Ring optical current transducer

• US 5,124,634 A
• Filed: 04/25/1990
• Issued: 06/23/1992
• Est. Priority Date: 03/14/1989
• Status: Expired due to Fees

• Current Assignee: BBA Canada Limited
• Original Assignee: Square D Company (Schneider Electric SE)
• Inventors: Ulmer, Edward A. Jr., Meyer, Thomas J.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): BURNS, WILLIAM
• Application Number:
  US07/514,197
• Time in Patent Office: 790 Days
• Field of Search: 324/72.5, 324/96, 324/117 R, 324/244.1, 250/225, 250/227.28, 250/227.32, 350/374-376
• US Class Current: 324/96
• CPC Class Codes: G01R 15/246 based on the Faraday, i.e. linear magneto-optic, effect

Abstract

An optical current transducer for measuring current in a high voltage transmission line includes a temperature compensated light source of nominal predetermined intensity and wavelength, a Faraday rotation device where Faraday rotation impressed on the light exiting the light source is proportional to the intensity of the electrical current to be measured. A hermetic tank encloses the Faraday rotation device to provide protection from the environment. An electronic circuit converts the optical output of the Faraday rotation device to an electrical signal in direct proportion to and in phase with the current to be measured.

Claims

1. A toroidal optical current transducer for measuring current in a conductor comprising:

(a) a generally planar optical bench defining a bench orifice through which the current to be measured is passed in an electrical bench conductor, said bench having a first bench mounting surface 30, and a second bench mounting surface 32;

(b) a light source supplying reference light of nominally predetermined intensity;

(c) a polarizer having a first polarizing angle mounted on said optical bench receiving the reference light and transmitting a portion of said reference light as polarized light;

(d) a first glass bar mounted on said optical bench, said bar having;

(1) a light transmission axis along which light propagates and a bench surface mounted to one of the bench mounting surfaces,

(2) an input end generally planar surface receiving polarized light from said polarizer, said input end surface oriented at an input angle to the transmission axis of approximately 90 degress, and

(3) an output generally planar surface transmitting the polarized light to an associated component, said output end surface oriented at an output angle to the transmission axis of approximately 45 degrees;

(e) a second glass bar mounted on said optical bench, said bar having;

(1) a light transmission axis along which light propagates and a bench surface mounted to one of the bench mounting surfaces,

(2) an input end generally planar surface receiving polarized light from an associated component, said input end surface oriented at an input angle to the transmission axis of approximately 45 degrees, and

(3) an output end generally planar surface transmitting the polarized light to an associated component, said output end surface oriented at an output angle to the transmission axis of approximately 45 degrees;

(f) a third glass bar mounted said optical bench, said bar having;

(1) a light transmission axis along which light propagates and a bench surface mounted to one of the bench mounting surfaces,

(2) an input end generally planar surface receiving polarized light from an associated component, said input end surface oriented at an input angle to the transmission axis of approximately 45 degrees, and

(3) an output end generally planar surface transmitting the polarized light to an associated component, said output end surface oriented at an ouput angle to the transmission axis of approximately 45 degrees;

(b) a fourth glass bar mounted on said optical bench, said bar having;

(1) a light transmission axis along which light propagates and a bench surface mounted to one of the bench mounting surfaces.

(2) an input end generally planar surface receiving polarized light from an associated component, said input end surface oriented at an input angle to the transmission axis of approximately 45 degrees, and

(3) an output end generally planar surface transmitting the polarized light to an associated component, said output end surface oriented at an output angle to the transmission axis of approximately 45 degrees;

(h) said bars prestressed to provide two stress axes, said axes orthogonal to each other and to the transmission axis;

(i) said bars surrounding the bench orifice, and optically coupled to each other by having an input end surface adjoining the output end of an adjoining bar;

(i) said bars mounted to said bench in a manner preserving their optical alignment while damping any vibrational coupling between said bench and said bars;

(k) an analyzer having a second polarizing angle mounted on said optical bench receiving the light transmitted from the fourth bar, said second polarizing angle being displaced from said first polarizing angle by about 45 degrees, said analyzer transmitting a single analyzer light beam; and

(l) a light activated device receiving said analyzer light beam and producing a current proportionate to the resulting Faraday rotation of the polarized light as a result of the magnetic field produced by the current to be measured.

2. The transducer of claim 1 further including:

an input collimating lens interposed between said light source and said polarizer, said input lens mounted on said bench to focus the reference light on said polarizer; and

an output collimating lens interposed between said analyzer and said light activated device, said output lens mounted on said bench to focus the polarized light for reception by said light activated device.

3. The transducer of claim 1 wherein:

said light source and said light activated device are remotely mounted from said optical bench, and further including

an input light fibre transmitting reference light from said light source to said input collimating lens; and

an output light fibre transmitting said polarized light from said output collimating lens to said light activated device.

4. The transducer of claim 1 wherein:

said first and third bars are mounted to said first bench mounting surface; and

said second and fourth bars are mounted to said second bench mounting surface.

5. The transducer of claim 4 wherein said mounting of said bars to said bench consists of:

(a) a flexible cured bonding material to adhere said bars to said optical bench; and

(b) a plurality of BALINTINE SPHERES dispersed throughout said bonding material.

6. The transducer of claim 3 further including:

an input assembly operatively optically coupling said input fibre, input lens and said polarizer in a rigid manner, said input assembly mounted to said first surface by the mounting media,

a flexible cured bonding material to adhere said bars to said optical bench; and

a plurality of BALINTINA SPHERES dispersed throughout said bonding material.

7. The transducer of claim 4 wherein:

(a) said bench has a semi-octagonal shape including bench parallel sides, and bench corner sides;

(b) said bars positioned with their first side surfaces parallel to said bench corner sides and for a portion of their length inward of said bench parallel sides, and with their end surfaces projecting beyond said bench corner sides.

8. The transducer of claim 5 wherein:

said mounting media is applied to localized media locations of said bar bench mounting surface to minimize stress on said bars from the adhesion between said bars and said bench.

9. The transducer of claim 6 wherein:

said media locations are toward each end of said bars one to one side of the transmission axis, and near the middle of said bars to a second opposite side of said transmission axis.

10. The transducer of claim 1 wherein:

each bar has a fast and a slow axis, the fast and slow axis being orthogonal to each other and to said transmission axis, the fast and slow axes of adjoining bars preserving the same handedness between adjoining bars,

whereby the s and p vectors associated with the polarized E vector are first interchanged by reflection from said output surface, and second interchanged by reflection from said input surface, with the result that birefringence effects tend to be cancelled because the association between the s and p vectors and the fast and slow axes in one bar is reversed in the adjoining bar.

11. The transducer of claim 1 wherein

said bench conductor is associated with a bench conductor assembly to preserve the location and orientation of said current fields with respect to said optical bars.

12. The transducer of claim 1 wherein said first through fourth bars are rate annealed to relieve internal glass stress.

13. The transducer of claim 1 further including:

a hermetic tank surrounding said transducer and isolating said transducer from the environment in which said transducer is located;

an input feed thru conductor connected to a first end of said bench conductor; and

an output feed thru conductor connected to a second end of said bench conductor; and

wherein

said bench conductor includes a plurality of cables within a bench insulative pipe.

14. The transducer of claim 1 further including

a temperature controller operatively interconnected with said light source to maintain said light source at a predetermined temperature.

15. The transducer of claim 14 further including

(a) a constant current source activating said light source, whereby said light source generates light of a predetermined intensity and predetermined wavelength.

16. The transducer of claim 14 further including

a standardizing circuit which applies a predetermined scaling factor to said magnitude signal.