# US 12,222,374 B1 · Method and system for optical calculation in relay protection based on the faraday magneto-optical rotation effect

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- Number: US 12,222,374 B1
- Document ID: US12222374B1
- Status: Granted
- Kind: B1
- Application number: 18/517,012
- Filed: 2023-11-22
- Published: 2025-02-13
- Granted: 2025-02-11
- Earliest claimed: 2023-09-21
- Assignees: Harbin Institute of Technology
- Applicants: Harbin Institute of Technology
- Inventors: Caiyun Mo; Guoqing Zhang; Wenbin Yu; Yuxin Zhang; Ying Xu; Zhizhong Guo
- Web page: https://patentgrep.com/patent/US12222374B1

## CPC

- G01R 15/246: {based on the Faraday, i.e. linear magneto-optic, effect}
- H02H 3/33: using summation current transformers (H02H3/347 takes precedence)
- H02H 1/0007: {concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445)}
- H02H 1/0092: {concerning the data processing means, e.g. expert systems, neural networks}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H)

## Abstract

Optical calculation method and system for relay protection based on Faraday magneto-optical rotation effect are provided. A cascaded optical computing approach is employed, where three optical current transformers are connected in series on a single optical path. Final output optical signal represented as a cascaded multiplication of outputs of three optical current transformers, carries a Faraday rotation angle containing differential current information. Differential current required for protection is computed by modulation ratio which is calculated by use of a carrier and modulation wave signals of the output optical signal detecting by filtering circuit from the third optical current transformer.

## Claims

### Claim 1

An optical calculation system for relay protection based on Faraday magneto-optical rotation effect, comprising:
a light source, a first optical current transformer, a second optical current transformer, a third optical current transformer, and a processing unit;
a light signal emitted from the light source passes through the first optical current transformer, the second optical current transformer, and the third optical current transformer in sequence, causing the light signal to carry a Faraday rotation angle φ, wherein the Faraday rotation angle φ comprises differential current information;
an outgoing light from the third optical current transformer enters the processing unit;
light signals between the light source and the first optical current transformer, the first optical current transformer and the second optical current transformer, the second optical current transformer and the third optical current transformer, as well as the third optical current transformer and the processing unit, are transmitted through multimode fibers;
Faraday magneto-optical elements of the first optical current transformer and the third optical current transformer are respectively located on a high-voltage side and low-voltage side of a protected phase of transformer;
a Faraday magneto-optical element of the second optical current transformer is located on a high-voltage side of adjacent phase to the protected phase of the transformer; under normal operating conditions, a phase difference between the protected phase and its adjacent phase on the high-voltage side of transformer share the same phase with the protected phase on the low-voltage side;
the Faraday magneto-optical elements of the first optical current transformer, the second optical current transformer, and the third optical current transformer are allowed to sense a magnetic field generated by use of a current on their respective sides; angles between optical paths of the first optical current transformer, the second optical current transformer, and the third optical current transformer and a current direction on their respective sides satisfy following relationship:
sin
⁢
θ
YA
:
sin
⁢
θ
YB
:
sin
⁢
θ
dA
=
1
:
1
:
3
n
T
,
wherein,
θYA represents the angle between the optical path of the first optical current transformer and the current direction on its respective side;
θYB represents the angle between the optical path of the second optical current transformer and the current direction on its respective side; and
θdA represents the angle between the optical path of the third optical current transformer and the current direction on its respective side; nT represents a transformation ratio of the transformer;
the processing unit comprises following modules:
a filtering unit, wherein the filtering unit is configured to detect a carrier signal JDC and a modulation wave signal JAC of an optical signal output from the third optical current transformer using a filtering circuit;
a modulation ratio calculation unit, wherein the modulation ratio calculation unit is configured to calculate a modulation ratio m based on the following equation:
m
=
J
AC
J
DC
,
and
a differential current calculation unit, wherein the differential current calculation unit is configured to calculate a differential current id with the following equation:
i
d
=
m
2
⁢
V
⁢
L
,
wherein, V is a Verdet constant of a Faraday magneto-optical element in the first, second and third optical current transformers, L is a coefficient of the multiple relationship between the magnetic field integral on the Faraday magneto-optical element in the first, second and third optical current transformers to its measured current.

