KR20060029022A - The measuring method of the unperfected circuiting current of underground cable - Google Patents

Abstract

The present invention relates to a method for measuring incomplete circulating current of underground transmission cables. More specifically, the present invention relates to a method for measuring an incomplete circulating current generated in an ultrahigh voltage (154 kV, 345 kV) underground cable cross-bonding system due to a sheath damage (and a failure of a cable arrester) which causes an incomplete influence of a circulating current.

According to the present invention, in the case of a poor connection of a metal sheath or a poor insulation between the anticorrosive layer and the cable arrester, an incomplete circulating current is calculated and a measurement method is suggested to predict an accident point of an underground cable by an incomplete circulating current. It can prevent large accidents.

Circulating current, incomplete, air distribution, cross bonding, ground resistance, ground cable

Description

The Measuring Method of the Unperfected Circuiting Current of Underground Cable             

1 is a view showing a conventional grounding system.

2 is a diagram of the underground line of the present invention.

3 is a diagram of a cross-bonding system of the underground transmission line of the present invention.

4 is a diagram of a crossbonding system when circulating current is incomplete.

5 is a diagram of a crossbonding system of an underground transmission line upon incomplete grounding.

6 is a conceptual diagram of the cable allowed current.

7 is a diagram of an ultra-high voltage cable system for incomplete ground resistance measurement.

<Explanation of Signs of Major Parts of Drawings>

1: substation 3: underground cable

5: Insulation protection device 7: Ground wire

8: Intermediate junction box 9: Insulated junction box (2 split)

10: crossbonding system 11,12, 13; 3-phase cable

16: Ground Resistance 17: Incomplete Ground Resistance (Corrosion Layer and CCPU Poor)

The present invention relates to a method for measuring incomplete circulating current of underground transmission cables. More specifically, it occurs in ultra-high voltage (154kV or 345kV) underground cable cross-bonding systems in the case of poor connection of metal sheaths with incomplete effects of circulating current, or damage to the coating of the anticorrosive layer and poor insulation of the cable arrestor (CCPU). It relates to a method for measuring an incomplete circulating current.

With the recent development of the industry, the demand for electricity is growing rapidly, and especially in urban areas, it is being replaced by underground transmission lines because of the limitations of urban aesthetics and overhead transmission lines. The use of cross-bonding systems is common in high voltages to increase the transmission capacity in 154kV and 345kV underground cables and to lower the induced voltages that induce interference on communication lines. Sheath induced voltage is generated when current flows through the transmission line.The sheath induced voltage is regulated to not exceed 65V for the safety of the inspector and the safety of the equipment, and to prevent the overvoltage I use it. However, the sheath circulating current has no specific regulation.

If the cable and corrosion protection layer is damaged due to deterioration over time, the cross-bonding system is affected, causing deformation of the sheath circulated current, which causes sheath loss. This can drastically reduce the cable allowable current. In other words, the reduction of the allowable current immediately causes abnormal heat generation of the cable, which eventually causes the cable fire.

Incomplete sheath circulating current can be caused by various factors such as the influence of other lines, mistake of cross bonding, incomplete grounding, influence of adjacent circuits, and sudden load fluctuations.

For example, if there is no defect in the cross bonding system, it is 760A, but if an incomplete ground occurs, it can be lowered to 76A. In this case, an overheating of the transmission capacity can lead to a fire accident due to abnormal heating of the cable.

In particular, incomplete grounding may occur due to damage to the coating of the anticorrosive layer when the cable is laid, a failure of the cable arrester, or the like.

1 is a view showing a conventional grounding system, Figure 2 is a diagram of the underground line after modification. 1 shows a cross bonding system of a ground cable. The underground cable is extended to measure the entire circulating current of the underground cable or cut off at the time of crisis. The underground cable (3) is connected to the insulation tube protection device (4: gapless type EB-G connection) through the gas terminal junction box (2) in the substation (1) and the reference numeral 6 is the insulation tube protection device (gapless type IJ connection) ) Is connected to the middle junction box (8) and the insulation junction box (9) to form a grounding system.

1 is a cable line diagram currently in use. When current flows in the conductor, current and voltage are generated in the sheath. When the cross-bonded lines have the same length, circulating current does not flow but only the sheath induced voltage is generated. Circulating currents are generated when the inequality and arrangement of the lengths of the lines are different. The problem with this system is that incomplete circulating currents and incomplete resistances cannot be measured.

