US 4,023,071 AGranted

Transient and surge protection apparatus

OwnerGerald W. Fussellinventor

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Abstract

Apparatus is disclosed for absorbing and dissipating the electrical energy present in voltage transients and surges occurring in a power distribution system for protecting the system and equipment connected thereto from damage due to such transients and surges. First bilateral nonlinear semiconductors having zener-type voltage breakdown characteristics and capability of essentially instantaneous breakdown for inputs exceeding a selected voltage breakdown are connected in parallel with the circuits to be protected. Such semiconductors have low energy-dissipating capability; therefore, second bilateral nonlinear semiconductors having much greater energy-dissipating capability, similar voltage breakdown characteristics, and slower response time are connected in parallel with the first semiconductors. The breakdown of the second semiconductors occurs in time to prevent the first semiconductors from being damaged from excessive dissipation. A gaseous discharge gap-type arrestor is connected essentially in parallel with the first and second semiconductors and has a selected striking voltage appropriate to the breakdown voltages of the semiconductors.Upon firing of the arrestor, the voltage is dropped to a very low value and the remaining surge energy is dissipated in the arrestor. Firing of the arrestor occurs after the breakdown of the second semiconductor in time to prevent the dissipation capability of the second semiconductor from being exceeded. The cooperative and consecutive breakdown of the three elements serves to limit the peak voltage of a surge to a safe value and dissipate the surge energy without damage to the elements, thereby preventing damage to the power distribution system and associated equipments.

Apparatus for protecting electrical power systems and equipment connected thereto from damage due to voltage transients and surges that exceed the maximum instantaneous peak voltages of the systems, comprising:

first electrical energy-dissipation means having a first breakdown voltage slightly greater than the maximum instantaneous peak voltage, said first means responsive essentially instantaneously to a voltage surge exceeding such first breakdown voltage, to dissipate a first portion of energy contained in such surge;
second electrical energy-dissipation means having a selected second breakdown voltage slightly less than said first breakdown voltage of said first means, said second means responsive after a selected first delay period to such voltage surge to dissipate a second portion of energy contained in such surge, causing the voltage across said first means to drop below said first breakdown voltage whereby said first means ceases to dissipate energy with said first delay period selected to limit the energy-dissipation in said first means to a value within the dissipation capability of said first means, said second means being electrically connected to said first means;
third electrical energy-dissipation means having a selected third breakdown voltage essentially equal to said first breakdown voltage, said third means responsive after a selected second delay period to such voltage surge to dissipate the remaining energy contained in such surge, causing the voltage across said second means to drop below said second breakdown voltage whereby said second means ceases to dissipate energy with said second delay period selected to limit the energy dissipated in said second means to a value within the dissipation capability of said second means, said third means being electrically connected to said second means;
and
wherein said first, second, and third electrical energy-dissipating means are electrically connected to an electrical power system whereby said first, second, and third means cooperate to dissipate the energy of said voltage surge without damage to said first and second means thereby preventing such voltage surge from exceeding a value slightly greater than the maximum instantaneous peak voltage of such power system.

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Abstract

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