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The Problem: A major railroad company modernizing their signal system for controlling train traffic discovers that the new electronic equipment is more sensitive to lightning damage than the older signals control technology. Safety is endangered because of damaged signals systems and money is lost because of stopped trains and equipment replacement.

The Need: A better surge arrestor with reduced levels of voltage and current leaking through to equipment. The new arrestor must also satisfy  the railroad's safety needs and fit into the form factor defined by tens of thousands of existing installations.

EMA's Solution: Design a hybrid arrestor with 2 levels of protection, a fail-safe fuse and trip indicator that fits in a standard AAR package. The key components are:

1. A spark gap to handle the high levels of current surges with some delay.
2. An metal oxide varistor (MOV) to handle the initial lower levels of current surges until the spark gap fires.
3. An inductor providing transient isolation of the fast-acting low-level MOV from the slower-acting high-level spark gap.

EMA constructed prototypes and subjected them to extensive testing for both performance and reliability. The plots below show the dramatic reduction in voltage from over 2200 V using the old air gap surge arrestors to less than 60 volts using the new two-stage hybrid arrestor designed by EMA.

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page last modified 6/29/2006