CN103235198B - Method for determining phase sequence arrangement modes of conducting wires of same-tower double-circuit transmission lines - Google Patents

Abstract

The invention discloses a method for determining the phase sequence arrangement of the conductors of the double-circuit transmission line on the same tower, which solves the problem that the phase sequence arrangement of the conductors of the existing double-circuit transmission line on the same tower is unreasonable, which leads to the prominent imbalance of the three-phase current in the transmission system question. Including, according to the tower type and the length of the actual line used by the double-circuit transmission line on the same tower, first select a phase sequence arrangement of the conductors on the double-circuit transmission line on the same tower, and use the electromagnetic transient calculation method to calculate the double-circuit transmission line on the same tower. The positive, negative and zero-sequence currents of the two circuits of the transmission line; the zero-sequence current unbalance of the <i>I</i> circuit under the arrangement of all the phase sequences of the conductors on the double-circuit transmission line on the same tower and After the zero-sequence current unbalance degree of the <i>II</i> circuit is calculated respectively, it is determined that the phase sequence arrangement of the wire with the smallest zero-sequence current unbalance degree is the same-tower dual The conductors of the return transmission line are arranged in phase sequence. A simple and practical method is provided for the optimal arrangement of the conductor phase sequence of double-circuit transmission lines on the same tower.

Description

A Method for Determining Phase Sequence Arrangement of Conductors in Double Circuit Transmission Lines on the Same Tower

technical field

The invention relates to a method for determining the phase sequence arrangement of the conductors of a double-circuit transmission line on the same tower, in particular to how to arrange the phase sequence of the transmission conductors on the double-circuit transmission line on the same tower to achieve low current imbalance and lightning resistance A method for determining the phase sequence arrangement of high-level conductors.

Background technique

With the continuous acceleration of my country's urbanization process and the rapid growth of electricity load, a large number of short-distance double-circuit transmission lines on the same tower appear in the power grid. Such double-circuit transmission lines on the same tower are generally erected without transposition. The problem of unbalanced three-phase current in the system caused by its phase sequence arrangement is becoming more and more prominent. Phase sequence arrangement can not only lead to misoperation of zero-sequence protection of transmission lines, but also affect lightning protection performance. According to the design requirements of the transmission line, transposition will not be performed when the entire transmission line is less than 100 kilometers. With the increase of short (or ultra-short) lines and the disconnection of some original full-transposition lines, as well as the successive operation of multiple double-circuit non-transposition lines on the same tower, some power grids are asymmetrical due to electrical parameters. As a result, the three-phase current is obviously unbalanced, causing malfunction or start-up of relay protection and safety automatic devices, and seriously affecting the safe operation of the power grid.

Contents of the invention

The invention provides a method for determining the phase sequence arrangement of the conductors of the double-circuit transmission line on the same tower, which solves the unreasonable arrangement of the conductor phase sequence of the existing double-circuit transmission lines on the same tower, which leads to unbalanced three-phase currents and counterattacks in the transmission system Technical issues with low lightning resistance levels.

The present invention solves the above problems through the following technical solutions:

A method for determining the phase sequence arrangement of conductors of a double-circuit transmission line on the same tower, comprising the following steps:

The first step, according to the length of the tower type used in the same-tower double-circuit transmission line and the actual line, first select a kind of conductor phase sequence arrangement on the same-tower double-circuit transmission line, and use I _I to represent the I loop transmission line Current, use I _II to represent the current of the second circuit transmission line;

The second step is to use the electromagnetic transient calculation method to calculate the positive, negative and zero-sequence currents of the two circuits of the double-circuit transmission line on the same tower;

The third step is to use the following formula to calculate the zero-sequence circulating current unbalance degree of the double-circuit transmission line on the same tower: ;

The fourth step is to use the following formula to calculate the negative-sequence circulating current unbalance degree of the double-circuit transmission line on the same tower:

;

Step 5. Use the following formula to calculate the zero-sequence crossing unbalance degree of the double-circuit transmission line on the same tower:

;

Step 6. Use the following formula to calculate the negative-sequence ride-through unbalance degree of the double-circuit transmission line on the same tower:

;

In the seventh step, the zero-sequence current unbalance degree of the first circuit transmission line is as follows:

;

The eighth step, the zero-sequence current unbalance degree of the second circuit transmission line is as follows:

;

