RU2723372C1 - Method of cable fault location determining - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to measurement equipment, and namely to determination of damage point of power cable on direct current, having at least two damaged burnt to each other, but whole strands and one serviceable strand, provided that there are no closed loops in the cable at the divorced strands on cable ends and not connected to the measuring leads. Resistance measurements are measured between strands on both ends of cable at open and short-circuited ends of strands of opposite end of cable. Based on the measurements, values of all resistances of the damaged cable replacement circuit are calculated, including transient resistances of the bridges between the strands.EFFECT: obtained resistance values are used to calculate distance to damage point.1 cl, 7 dwg, 2 tbl

Description

The invention relates to a method for determining the location (region) of damage to a direct current power cable with three or more cores, of the same or different cross-section.

Known methods for determining the location (region) of damage to a direct current cable by the Varley loop and Murray loop (see, for example: https://studopedia.ru/5_4385_metod-varleya.html) have low accuracy and require special cable bridges, which often at power plants does not happen. The low accuracy of the above methods is also due to the fact that the cross-sections of the conductors, and, consequently, the resistance of the cable conductors and their ratios are determined by non-electric methods. At the same time, it is very difficult to correctly calculate the cross-section of a cable core of a segment section.

The device manufactured by the industry, which is included in the Flight-205 instrument set (see, for example: https://www.eurostell.com/products/reis-205/), is the closest analogue (prototype) to the proposed method, but has the disadvantage is that the method used in it uses a 2-wire measurement circuit and does not take into account the transition resistance between the conductors. This device is well suited for communication cables, the cores of which have significantly greater resistance compared to power cables. When applying the existing method on power cables, the error is significant.

The proposed method solves the problem of eliminating many of the shortcomings of the above methods of Varley and Murray and the method used in conjunction with “Flight 205”. The inventive method assumes good accuracy and is designed for the use of widespread bridges R-4833, MO-62 and others on a 4-wire circuit.

The problem is solved in that in the proposed method by conducting a group of measurements (the number of measurements is the maximum possible or sufficient to calculate the values of all the resistances of the equivalent circuit of the damaged cable, including the transition resistances of the bridges between the cores or between the core and the metal sheath of the power cable), performed with sufficient accuracy, with the help of calculations, the values of all resistances of the equivalent circuit of the damaged cable are determined, including the transient resistances of the bridges between the conductors or between the core and the metal sheath of the power cable, and the true values of the resistances of the conductors from the place of damage to the ends of the wires, this significantly increases the accuracy of determining the area of the place of damage ( up to a fraction of a percent of the cable length).

The proposed method for determining the area of cable damage is designed for the following:

- the diagnosed cable can have at least two damaged conductors (burnt together, but intact) and one operational core or a separate operational wire.

- the cable can have any number of cores and several damages, but such that in case of separated conductors at the ends of the cable and not connected test leads, no closed loop would form in the cable.

Under the indicated conditions, in all elements of the circuit through which the measuring current will flow, it will have the same value equal to the current from the measuring device, which in each measurement circuit will have its own value. Damage can be in one place or in different places. Cross sections of different cores may be different. Short cable inserts of a different section slightly reduce the accuracy of the determination. The method can also be used if the cable consists of several pieces of different cables of known sections, lengths and material.

An example of the calculated cable damage (for cores 1, 2, 3, ..., n + 5) is shown in FIG. 1.

In FIG. Figures 2 - 7 show, for example, the equivalent circuit of the three cores of a 6 kV AAB cable of the 6 / 0.4 kV transformer and the measurement scheme (two damaged cores burned together, the nature of the damage is determined in a known manner) Each arrow from the device Rz0 -Rz5 - these are two wires connected to each residential separately.

