Power Cable Ratings and Soil Considerations

Presented jointly by:
Power Delivery Consultants, Inc.
Geotherm, Inc.

Ampacity Is Important ! Underground cables generally have lower ratings than the utility's overhead lines - and the dollars per ampere are much higher.  Over-designing is costly - and under-designing is very costly.  It is therefore desirable to confidently rate the cables near their ultimate limit.

Important issues include:

The PDC/Geotherm ampacity course, which has been presented to more than 200 engineers in the last six years, addresses these and many more ampacity issues.   The course provides good analytical background, plus important hands-on experience in mixing controlled backfills and performing soil thermal property measurements.

Overview: Cable ampacity analysis has assumed new importance in the last several years, as first-time users need to evaluate underground cable alternatives, as guided boring has become an accepted installation method, and as the use of submarine cables increases.

Material: The course will focus on discussing various topics regarding ampacity and the effects of soil - the most significant variable and often the least understood - on ampacity, installation design and operation.  While PC-based ampacity programs exist, a good understanding of the ampacity techniques (e.g., Neher-McGrath, IEC-287/853) is extremely important. Trench optimization is becoming more common as utilities attempt to obtain the most amperes from a cable.  More attention is being paid to proper modeling of daily, weekly, and even monthly load shapes to take into account "cool-down" periods during load cycling, which permit higher loading during peak periods.  The earth gives the largest single thermal resistance and thermal capacitance, and it also has by far the greatest variability-with distance along the route, and even with time.  Earth thermal resistance can easily vary threefold on a specific circuit, and the cable must be rated for the worst-case condition. Recent improvements in thermal measurement instruments and techniques, coupled with a better understanding of soil mechanics and innovations in controlled backfill-such as Fluidized Thermal Backfill-permit much better representation and control of the earth thermal circuit, with the resulting ampacity increases.

Expected Learning Objectives/ Outcomes

PDC has identified learning objectives we expect each student to obtain on completion of this course.  The student completing this course should be able to:
  1. Perform a basic ampacity (cable rating) calculation using a hand calculator.
  2. Understand the importance of soils and list the thermal characteristics that should be considered for cable ratings.
  3. Describe the basic cable components, including the functions of the conductor and insulation.
  4. Describe the impact of dielectric losses, system voltage and insulation material on ampacity.

Participants: This course is intended for engineers and field personnel concerned with planning cable systems, calculating ampacity, performing soil thermal analysis, and insuring field quality control.  Experience in ampacity calculations is not necessary.  Much of the course content is devoted to developing a thorough understanding of the earth thermal resistance, capacitance, and stability.  Theoretical analysis, practical applications, and hands-on measurements are provided. Samples of Fluidized Thermal Backfill are prepared and tested in the classroom.

Course Topics

Notes   We provide a comprehensive set of course notes, more than 400 pages long.

This course will be held at the:
Alden Beach Resort
5900 Gulf Boulevard
St. Pete Beach, FL 33706
A block of rooms has been reserved at the hotel at a special rate which will be honored for several days before and after the course.  Reservations must be  made 30 days in advance to obtain this low rate.   Please mention the PDC Ampacity Course when you make reservations.  The hotel is on the Gulf of Mexico, near many restaurants, etc. [map]

Instructors for the course may include:
Jay Williams , Principal Engineer, Power Delivery Consultants, Inc. Mr. Williams has been conducting ampacity analyses for more than 40 years. He developed the original EPRI ACE program for ampacity calculations for underground cable systems, and conducts several ampacity studies for utilities and others each year.
Deepak Parmar, President, Geotherm, Inc. Mr. Parmar has specialized in soil thermal analysis and soil mechan-ics for more than 25 years.  He has performed soil thermal analyses throughout the world, and has taught several dozen seminars on soil thermal analysis. He performs field surveys and laboratory analyses, and provides soil thermal test equipment.

Continuing Education Units
PDC will issue students a course certificate indicating the number of Continuing Education Units for the course completed based on national guidelines and the number of classroom hours.  1.8 Continuing Education Units (CEUs) will be awarded for successful completion of this course. The CEU is the nationally recognized unit for recording participation in noncredit educational programs. One CEU is equal to ten classroom hours.

Tuition and Enrollment:
The tuition cost includes enrollment, a comprehensive set of course notes, breakfast, lunch, and coffee breaks.