Transformer Oil Testing: Case Studies for Managing the Risk of Electrical Outages

Executive summary

Paul Boman, Hartford Steam Boiler

Transmission and distribution system reliability is normally measured after a period of operating time — too late to prevent losses due to an unscheduled electrical outage. Hartford Steam Boiler’s Transformer Oil Gas Analyst program (TOGA®) can help mitigate an unscheduled outage by identifying about 50 percent of the problems found with oil filled transformers. The early detection of a problem can help with two types of risk: potential equipment damage, and the consequences of an outage that can shut down production.

Early Detection Savings

Understanding equipment condition is the key to evaluating the level of risk posed to a company. The full-text article uses case studies and detailed charts to show the benefits of a transformer oil testing program and to help you weigh the costs and benefits of taking preventive action:
TOGA identified arcing in a medium-sized distribution transformer. It was traced to a lightning event the previous spring. After subsequent testing, TOGA noted additional arcing activity and an internal inspection pinpointed the problem. In this instance, the customer was able to save nearly $52,000, mostly by avoiding additional repair costs through early detection.
TOGA detected a deterioration of winding insulation in a step-up transformer. A review of the probable gassing source combined with the unit’s age indicated the early detection repair cost was equal to a complete transformer rewind. But there was an early detection unscheduled outage savings of nearly $3 million, based on the inability of the plant to export electricity if the transformer was not operating.

About the Author

Paul Boman has worked in several positions for Hartford Steam Boiler since 1988. In 1999, he became TOGA® (Transformer Oil Gas Analyst) Program Director, and was responsible for the redesign of the program. TOGA is an Internet-based analytic program that performs asset management services for more than $520 million of equipment. Paul has a M.B.A. degree and is a member of the Institute of Electrical and Electronics Engineers (IEEE).

The full article

Transformer Oil Testing: Case Studies for Managing the Risk of Electrical Outages

Incentives and Penalties

Many governmental regulatory agencies are resorting to an incentive/penalty system for controlling the reliability issue for their constituents. An example of a regulatory system would be an electrical generating municipality that has a reduced generating capacity and might be required to purchase additional energy over and above their consumption to ensure an adequate supply is available to their customers.

The additional energy purchase price may be at a premium depending on the time or season, which can greatly add to the unscheduled outage cost or level of risk. Combining the additional electricity purchase cost with the equipment damage and loss of consumer confidence, the cost can stress the financial resources of a company.

"Severity x Frequency"

The definition used in this article for risk is “severity times frequency.” Severity captures the risk-specific implications and the frequency shows how often a problem or outage occurs. The implication may be a safety concern, a timeliness issue with production, or monetary consideration. Risk is not always quantifiable and it may be difficult to capture the benefit of reducing risk factors. A typical method of evaluating risk factors is to find a problem, then extrapolate it to a conclusion using likely scenarios.

TOGA® Helps Spot Problems

The Transformer Oil Gas Analyst program (TOGA®) offered by Hartford Steam Boiler (see “Transformer Oil Testing: An Early Warning System That Works,” The Locomotive, Vol. 72, No. 3, Summer 1998) can help mitigate the risk of an unscheduled outage by identifying about 50 percent of the problems found with oil filled transformers. Actually, TOGA will find a symptom or telltale indications of a problem like abnormal gas development from an elevated temperature.

The insulating fluid is an integral part of the transformer’s insulation system and maintaining the proper fluid characteristics is critical to the equipment condition. The deterioration in the transformer insulation system can reduce its ability to sustain transits that would not normally damage the transformer. Elevated insulating oil moisture content is a good example of reducing the insulation systems’ ability to safely sustain the rated voltage levels.

The early detection of a problem can help with two types of risk, potential equipment damage and the consequences of an unscheduled outage that can shutdown a production activity. The significance of each risk type is largely dependent on the type of business the equipment serves.

Early Detection Repair Cost Benefit

TOGA03-1An example of equipment damage risk would involve a transformer supplying a location with a redundant electricity supply. The availability of an alternate power supply can help limit the unscheduled outage costs. Depending on the system configuration and type of fault, the loss of a single supply would not have an effect on the system load, because the load would shift to the alternate or redundant supply.

 Any cost savings must take into account the estimated major failure scenario offset by the actual early detection repair cost. Since there is no guarantee of a future failure, we must adjust for the uncertainty of the problem with an estimated failure probability.

 

Case Examples: Gas Concentration Indicates Arcing

Case 1: TOGA identified arcing activity in a medium-sized distribution transformer and further investigation traced it to a lightning event the previous spring. The combustible gas concentrations were stable following the initial arcing event. The owner took no additional actions after electrical testing indicated no immediate concerns.

TOGA noted the re-initiation of arcing activity after several sample cycles mainly through the increase in acetylene gas concentration. The change in equipment condition prompted the owner to perform an internal inspection for the gassing source. The transformer internal inspection found flashover indications near the no-load tap changer mechanism. The substation had two parallel transformers, each able to support 100 percent of the electrical load. The main concern was additional equipment damage and the increased possibility of failure due to the arcing activity.

 TOGA03-2Table 1 shows the factors for a Case 1 cost-benefit analysis. The low repair cost compared to the major repair cost explains the early detection repair savings. The early detection repair savings is adjusted for the uncertainty that a major repair will be needed if the problem had not been repaired. The lack of an unscheduled outage cost is attributed to the distribution system configuration.

Early Detection Unscheduled Outage Benefit

Depending on the type of facility, an unscheduled outage can severely affect revenue. The loss of production is also related to the discontinuation of services during an outage. The next example describes an electric generating station that produces electricity as the main source of revenue, but it could also relate to a manufacturing plant. A failure in the main generator step-up transformer will cause a complete shutdown of the plant, which is normally referred to as energy not served. The early detection unscheduled outage savings captures the cost of avoiding a forced outage. The cost benefit analysis must also be reduced by any cost needed for the scheduled outage.

Case 2: TOGA identified a winding insulation deterioration problem in an electric generating station step-up transformer. A conservative example of failure probability was used, but the actual unit condition with the likely involvement of the windings greatly increased the possibility of a sudden failure. A review of the probable gassing source combined with the unit’s age indicated that the early detection repair cost was equal to a major repair of the transformer (complete transformer rewind). The owner ordered a replacement transformer because of the large impact this transformer had on plant sales revenue.

 TOGA03-3Table 2 shows the factors for the Case 2 cost-benefit analysis. The early detection savings was reduced because the early detection repair cost equaled the major repair cost. The main benefit was in the large savings in the early detection unscheduled outage savings, because of the inability of the plant to export electricity if the transformer was not available for operation.

Summary

Understanding equipment condition is the key to evaluating the level of risk posed to a company. Properly identifying an abnormal condition will allow calculation of a cost-benefit analysis to justify actions to protect your company’s profitability. The two case studies illustrate the effects of early detection savings for both equipment damage and unscheduled forced outage costs.

About the Author

Paul Boman has worked in several positions for Hartford Steam Boiler since 1988. In 1999, he became TOGA® (Transformer Oil Gas Analyst) Program Director, and was responsible for the redesign of the program. TOGA is an Internet-based analytic program that performs asset management services for more than $520 million of equipment. Paul has a M.B.A. degree and is a member of the Institute of Electrical and Electronics Engineers (IEEE).

Disclaimer statement:

All recommendations are general guidelines and are not intended to be exhaustive or complete, nor are they designed to replace information or instructions from the manufacturer of your equipment. Contact your equipment service representative or manufacturer with specific questions.

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