Notificaciones sobre tratamiento de datos efectuado por el Operador del Sistema

ABSTRACT

Mississippi Power Company has been a leader and trend-setter in finding new and better ways to increase customer satisfaction. For this reason, we implemented a program of infrared thermo- graphic inspection using infrared thermal imaging cameras, on all the electrical equipment in our facilities, including all of our 750 KVA to 2500 KVA padmount trans- formers, one of which had failed disastrously.

During a survey of these trans- formers, I detected thermal prob- lems with more than 30% of the 400 scanned, all associated with the high side elbow connection. Further investigation related the failure mechanisms to improper installation techniques during both the original installation and the routine preventive-maintenance replacement of the elbows.

Using newer improved equip- ment and holding training classes on proper installation and removal of this equipment, we reduced the occurrence rate of these anoma- lies from 30% to less than 2%. Our management authorized the pur- chase of an additional infrared camera, also known as a thermal imaging camera.

This paper describes the pro- gram and the findings, explains the diagnostics and illustrates the contrast between properly and improperly installed equipment.

1. INTRODUCTION

Mississippi Power Company began doing infrared scans, using an infrared thermal imaging cam- era in 1994, as a support service to our industrial and commercial customers. Over the past several years, we have come to realize the value of using infrared ther- mal imaging cameras to find and solve problems for our customers as well as for ourselves. Being proactive, our department added more people to keep up with the

increased needs of our customers and to provide the best reliable service to our customers. We did this by purchasing additional in- frared thermal imaging cameras and increasing the scope of work to include infrared scans of our substations, feeders and all of our padmount transformers rated from 750KVA up to 2500KVA. We now have three infrared thermal imaging cameras in Mississippi Power Company.

Padmount transformers are transformers that are sealed in metal containers and filled with oil. They are used to step up or down the output voltages depend- ing on customer needs. They range in size form 50KVA to 2500KVA and vary in shape. The main reason for using padmount transformers is that they offer a wide selec- tion of load capacity in modular, encapsulated form. Other reasons include esthetics and safety; in designated areas such as in sub- divisions, encapsulated padmount transformers are safer to operate and can be placed underground, where they are out of sight and impervious to falling trees and other hazards.

The elbow problems that we found and identified with the use of the Infrared camera were put into three categories for the pur- pose of identifying, tracking and repairing the problems. They are contact, probe and crimp prob- lems. With the use of the infrared camera and through training we have reduced the problems from 30% to less than 2%.

2. CLASSIFICATION OF

PROBLEMS

My job consists of doing in- frared scans for customers, on padmount transformers and on our feeders. Since additional personnel were assigned to the department, I have been able to concentrate on padmount trans- formers more than was possible in

Infrared

Diagnostics

On Padmount

Transformer

Elbows

Jeff Sullivan,

Mississippi

Power Company,

Hattiesburg, MS

the past. I have used this opportunity to track and record the data from my findings. As it turned out, I discovered that we have a serious ongoing problem with padmount transformer elbows. With 400 transformers scanned, I found that 30% of the padmount transformers had an elbow problem. With ex- perience gained from working in electrical substations for 12 years as an electrician, and from other sources, I was able to determine what caused the problems and how to correct them. After reviewing them, I classified them into three categories, contacts, probes and crimps.

The first category is the contact problem. This occurs when the female bushing is replaced after a failure. If grease is applied incorrectly on the stud of the internal winding of the transformer, when the female bushing is threaded onto the stud, it forces the grease into the contacts of the female bush- ing. When the transformer is energized, the grease heats up, turning into a liquid and acting like a hydraulic pump, forcing the probe backwards. This action causes the contacts to arc and eventually burn up. Similar heating will occur if the elbow is not properly seated when installed. Fig. 1 illustrates two examples of an elbow that is not properly seated due to a me- chanical error or grease being applied improperly.

The second problem category is the loose probe; related to the method of removing the elbow from the transformer after the unit had been in service. When an elbow has been installed for a period of time, it creates a vacuum or suction due to the load of the transformer. To remove the elbow from the transformer, it has to be twisted back and forth several times to break the vacuum or suction it had created due to load changes. Each time the elbow is twisted counterclockwise, it causes the probe to loosen from the threaded crimp and even- tually causes the probe to burn up. Through proper training and the use of a ring stick with a slide weight on it, the elbows could be removed by one person and installed properly, there- fore practically eliminating this problem. Fig. 2 illustrates two examples of loose probes.

The third problem category concerns the crimp on the un- derground dip wire. There are two different problems associ- ated with the crimp. The first occurs when the wrong size crimp is used. The second occurs as a result of an improperly executed crimp connection. Either one will cause overheating that will lead to a failure. Fig. 3 is an example of the result of a bad crimp connection.

3. CONCLUSIONS AND COST AVOIDANCE SUMMARY

Through the use of the infrared camera, we have found and solved problems that would have been disastrous if they had not been detected in time. One of the best results of doing infrared scans is that it has allowed Mississippi Power Company to greatly improve customer relations in dependability and re- liability. Unscheduled outages are a big problem to a company like ours, and by using the infrared camera in routine predic- tive maintenance we perform, we have greatly reduced our customers’ outages.

If a padmount transformer elbow were to fail for one of our

larger customers, the average time to get the customer back to 100% production would be about four hours of outage time. Several of our customers estimate their losses to be about $1,000 a minute when they are out of power due to an elbow failure problem. This computes to a $240,000 customer loss for an outage.

By using the infrared camera to find the problems, identify and fix the problems on a controlled outage situation, Missis- sippi Power Company and our customers have shared in the rewards. The elbow problems found on padmount transformers were found, identified and fixed, reducing the problem by 28% through proper training of everyone involved with installation and removal of padmount transformer elbows. This saved Mis- sissippi Power Company from loss of revenue, having to pay overtime and from destruction of expensive equipment, there- by improving customer relations and satisfaction. Also, the customer benefited greatly from Mississippi Power Company being proactive by offering infrared services to them. The bot- tom line is that the infrared camera is a win/win for everyone. It is one of the best purchases a company can make. Not having an Infrared camera in our business would be like going back into the Stone Age.

Figure 1. Two examples of heating on a padmount transformer due