White Paper
By Francisco de León, CYME International T&D

Abstract - This paper introduces the heat transfer mechanisms in underground cable installations and analyzes the available solution methods of the diffusion equation. The heat sources and thermal resistances of the different layers of a cable installation are described. The basic concepts behind the Neher-McGrath method (IEEE) are discussed, along with its differences with the IEC standards for underground cable installations. The available commercial computer programs, designed to perform ampacity calculations are listed along with a description of the modeling capabilities of CYME's CYMCAP.

This paper is part of the Wire and Cable Handbook, Vol. 1, published by The Electricity Forum, which regroups 22 focused articles exploring the many aspects of predictive electrical maintenance.

 White Paper
By Francisco de León, Patrick St-Roch and Christian Beauregard, CYME International T&D

Abstract - The Cable Historical Operating Temperature Estimator (CHOTE) is an innovative way to evaluate the temperature at which underground cable systems have operated during their in-service life. Engineers need answers to the following questions:

• Which cables have exceeded their normal operating temperature and for how long?
• Which cables have exceeded their emergency temperature and for how long?
• Given a predicted load growth: when in the future cables will reach their maximum design temperature.

CHOTE analyzes automatically all the thermal section of a system. This may include transmission and the entire distribution system (manhole-to-manhole). The input to the temperature estimator is the archived loading information usually available through the SCADA/PI. As output CHOTE produces a list of cable sections that have exceeded the normal and/or emergency target temperatures.

This paper was presented at the North American Transmission and Distribution Conference, June 13-15, 2006, Montreal, Canada