Electrical machine

An electrical machine includes a stator including a plurality of electrical phases and a rotor having a plurality of magnets. Each electrical phase includes at least one coil and power electronics. There are means to detect an electrical short circuit in a faulted coil and means to supply an electrical current to the faulted coil when an electrical short circuit is detected in the faulted coil. The means to supply the electrical current to the faulted coil includes one or more un-faulted electrical phases of the electrical machine. The un-faulted electrical phases of the electrical machine are arranged to supply the electrical current to the electrical phase containing the faulted coil. The power electronics of the un-faulted electrical phases are arranged to supply the electrical current from the un-faulted electrical phase to the power electronics of the electrical phase having the faulted coil. This overcomes a problem of a fault in the DC or AC busbar of the electrical machine.

The present invention relates to electrical machines and in particular to fault tolerant electrical machines, particularly for use in gas turbine engines, on aircraft or on ships. The fault tolerant electrical machines may be electrical generators, electrical motors or electrical machines arranged to act as both electrical motors and electrical generators.

It is known from our published International patent application WO2005/011078A1 to inject current into a coil, or phase, of an electrical machine which has a short-circuited turn in the coil, or phase. The magnetic flux of the current injected into the coil, or phase, has to be of such a magnitude, frequency and phase that it opposes the magnetic flux from the permanent magnets of the rotor of the electrical machine.

In the prior art a suitable power supply, either a DC or AC busbar, is available to supply a current to the power electronics (PE) of the electrical machine and the power electronics supplies an electrical current to the coil, or phase, which has a short-circuit in a turn in the coil, or phase.

A problem with the prior art is that if there is a fault, e.g. an open-circuit, with the power supply, the DC or AC busbar, then it is not possible to supply an electrical current to the coil, or phase, which has a short-circuit in the turn in the coil, or phase.

Accordingly the present invention seeks to provide a novel electrical machine, which reduces, preferably overcomes, the above mentioned problem.

Accordingly the present invention provides an electrical machine comprising a stator including a plurality of electrical phases and a rotor having a plurality of magnets, each electrical phase comprising at least one coil and power electronics, means to detect an electrical short circuit in at least one of the coils to determine a faulted turn of the at least one coil, and means to supply an electrical current to the at least one of the coils having a faulted turn when an electrical short circuit is detected in the at least one of the coils, the means to supply the electrical current to the at least one of the coils having a faulted turn comprises at least one un-faulted electrical phase of the electrical machine.

Preferably the at least one un-faulted electrical phase of the electrical machine is arranged to supply the electrical current to the electrical phase containing the at least one of the coils having a faulted turn.

Preferably the power electronics of the at least one un-faulted electrical phase is arranged to supply the electrical current from the at least one un-faulted electrical phase to the power electronics of the electrical phase having the at least one of the coils having a faulted turn.

Preferably two or more of the un-faulted electrical phases of the electrical machine are arranged to supply the electrical current to the electrical phase containing the at least one of the coils having a faulted turn.

Possibly all of the un-faulted electrical phases of the electrical machine are arranged to supply the electrical current to the electrical phase containing the at least one of the coils having a faulted turn.

The power electronics of the at least one un-faulted phase of the electrical machine is arranged to store the electrical current in the power electronics before the power electronics of the at least one un-faulted electrical phase is arranged to supply the electrical current from the at least one un-faulted electrical phase to the power electronics of the electrical phase having the at least one of the coils having a faulted turn.

Preferably the magnets are permanent magnets.

Preferably the electrical machine is an electrical motor, an electrical generator or a combined electrical motor and electrical generator.

Preferably the electrical machine is an electrical starter/electrical generator.

Preferably the electrical machine is a fault tolerant electrical machine.

Preferably the electrical machine is an electrical machine of a gas turbine engine, an aircraft or a ship.

The electrical machine is connected to a busbar. The means to supply the electrical current to the at least one of the coils having a faulted turn comprises means to detect a short circuit or fault in the busbar and the means to detect a short circuit or fault in the busbar is arranged to allow the at least one un-faulted phase of the electrical machine to supply the electrical current to the at least one of the coils having a faulted turn if there is a short circuit or fault in the busbar.

The electrical machine may be connected to a busbar via a circuit breaker. The means to supply the electrical current to the at least one of the coils having a faulted turn comprises means to detect a disturbance in the voltage of the busbar and the means to detect a disturbance in the voltage in the busbar is arranged to open the circuit breaker if there is a disturbance in the voltage in the busbar to allow the at least one un-faulted phase of the electrical machine to supply the electrical current to the at least one of the coils having a faulted turn.

