conditioning unit was installed.\u00a0 In the third year of the conservation process a second transportable conditioning unit was installed to further augment the conditioning of a second GSU transformer.<\/p>\n

The data being collected from on-line gas monitoring systems over the first three years of the lifetime extension program provided a significant amount of baseline information on the trend of RS. The analysis of this data raised the possibility of a longer lifetime extension.\u00a0 Because of this, it was decided to augment the assessment of critical assets in the plant. The scope was changed to include the evaluation of three scenarios where the cost and risks of a longer operating period would be evaluated.\u00a0 The three scenarios would allow the plant owner to compare the different alternatives so that he could determine whether a further ten-year extension was feasible and, if so, which course of action would be optimal. The motivation for this broader scope was to determine if the plant could continue to generate power and heat production revenues at a reasonable cost without incurring significant operating risks.<\/p>\n

The Mapping steps to accomplish this broader assessment of the CHP follow:<\/p>\n\n\n\n
Related Content: <\/strong>Cost Effective On-Site Leak Repair of Power Transformers<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Mapping Step 1:<\/strong> Statement of Objectives<\/h4>\n

Identify the life extension options available to the CHP transformer block to ensure safe and reliable operation until a scheduled extended plant shutdown in 12 years.\u00a0 Provide the asset owner a complete risk\/reward assessment of the proposed options.<\/p>\n

Mapping Step 2:<\/strong> Data Collection and Documentation<\/h4>\n

A complete history of the following data should be available and must include:<\/p>\n