阅读说明：本技术 一种串联变压器故障下启机的快速继电保护判别方法 (Quick relay protection judgment method for startup under fault of series transformer ) 是由 顾乔根 吕航 张晓宇 文继锋 程骁 莫品豪 郑超 孙仲民 龚啸 于 2019-09-26 设计创作，主要内容包括：本发明公开一种串联变压器故障下启机的快速继电保护判别方法,包括如下步骤：步骤A,判断如下三点：第一,判别串联变压器是否处于启机状态；第二,判别串联变压器纵差保护是否有差流：第三,判别串联变压器的平衡绕组中是否有电流：步骤B,当步骤A中三点的判别结果都为是时,则判断串联变压器区内存在故障,继电保护动作。此种判别方法可克服现有的纵差保护方法应用于串联变压器时,当串联变压器启机过程中发生轻微绕组故障保护速动性和灵敏性不足的缺陷。(The invention discloses a quick relay protection judging method for starting a series transformer under a fault, which comprises the following steps of: step A, judging the following three points: firstly, judging whether a series transformer is in a startup state or not; secondly, judging whether the longitudinal differential protection of the series transformer has differential flow: thirdly, judging whether the balance winding of the series transformer has current: and step B, when the judgment results of the three points in the step A are all yes, judging that a fault exists in the series transformer area, and performing relay protection action. The judging method can overcome the defects that when the existing longitudinal differential protection method is applied to the series transformer, the protection speed and the sensitivity of slight winding faults are insufficient in the starting process of the series transformer.)

1. A quick relay protection judging method for starting a series transformer under a fault is characterized by comprising the following steps:

step A, judging the following three points:

firstly, judging whether a series transformer is in a startup state or not;

secondly, judging whether the longitudinal differential protection of the series transformer has differential flow:

thirdly, judging whether the balance winding of the series transformer has current:

and step B, when the judgment results of the three points in the step A are all yes, judging that a fault exists in the series transformer area, and performing relay protection action.

2. The method for judging the rapid relay protection of the startup under the fault of the series transformer as claimed in claim 1, wherein: in the first point, the method for judging whether the series transformer is in the startup state comprises the following steps: if:

the switch position of the bypass switch at the network side of the series transformer is in a closed position, and the switch position of the bypass switch at the valve side of the series transformer is in a separated position; or:

the valve control protection system outputs any switching value signal or message representing that the system is in the starting process;

and when any one condition is met, judging that the series transformer is in a starting state.

3. The method for judging the rapid relay protection of the startup under the fault of the series transformer as claimed in claim 1, wherein: in the second point, the method for judging whether the differential current exists in the longitudinal differential protection of the series transformer is as follows: differential flow I when longitudinal differential protection_dGreater than a discrimination threshold I_dsetAnd judging that the series transformer longitudinal differential protection has differential current.

4. The method for judging the rapid relay protection of the startup under the fault of the series transformer as claimed in claim 3, wherein: the discrimination threshold I_dsetIs less than the longitudinal differential protection starting value I_qdThe value is 0.06I_e～0.15I_e。

5. The method for judging the rapid relay protection of the startup under the fault of the series transformer as claimed in claim 1, wherein: in the third point, the method for judging whether the current exists in the balance winding of the series transformer is as follows: if:

phase current I of any phase of balanced winding_pGreater than a discrimination threshold I_pset(ii) a Or:

zero sequence current 3I of balance winding₀Greater than a discrimination threshold I_0set；

If any of the above conditions is satisfied, it is determined that there is a current in the balance winding.

6. The method for judging the rapid relay protection of the startup under the fault of the series transformer as claimed in claim 5, wherein: the discrimination threshold I_psetAnd a discrimination threshold I_0setAll values of (A) are 0.06I_n～0.15I_n，I_nIs the secondary rating of the current transformer.

Technical Field

The invention belongs to the field of power systems, and particularly relates to a method for quickly judging faults in a transformer area in the startup process of a series transformer.

Background

The series transformer has a special structure, a series winding of the series transformer is connected in series in a circuit, and a valve side star winding is connected with a valve side converter; under the wiring mode, the series transformer is difficult to carry out the empty charge test to verify whether the transformer body has faults or not, so that the empty charge test is not always carried out when the series transformer is put into operation, and the transformer is directly put into operation.

However, the winding voltage of the series transformer is from the valve side converter, when the UPFC system is in the startup state, generally speaking, the output voltage of the valve side converter does not suddenly change, and the output voltage thereof always gradually rises from 0 to the target voltage according to a predetermined control strategy, and this process is the startup process of the series transformer. Since the voltage across the series transformer is stepped up, if there is a slight winding short in the series transformer, the differential current of the conventional longitudinal differential protection in this phase is also stepped up from 0, that is: the process of generating the differential current is slow, and the value is small, so that if the transformer has a fault in the process, the differential protection cannot act quickly.

Disclosure of Invention

The invention aims to provide a quick relay protection judging method for startup under a fault of a series transformer, which can overcome the defects of low protection speed and sensitivity of slight winding fault in the startup process of the series transformer when the conventional longitudinal differential protection method is applied to the series transformer.