In order to solve the problems of the prior art as described above, the object of the present invention is an incomplete circulating current generated in the system of underground high-voltage cable cross-bonding system due to the damage of the sheath and the arrester among the effects of the incomplete effect of the circulating current It is to provide a method of measuring.

Incomplete circulating current measurement method of the underground transmission cable of the present invention for realizing the object of the present invention is to calculate the sheath circulating current of the cross-bonding system of underground high voltage cable, the ground based on the circulating current value Characterized in that it consists of the step of identifying the point of accident of the Keul.

However, if the anticorrosive layer or CCPU is bad,

If the sheath connection is incomplete

단일접지불완전

Single ground incomplete

3상접지불완전

Incomplete 3-phase grounding

Where L, M, N: span length [km], [Z1], [Z2], [Z3] of the cross-bond section, impedance matrix [Ω / km], [Isi]: Circulation current matrix, [Vs]: Cable sheath induced voltage matrix, Re: Ground resistance.

On the other hand, in the present invention, if the current measuring device is attached to the four ends of the complementary line, the anticorrosive layer resistance and the line incomplete contact resistance can be measured by the four current measurements, thereby preventing the accident of the cable.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

2 is a diagram of the underground cable line of the present invention. 3 is a diagram of a cross-bonding system of the underground transmission line of the present invention. 4 is a diagram of a cross-bonding system when the circulating current is incomplete, and FIG. 5 is a diagram of a cross-bonding system of an underground transmission line when incomplete grounding. 6 is a conceptual diagram of the cable current allowance, and FIG. 7 is a diagram of an ultra-high voltage cable system for incomplete ground resistance measurement.

Example 1

Figure 2 is a line diagram of the underground line diagram of the present invention to improve the Figure 1 is a line diagram that can measure the circulating current and incomplete resistance. Since it is continuously crossbonded, the sheath induced voltage does not increase and the sheath circulating current does not increase significantly due to the section equilibrium. In addition, by measuring the incomplete circulating current and resistance in the terminal it is possible to prevent a fire accident due to the circulating current in advance. In addition, partial degradation diagnosis can be made. That is, the incomplete circulating current and the resistance can be measured by configuring the line diagram circuit as shown in FIG. 2. That is, when the current measuring device CT is attached to four end portions of the line, the anticorrosive layer resistance and the line incomplete contact resistance can be measured by the four current measurements.

3 is a cross-bonding system in a steady state. However, if the sheath becomes incomplete ground, the [Za] matrix will be generated. If the sheath is incompletely connected, the [ZZ] incomplete ground matrix will occur.

In this case, the formula of the sheath circulating current of the cross-bonding system is shown in Equation 1.

However, in the case of incomplete grounding of the anticorrosive layer, i.e., the bad corrosion layer and the bad CCPU

If the sheath connection is incomplete

단일접지불완전

Single ground incomplete

3상접지불완전

Incomplete 3-phase grounding

Where L, M, N: span length [km], [Z1], [Z2], [Z3] of the cross-bond section, the impedance matrix [Ω / km], [Isi]: Circulation current matrix, [Vs]: Cable sheath induced voltage matrix, Re: Ground resistance.

In FIG. 3, the circulating currents flowing through the three-phase cables 11, 12, and 13, the intermediate junction box 14, the insulation junction box 15, the cross bonding connection line, and the three-phase cable are Is1, Is2, and Is3, respectively. Ground resistance 16 is Re. If the current measuring device (CT) is attached to four places at the end of the line complemented in FIG. 3, the anticorrosive layer resistance and the line incomplete contact resistance can be measured by the four current measurements, thereby preventing an accident.

However, in the case of the anticorrosive layer failure and the sheath ground failure, FIG. 3 is modified as shown in FIG. 4. As can be seen in Figure 4, the cross-bonding system 10 is the case of incomplete circulating current in the three-phase cable of Figure 3 i) the effect of the adjacent cable, ii) the effect of the ground current Ii (2 in Figure 4 Ii), i) i) cross-bond mistake (3) in FIG. 4) i) poor corrosion protection layer (4 in 4) zz), i) imperfect ground (5 in 4) Ri)) One. In the present invention, the cases of i) and i) are analyzed.

In this embodiment of the present invention, the cross bonding system is affected by zz (17: ground resistance in case of accident). That is, the sheath circulating currents Is1, Is2, Is3 are changed by zz. In this case, Equation 1 is converted as in Equation 2. In other words, zz 17 causes the circulating current to be distorted to flow.