Step 9: Select the other 35 wire phase sequence arrangements of the wires on the double-circuit transmission line on the same tower in turn. For each wire phase sequence arrangement, repeat the above second to eighth steps to calculate the phase sequence of each wire. The zero-sequence current unbalance degree of the first loop transmission line and the zero-sequence current unbalance degree of the II loop transmission line under the sequence arrangement;

Step 10: Sum the zero-sequence current unbalance degree of the first loop transmission line and the zero-sequence current unbalance degree of the II loop transmission line under each conductor phase sequence arrangement and divide by 2 to obtain the zero-sequence current unbalance According to the comprehensive value of zero-sequence current unbalance degree, arrange the phase sequence of 36 kinds of conductors, and sort them from small to large according to the comprehensive value of the zero-sequence current unbalance degree. Balance current optimization sequence number N;

Step 11. Select a conductor phase sequence arrangement on the double-circuit transmission line on the same tower, and calculate the lightning current value of the single-circuit line flashover under the conductor phase sequence arrangement Lightning current value for simultaneous flashover with double-circuit lines , according to the formula: Calculate the comprehensive lightning resistance level of counterattack under the phase sequence arrangement of the conductors value;

The twelfth step, and then select the other 35 kinds of conductor phase sequence arrangements on the double-circuit transmission line on the same tower in turn, and repeat the above tenth step for each conductor phase sequence arrangement, and calculate the comprehensive value of each conductor phase sequence arrangement. Counter-thunder resistance level Value; Arrange 36 types of conductors in phase sequence, according to the comprehensive lightning resistance level The size of the value is sorted from small to large, so as to determine the optimal order number M of the lightning resistance level of counterattack for each phase sequence arrangement of these 36 conductors;

The thirteenth step, add the unbalanced current optimal sequence number N of each of the 36 conductor phase sequence arrangements to the optimal sequence number M of the counter-lightning resistance level and divide it by 2 to obtain the final optimal sequence number W , compare the optimal sequence number W of 36 conductor phase sequence arrangements, and the conductor phase sequence arrangement corresponding to the smallest W value is the determined conductor phase sequence arrangement of the double-circuit transmission line on the same tower.

The invention solves the technical problems that the unreasonable phase sequence arrangement of the conductors of the existing double-circuit transmission lines on the same tower leads to unbalanced three-phase currents in the power transmission system and a low counter-attack lightning resistance level. The optimal permutation of provides a simple and practical method.

Description of drawings

Fig. 1 is a schematic diagram of the current of the double-circuit line on the same tower in the present invention.

Detailed ways

Concrete implementation process of the present invention is as follows:

1. Firstly, according to the tower type, phase sequence arrangement and actual line length, establish a simulation unbalanced current calculation model.

2. Calculate the positive, negative and zero-sequence currents of the double-circuit transmission line on the same tower, as well as the unbalance degree of zero-sequence and negative-sequence currents.

3. Change the phase sequence arrangement of the conductors of the double-circuit transmission line on the same tower until all 36 phase sequence arrangements are calculated;

4. Establish a single-circuit and double-circuit line counter-attack lightning resistance level calculation model, and calculate the single-circuit and double-circuit line counter-attack lightning resistance level of the phase sequence arrangement calculated in 3.

5. According to the sorting of the current unbalance degree and the sorting of the counter-lightning withstand level of the single-circuit and double-circuit lines in the above calculation, select the one with the smallest current unbalance degree and the best counter-lightning withstand level (the difference between the single-circuit and double-circuit line counter-lightning withstand levels is the smallest is the best) is the best phase sequence arrangement.

6. Calculation method of current unbalance degree.

For double-circuit lines on the same tower, the coupling between the two-circuit lines leads to differences in double-circuit parameters, and both ends of the double-circuit lines on the same tower are connected to the same bus, so there must be an unbalanced circulating current I _h between the double-circuit lines,

Let the current of each circuit of the double-circuit transmission line on the same tower be the sequence current vector, that is, satisfy , then the size of the unbalanced circulating current can measure the unbalanced current difference between the double-circuit lines, which is defined as follows: (subscripts I and II represent two circuits of overhead transmission lines respectively)

Unbalance degree of zero sequence circulation: ;

Unbalance degree of negative sequence circulation: ;

For lines other than double-circuit lines on the same tower, the influence of double-circuit lines on the same tower on the unbalanced current is reflected in the total current after parallel connection , so the unbalance degree of current passing through can be defined to reflect its influence on the unbalanced current of other lines in the system:

