US 4,068,273 AGranted

Hybrid power switch

AssigneeInternational Telephone and Telegraph Corporation

InventorAlbert Metzler

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Abstract

A hybrid AC power switching arrangement in which two ganged switch banks in series are employed along with a pair of reverse parallel (back-to-back) SCRs across each contact pair of the second switch gang. SCR control means and interlock control means are provided so that the first switch gang (closest to the power source) closes first, energizing the SCR control and permitting the SCRs to conduct load current in a corresponding phase leg, beginning at or near a zero voltage cross-over point. After all phase legs are conducting through the SCRs, the second switch gang is closed bypassing the SCRs. On circuit break, the second switch gang (i.e., the one closest to the load) is opened first, the load current diverting immediately through the SCRs for another interim period until the SCRs in each individual phase leg are extinguished as the instantaneous current in the corresponding phase lead passes through or near zero. The first switch gang is then opened to completely disconnect from the line to insure against spurious SCR operation thereafter.

Claims7

Dependent claims

An AC electric power switching device for automatically energizing and deenergizing a three-phase power circuit in response to a corresponding single manual action for each of said energizing and deenergizing functions, comprising:

first and second switch banks in series between a power source and a load with said first switch bank being nearest said power source, said first switch bank comprising three pairs of switch contacts, one to each phase line, said second switch bank comprising two pairs of switch contacts with one pair to each of a predetermined two of said three phase lines;
electronically controllable means comprising a pair of solid state devices of the thyristor family, one of which is connected in parallel with each of said second contact pairs in said two predetermined phase lines, the phase line other than said predetermined two being connected directly from a corresponding contact of said first switch bank to said load;
first means activated by closing of said first switch bank for initiating current conduction in each of the current-carrying paths provided by said electronically controllable means when the instantaneous phase voltage is zero within a predetermined ignition tolerance in the corresponding phase line of said sources, said first means also including circuits for closing said second switch bank after a predetermined delay time to bypass current around said electronically controllable means in each of said current-carrying paths, said first means further including circuits for causing interruption of current in each of said paths as said electronically controlled means senses zero instantaneous current within a predetermined tolerances after said second switch bank has been opened to begin the disconnect process;
and second means for opening said first switch bank after a second predetermined delay time after all of said current-carrying paths through said electronically controlled means have interrupted at said zero instantaneous currents.

1 more element

A hybrid switching system for energizing and de-energizing a load from an AC source of at least single phase substantially without switch contact erosion, comprising:

first means including a first switch gang including at least one pair of first switch contacts for each phase of said AC source, said contact pairs each being in series with a lead corresponding to one voltage phase between said source and said load;
second means including a sufficient number of pairs of ganged second switch contacts each arranged in series with a corresponding one of said leads between said first means and said load to make and break all current paths between said source and said load;
third means comprising a solid state switchable conduction device for providing controllable separate current paths in parallel with each of said second contact pairs, said solid state devices being responsive to control signals for separately controlling the shunt conductivity thereby provided in parallel with each of said second contact pairs;
fourth means oprative upon closure of said first means switch gang for generating said control signals in a sense causing said third means solid state devices to conduct beginning after closure of said first means switch gang, said fourth means being responsive to the voltage across each of said second switch contact pairs to generate and apply a discrete control signal to the corresponding third means solid state device beginning substantially when the instantaneous AC voltage across said corresponding second switch contact pair is substantially zero, thereby energizing said load through said third means when said switch contacts of said first means have been closed;
fifth means responsive to closure of said switch contacts of said first means for closing said ganged second switch contacts, said fifth means including delay means whereby a first transition time is allowed after which said second switch contacts are closed in parallel with said third means, and
sixth means for preventing the opening of the contact pairs of said first means for de-energizing said load before the expiration of a second transition time after opening of said contact pairs of said second means;
and also including means responsive to the opening of said second means contact pairs and to the current flowing through each of said contact pairs of said second means for interrupting said fourth means control signals to each of said third means solid state devices at the time the instantaneous current in the corresponding third means element passes substantially through zero.

4 more elements

Dependencies are inferred from the claim text.