Method for quickly identifying disconnection of CT in protection of 3/2 connection mode based bus

Patent metadata

Field	Value
Publication number	US-10551425-B2
Application number	US-201615358222-A
Country	US
Kind code	B2
Filing date	Nov 22, 2016
Priority date	Jan 4, 2016
Publication date	Feb 4, 2020
Grant date	Feb 4, 2020

Abstract

The present disclosure relates to a method for quickly identifying disconnection of a Current Transformer (CT) in protection of a 3/2 connection mode based bus. The present disclosure can quickly and accurately identify the disconnection of the CT, thereby avoiding the problem of a maloperation in protection of a bus caused by the disconnection of the CT.

First claim

What is claimed is:

1. A method for quickly identifying disconnection of a Current Transformer (CT) in protection of 3/2 connection mode based bus, characterized by comprising:
Step 1, collecting currents of all running branches on a current bus, calculating a current differential current and brake current, then judging, interval by interval, whether a load current abruptly varies, and if the load current of only one branch abruptly varies, targeting the interval;
Step 2, judging whether a variation of the current differential current in Step 1 is larger than a constant value of CT disconnection locking, and judging whether a variation of the current brake current meets a feature of decreasing;
Step 3, judging whether the targeted interval in Step 1 varies from a state in which there is the load current to a state in which there is no current, and judging whether a variation in a current load current per cycle of the targeted interval is equal to a variation in a current differential current per cycle;
Step 4, if the above judgment conditions in Steps 2 and 3 are met, judging that the disconnection of the CT occurs at the targeted interval.

2. The method for quickly identifying the disconnection of the CT in the protection of the 3/2 connection mode based bus of claim 1 , wherein the differential current in Step 1 is a vector sum of the currents of all the branches, and the brake current is a scalar sum of the currents of all the branches.

3. The method for quickly identifying the disconnection of the CT in the protection of the 3/2 connection mode based bus of claim 1 , wherein a criterion for judging whether the variation of the current differential current is larger than the constant value of CT disconnection locking in Step 2 is as follows:
| I cd(i) −I cd(i−2T) |>|I cd(i−2T) −I cd(i−4T) |+I constant value of CT disconnection locking ,
where I cd(i) is a value of the current differential current, I cd(i−2T) is a value of a differential current of a cycle which is located before the current cycle and separated from the current cycle by one cycle, I cd (i−4T) is a value of a differential current of a cycle which is located before the current cycle and separated from the current cycle by three cycles, and I CT disconnection locking constant value is the constant value of CT disconnection locking.

4. The method for quickly identifying the disconnection of the CT in the protection of the 3/2 connection mode based bus of claim 1 , wherein a judgment condition for judging whether the variation of the current brake current meets the feature of decreasing in Step 2 is as follows:
| I r(i−2T) −I r(i−4T) |>|I r(i) −I r(i−2T) |+I mk2 ,
where I r(i) is a value of the current brake current, I r(i−2T) is a value of a brake current of a cycle which is located before the current cycle and separated from the current cycle by one cycle, I r(i−4T) is a value of a brake current of a cycle which is located before the current cycle and separated from the current cycle by three cycles, and I mk2 is a fixed threshold value.

5. The method for quickly identifying the disconnection of the CT in the protection of the 3/2 connection mode based bus of claim 1 , wherein a judgment condition for judging whether the variation of the current brake current meets the feature of decreasing in Step 2 is as follows:
| I r(i−2T) −I r(i−4T) |>|I r(i) −I r(i−2T) |+I mk2 ,
where I r(i) is a value of the current brake current, I r(i−2T) is a value of a brake current of a cycle which is located before the current cycle and separated from the current cycle by one cycle, I r(i−4T) is a value of a brake current of a cycle which is located before the current cycle and separated from the current cycle by three cycles, and I mk2 is a fixed threshold value.

6. The method for quickly identifying the disconnection of the CT in the protection of the 3/2 connection mode based bus of claim 1 , wherein a judgment condition for judging whether the targeted interval varies from the state in which there is the load current to the state in which there is no current in Step 3 is as follows:
| I fh·A |<0.04 I n or | I fh·B |<0.04 I n or | I fh·C |<0.04 I n ,
where I fh·A is a value of an A-phase load current of the targeted interval, I fh·B is a value of an B-phase load current of the targeted interval, I fh·C is a value of an C-phase load current of the targeted interval, and I n is a current threshold value.

7. The method for quickly identifying the disconnection of the CT in the protection of the 3/2 connection mode based bus of claim 1 , wherein a condition for judging whether the variation in the current load current per cycle of the targeted interval is equal to the variation in the current differential current per cycle in Step 3 is as follows:
| I fh(i) −I fh(i−2T) |−|I cd(i) −I cd(i−2T) |<0.06 I n ,
where I fh(i) is a value of a current load current, I fh(i−2T) is a value of a load current of a cycle which is located before the current cycle and separated from the current cycle by one cycle, I cd(i) is a value of the current differential current, I cd(i−2T) is a value of a differential current of a cycle which is located before the current cycle and separated from the current cycle by one cycle, and I n is a current threshold value.

Assignees

• Xj Group Corp
• Xj Electric Co Ltd
• Xuchang Xj Software Technology
• State Grid Corp China

Inventors

• Huang Jidong
• Ni Chuankun
• Tang Hui
• Wang Zhiyong
• Xiao Feng
• Hu Shasha
• Gong Yun
• Feng Guangjie
• Li Shusheng
• Yang Ning
• Zhang Yanhai

Classifications

• G01R31/62 Primary

  Testing of transformers · CPC title

• G01R31/50

  Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58) · CPC title

• G01R31/58 Primary

  Testing of lines, cables or conductors (testing of electric windings G01R31/72) · CPC title

• G01R31/027 Primary

  Physics · mapped topic