Measurement schemes include cores 1, 2, 3 of damaged cable; the ends of the cores are designated 0-1 and 1-1, 0-2 and 1-2, 0-3 and 1-3, respectively. In the process of measurements and calculations, it is necessary to obtain the values of the following resistances:

R0 - resistance of the core 2 from the end 0-2 to the place of damage to the cable;

R1 - resistance of the core 2 from the point of damage to the end of 1-2 cable;

R2 - resistance of the core 3 from the end 0-3 to the place of cable damage;

R3 - resistance of the core 3 from the place of damage to the end of the 1-3 cable;

R4 - bridge between cores 2 and 3 in the place of cable damage;

R5 - resistance of intact core 1.

The following measurements are carried out:

1. Rz0 = R0 + R4 + R2 (Fig. 2).

2. Rz1 = R1 + R4 + R3 (Fig. 3).

3. Rz2 = R5 + R1 + R4 + R2 (Fig. 4).

4. Rz3 = R5 + R1 + R0 (Fig. 5).

5. Rz4 = R5 + R3 + R2 (Fig. 6).

6. Rz5 = R5 + R3 + R4 + R0 (Fig. 7).

The measurement results are presented in table 1 (numerical values represent real results for a particular damaged cable).

Table 1

To calculate the resistances of the sections on the 6 kV cable, we compose a system of equations. (Similarly, it is possible to calculate on a 0.4 kV cable with different cross-sections of conductors).

We have 6 measurements and we want to identify 6 unknowns (from No. 0 to No. 5).

For measurement No. 0, we write:

Rz0 = R0 + R4 + R2

Or

Coefficients before the letter name of the resistance values will be the first line

matrix A for calculating the resistance values of the cable core sections. The first row of matrix A will look like this: (1 0 1 0 1 0).

Similarly, write down the coefficients for each of the following measurements: (No. 1, No. 2, No. 3, No. 4, No. 5).

As a result, we obtain the matrix A.

We write the measurement results in the form of a column vector of the matrix Rz, starting from measurement No. 0 and beyond.

We compose the matrix equation:

The desired values of the resistances of the cable core sections are denoted by the column vector R, where the top element of the column is number 0, the second is No. 1, and so on.

In Mathcad, to prevent errors, immediately after the declaration of a vector or matrix, you should assign some value to their elements, which will be later replaced by the results of the calculations.

As a result of solving the matrix equation R = A ^-1 * Rz

(where A ^-1 is the inverse matrix of A. (Matkad himself calculates it))

we get the vector matrix of the desired values of the resistance of the sections of cable conductors R.

The results of calculations of the resistance of the sections on the cable of the 6kV transformer are presented in table. 2.

table 2

Cable length L_ _CC = 600.6 m.

The distance L_0-2 from the end 0-2 to the place of damage to the core 2:

The distance L_1-2 from the end of 1-2 to the place of damage to the core 2:

The distance L_0-3 from the end 0-3 to the place of damage to the core 3:

The distance L_1-3 from the end of 1-3 to the place of damage to the core 3.

Difference in determining the distance between cable damage locations defined

on the 2nd and 3rd veins is:

ΔL2,3 = L_1-2 - L_1-3 = 68.2 - 67.6 = 0.6m

The difference in determining the distance between the place of damage determined by the proposed method of measurement and calculation and the actual place of damage:

- in core 2: the calculated value L_1-2 = 68.2 m, the actual L_1-2 = 64.2 m, the difference (error) is 4 m, or 0.67% of the cable length;

- for core 3: the calculated value L_1-3p = 67.6 m, the actual L_1-3 = 64.2 m, the difference (error) is 3.4 m, or 0.57% of the cable length.

Claims (1)

A method for determining the place of damage to a cable having at least two damaged burned together, but whole conductors and one serviceable conductors, provided that there are no closed circuits in the cable when the conductors are separated at the ends of the cable and not connected test leads, which consists in the fact that measurements the resistance between the conductors from both ends of the cable with open and shorted ends of the conductors of the opposite end of the cable, based on measurements, calculate the values of all the resistances of the equivalent circuit of the damaged cable, including the transition resistance of the bridges between the conductors, and the obtained resistance values are used to calculate the distance to the place of damage.

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