Exciter assemblies
View Patent ↗An exciter assembly for supplying a field current to the rotor windings of a superconducting synchronous machine includes a pulse transformer having a stationary primary winding and a secondary winding that is mounted to the rotor of the superconducting synchronous machine for rotation therewith. A switched mode power supply supplies a pulsed voltage to the primary winding of the pulse transformer. The pulsed voltage developed at the secondary winding of the pulse transformer is supplied to the rotor windings through a rectifier semiconductor device and a pair of transfer leads. The rotor windings and a flywheel semiconductor device are located inside a cryogenic chamber or cryostat. The flywheel semiconductor device is connected in parallel with the rotor windings and operates in unison with the rectifier semiconductor device in order to provide synchronous rectification of the switched mode power supply output. The switched mode power supply and both the primary and secondary windings of the pulse transformer are located outside the cryostat.
1. An exciter assembly for supplying a field current to the rotor windings of a superconducting synchronous machine, the exciter assembly comprising:
a pulse transformer having a primary winding, a secondary winding and a tertiary winding;
a switched mode power supply for supplying a pulsed voltage to the primary winding of the pulse transformer;
a pair of transfer leads for supplying a pulsed voltage from the secondary winding of the pulse transformer to the rotor windings; and
a controller for controlling synchronous rectification of the pulsed voltage supplied to the rotor windings based on a signal from the tertiary winding of the pulse transformer.
2. The exciter assembly of claim 1 , where the primary winding of the pulse transformer is stationary and the secondary winding rotates in use.
3. The exciter assembly of claim 1 , further comprising a rectifier semiconductor device in series with the rotor windings and a flywheel semiconductor device in parallel with the rotor windings.
4. The exciter assembly of claim 3 , wherein the rectifier semiconductor device and the flywheel semiconductor device are controlled for synchronous rectification of the pulsed voltage supplied to the rotor windings.
5. The exciter assembly of claim 3 , wherein the rectifier semiconductor device is a thyristor or Gate Turn Off Thyristor (GTO).
6. The exciter assembly of claim 3 , wherein the flywheel semiconductor device is a Junction Field Effect Transistor (JFET) or Vertical Junction Field Effect Transistor (VJFET).
7. The exciter assembly of claim 1 , wherein synchronous rectification of the pulsed voltage causes power to be transmitted from the primary winding of the pulse transformer to the secondary winding of the pulse transformer only in a single quadrant of the B-H loop of the magnetic circuit of the pulse transformer.
8. The exciter assembly of claim 1 , further comprising switchable means for protecting the rotor windings against incipient quench.
9. The exciter assembly of claim 8 , wherein the switchable means includes a resistor in series with a semiconductor switch device.
10. The exciter assembly of claim 8 , wherein the switchable means includes a non-linear resistive device in series with a semiconductor switch device.
11. The exciter assembly of claim 10 , wherein the non-linear resistive device has a substantially “square” voltage current characteristic.
12. The exciter assembly of claim 11 , wherein the non-linear resistive device is a Metal Oxide Varistor (MOV).
13. The exciter assembly of claim 11 , wherein the semiconductor switch device is a Junction Field Effect Transistor (JFET) or Vertical Junction Field Effect Transistor (VJFET).
14. The exciter assembly of claim 9 , wherein the controller controls the operation of the semiconductor switch device based on a current feedback signal indicative of the field current in the rotor windings during a first period of time when a pulse of voltage is supplied to the rotor windings and a voltage feedback signal indicative of the field current in the rotor windings during the first period of time and during a second period of time when a pulse of voltage is not being supplied to the rotor windings.
15. The exciter assembly of claim 14 , wherein the current feedback signal is derived from a current transducer in series with the rotor windings and the voltage feedback signal is derived from a voltage transducer in parallel with the rotor windings.
16. The exciter assembly of claim 1 , further comprising a filter or switching aid network including an inductor in series with the rotor windings and a capacitor in parallel with the rotor windings.