Early Time (E1) High Altitude Electromagnetic Pulse Effects on Lightning Surge Arresters and Trip Coils

A High Altitude Electromagnetic Pulse (HEMP) is a potential threat to the power grid. HEMP can couple on transmission lines causing large overvoltages, which could be harmful to the line and everything else connected to it. The effects of overvoltages on all sorts of devices in the power grid need to be understood. The work developed here is a joint effort between The University of New Mexico and Sandia National Laboratories; The devices that are within the scope of this effort are Trip Coils and Lightning Surge Arresters (LSA). Existing data on HEMP, existing standards, and a previous analysis, were used to determine the wave shape, rise time, and pulse width characteristics of the transient to be replicated. The estimated rise time of the conducted insult is within the range of 10ns to 20ns and the pulse width within the range of 30ns to 75ns. The Lightning Surge Arrester (LSA) devices were tested with two existing pulsers, both different and selected based on the compliance with the rise time or pulse width needed. The tests performed with both pulsers resulted in similar results; the two tests were conducted with varying voltage magnitudes ranging from 5 kV to 50 kV. A degradation test was performed after the LSA was exposed to the insults an approximate total of 150 times, the degradation test consisted of measuring the response to a particular insult before and after several insults and comparing the diagnostics, which comprise voltage and current readings for each LSA. A pulser was designed and built for the Trip Coil test, with the objective of generating a transient that meet both requirements, rise time and pulsewidth; analytic solution, simulation, and experimental data are provided to prove the adequate performance of the pulser for this task. The rise time achieved was 12.3 ns, and the pulse width was 52 ns. The Trip Coils were tested multiple times, with pulses varying in magnitude from 20 kV up to 80 kV. The state of health (SOH) of the Trip Coils was measured before and after the insult, which facilitates the identification of any damage or degradation. This state of health measurement comprises a peak force measurement using a force gauge, and an internal impedance measurement, using a vector network analyzer and an LCR meter. Impedance is presented as plots, where it is measured and displayed in a wide frequency range. The force measurement results are presented in a graph indicating the device number and the measured force before and after the insult. Diagnostics for the Trip Coils include current and voltage measurements, and a camera which captures open shutter images of the breakdown. The camera setup generated pictures of a visible discharge present in the outer part of the Trip Coil casing. The combined results obtained from the testing suggested that the Trip Coils exhibited insulation degradation. However, no functional damage was detected. Meaning that even though physical damage is evident from the waveforms, it did not affect the performance of the coil operating at the rated voltage and current