Twelve-pulse autotransformer rectifier units
A method and apparatus for detecting a missing phase in a 3-phase twelve-pulse autotransformer rectifier unit (ATRU) which, in use, receives a 3-phase input and delivers a nominal DC output on which a common-mode voltage is impressed. At least one of the frequency and amplitude of the common-mode voltage are monitored thereby to determine whether there is a missing phase in the input. The frequency and/or amplitude of the common-mode voltage may also be monitored thereby to determine whether there is a loss of input voltage.
1. A method of detecting a missing phase in a 3-phase twelve-pulse autotransformer rectifier unit (ATRU), the ATRU, in use, receiving a 3-phase input and delivering a rectified nominal DC output on which a common-mode voltage is impressed, the method comprising:
monitoring, using a monitoring circuit, at least one of a frequency or an amplitude of the common-mode voltage so as to determine whether there is a missing phase in the 3-phase input, wherein the monitoring circuit is not connected to the 3-phase input.
2. The method of claim 1 , wherein the frequency of the common-mode voltage is detected, and
wherein a missing phase event is determined if the frequency of the common-mode voltage is below a preset threshold frequency.
3. The method of claim 2 , wherein the monitoring circuit comprises an analog circuit.
4. The method of claim 2 , wherein the monitoring circuit comprises a digital circuit.
5. The method of claim 1 , wherein the amplitude of the common-mode voltage is detected, and
wherein a missing phase event is determined if the amplitude of the common-mode voltage exceeds a preset, threshold.
6. A method of detecting an input supply drop out in a 3-phase twelve-pulse autotransformer rectifier unit (ATRU), the ATRU, in use, receiving a 3-phase input and delivering a rectified nominal DC output on which a common-mode voltage is impressed, the method comprising:
monitoring, using a monitoring circuit, at least one of a frequency or an amplitude of the common-mode voltage so as to determine whether there is an input supply drop, wherein the monitoring circuit is not connected to the 3-phase input.
7. The method of claim 6 , wherein the amplitude of the common-mode voltage is monitored and compared with a predetermined threshold amplitude.
8. The method of claim 5 , wherein the monitoring circuit comprises an analog circuit.
9. The method of claim 5 , wherein the monitoring circuit comprises a digital circuit.
10. The method of claim 1 , wherein the common-mode voltage is detected relative to a 3-phase generator neutral voltage.
11. An apparatus for detecting a missing phase in a 3-phase twelve-pulse autotransformer rectifier unit (ATRU), the ATRU, in use, receiving a 3-phase input and delivering a rectified nominal DC output on which a common-mode voltage is impressed, the apparatus comprising:
a monitoring circuit configured to monitor at least one of a frequency or an amplitude of the common-mode voltage so as to determine whether there is a missing phase in the input, wherein the monitoring circuit is not connected to the 3-phase input.
12. The apparatus of claim 11 , wherein the monitoring circuit is configured to monitor the amplitude of the common-mode voltage and to determine if the amplitude is less than a predetermined threshold amplitude.
13. The method of claim 7 , wherein the monitoring circuit comprises an analog circuit.
14. The method of claim 7 , wherein the monitoring circuit comprises a digital circuit.