JPH0524465B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a fault point locating device for a DC power transmission system that detects the distance from a power transmission end to a fault point in a DC power transmission system.

[Technical background]

Conventionally, in AC power transmission systems, methods have been used to locate the distance from the transmission end to the fault point by applying the superposition theorem and Thevenin's theorem, but in DC power systems, there is still no practical locating device. Not put into practical use.

[Purpose of the invention]

The present invention was made against this technical background, and its purpose is to provide a DC power transmission system that is sufficiently practical and capable of locating the distance from the DC power transmission end to the failure point with a simple configuration. An object of the present invention is to provide a failure point locating device.

[Summary of the invention]

The present invention is configured to continuously sample the voltage and current at the power transmission end, and calculate and obtain the distance to the fault point based on the temporal changes and known line constants.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 is a diagram showing an equivalent circuit of a DC power transmission system. Transmission voltage v from DC source 1 is applied to fault point x via line resistance r and line impedance l, and current i is applied to fault point resistance R _f flows to Note that r ₀ is the internal resistance of the DC source 1 and will be ignored below.

By the way, this equivalent circuit has an LR series circuit configuration, so if the fault point x causes a ground fault via the fault resistor R _f , the sending end voltage v(t) at any time t will be as follows: It can be expressed as a differential equation.

v(t)=Ldi/dt+Ri(t)...(1) However, L=l×x(m), R=r×x(m)+R _f .

Therefore, if we now sample at a constant sampling interval Δt and let the currents i at sampling times _t1 to _t5 be _i1 to _i5 , respectively, then at t= _t2 , _v2 = _Li1 − _i3 /2Δt+Ri ₂ ...(2) At t=t ₃ , v ₃ = Li ₂ − _{i 4} /2Δt+Ri ₃ ...(3) At t=t ₄ , v ₄ = Li ₃ − i ₅ /2Δt+Ri ₄ ...( 4) At t= _t5 , _v5 = _Li4 - _i5 /2Δt+ _Ri6 ...(5).

Therefore, if we perform first-order linear approximation to v(t) and i(t) as shown in Fig. According to formula 5), v ₂ + v ₄ = Li ₁ − i ₅ /2Δt+R (i ₂ + i ₄ ) ……(6) v ₃ + v ₅ = Li ₂ − i ₅ /2Δt+R (i ₃ + i ₆ ) ……(7 ) (v ₂ + v ₄ ) (i ₃ + i ₅ ) − (v ₃ + v ₅ ) (i ₂ + i ₄ ) = L (i ₁
−i ₅ )(i ₃ +i ₅ )−(i ₂ −i ₆ )(i ₂ +i ₄ )/2, and L/2Δt=(v ₂ +v ₄ )(i ₃ +i ₅ )−(v ₃ +v ₅ ) (i ₂ + i ₄
)/(i ₁ − i ₅ ) (i ₃ + i ₅ ) − (i ₂ − i ₆ ) (i ₂ + i ₄ ) ……(8). (However, i ₆ is the current value at time t _6. ) Since L=lx here, if L/2Δt=A, the failure point x is x=2Δt/l. A=2Δt/l. (v ₂ + v ₄ ) (i ₃ + i ₅ ) −
(v ₃ + v ₅ ) (i ₂ + i ₄ ) / (i ₁ − i ₅ ) (i ₃ + i ₅ ) − (i ₂ −
i ₆ ) (i ₂ + i ₄ )...(9), and the voltages v ₁ to _{v 5 and} currents i ₁ to i 6 detected in 6 samplings from time t ₁ to t ₆ and the known inductance per unit length. The fault point distance x can be approximately determined by l and the sampling interval Δt.

In this case, when calculating the current value i _o at time _{t o} , as shown in Figure 3,
By correcting io using the currents io _{-1 and} io _{+1 of t o+1 through} interpolation, a more accurate failure distance can be obtained.

FIG. 4 is a block diagram showing an embodiment of the present invention based on such a principle, and is composed of a detection section 10, a sampling section 11, an AD conversion section 12, and a calculation section 13. The voltage v and current i at the power transmission end are detected by a Hall CT element and a shunt resistor. Sampling section 11
continuously samples the sending end voltage v and current detected by the detection unit 10 at predetermined time intervals Δt,
The sample value is supplied to the AD converter 12.
The AD converter 12 converts the transmission end voltage v and current sampled by the sampling unit 11 into digital signals in synchronization with the sampling operation, and supplies the digital signals to the calculation unit 13 . Then, the calculation unit 13
Changes in the sending end voltage v and current i for each Δt time given by the digital signal from the AD converter 12 are monitored, and if the voltage v or current i shows an abnormal change due to a ground fault, etc., at this point The above-mentioned item (9) is obtained by the time change of voltage v and current i from
The calculation shown in the formula is executed to calculate the fault point distance x. The fault point distance x calculated in this manner is displayed on a display section (not shown).

With this, recovery work can be carried out quickly.

〔Effect of the invention〕

As is clear from the above description, the present invention locates the distance to the failure point by monitoring temporal changes in the voltage and current at the sending end from the time when the failure occurs. Therefore, it is possible to realize a failure point locating device that is sufficiently durable for practical use with an extremely simple configuration that only combines known sampling circuits and arithmetic devices such as microcomputers, and is extremely useful for maintenance of DC power transmission systems. be effective.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram of a DC power transmission system, Figure 2 is a diagram approximating changes in voltage and current from the time of failure occurrence, and Figure 3 is an explanatory diagram when an approximate value of current is obtained by interpolation calculation. , FIG. 4 is a block diagram showing one embodiment of the present invention. 1... DC source, 10... Detection section, 11... Sampling section, 12... AD conversion section, 13... Arithmetic section.

Claims (1)

[Claims] 1. A detection unit that detects the voltage and current at the power transmission end of the DC power transmission system, and the voltage detected by this detection unit,
a sampling section that continuously samples the current at predetermined time intervals; a first means for determining a doubling ratio between the sampling interval and a known line constant; From the multiplication value of the sum of the third and fifth currents at the time point, the multiplication value of the sum of the third and fifth voltages at the sampling time point and the sum of the second and fourth currents at the sampling time point is calculated. a second means for subtracting, from the multiplication value of the difference between the first and fifth currents at the sampling time and the sum of the third and fifth currents at the sampling time, the second and sixth currents at the sampling time; third means for subtracting the multiplication value of the difference between the currents and the sum of the second and fourth currents at the time of sampling; and fourth means for calculating the ratio of the second means and the third means;
A failure point locating device for a DC power transmission system, characterized in that the distance from the power transmission end to the failure point is calculated by calculating the ratio obtained by the fourth means and the first means.