EMI line filter

• US 5,619,079 A
• Filed: 07/28/1995
• Issued: 04/08/1997
• Est. Priority Date: 07/28/1995
• Status: Expired due to Fees

• Current Assignee: Navy Department United States of America The As Represented By The Secretary of The Navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Stewart, David W., Wiggins, Charles L.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): GANJIAN, PETER
• Application Number:
  US08/508,872
• Time in Patent Office: 620 Days
• Field of Search: 307/89, 307/90, 307/91, 307/106, 307/108, 307/105, 361/111, 361/56, 333/12, 333/172, 333/177, 333/181, 379/116, 331/67, 343/841, 343/851, 343/905, 178/69, 336/83, 336/84
• US Class Current: 307/89
• CPC Class Codes: H02H 9/005 avoiding undesired transient conditions
• CPC Class Codes: H02J 2310/44 for aircrafts
• CPC Class Codes: H02J 3/01 Arrangements for reducing harmonics or ripples
• CPC Class Codes: H03H 1/0007 of radio frequency interference filters

Abstract

A filter circuit for reducing electromagnetic interference in an ungroundedhree-phase delta electrical system. The filter circuit includes a low- pass filter associated with each power phase having one input and output terminal placing an inductor in series with a phase conductor from a power supply. Input and output capacitors connect to a second input and output terminals respectively. An inductor connects in common between the second input and second output terminals thereby to complete a loop that is isolated from ground. Voltage suppression circuits connect from each phase to ground on the input side of the filter.

Claims

1. A filter circuit for reducing electromagnetic interference in an electrical system including a multiple-phase power supply and a multiple phase electrical load, each of which is isolated from a ground, said filter circuit comprising:

a plurality of four-terminal low-pass filters for connection between the electrical supply and the electrical load, each said low-pass filter having first and second input terminals and first and second output terminals, said first input terminal being for connection to a given phase conductor from the electrical supply, the second input terminal being electrically coupled to said first input terminal, said first output terminal being for connection to a corresponding phase conductor from the electrical load and said second output terminal being electrically coupled to said first output terminal, said second input terminal and said second output terminal of each of said low-pass filters being isolated from ground; and

a two-terminal inductive reactance having a first terminal connected to all said second input terminals and a second terminal connected to all of said second output terminals.

2. A filter circuit as recited in claim 1 wherein each of said low-pass filters comprises:

a inductor in series between said first input terminal and said first output terminal;

an input capacitive impedance connected between said first and second input terminals; and

an output capacitive impedance connected between said first and second output terminals.

3. A filter circuit as recited in claim 2 wherein said input capacitive impedance in each said low-pass filter comprises a resistor and capacitor in parallel.

4. A filter circuit as recited in claim 2 wherein said output capacitive impedance in each said low-pass filter comprises a capacitor.

5. A filter circuit as recited in claim 1 additionally comprising means for suppressing electrical transients connected to each of said first input terminals.

6. A filter circuit as recited in claim 1 wherein the electrical power supply and load operate with respect to an electrical ground and said apparatus additionally comprises means for suppressing electrical transients connected between each of said first input terminals and electrical ground.

7. A filter circuit as recited in claim 6 wherein each of said suppression means includes a line transient voltage suppressor.

8. A filter circuit as recited in claim 6 wherein each of said suppression means includes an over-voltage line protector.

9. A filter circuit as recited in claim 6 wherein each said suppression means includes an over-voltage line protector and a line transient voltage suppressor in parallel between a corresponding phase conductor and ground.

10. In a three-phase power system for operating in an environment with a ground in which the three-phase power system includes an ungrounded three-phase delta power supply with three phase power connections and an electrical load with ungrounded three-phase delta power connections, the improvement of a filter circuit for reducing electromagnetic interference comprising:

first, second and third low-pass filters, each having first input terminals for connection to each of the power supply phase connections, second input terminals being electrically coupled to said first input terminals, first output terminals for connection to each of the electrical load phase connections and second output terminals being electrically coupled to said first output terminals, said second input terminal and said second output terminal being isolated from the ground; and

a two-terminal inductance having a first inductor terminal connected to all said second input terminals and a second inductor terminal connected to all said second output terminals.

11. A filter circuit as recited in claim 10 wherein each of said low-pass filter means comprises:

inductor means connected in series between said first input terminal and said first output terminal;

input capacitive impedance means connected between said first and second input terminals; and

output capacitive impedance means connected between said first and second output terminals.

12. A filter circuit as recited in claim 11 wherein each said input capacitive impedance means comprises a resistor and capacitor in parallel.

13. A filter circuit as recited in claim 11 wherein each of said output capacitive impedance means comprises a capacitor.

14. A filter circuit as recited in claim 11 additionally comprising suppression means connected between each said first input terminals and ground for suppressing electrical transients.

15. A filter circuit as recited in claim 14 wherein each of said suppression means includes a line transient voltage suppressor.

16. A filter circuit as recited in claim 14 wherein each of said suppression means includes an over voltage line protector.

17. A filter circuit as recited in claim 14 wherein each said suppression means includes an over voltage line protector and a line transient voltage suppressor in parallel.

18. In a three-phase power system for operating in an environment with a ground in which the three-phase power system includes a three-phase power supply with three ungrounded phase connections in a delta configuration and an electrical load with three ungrounded phase connections in a delta configuration, the improvement of an electromagnetic interference reducing filter circuit for interconnecting the power supply and the electrical load comprising:

first, second and third inductors having input terminals for connection, respectively, to each of the first, second and third phase connections of the power supply and output terminals for connection, respectively, to the corresponding first, second and third phase connections of the electrical load;

a fourth inductor having first and second terminals, said first and second terminals being isolated from ground;

first, second and third input impedance means connected, respectively, to each of said input terminals of said first, second and third inductors and in common to the first terminal of said fourth inductor, each of said impedance means including a capacitor and resistor in parallel;

first, second and third output capacitors connected, respectively, to each of said output terminals of said first, second and third inductors and in common to the second terminal of said fourth inductor; and

first, second and third voltage suppression means for suppressing voltage transients, each of said suppression means having a first connection to a corresponding one of said first, second and third inductor input terminals and having a second connection to ground, each of said voltage suppression means comprising an over voltage line protector and a line transient voltage suppressor in parallel.