Phase angle drift method for loss of mains/grid protection

Patent metadata

Field	Value
Publication number	US-9325175-B2
Application number	US-200913499669-A
Country	US
Kind code	B2
Filing date	Sep 30, 2009
Priority date	Sep 30, 2009
Publication date	Apr 26, 2016
Grant date	Apr 26, 2016

Abstract

A phase angle drift method for loss of mains/grid protection is disclosed. According to one aspect, an accumulated electrical phase angle drift derived from the difference between the current measured local frequency and the estimated frequency using historical data is compared to an angle threshold. An estimated grid frequency may be calculated based on the historical delay, and the window, over which the estimated frequency is calculated. An addition/subtraction of a phase angle offset value is calculated for a half cycle is performed when the frequency difference between the estimated frequency f n est and the measured frequency f n is greater or equal to a first determined value.

First claim

What is claimed is:

1. A phase angle drift detection method for loss of mains/grid protection, wherein the accumulated electrical phase angle drift derived from the difference between a current measured local frequency from a tracking algorithm and an estimated frequency calculated using historical data is compared to an angle threshold with the phase angle drift α n being such that:
α n =α n-12 +2π( f n est −f n ) T 12samples

where:
n: Sample index
α n : Updated phase angle
α n-12 : Previous phase angle
Δα: 2π(f n est −f n )T 12samples
f n est : Estimated frequency
f n : Measured frequency
T 12samples : Time interval between two algorithm executions

the estimated grid frequency being calculated using the following equation based on the historical delay, D cycles, and the window, W cycles, over which the estimated frequency is calculated:

f
n
est

=

f

n
-
D
-
W

+

(

T
W

+

T
D

)

T
W

⁢

(

f

n
-
D

-

f

n
-
D
-
W

)

where:
f n-D-w : Oldest frequency value
f n-D : Newest frequency value
T D : Historical time delay
T W : Estimation window
wherein the addition/subtraction of the phase angle increase/decrease Δα calculated for the half cycle in the phase angle drift equation is not carried out unless the frequency difference between the estimated frequency f n est and the measured frequency f n is greater or equal to a first determined value, and in that the phase angle is reset to zero once changes Δα in the phase angle have fallen below a second determined value over a moving window equal to the size of the estimation window T W .

2. The method of claim 1 , wherein, if the difference between a new estimated frequency and a previous estimated frequency is greater or equal to a third determined value, then the new estimated frequency is discarded and replaced with the previous estimated frequency plus the third determined value.

3. The method of claim 1 , wherein, if a three phase fault is detected with a retained positive sequence voltage magnitude of less than a fourth determined value and negative sequence voltage magnitude less than a fifth determined value, then the angle threshold is increased to twice its set value for the duration of the fault.

4. The method of claim 3 , wherein once the fault has been cleared, the angle threshold is linearly reduced to its set value over a period of a sixth determined value.

5. The method of claim 1 , wherein the first determined value is 0.05 Hz.

6. The method of claim 1 , wherein the second determined value is 0.08°.

7. The method of claim 2 , wherein the third determined value is 0.002 Hz.

8. The method of claim 3 , wherein the fourth determined value is 60%.

9. The method of claim 3 , wherein the fifth determined value is 40%.

10. The method of claim 4 , wherein the sixth determined value is 0.25 second.

11. A phase angle drift detection apparatus for loss of mains/grid protection, the apparatus comprising circuitry configured to:
derive an accumulated electrical phase angle drift from the difference between a current measured local frequency from a tracking algorithm and an estimated frequency calculated using historical data by comparing an angle threshold with the phase angle drift such than an updated phase angle value α n is calculated according to a phase angle drift equation as:
α n =α n-12 +2π( f n est −f n ) T 12samples

where:
n: Sample index
α n-12 : Previous phase angle
Δα: 2π(f n est −f n )T 12samples
f n est : Estimated frequency
f n : Measured frequency
T 12samples : Time interval between two algorithm executions

the estimated grid frequency f n est being calculated as:

f
n
est

=

f

n
-
D
-
W

+

(

T
W

+

T
D

)

T
W

⁢

(

f

n
-
D

-

f

n
-
D
-
W

)

based on the historical delay, D cycles, and the window, W c

Assignees

• Tumilty Ryan M
• Dysko Adam
• Burt Graeme
• Alstom Technology Ltd
• Schneider Electric Energy Uk Ltd

Inventors

• Tumilty Ryan M
• Dysko Adam
• Burt Graeme

Classifications

• H02J3/388

  Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power · CPC title

• H02J3/38 Primary

  Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel · CPC title

• H02J2003/388

  Electricity · mapped topic