Zero-sequence crossing unbalance degree: ;

Negative sequence crossing unbalance degree: ;

According to the above definition, taking the zero-sequence unbalance degree as an example, the zero-sequence circulation unbalance degree and the zero-sequence crossing unbalance degree can be obtained as follows:

;

In general, there are ,and are much larger than , so the above formula can be written as:

;

In the same way: ;

Therefore, it can be approximately considered that the zero-sequence current unbalance degree of the first circuit is the vector sum of the zero-sequence ride-through unbalance degree and the zero-sequence circulating current unbalance degree, and the zero-sequence current unbalance degree of the second circuit circuit is the zero-sequence ride-through unbalance degree Balance degree and zero-sequence circulation unbalance degree vector difference. For the negative sequence unbalance degree, it can also be calculated in the same way.

Claims (1)

1. a defining method for the Traverse phase-order arrangement of same tower double back transmission line, comprises the following steps:

The first step, according to same tower double back transmission line use the length of tower and actual track, a kind of Traverse phase-order arrangement first on this same tower double back transmission line selected, uses i _i represent the ithe electric current of loop transmission line, uses i _iI represent the iIthe electric current of loop transmission line;

Second step, utilize EM transient calculation method, calculate positive and negative, the zero-sequence current in two loops of same tower double back transmission line;

3rd step, utilize the zero sequence circulation degree of unbalancedness of following formulae discovery same tower double back transmission line: ;

4th step, utilize the negative phase-sequence circulation degree of unbalancedness of following formulae discovery same tower double back transmission line:

；

5th step, utilize the zero sequence through unbalance degree of following formulae discovery same tower double back transmission line:

；

6th step, utilize the negative phase-sequence through unbalance degree of following formulae discovery same tower double back transmission line:

；

7th step, ithe zero-sequence current degree of unbalancedness of loop transmission line is as follows:

；

8th step, iIthe zero-sequence current degree of unbalancedness of loop transmission line is as follows:

；

Other 35 kinds of Traverse phase-order arrangements of 9th step, again this same tower double back transmission line upper conductor selected successively, for often kind of Traverse phase-order arrangement, repeat above second step to the 8th step, calculate the under often kind of Traverse phase-order arrangement ithe zero-sequence current degree of unbalancedness of loop transmission line and iIthe zero-sequence current degree of unbalancedness of loop transmission line;

Tenth step, by the under the arrangement of often kind of Traverse phase-order ithe zero-sequence current degree of unbalancedness of loop transmission line and iIzero-sequence current degree of unbalancedness integrated value is obtained divided by 2 after the zero-sequence current degree of unbalancedness summation of loop transmission line, by 36 kinds of Traverse phase-order arrangements, by the size of this zero-sequence current degree of unbalancedness integrated value, sort from small to large, thus determine the out-of-balance current preference ordering N of often kind of Traverse phase-order arrangement of these 36 kinds of Traverse phase-order arrangements;

A kind of Traverse phase-order arrangement on 11 step, this same tower double back transmission line selected, calculates the lightning current numerical value of the single back line flashover under the arrangement of this Traverse phase-order with the lightning current numerical value of flashover while of double-circuit line , according to formula: calculate the comprehensive counterattack lightning withstand level under the arrangement of this Traverse phase-order value;

12 step, again other 35 kinds of Traverse phase-order arrangements on this same tower double back transmission line selected successively, for often kind of Traverse phase-order arrangement, repeat above tenth step, calculate the comprehensive counterattack lightning withstand level under often kind of Traverse phase-order arrangement value; By 36 kinds of Traverse phase-order arrangements, by comprehensively strikeing back lightning withstand level the size of value, sorts from small to large, thus determines the counterattack lightning withstand level preference ordering M of often kind of Traverse phase-order arrangement of these 36 kinds of Traverse phase-order arrangements;

13 step, the out-of-balance current preference ordering N each Traverse phase-order in 36 kinds of Traverse phase-order arrangements arranged obtain final preference ordering W divided by 2 after being added with counterattack lightning withstand level preference ordering M, the relatively preference ordering W of 36 kinds of Traverse phase-order arrangements, the corresponding Traverse phase-order arrangement that W value is minimum, for the Traverse phase-order of determined same tower double back transmission line arranges.