### Claim 2 (depends on 1)

The optical calculation system for the relay protection based on the Faraday magneto-optical rotation effect according to claim 1, wherein internal structural composition of the first optical current transformer, the second optical current transformer, and the third optical current transformer is identical;
wherein each of the first to third optical current transformers comprises a few collimators, a polarizer, the Faraday magneto-optical element, and an analyzer;
wherein an incident light is collimated by the collimator and enters the polarizer, becoming a polarized light; the polarized light passes through the Faraday magneto-optical element and undergoes a rotation under a modulation of the magnetic field, wherein the Faraday magneto-optical element is located in the magnetic field;
the rotated polarized light passes through the analyzer and is emitted again through the collimator;
output ends of the analyzer comprise output π/4 and output −π/4;
angles between an optical axis of the polarizer and an optical axis of the output π/4 and output −π/4 of the analyzer are π/4 and −π/4 respectively;
optical signals output from the first optical current transformer and the third optical current transformer are both emitted from the output −π/4 of their respective analyzers; and
an optical output signal of the second optical current transformer is emitted from the output π/4 of its analyzer.

### Claim 3 (depends on 2)

The optical calculation system for the relay protection based on the Faraday magneto-optical rotation effect according to claim 2, wherein the Faraday rotation angle is allowed to be expressed as φ=φYA−φYB+φdA;
wherein,
φYA represents an angle of rotation of polarization light caused by magnetic field sensed by the first optical current transformer;
φYB represents an angle of rotation of emitted light from the first optical current transformer caused by magnetic field sensed by the second optical current transformer; and
φdA represents an angle of rotation of emitted light from the second optical current transformer caused by magnetic field sensed by the third optical current transformer.

### Claim 4 (depends on 3)

The optical calculation system for the relay protection based on the Faraday magneto-optical rotation effect according to claim 3, wherein an optical intensity Pout is an output light signal from the third optical current transformer, and is allowed to be given by:
P
o
⁢
u
⁢
t
≈
1
8
⁢
P
o
+
1
4
⁢
P
o
(
φ
Y
⁢
A
-
φ
Y
⁢
B
+
φ
dA
)
=
1
8
⁢
P
o
+
1
4
⁢
P
o
⁢
φ
,
wherein Po represents an optical intensity of emitted light from the light source.

### Claim 5 (depends on 1)

The optical calculation system for the relay protection based on the Faraday magneto-optical rotation effect according to claim 1, wherein the Faraday rotation angle is allowed to be expressed as φ=φYA−φYB+φdA;
wherein,
φYA represents an angle of rotation of polarization light caused by magnetic field sensed by the first optical current transformer;
φYB represents an angle of rotation of emitted light from the first optical current transformer caused by magnetic field sensed by the second optical current transformer; and
φdA represents an angle of rotation of emitted light from the second optical current transformer caused by magnetic field sensed by the third optical current transformer.

### Claim 6 (depends on 5)

The optical calculation system for the relay protection based on the Faraday magneto-optical rotation effect according to claim 5, wherein an optical intensity Pout is an output light signal from the third optical current transformer, and is allowed to be given by:
P
o
⁢
u
⁢
t
≈
1
8
⁢
P
o
+
1
4
⁢
P
o
(
φ
YA
-
φ
YB
+
φ
dA
)
=
1
8
⁢
P
o
+
1
4
⁢
P
o
⁢
φ
,
wherein Po represents an optical intensity of emitted light from the light source.

### Claim 7 (depends on 1)

The optical calculation system for the relay protection based on the Faraday magneto-optical rotation effect according to claim 1, wherein the light source is a Super Luminescent Diode (SLD) light source with a wavelength of 850 nm.

### Claim 8

An optical calculation method for relay protection based on Faraday magneto-optical rotation effect, wherein the optical calculation method is implemented by using an optical calculation system; the optical calculation system comprises:
a light source, a first optical current transformer, a second optical current transformer, and a third optical current transformer;
a light signal emitted from the light source passes sequentially through the first optical current transformer, the second optical current transformer, and the third optical current transformer, allowing the light signal to carry a Faraday rotation angle φ, wherein the Faraday rotation angle φ comprises differential current information;
a transmission of the light signal from the light source to the first optical current transformer, from the first optical current transformer to the second optical current transformer, and from the second optical current transformer to the third optical current transformer is achieved through multimode fibers;
Faraday magneto-optical elements of the first optical current transformer and the third optical current transformer are located on a high-voltage side and low-voltage side, respectively, of a protected phase of transformer;
a Faraday magneto-optical element of the second optical current transformer is located on a high-voltage side of adjacent phase to the protected phase of the transformer;
under normal operating conditions, a phase difference between a high-voltage side of the protected phase and its adjacent phase is the same as a phase of the low-voltage side of the protected phase;
the Faraday magneto-optical elements of the first optical current transformer, the second optical current transformer, and the third optical current transformer are allowed to sense a magnetic field generated by a current on their respective sides;
wherein angles between an optical path of the first optical current transformer and a current direction on its respective side, an optical path of the second optical current transformer and its current direction, and an optical path of the third optical current transformer and its current direction satisfies the following condition:
sin
⁢
θ
YA
:
sin
⁢
θ
YB
:
sin
⁢
θ
dA
=
1
:
1
:
3
n
T
,
wherein θYA represents the angle between the optical path of the first optical current transformer and the current direction on its respective side, θYB represents the angle between the optical path of the second optical current transformer and the current direction on its respective side, θdA represents the angle between the optical path of the third optical current transformer and the current direction on its respective side, and nT represents transformation ratio; and
the optical calculation method is as follows:
detecting a carrier signal JDC and a modulation wave signal JAC of an output light signal from the third optical current transformer by using a filtering circuit;
calculating a modulation ratio m based on the following equation:
m
=
J
AC
J
DC
,
and
calculating a differential current id based on the following equation:
i
d
=
m
2
⁢
V
⁢
L
,
wherein V is a Verdet constant of a Faraday magneto-optical element in the first, second and third optical current transformers, and, L is a coefficient of the multiple relationship between the magnetic field integral on the Faraday magneto-optical element in the first, second and third optical current transformers to its measured current.

