In electrical engineering, the Ferranti effect is an increase in voltage occurring at the receiving end of a long transmission line, above the voltage at the sending end. This occurs when the line is energized, but there is a very light load or the load is disconnected. The capacitive line charging current produces a voltage drop across the line inductance that is in-phase with the sending-end voltage, assuming negligible line resistance. Therefore, both line inductance and capacitance are responsible for this phenomenon.
The Ferranti Effect will be more pronounced the longer the line and the higher the voltage applied. The relative voltage rise is proportional to the square of the line length and the square of frequency.
The Ferranti effect is much more pronounced in underground cables, even in short lengths, because of their high capacitance.
- Ferranti Effect handout, Kathmandu University (internet archive)[dead link]
- Line-Charging Current Interruption by HV and EHV Circuit Breakers, Carl-Ejnar Sölver, Ph. D. and Sérgio de A. Morais, M. Sc. Archived January 26, 2007, at the Wayback Machine.
- A Knowledge Base for Switching Surge Transients, A. I. Ibrahim and H. W. Dommel Archived May 12, 2006, at the Wayback Machine.
- J. F. Wilson, Ferranti and the British Electrical Industry, 1864-1930, Manchester University Press, 1988 ISBN 0-7190-2369-6 page 44