Embodiments presented herein relate generally to diagnostics of synchronous machines and more specifically to health monitoring of synchronous machines.
A synchronous machine is one where the rotor rotates at a speed synchronous with the supply alternating current (AC) frequency. A conventional synchronous machine includes laminated armature windings disposed on a stator, and laminated field windings disposed on a rotor. The field winding of the synchronous machine is supplied with Direct Current (DC). Some small synchronous machines use permanent magnets in place of the field winding. Synchronous machines are extensively used in power plants, aviation power systems, power factor correction systems, and so forth.
Synchronous machines may operate in a generator mode, where an external prime mover rotates the rotor to produce AC power. Alternatively, synchronous machines may operate in a motoring mode, where external AC power generates a rotating magnetic field, thus turning the rotor. In both modes, the armature winding is subjected to a high electrical current and/or voltage during operation. The lamination of the armature windings may degrade with time and prolonged use, thus causing short circuits between successive turns of the armature winding. A short circuit tends to create circulating currents which in turn result in local hot spots within the armature.
If not detected and repaired in time, such faults may cause unplanned outages. In aviation engines, a failure of the synchronous generator may lead to loss of power to all control and support systems. Therefore, it is important that armature winding faults are detected at incipient stage, to plan appropriate maintenance tasks.
One known method for synchronous machine health monitoring includes creating a model of the synchronous machine, and simulating synchronous machine operation. However, synchronous machine models are created on the assumption that the spatial distribution of windings inside the machine is sinusoidal. The windings of a synchronous machine with an inter-turn fault no longer have a sinusoidal distribution. In other words, the model may not take into account the inherent asymmetry in winding distribution under fault conditions. This may lead to erroneous fault detection.