Foreign track current suppression system and method

1. A track current suppression device, comprising:

an input coupled between rails of a railway track and configured to receive an input voltage corresponding to a track current;

an amplifier configured to receive the input voltage and generate a cancellation current;

a transformer coupled between the rails of the railway track and configured to deliver the cancellation current to the rails at a frequency of interest and with reversed polarity compared to the track current; and

an LC circuit coupled between the rails and series tuned to the frequency of interest, the LC circuit operably coupled to the amplifier to receive the cancellation current from the amplifier, wherein an inductor of the LC circuit is an output winding of the transformer.

2. The track current suppression device recited in claim 1 , wherein the LC circuit is series tuned to a center frequency of approximately 60 hertz.

3. The track current suppression device recited in claim 1 , further comprising another transformer disposed between the rails and coupled to an input of the amplifier, for isolating the input of the amplifier from the rails.

4. The track current suppression device recited in claim 1 , wherein the device is disposed inside a track circuit limit of a train detection system.

5. The track current suppression device recited in claim 1 , wherein the device is disposed inside a housing of a grade crossing control unit.

6. A grade crossing system, comprising:

a train detection system configured to deliver an electrical signal to rails of a railway track and monitor the signal to determine a presence of an approaching train;

a warning device activated by the train detection system; and

a track current suppression circuit comprising:

an input coupled between the rails and configured to receive an input voltage corresponding to a track current;

an amplifier configured to receive the input voltage and generate a cancellation current;

a transformer coupled between the rails of the railway track and configured to deliver the cancellation current to the rails at a frequency of interest and with reversed polarity compared to the track current; and

an LC circuit coupled between the rails and series tuned to the frequency of interest, the LC circuit operably coupled to the amplifier to receive the cancellation current from the amplifier, wherein an inductor of the LC circuit is an output winding of the transformer.

7. The grade crossing system of claim 6 , wherein the LC circuit is series tuned to a bandwidth centered at a frequency of approximately 60 hertz or harmonics of 60 Hertz.

8. The grade crossing system of claim 6 , wherein the track current suppression circuit further comprises another transformer disposed between the rails and coupled to an input of the amplifier, for isolating the input of the amplifier from the rails.

9. The grade crossing system of claim 6 , wherein the track current suppression circuit is disposed inside a track circuit limit of the train detection system.

10. The grade crossing system of claim 6 , wherein the track current suppression circuit and the train detection system are disposed inside a common housing.

11. A track current suppression device, comprising:

an input coupled between rails of a railway track and configured to receive an input voltage corresponding to a track current;

an amplifier configured to receive the input voltage and generate a cancellation current; and

an output coupled between the rails of the railway track and configured to deliver the cancellation current to the rails with reversed polarity compared to the track current, wherein a total loop gain of the device is approximately 0.8 to 0.95.

12. A track current suppression device, comprising:

a first transformer coupled between rails of a railway track for receiving an input voltage corresponding to a track current;

an amplifier having an input coupled to the first transformer, for receiving the input voltage from the first transformer, wherein the amplifier is configured to generate a cancellation signal based on the input voltage, wherein the cancellation signal has a reversed polarity compared to the track current; and

an LC circuit disposed between the rails of the railway track and operably connected to an output of the amplifier for receiving the reversed polarity cancellation signal from the amplifier, wherein the LC circuit is configured to generate a cancellation current proportional to the cancellation signal and to deliver the cancellation current to the rails;

wherein the LC circuit comprises a capacitor and a second transformer connected to the capacitor in series, wherein the output of the amplifier is coupled to a winding of the second transformer.

13. A grade crossing system, comprising:

a train detection system configured to deliver an electrical signal to rails of a railway track and monitor the signal to determine a presence of an approaching train;

a warning device activated by the train detection system; and

a track current suppression circuit comprising:

an input coupled between the rails and configured to receive an input voltage corresponding to a track current;

an amplifier configured to receive the input voltage and generate a cancellation current; and

an output coupled between the rails of the railway track and configured to deliver the cancellation current to the rails with reversed polarity compared to the track current, wherein a total loop gain of the track current suppression circuit is approximately 0.8 to 0.95.

14. A method of suppressing foreign current on a railway track, the method comprising:

detecting an input voltage between rails of the railway track, the input voltage corresponding to a track current;

amplifying the input voltage to generate a cancellation current; and

delivering the cancellation current to an input winding of a transformer coupled between the rails with reverse polarity compared to the track current, wherein an output winding of the transformer is series coupled to a capacitor to form an LC circuit that is tuned to a frequency to be canceled.