In this case, the circulating current is also divided into four types. That is, the circulating current is divided in the order of the left Is1 + zz, the right Is1 + zz, Is2, and Is3, and the circulating current matrix is created.

5 is a diagram of a crossbonding system of an underground transmission line during incomplete grounding.

In this case, it is possible to obtain the change of the resistance Re due to the anticorrosive layer and the ground incompleteness and the circulating currents Is1, Is2, Is3 flowing through the ground resistance zz in case of an accident by zz (17).

When the anticorrosive layer failure and CCPU failure are obtained, the cross-bond is obtained and the cyclic current of l = 511 [m], m = 456 [m] and n = 499 [m] of 154 [kV] 1c x 400SQMM is obtained. It can be obtained in 1) of the case, the case of the sheath incomplete L = 340m, M = 1169m, N = 389m, single- and three-phase sheath current calculation examples are shown in 2) of [Table 1].

As the value of zz changes, the circulating current and the circulating current loss change.

There are three types of cable laying: underground, aerial, and direct laying. This laying is limited to aerial laying. In underground or direct laying, if the cross bond method is used, the allowable current may be different.

1) Example of sheath current calculation in case of corrosion prevention layer and CCPU Za (U / km) 0.001 0.1 One 10 100 Isa (A) 277 89 22 13 12 Isb (A) -129 -29 6 11 12 Isc (A) 18 18 18 18 18 Isd (A) 18 18 18 18 18

2) Example calculation of single-phase and three-phase sheath current

Calculation of the Sheath Circulating Current (Limit Incomplete Ground)

Za (U / km) 0 0.02 0.1 0.375 One 10 Isa (A) 47.-j60 42-j60 27-j59 3-j41.6 -3.8-j20 -1-j2.3 Isb (A) 33 + j38 36 + j38 44 + j37 57.8 + 28 62 + j8 60 + j7 Isc (A) -81 + j30 -79 + j30 -71 + j30 -58 + j21 -53 + j10 -54 + j0.9 Io (A) -0.7 + j8 -0.4 + j8 0.6 + j8 2.8 + j8 4 + j8 4 + j6

Calculation of the Sheath Circulating Current (Three Phase Incomplete Ground)

Za (U / km) 0.02 0.1 0.11 One 10 100 Isa (A) 40-j61 18-j56 16-j54 -4.9-j12 -1.6-j1 -0.1-j0.1 Isb (A) 33 + j33 29 + j20 28 + j19 -7 + j3 0 + j0.5 -0 + j0 Isc (A) -74 + j36 -48 + j43 -45 + j43 -4.6 + 15 -1 + j2 0.1 + 0.1 Io (A) -0.7 + j8 -0.6 + j8 -0.6 + j8 -1.1 + j7 -2 + j1 -0 + j0

6 is a conceptual diagram of the cable current allowance. In the case of airborne allowance current (I) can be obtained by the equation (3).

I: Cable Allowable Current [A]

T1: conductor temperature [° C], T2: air temperature [° C]

Td: temperature rise of dielectric [℃]

Rth: Heat resistance [℃ .cm / W], Rth = R1 + (1 + Ps) (R2 + R3)

R1: Heat resistance of insulator [℃ .cm / W], R2: Heat resistance of anticorrosive layer [℃ .cm / W]

R3: Surface Dissipation Heat Resistance [℃ .cm / W]

Ps: Circuit Loss Rate: Ps = P1 + P2

P1: circuit loss rate, P2: sheath eddy current loss rate

P1 = Ws / Wc

Ws: Sheath loss rate (Is ^ 2 x Rs), Wc: Conductor loss rate (I ^ 2 x Rc)

Rs: sheath resistance

Rc: AC conductor effective resistance

In this case, if the sheath loss rate is calculated due to ground incompleteness, it is changed as shown in [Table 2]. Thus, the allowable current according to the sheath incomplete ground is calculated as shown in [Table 2].

