HEMP Transformer Defense Through Power Electronics
High altitude electromagnetic pulse (HEMP) generated by exoatmospheric nuclear burst has the ability to affect the electric power grid. The main power grid components, cables and transformers, act as large antennas that have current induced in them from the HEMP. These currents are called geomagneticallyinduced currents (GIC), and they can occur during geomagnetic disturbances from HEMP or solar flares. HEMPs produce pulses with high electric field strengths that breakdown the dielectric of most electronics and, it is broken into three stages: E1 pulse with a microsecond width, E2 the falling trail of the pulse, and E3 a constant DC component. Oak Ridge National Laboratory has proven that transformers fitted with lightning arrestors do not receive damage from E1 and E2 pulses. However, the DC component of the E3 causes the transformer’s core to saturate and induce rapid heating that damages the transformer. SRNL is developing a power electronic system that is connected to the neutral of the high voltage side of large power transformers (LPT). This system will inject the inverse of the DC effect from the HEMP into the primary side of the transformer canceling out the E3 waveform and protecting the transformer from half-cycle-saturation. This year SRNL successfully simulated removing the DC injected and accurately simulated saturation on the transformer.