### Claim 9 (depends on 6)

The optical calculation method for the relay protection based on the Faraday magneto-optical rotation effect according to claim 6, wherein internal composition structures of the first optical current transformer, the second optical current transformer, and the third optical current transformer are identical;
each of the first to third optical current transformer comprises a few collimators, a polarizer, the Faraday magneto-optical element, and an analyzer;
an incident light is collimated by the collimator and enters the polarizer, becoming a polarized light; the polarized light passes through the Faraday magneto-optical element and undergoes a rotation due to a modulation by the magnetic field, wherein the Faraday magneto-optical element is located in the magnetic field; the rotated polarized light exits the optical calculation system after passing through the analyzer and the collimator;
output ends of the analyzer comprise output end π/4 and output end −π/4;
angles between an optical axis of the polarizer and an optical axis of the output end π/4 and output end −π/4 of the analyzer are π/4 and −π/4 respectively;
output optical signals of the first optical current transformer and the third optical current transformer are both emitted from the output end −π/4 of their respective analyzers; and
the output optical signal of the second optical current transformer is emitted from the output end π/4 of its analyzer.

### Claim 10 (depends on 9)

The optical calculation method for the relay protection based on the Faraday magneto-optical rotation effect according to claim 9, wherein the Faraday rotation angle is denoted as φ=φYA−φYB+φdA;
wherein,
φYA represents an angle of rotation of polarization light caused by magnetic field sensed by the first optical current transformer;
φYB represents an angle of rotation of emitted light from the first optical current transformer caused by magnetic field sensed by the second optical current transformer; and
φdA represents an angle of rotation of emitted light from the second optical current transformer caused by magnetic field sensed by the third optical current transformer.

### Claim 11 (depends on 10)

The optical calculation method for the relay protection based on the Faraday magneto-optical rotation effect according to claim 10, wherein an intensity Pout of an output light signal from the third optical current transformer is given by:
P
o
⁢
u
⁢
t
≈
1
8
⁢
P
o
+
1
4
⁢
P
o
(
φ
Y
⁢
A
-
φ
Y
⁢
B
+
φ
dA
)
=
1
8
⁢
P
o
+
1
4
⁢
P
o
⁢
φ
,
wherein Po represents an intensity of the light signal emitted by the light source.

### Claim 12 (depends on 8)

The optical calculation method for the relay protection based on the Faraday magneto-optical rotation effect according to claim 8, wherein the Faraday rotation angle is denoted as φ=φYA−φYB+φdA;
wherein,
φYA represents an angle of rotation of polarization light caused by magnetic field sensed by the first optical current transformer;
φYB represents an angle of rotation of emitted light from the first optical current transformer caused by magnetic field sensed by the second optical current transformer; and
φdA represents an angle of rotation of emitted light from the second optical current transformer caused by magnetic field sensed by the third optical current transformer.

### Claim 13 (depends on 12)

The optical calculation method for the relay protection based on the Faraday magneto-optical rotation effect according to claim 12, wherein an intensity Pout of an output light signal from the third optical current transformer is given by:
P
o
⁢
u
⁢
t
≈
1
8
⁢
P
o
+
1
4
⁢
P
o
(
φ
YA
-
φ
YB
+
φ
dA
)
=
1
8
⁢
P
o
+
1
4
⁢
P
o
⁢
φ
,
wherein Po represents an intensity of the light signal emitted by the light source.

### Claim 14 (depends on 8)

The optical calculation method for the relay protection based on the Faraday magneto-optical rotation effect according to claim 8, wherein the light source is a SLD with a wavelength of 850 nm.