1) Example of calculation of allowable current in case of corrosion protection layer and CCPU failure Za (Ω / km) standard 0.001 0.01 One 10 100 Sheath loss rate 0.2 5.85 302 12.1 0.64 0.06 Allowable Current (A) 760 464 76 342 693 755

2) Allowable current due to incomplete sheath connection

Single phase grounding standard

Za (Ω / km) standard 0.0 0.02 0.1 0.375 One 10 Sheath loss rate 0.2 0.01 0.35 1.95 4.35 2.22 0.075 Allowable Current (A) 760 762 723 595 487 570 750

3-phase grounding standard

Za (Ω / km) standard 0.02 0.1 0.11 One 10 Sheath loss rate 0.2 0.35 1.5 4.35 0.57 0.05 Allowable Current (A) 760 724 623 570 699 759

3-phase grounding standard

Za (Ω / km) standard 0.02 0.1 0.11 One 10 Sheath loss rate 0.2 3.8e-4 9.4e-4 1.8e-3 1.1e-3 5.5e-3 Allowable Current (A) 760 763 763 763 763 762

Single phase ground wire standard

Za (Ω / km) standard 0.02 0.1 0.5 One 10 Sheath loss rate 0.2 4e-4 2e-3 1.1e-3 7e-3 6e-3 Allowable Current (A) 760 763 763 763 762 762

Since the cable allowable current I is affected by the circulated current loss, the remaining coefficients except for the circulating current may be set identically. The cyclic current loss is affected by the sheath loss rate (Ws), which can be applied to the circuit loss rate (Ps).

Ps (32) = P1 + P2

P1: circuit loss rate, P2: sheath eddy current loss rate: 0.157

The sheath circuit loss rate is determined as in Equation 4.

P1 = Ws / Wc = Is ^ 2 Rs / I ^ 2 / r

Ws: Sheath loss rate [w / cm], Wc: Conductor loss rate [w / cm], Rs: Sheath resistance [Ω / km]

Since Ws and Rc are constants determined by the cable shape, only allowable current remains.

It can be seen from Table 2 that the allowable current according to the ground resistance gradually decreases as the insulation resistance increases and then increases again. That is, in the case of cross-bonding system without considering the grounding resistance, the allowable current was 760 [A], but if an incomplete ground (grounding resistance: 0.1 Ω) occurs, it can be reduced to 76 [A]. This can lead to an accident.

Incomplete grounding may be caused by damage to the coating of the anticorrosive layer during cable installation and failure of the cable arresters. As shown in [Table 2], when the circulating current flows a lot, the allowable current is not lowered, but when the incomplete current is 118 [A], that is, the allowable current is further lowered in the vicinity of 0.1 [Ω / km].

Thus, although the cross bonding system is an ideal system for reducing the allowable current, it can be seen that the allowable current is drastically lowered when a cross bonding abnormality occurs.

(Example 2)

In the industry, the cable's allowable current is applied to IEC 287 and JCS 168. However, in general, no ratio of circulating current is applied.

The incompleteness of the circulating current changes rapidly due to the influence of other cables, cross-bond misses, poor grounding, and corrosion protection layer, which leads to sheath losses. In case of incomplete sheath loss, the cable's power transmission capacity drops to about 1/10, but there are no systemic measures against this. Therefore, the check of incomplete ground resistance by the corrosion protection layer and the cable arrestor (CCPU) is necessary for the diagnosis of the power cable system.

7 is an ultrahigh voltage cable system diagram for measuring incomplete ground resistance.

In the case of the circulating current, it is necessary to remove the circulating current of the dangerous part because the reduction of the transmission capacity occurs in a certain part rather than an unconditional reduction. To do this, it is necessary to check the ground resistance to avoid the point where the sheath loss is at its peak. In addition, it is the thermal resistance that affects the allowable current. The comparison of the thermal resistance of the conductor and the insulator is shown in [Table 3].

Material type Cu Al PE PVC Thermal resistance (Ω.cm / W) 0.25 0.4 450 600

Assuming that the heat dissipation is the same, in case of Al sheath and PE type layer, it is possible to transmit normal allowable current (760A) at 487A or 4.5m near the ground resistance.

The sheath circulating current has no significant difference in the case of the normal cross bond when the incomplete ground is above a certain value and 100 [Ω / km]. Abnormal circulating current is generated when failure of installation and arrester occurs. In this case, the allowable current is reduced to about 1/10 than normal.

A device is needed to check the sheath incomplete ground resistance. In particular, there is a need for a way to avoid the point where the sheath incomplete ground resistors generate the lowest allowable current. This is all different for each grounding system, so system specific calculations are required. In other words, if the resistance and the circulating current of the four places in Fig. 2 are measured, the circulating current and the resistance flowing through the canister are measured. have.

