Abstract: This surge arrester is for protecting against high-energy and very fast surges and comprises first and second electrodes and a metal oxide varistor (MOV) disk between the electrodes. Each electrode has a central region and, at generally diametrically-opposed sides thereof, a source terminal and a load terminal. The terminals of each electrode are connected in the protected circuit in such a manner that load current in each of the conductors of the protected circuit flows through the electrode via a path that extends in series through the source terminal, the central region, and the load terminal. The source terminals of the two electrodes are generally aligned with each other about the periphery of the MOV disk, and the load terminals are also generally aligned with each other about the periphery of the disk.

Abstract: For evaluating the condition of a first lightning arrester of the gapless metal-oxide varistor type that is connected across the high voltage winding of a transformer, I connect externally of the transformer a second arrester of the same type, but with means for selectively changing its breakdown voltage between a first value that is higher than the normal breakdown voltage of the first arrester and a second value that is lower than said normal breakdown voltage. Pulses are applied to the low voltage winding of the transformer while the second arrester has its breakdown voltage set at the first value and while said breakdown voltage is set at said second value. By determining whether or not the second arrester conducts in response to each of these pulses, it can be established whether the first arrester is then undamaged, damaged in a shorted mode, or damaged in an open mode.

Abstract: To record significant discharges of a surge arrester, the energy dissipated in a separate varistor element equivalent to the varistor elements in the arrester and connected in the arrester discharge path is monitored. When an arrester discharge results in a temperature increase above a predetermined minimum in the separate varistor element, heat sensing means thermally coupled therewith triggers a counter to record the event.

Abstract: A zinc oxide varistor disc is provided with one or more circumferential recesses in its rim to reduce the current density at the edges of the electrodes on the opposed disc faces, which electrodes are of a lesser diameter than the varistor disc. It has been discovered that optimum results are achieved when the diameter at the bottom of the recess is somewhat less than the diameter of the electrodes.

Abstract: A high voltage varistor for DC operation is manufactured by applying a glass collar to the perimeter of a sintered zinc oxide disc and heat treated between about 750.degree. C. and 400.degree. C. for several cycles in air. After heat treating, an organic resin or ceramic coating is applied to the glass collar to further insulate the varistor for high voltage application.

Abstract: Capacitance grading is provided within gas insulated lightning arresters containing stacked zinc oxide varistors by means of a grading ring electrically connected to the line terminal or, for arresters of the higher voltage ratings, by means of a plurality of telescoping external electrostatic shields. The shields are arranged so that the degree of overlap between sequential shields decreases from the line end to the ground end of the varistor stacks. The capacitance grading is provided by the degree of overlap between the sequential shields and the ratio of the radii of the overlapping shields.

Abstract: A high voltage varistor for DC operation is manufactured by applying a glass collar to the perimeter of a sintered zinc oxide disc and heat treated between about 750.degree. C. and 400.degree. C. for several cycles in air. After heat treating, an organic resin or ceramic coating is applied to the glass collar to further insulate the varistor for high voltage application.

Abstract: Zinc oxide varistors are thermally treated, after sintering, at temperatures between 400.degree. C. and 800.degree. C. in air for a period of one to ten hours. The thermal treatment apparently removes residual strains resulting from the sintering process and substantially reduces voltage drift.

Abstract: Voltage surge arrester devices having predetermined shunt gap sparkover voltages are provided by the series combination of high- and low-exponent varistors. In one embodiment the high-exponent varistor comprises zinc oxide and the low-exponent varistor comprises silicon carbide.

Abstract: Zinc oxide varistor protective devices for vapor cooled transformers are integrally located in contact with the transformer coolant liquid to provide cooling capacity to the zinc oxide materials. The zinc oxide varistors are prevented from becoming electrically unstable by keeping the varistor operating temperature at or below the boiling point of the coolant.

Abstract: The arrester comprises an insulating housing with end terminals and a plurality of varistors inside the housing electrically connected between the terminals. The varistors are provided individually or in groups with a heat transfer and sinking collar which is electrically insulating and thermally conducting. The collar may be in thermally conducting contact with the inside wall of the housing to improve heat dissipation to the housing. The configuration of the collar is such that when it is installed in the housing, there is a passageway through it to provide a longitudinal space in the arrester for accommodating arcing and for the venting of gas in the event of an arrester failure.

Abstract: A process for making overvoltage surge protection varistors of the zinc oxide type includes the steps of:A. sintering a varistor body at an elevated temperature of at least about 1100.degree. C; thenB. cooling the body to a temperature below about 400.degree. C; thenC. reheating the body to a temperature below about 700.degree. C; thenD. recooling the body slowly to a temperature below about 400.degree. C; and thenE. repeating at least once the steps (c) and (d)For improving the current stability of the varistor under alternating voltage stresses while preserving the level of current leakage through the varistor.

Abstract: The arrester includes a valve section made up of high current-voltage characteristic exponent metal oxide varistor valve blocks having a relatively high capacitance and a series gap section made up of simple gap units, the gap section carrying less than about one fifth of the total arrester voltage during a discharge. The valve blocks of the valve section are each provided with a parallel-connected bleeder resistor to adjust the time constant of the valve section so that the faces of the valve blocks are returned to a common potential within a time interval of between about one and about two milliseconds for allowing sufficient deionization of arc gases without degrading multiple lightning surge performance.

Abstract: A metal oxide resistor of the type consisting essentially of zinc oxide and containing significant amounts of the impurities bismuth trioxide, cobalt trioxide, manganese dioxide, antimony oxide, chromic oxide, and silicon dioxide contains also significant amounts of the impurities barium oxide and boron oxide.

Abstract: A plurality of series connected main spark gaps are connected in shunt circuit relation with a voltage grading impedance network which includes a trigger gap that is connected though frequency responsive coupling means in shunt relation with approximately one-half of the series connected main spark gaps. The trigger gap is operative, as a substantially linear function of a voltage impressed across the series connected gaps, to cause the main gaps to spark over in cascade fashion. The triggered control network allows use of a large number of main gaps but with a controlled total sparkover very much less than the sum of the sparkover of the individual main gaps, thus, providing a desirably high ratio of reseal voltage to sparkover voltage for the main gap series circuit.