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US 7,119,467 B2Granted
Current limiting means for a generator
AssigneePratt & Whitney Canada Corp.
InventorKevin Allan Dooley
Life of this patent
Estimating the term…
Abstract
The invention provides means of limiting maximum current conducted through windings of an electric machine having a rotor and a stator. By encouraging an appropriate leakage flux around a winding, a leak impedance can be achieved which may be used, according to the invention, to limit the maximum current in the winding as a matter of machine design.
Claims40
An electric machine operable as an alternator, the machine comprising:
- a moveable magnetic rotor assembly;
- and
- a stationary stator assembly mounted adjacent the rotor assembly, the stator assembly including at least one electrical winding disposed in at least one slot defined in the stator assembly, the at least one electrical winding being electrically connected to a machine output adapted to deliver generated output electricity from the machine, the slot having an upper end, the slot upper end having a shape and construction, the slot upper end being disposed between the at least one winding and the rotor,
- wherein, in use, movement of the rotor assembly induces a first alternating voltage and current in the at least one winding,
- and wherein, said slot upper end shape and construction have an associated inductance which is sufficiently high relative to said induced alternating current such that, in use, a magnetic flux flows through said slot upper end and around the at least one winding in response to said induced alternating current in said winding, thereby inducing a second alternating voltage and current in the at least one winding opposite in polarity to said first alternating voltage and current, thereby limiting an output current in the at least one winding to a pre-selected value.
2 more elements
An electric machine operable as an alternator, the machine comprising:
- at least one primary magnetic circuit, the primary magnetic circuit at least partially defined by a stator assembly, a rotor and a plurality of permanent magnets mounted to the rotor, the rotor mounted adjacent the stator assembly and adapted for movement relative to the stator assembly, the stator assembly having at least one electrical winding disposed in at least one slot defined in the stator assembly, the at least one electrical winding electrically connected to a machine output adapted to deliver generated output electricity from the machine, wherein, in use, relative movement between the rotor and the stator assembly causes a primary magnetic flux to flow around the primary magnetic circuit, the slot and winding being disposed in the stator assembly such that, in use, the primary magnetic flux flowing around the primary magnetic circuit induces a primary voltage across the winding and an associated alternating current flow in the winding to thereby deliver output electricity from the machine;
- and
- at least one secondary magnetic circuit defined in the stator assembly and encircling the winding within the stator assembly, the secondary magnetic circuit at least partially defined by the slot, wherein the secondary magnetic circuit has a magnetic inductance which is sufficiently high such that, in use, said induced alternating current in the winding induces a secondary magnetic flux of sufficient magnitude to flow around the secondary magnetic circuit to thereby induce a secondary voltage across the winding opposite in polarity to the primary voltage and of sufficient magnitude to limit a maximum current flow in the winding to at least a desired maximum current flow limit.
An electric machine comprising:
- a stator, the stator having a plurality of spaced-apart teeth, a core portion, a plurality of slots defined at least in part by the core portion and pairs of adjacent said teeth, the stator additionally including at least one slot top portion extending between a first pair of adjacent teeth to substantially close at least one of said slots, the slot top portion having a shape and construction;
- a magnetic rotor mounted adjacent the stator for movement relative to the stator;
- and
- at least one current-carrying winding disposed in said substantially closed slot of the stator such that the at winding is encircled by said first pair of adjacent teeth, the core portion and the slot top portion,
- wherein, when the machine is operated and the rotor is moved relative to the stator to induce a current in the winding, a magnetic flux of pre-selected strength is permitted to flow through the slot top portion by reason of the slot top portion shape and construction, thereby causing a maximum current in the at least one winding to be limited to a pre-selected maximum magnitude.
2 more elements
An alternator comprising:
- a stator assembly, the stator assembly having at least one electrical winding disposed in the stator assembly, the at least one electrical winding electrically connected to a machine output adapted to deliver generated output electricity from the machine;
- a rotor having a plurality of permanent magnets mounted to the rotor, the rotor mounted adjacent the stator assembly and adapted for movement relative to the stator assembly, whereby in use relative movement between the rotor and the stator assembly induces a primary voltage across the winding and an associated alternating current flow in the winding;
- and
- at least one secondary magnetic circuit circling the winding in the stator assembly, the secondary magnetic circuit having a selected magnetic inductance by reason of its shape and construction such that, in use, said induced alternating current in the winding induces a secondary magnetic flux in the secondary magnetic circuit sufficient to induce a secondary voltage across the winding to thereby limit a maximum short circuit current of the at least one winding to a level below that at which irreparable thermal damage is caused to the machine.
1 more element
Dependencies are inferred from the claim text.