According to the present invention, when the sheath circulating current is a normal cross bond, when the incomplete ground becomes more than a predetermined resistance, the allowable current is not significantly different. It is about 5m in case of AL and PE anticorrosive layers In the case of incomplete grounding, the transmission capacity varies greatly depending on the ground resistance, and the allowable current drops sharply at a specific resistance. In case of single phase incomplete, about 63% of normal allowable current and about 75% of three phase incomplete. In addition, there is a possibility of a fire due to a sudden drop in the transmission capacity at the incomplete ground point. Therefore, a systematic method of checking the sheath incomplete ground resistance is required, and an experiment on the incomplete circulating current of the grounding system of the actual installation cable is required. Improving the grounding diagram as shown in the attached line diagram as shown in FIG. 2 greatly reduces the risk of an accident by on-line check of the sheath insulation resistance. However, in current grounding schemes, there is no way to check ground line resistance.

To those skilled in the art, the present invention is not limited to the above-described embodiments and the present invention may be embodied in other forms without departing from the spirit of the invention. All design changes made within the scope of the claims and equivalents are considered to be included within the scope of the present invention.

According to the present invention, it is possible to predict the accident point of the underground cable by calculating the incomplete circulating current has the effect of preventing a large accident. In addition, it is possible to implement a basic system for live diagnosis in case of an abnormality.

 In addition, it is possible to check the insulation diagnosis of the cable system and the corrosion protection layer during operation, and to check the allowable current decrease even when the ground is incomplete. In particular, the three-phase batch grounding has an effect of reducing the loss than grounding one by one.

In particular, the thermal resistance contacted by the anticorrosive layer and the thermal resistance due to the bonding miss are also about 2000 times the thermal resistance of the insulator. Therefore, even if the heat due to the bonding is transferred to the sheath and the thermal equilibrium is assumed, Does not affect However, contact thermal resistance has not been examined yet, so creating an equivalent resistance of the incomplete contact resistance of the conductor is a subject for further study. In order to measure the incomplete resistance of the anticorrosive layer and the arrester, the circuit of FIG. 2 may be configured to more effectively manage the incomplete resistance.

Claims (4)

In the method of measuring the incomplete circulating current of underground transmission cable, calculating the ground resistance value (zz) in case of failure of the anticorrosive layer and sheath ground of the cable, obtaining [Za] by the following matrix formula, and the cis circulation Comprising the step of obtaining a current, predicting the accident point on the basis of the cis circulating current measuring incomplete circulating current of the underground transmission cable.

but,

L, M, N: span length [km] of the cross bond section, [Z1], [Z2], [Z3]: Impedance matrix [Ω / km], [Za]: Impedance matrix generated when incomplete ground [Ω / km] [Isi]: Circulating current matrix, [Vs]: Cable sheath induced voltage matrix, Re: Ground resistance. In the method of measuring the incomplete circulating current of the underground transmission cable, calculating the sheath circulating current of the cross-bonding system of the underground high voltage cable in the case of incomplete contact, and identifying the fault point of the underground cable based on the circulating current value. Incomplete circulating current measurement method of the underground transmission cable, characterized in that consisting of a step.

but,

Single ground incomplete

Incomplete 3-phase grounding

L, M, N: Span length [km], [Z1], [Z2], [Z3]: Impedance matrix [Ω / km], [Isi]: Circulation current matrix in each section , [Vs]: cable sheath induced voltage matrix, Re: ground resistance. The method of measuring incomplete circulating current of an underground power cable according to claim 1 or 2, wherein the allowable current is calculated according to the following formula when the underground power cable is airborne.

However, I: Cable allowable current [A] T1: temperature of the conductor [° C], T2: temperature in the air [° C] Td: temperature rise of dielectric [℃] Rth: Heat resistance [℃ .cm / W], Rth = R1 + (1 + Ps) (R2 + R3) R1: Heat resistance of insulator [℃ .cm / W], R2: Heat resistance of anticorrosive layer [℃ .cm / W] R3: Surface Dissipation Heat Resistance [℃ .cm / W] Ps: Circuit Loss Rate: Ps = P1 + P2 P1: circuit loss rate, P2: sheath eddy current loss rate P1 = Ws / Wc Ws: Sheath loss rate (Is ^ 2 x Rs), Wc: Conductor loss rate (I ^ 2 x Rc) Clause 1 Measures these four currents by attaching a current measuring device (CT) to the four ends of the line supplemented by the incomplete circulating current measurement method of underground transmission cables, and measures the anticorrosive layer resistance and the line incomplete contact resistance. Incomplete circulating current measurement method of underground transmission cable.

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