In order to achieve the above purpose, the solution of the invention is:

a quick relay protection judging method for starting a series transformer under a fault comprises the following steps:

step A, judging the following three points:

firstly, judging whether a series transformer is in a startup state or not;

secondly, judging whether the longitudinal differential protection of the series transformer has differential flow:

thirdly, judging whether the balance winding of the series transformer has current:

and step B, when the judgment results of the three points in the step A are all yes, judging that a fault exists in the series transformer area, and performing relay protection action.

In the first aspect, the method for determining whether the series transformer is in the startup state includes: if:

the switch position of the bypass switch at the network side of the series transformer is in a closed position, and the switch position of the bypass switch at the valve side of the series transformer is in a separated position; or:

the valve control protection system outputs any switching value signal or message representing that the system is in the starting process;

and when any one condition is met, judging that the series transformer is in a starting state.

In the second point, the method for determining whether the differential current exists in the longitudinal differential protection of the series transformer is as follows: differential flow I when longitudinal differential protection_dGreater than a discrimination threshold I_dsetAnd judging that the series transformer longitudinal differential protection has differential current.

The above-mentioned discrimination threshold I_dsetIs less than the longitudinal differential protection starting value I_qdThe value is 0.06I_e～0.15I_e。

In the third point, the method for determining whether there is current in the balance winding of the series transformer is as follows: if:

phase current I of any phase of balanced winding_pGreater than a discrimination threshold I_pset(ii) a Or:

zero sequence current 3I of balance winding₀Greater than a discrimination threshold I_0set；

If any of the above conditions is satisfied, it is determined that there is a current in the balance winding.

The above-mentioned discrimination threshold I_psetAnd a discrimination threshold I_0setAll values of (A) are 0.06I_n～0.15I_n，I_nIs the secondary rating of the current transformer.

After the scheme is adopted, the invention has the beneficial effects that:

the invention provides a quick relay protection judging method for starting a series transformer under a fault, which comprises the following steps of firstly judging whether the series transformer is in a starting process; if the series transformer is in the starting process, the grid side winding of the series transformer is isolated from the alternating-current transmission line in principle, so that whether the series transformer has a fault can be judged only by judging whether the longitudinal differential protection has two electrical characteristics of differential current and whether the balance winding has current, and the fault is judged to exist in the series transformer without judging that the transformer has the fault after a series of criteria such as a braking characteristic curve, a CT saturation criterion, an excitation inrush current criterion and the like in the conventional longitudinal differential protection are met. The invention can improve the speed and the sensitivity of the relay protection action when the UPFC system is started in the state that the series transformer has a slight winding short circuit.

Drawings

FIG. 1 is a diagram of a series transformer configuration and transformer arrangement;

fig. 2 is a logic block diagram of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The technical solution and the advantages of the present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 1, CT1 and CT2 form a longitudinal differential protection differential circuit of a series transformer, and the differential flow of the differential protection formed by CT1 and CT2 is I_d。

The invention provides a quick relay protection judging method for starting a series transformer under a fault, which comprises the following steps:

step 1, judging whether the series transformer is in a startup state:

the criteria include:

criterion 11: if the switch position of the bypass switch at the network side of the series transformer is in the closed position, and the switch position of the bypass switch at the valve side of the series transformer is in the separated position;

criterion 12: the valve control protection system outputs any switching value signal or message representing that the system is in the starting process;

when any one of the criterion 11 and the criterion 12 meets the condition, judging that the series transformer is in a startup state;

step 2, judging whether the longitudinal differential protection of the series transformer has differential flow:

the criteria include:

criterion 21: differential flow I when longitudinal differential protection_dGreater than a discrimination threshold I_dsetIn the process, the differential current exists in the longitudinal differential protection of the series transformer, wherein the longitudinal differential protection can be differential protection which arbitrarily adopts a magnetic balance principle in the prior art;

discriminating threshold I_dsetIs less than the longitudinal differential protection starting value I_qdGenerally at 0.06I_e～0.15I_eIt is preferable. According to the standard, the common longitudinal differential protection starting value I_qdGenerally not less than 0.3I_ePartial region and even custom setting differential starting value is 0.6I_eThe above. Due to the discrimination threshold I_dsetIs less than the longitudinal differential protection starting value I_qdTherefore, the longitudinal differential protection can reach the discrimination condition with differential flow, and is much easier to satisfy the differential characteristic curve than the longitudinal differential protection, so the criterion 21 ensures the sensitivity of the method of the invention.

Step 3, judging whether the balance winding of the series transformer has current:

the criteria include:

criterion 31: phase current I of any phase of balanced winding_pGreater than a discrimination threshold I_pset；

Criterion 32: zero sequence current 3I of balance winding₀Greater than a discrimination threshold I_0set；

When any one of the criteria 31 and 32 meets the condition, judging that the balance winding has current;

discriminating threshold I_psetAnd a discrimination threshold I_0setThe value of (b) can be smaller, generally 0.06I_n～0.15I_nPreferably, I_nIs the secondary rating of the current transformer. The common overcurrent protection constant value in the existing relay protection should avoid the maximum unbalanced current or the load current in principle, so that the threshold I is judged_psetAnd a discrimination threshold I_0setThe value of (a) is much smaller than the common over-current protection constant value, so the criterion 31 ensures the sensitivity of the method of the invention.

As shown in fig. 2, when the determination results in step 1, step 2, and step 3 are all yes, it is determined that a fault exists in the series transformer area, and the relay protection is performed.

The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.