The present invention also provides a method of operating an electrical machine, the electrical machine comprising a stator including a plurality of electrical phases and a rotor having a plurality of magnets, each electrical phase comprising at least one coil and power electronics, the method comprising detecting an electrical short circuit in at least one of the coils to determine a faulted turn of the at least one coil, supplying an electrical current to the at least one of the coils having a faulted turn when an electrical short circuit is detected in the at least one of the coils and supplying the electrical current to the at least one of the coils having a faulted turn from at least one un-faulted electrical phase of the electrical machine.

A turbofan gas turbine engine10, as shown inFIG. 1, comprises in flow series an intake12, a fan section14, a compressor section16, a combustion section18, a turbine section20and an exhaust22. The fan section14comprises a fan (not shown). The compressor section16comprises in flow series an intermediate-pressure compressor (not shown) and a high-pressure compressor (not shown). The turbine section20comprises in flow series a high-pressure turbine (not shown), an intermediate-pressure turbine (not shown) and a low-pressure turbine (not shown). The low-pressure turbine is arranged to drive the fan via a first shaft (not shown), the intermediate-pressure turbine is arranged to drive the intermediate-pressure compressor via a second shaft (not shown) and the high-pressure turbine is arranged to drive the high-pressure compressor via a third shaft (not shown). The turbofan gas turbine engine10also comprises an electrical machine30which is driven by the first shaft, the second shaft or the third shaft either directly or via a gearbox, a drive shaft and an accessory gearbox.

The electrical machine30as shown inFIGS. 2 and 3comprises a stator32and a rotor42. The stator32has a plurality of electrical phases, in this example three electrical phases34A,34B and34C but the stator32may have any suitable number of electrical phases, and each electrical phase34A,34B,34C comprises at least one electrical coil36. The stator32has a plurality of circumferentially spaced radially inwardly extending teeth38and each electrical coil36is arranged around one of the teeth38of the stator32. The electrical coils36in each of the electrical phases34A,34B, and34C are circumferentially spaced around the stator32and the electrical coils36of different electrical phases34A,34B, and34C are arranged circumferentially sequentially around the stator32. Each of the electrical phases34A,34B,34C is provided with respective power electronics40A,40B,40C to control the respective electrical phase34A,34B,34C of the electrical machine30. The rotor42comprises a plurality of circumferentially spaced permanent magnets44.

The electrical machine30also has means50to detect an electrical short circuit in one of the coils36to determine a faulted turn of the coil36. The electrical machine30also has means52to supply an electrical current to the coil36, with a faulted turn or a short circuit, when the electrical short circuit is detected in the coil36and the means52to supply the electrical current to the coil36, with a faulted turn or a short circuit, comprises at least one un-faulted electrical phase34A,34B,34C of the electrical machine30. For example, if there is a short circuit due to a faulted turn in a coil36A in the electrical phase34A, this is detected and the un-faulted electrical phase34B, the un-faulted electrical phase34C or two or more or all of the un-faulted electrical phases34B and34C are arranged to supply an electrical current to the coil36A with a faulted turn in the electrical phase34A. The coil36A with a faulted turn is known as a faulted coil and the electrical phase34A with a faulted coil is known as a faulted electrical phase. It is to be noted that a faulted coil will generally mean a coil having one or more short circuited turns and also a plurality of un-short circuited turns such that an electrical current can be into the un-short circuited turns of the faulted coil.

The un-faulted electrical phase/phases34B,34C of the electrical machine30is/are arranged to supply the electrical current to the faulted electrical phase34A containing a faulted coil36A, a coil36A with a faulted turn or a short circuit, to prevent excessive current flow in the faulted electrical phase34A containing the faulted coil36A, coil36A with a faulted turn or a short circuit, to prevent over heating of the faulted coil36A and the associated faulted electrical phase34A. The magnetic flux of the current injected into the faulted coil36A, or faulted electrical phase34A, has to be of such a magnitude, frequency and phase that it opposes the magnetic flux from the permanent magnets44of the rotor42of the electrical machine30.

