Saturable reactor current limiter

A direct current limiter comprising:

• a first leg of magnetically saturable material;
• a second leg in flux transfer relationship to said first leg;
• means for biasing said first leg into saturation;
• a winding wound on said first leg and arranged to provide said first leg to be saturated at normal current level flow through said winding and to be driven out of saturation by an abnormally high transient current flow;
• said second leg providing a flux shunting path for said first leg.

A direct current limiter comprising:

• an C-shaped saturable magnetic core with end surfaces defining an air gap therebetween;
• a permanent magnet bridging the inside of said core to bias an elongate center portion into saturation and set a low level of flux in a remaining air gapped portion;
• a winding wound on said center portion arranged to provide said center portion to be saturated at normal current level flow through said winding and to be driven out of saturation by an abnormally high transient current flow;
• said air gapped portion providing a flux shunting path for said center portion.

A direct current limiter comprising:

• a C-shaped high permeability saturable core;
• an I-shaped low permeability section bridging the ends of said core;
• a permanent magnet bridging the inside of said core to bias a center portion of said core into saturation and set a low level of flux in said low permeability section;
• a winding on said center portion arranged to provide said center portion to be saturated at normal current level flow through said winding and to be driven out of saturation by an abnormally high transient current flow;
• said low permeability section providing a flux shunting path for said core.

An alternating current limiter comprising:

• a continuous high permeability saturable core having first and second opposing legs;
• a permanent magnet centrally bridging the inside of said continuous core to bias said first and second legs into saturation;
• a C-shaped magnetic core centrally bridging the outside of said continuous core to provide a low permeance magnetic path in parallel to said first and second legs;
• a winding having a first section wound on said first leg and a second section wound on said second leg;
• said winding arranged to provide said first and second legs to be saturated at normal levels of alternating current flow and to be alternately driven out of saturation by abnormally high alternating current flow.

A device for limiting current in an electrical circuit comprising:

• A. a multiple branch element magnetic circuit including:
• i. a bridge network having at least four nodes and a pair of upper leg elements joined at one end at a first of said nodes, a pair of lower leg elements joined at one end at a second of said nodes, and a cross element having one of its ends joined to one of said lower and upper leg elements at a third node, said cross element having the other of its ends joined to the other lower and upper leg elements at a fourth node,
• wherein said upper and lower leg elements joining said third node are characterized by non-linear permeances P.sub.A and P.sub.B, respectively, and have saturated and non-saturated states, P.sub.A and P.sub.B being greater when the corresponding one of said third node leg elements is in its non-saturated state than when in its saturated state, and the magnetic flux density in one of said third node leg elements being equal to a saturation flux density which is relatively invariant with respect to magneto-motive force applied across that element when in said saturated state and said magnetic flux density being less than said saturated flux density otherwise, and
• wherein the flux path between said first and third nodes along said cross-element and said upper leg element joining said fourth nodes is characterized by a permeance P.sub.C, and the flux path between said second and third nodes along said cross element and said lower leg element joining said fourth node is characterized by a permeance P.sub.D,
• ii. a magnetic bias element connected between said first and second nodes, said bias element being characterized by a permeance P.sub.E and including a magneto-motive force (mmf) bias means for establishing a substantially constant magnetic flux density in said bias element, and
• B. an input coil including means for electrically coupling said device to said electrical circuit so that said current passes therethrough, said coil having a plurality of windings extending about said cross element so that magnetic fluxes induced in said cross element in response to said current,
• wherein said elements are magnetically coupled at said nodes, and
• wherein P.sub.C and P.sub.D are relatively high with respect to the medium external to said device, P.sub.A and P.sub.B are greater than P.sub.C and P.sub.D and are relatively high with respect to the medium external to said device when the respective third node leg elements are non-saturated, and P.sub.E is relatively low with respect to P.sub.C and P.sub.D and with respect to P.sub.A and P.sub.B when the respective third node leg elements are non-saturated,
• wherein further the net magnetic flux density in one of said third node leg elements is equal to the saturation flux density for that element when said current is below an upper threshold value and said net flux density is below said saturation flux density when said current is in a predetermined range above and extending from said upper threshold value, and
• wherein further the net magnetic flux density in the other of said third node leg elements is equal to the saturation flux density for that element when said current is above a lower threshold value, and said net flux density is below said saturation flux density when the magnitude of said current is in a predetermined range below and extending from said lower threshold value.