Electrical fast transient tests: applications and limitations

The IEC Electrical Fast Transient (EFT) test was performed on two line configurations selected as typical of low-voltage power lines: a three-conductor line in a steel conduit and a three-conductor cable with a nonmetallic jacket. An attenuation model that provides a tool for understanding the significance of the line parameters and extends the usefulness of results to general cases is proposed. The two line configurations and their models yield similar results for measurements and for computations. Some differences might be expected between the quasi-coaxial configuration of a conduit-enclosed line and the open-line configuration with unshielded conductors of a nonmetallic jacket. The effects of propagation of an EFT pulse in the lines are a reduction in the amplitude, a decrease in the steepness of the front, and an increase in the duration of the pulse. The first two effects reduce the severity of a pulse arriving at the victim equipment; the third effect is less significant for victim equipment sensitive to rate-of-change disturbances. It is concluded that equipment likely to be installed close to sources of EFT pulses would benefit from immunity demonstration.<>