In particular the electrical machine30is so arranged that the power electronics40B or40C of an un-faulted electrical phase34B or34C is arranged to supply the electrical current from the un-faulted electrical phase34B or34C to the power electronics40A of the faulted electrical phase34A having the faulted coil36A, the coil36A with a faulted turn or a short circuit via electrical connections52A or52B. It may also be possible to arrange the electrical machine30such that two, more than two or all of the un-faulted electrical phases34B and34C of the electrical machine30are arranged to supply the electrical current to the faulted electrical phase34A containing the faulted coil36A, the coil36A with a faulted turn or a short circuit. The power electronics40B and40C of un-faulted electrical phase34B and34C are arranged to supply the electrical current from the un-faulted electrical phase34B and34C to the power electronics40A of the faulted electrical phase34A having the faulted coil36A, the coil36A with a faulted turn or a short circuit via the electrical connections52A and52B. A further electrical connection52C is provided between the power electronics40B and40C to enable supply the supply of electrical current there between should one of these electrical phases40B or40C have a coil which suffers from a short circuit in a turn.

The power electronics40B,40C of the at least one un-faulted phase34B,34C of the electrical machine30may be arranged to store the electrical current in the power electronics40B,40C before the power electronics40B,40C of the un-faulted electrical phase34B,34C is arranged to supply the electrical current from the un-faulted electrical phase34B,34C to the power electronics40A of the faulted electrical phase34A having the faulted coil36A, the coil36A with a faulted turn or a short circuit. Alternatively the power electronics40B,40C of the at least one un-faulted phase34B,34C of the electrical machine30may be arranged to supply the electrical current immediately from the un-faulted electrical phase34B,34C to the power electronics40A of the faulted electrical phase34A having the faulted coil36A, the coil36A with a faulted turn or a short circuit. Thus, the faulted electrical phase34A with the faulted coil36A, coil36A with a faulted turn or short circuit is protected from further damage by heating due to over currents in the faulted electrical phase34A.

The electrical machine30is electrically connected to a DC or AC busbar60and the means52to supply the electrical current to the faulted coil36, with the faulted turn or short circuit, comprises means62to detect a short circuit of the busbar60and the means62to detect a short circuit of the busbar60is arranged to allow the at least one un-faulted phase34B,34C of the electrical machine30to supply the electrical current to the faulted coil36A, the coil36A with a faulted turn or a short circuit, if there is a short circuit or other fault in the busbar60.

The means50to detect an electrical short circuit in one of the coils36to determine a faulted turn of the coil36may comprise a temperature sensor or temperature sensors to measure the temperature of the coil36, a voltmeter to measure the voltage of the coil36or any other suitable device to detect a faulted turn in the coil36.

The means62to detect a short circuit of the busbar60may comprise a voltmeter, an ammeter or a combination of a voltmeter and ammeter to monitor the voltage and current in the busbar60.

Although the present invention has been described with reference to the use of a rotor with permanent magnets, it may be possible to use other types of magnets, e.g. electromagnets.

The electrical machine30is an electrical motor, an electrical generator or a combined electrical motor and electrical generator. It is preferred that the electrical machine30is an electrical starter/electrical generator such that the electrical machine30is used to start the turbofan gas turbine engine10and once the turbofan gas turbine engine10is operational the electrical machine30is used to generate electricity.

Preferably the electrical machine30is a fault tolerant electrical machine30, such that it is particularly suitable for use on/in a gas turbine engine, an aircraft or a ship.

The advantage of the present invention is that if there is a fault, e.g. an open circuit fault, in the DC or AC busbar supplying electric current to the electrical machine and it is not possible to supply an electrical current from the DC or AC busbar into a faulted electrical phase with a faulted coil which has a faulted turn or short circuit then one or more of the un-faulted phases of the electrical machine are able to supply an electrical current to the faulted electrical phase with the faulted coil which has a faulted turn or short circuit. Furthermore, the present invention may also be used if there is a disturbance in the DC or AC busbar60, which takes the system voltage outside its normal operating range. In these circumstances it may be possible to use a circuit breaker64to electrically disconnect the DC or AC busbar60from the power electronics40A,40B and40C of the electrical machine30in order to supply the electrical current from the un-faulted electrical phases of the electrical machine30. Thus, the means52to supply the electrical current to the at least one of the faulted coils comprises means62to detect a disturbance in the voltage of the busbar and the means to detect a disturbance in the voltage in the busbar is arranged to open the circuit breaker64if there is a disturbance in the voltage in the busbar60to allow the at least one un-faulted phase of the electrical machine30to supply the electrical current to the at least one of the faulted coils.

The means62to detect a disturbance in the voltage of the busbar60is also the means62to detect a short circuit of the busbar60.