When a HV circuit breaker is subjected to an earthquake, the motion of the ground will induce oscillations in the circuit breaker with corresponding mechanical stress. The mechanical stress will normally be most severe at the lower end of the support column. The circuit breaker will have one or more natural oscillation frequencies, eigenfrequencies, where the predominant one is typically a few Hz. Since the frequency of typical earthquake oscillations is also of the order of a few Hz, the actual stress on the breaker may be is amplified due to mechanical resonance. The degree of amplification depends on the eigenfrequency (natural oscillation frequency) and damping of the circuit breaker, and may be deduced from response spectra,published e.g. by IEC.
High Voltage Products
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