JPS6035628B2 - How to apply DC voltage to high voltage distribution lines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In order to measure the respective insulation resistances of a high-voltage distribution line and a power cable connected thereto under live conditions, the present invention applies a DC voltage to the high-voltage distribution line and the power cable connected to the high-voltage distribution line. Regarding the method of applying .

Conventionally, the method shown in FIG. 1 has been adopted as this type of DC voltage application method.

To explain this, in Fig. 1, Tr is a power transformer, and T
is a high-voltage distribution line, and GPT is a grounding transformer connected to the high-voltage distribution line T. The primary side is a human connection and the secondary side is an open Δ connection. S is a DC power source, one end of which is connected to the neutral point 0 of the grounding transformer OPT through a fixed resistor RS so as to apply a direct voltage, and the end of the voltage source is grounded through an ammeter Ms. Co is a capacitor inserted between the neutral point 0 and the earth, and a safety arrester Ar is connected to the capacitor in parallel between both ends of O.
is inserted.

Based on the above configuration, the power supply S is activated and the DC power generation voltage B is applied via the neutral point 0 to the high voltage distribution line T and the power cable (not shown) connected thereto. At this time, since the above configuration does not have a function to measure the voltage E actually applied to the high voltage distribution line T and the power cable, the value of the voltage is ET=E-IS.
There is no choice but to estimate it by calculation from the formula for Rs. In the above equation, ls is the output current of the power source S, which is read by the ammeter NL, and the value of the power source generated voltage E is the nominal generated voltage of the DC power source S, since the above configuration does not have a function to measure this. Use value. Therefore, the value of ET calculated from the above formula is obtained by double estimation and cannot be said to be accurate. Also, the insulation resistance R of the high voltage distribution line T
The value of T is RT:E, . It is obtained by substituting the values of S and RS, but as mentioned above, the value of E is hardly accurate, so the value of RT inevitably contains an error. Therefore, applying the DC voltage to the high-voltage distribution line and the power cable connected to it while the line is live and determining the insulation resistance of each using the above method requires calculations that are troublesome, and the accuracy of the determined value decreases, reducing reliability. There was a drawback that the value decreased. Furthermore, after the measurement is completed, it takes time to naturally discharge the charge accumulated in the high-voltage distribution line under test because the capacitance of the distribution line is relatively large, and if the line is short-circuited and discharged immediately, the switch contacts may burn out. , loud discharge noise etc. may occur,
Alternatively, there is a drawback that the neutral point potential oscillates, which may cause a dangerous local situation in the power distribution line. An object of the present invention is to provide a method for applying DC voltage to a high-voltage power distribution line and a power cable connected thereto, which eliminates the above-mentioned drawbacks and allows for simple and quick measurement of highly accurate insulation resistance values. .

The gist of the invention lies in the structure of a method for applying a DC voltage to a high voltage distribution line as described in the claims above.

The present invention will be described below based on illustrated embodiments.

In Fig. 2, 1 is a power transformer, 2 is a high-voltage distribution line connected to the secondary side of the transformer 1, and cables C, , and C are connected to it.
2,... are connected. 3 is a grounding transformer connected to the high voltage distribution line 2; the primary side is used for human connection, the secondary side is used for open delta connection, and 0 is the negative side neutral point.

A capacitor 4 is connected between the neutral point 0 and the ground, and safety arresters 7 are inserted in parallel at both ends of the capacitor 4. In the short circuit of the capacitor 4, switches 5 and 6 are connected in series, and a resistor Ro is inserted in series with the switch 5 and in parallel with the switch 6. The switches 5 and 6 are kept open at all times except when a DC voltage is applied. Furthermore, between the neutral point 0 and the ground, there is a multiplier resistor R for measuring DC voltage.
M and a DC voltmeter Mv are connected and inserted in series, and a fixed resistor RS, a variable resistor Rv,
A DC power supply 8 and an ammeter NL for measuring the output current ls from the DC power supply 8 are connected and inserted in series, respectively. In addition, in Fig. 2, power cables C,
Shown only.

The near and far ends of the metal sheath (indicated by dotted lines in the figure) of the power cable C are electrically grounded via capacitors 9 and 11, respectively, while the near end is connected to a short-circuit switch that is kept closed at all times. 12, and the switch 12 is opened when measuring the insulation resistance of the power cable.
The DC voltage applied to the high-voltage distribution line 2 passes through the insulation resistance Rx of the power cable C, a DC leakage current lx that does not change over time, and a furnace wave circuit consisting of capacitors 9 and 10 and a choke coil 13. The current flows back to the DC power supply 8 via the ammeter Mx and the ground.

Using the circuit shown in FIG. 2 and configured as described above, when applying a DC voltage to the high-voltage distribution line 2 and the power cable C among the power cables connected thereto, for example, in a live line state, The operation will be explained.

In FIG. 2, the switches 5 and 6 are always open except when DC voltage is applied, so the neutral point of the grounding transformer 3 is 0.
is directly connected to the earth. First, the DC power supply 8 is activated, and the generated voltage value is equal to the voltage value of the high-voltage distribution line 2, which is V.
In the case of IsoV, it is preferable to use DCIKV, and in the case of IsoV, it is preferable to use DCIKV or so.As the DC power source, a battery or an eliminator, or a combination of both, is used, but for the purpose of insulation resistance measurement, It is necessary that the voltage stability be extremely high. When the DC power supply 8 is activated, an output current ls is sent out, the value of which is read with an ammeter Ms (if the scale is displayed in current).

In this case, the variable resistor Rv is adjusted so that the value of the output current ls indicates the full scale of the ammeter NL. In this state, the current flowing through the multiplier resistor RM is 0, so the pointer of the voltmeter Mv does not swing at all. Next, when the switches 5 and 6 are opened simultaneously or in the order of switch 6 and switch 5, a DC voltage is applied to the high voltage distribution line 2. At this time, the actually applied DC voltage value ET is not the generated voltage value E of the DC power supply 8, but the insulation resistance value RT to ground of the entire line of the high-voltage distribution line 2 (power cable C...), etc. (including all resistors in parallel)
In this case, the multiplier resistance RM
said voltmeter MV operated by a current IM flowing through
can read the DC voltage value ET, and at the same time the output current ls becomes the value indicated by the ammeter Ms (
(full scale of the ammeter MS), its value is indicated as a function that varies primarily due to variations in the insulation resistance RT of the entire high voltage distribution line. (The current IM
Since the value of is very small, its influence on the value of the ammeter M indicated by the above-mentioned function may be omitted, and if necessary, correction based on the influence may be taken into consideration). For example, when the ammeter Ms indicates half of its full scale, RT = Rs + Rv (taking into consideration the internal resistance of the DC power supply 8), so the indication of the ammeter Ms is not based on the current scale, but on the high voltage distribution line. It can be scaled by the value of the insulation resistance RT of the entire line (No. 2). Further, the value of the fixed resistor Rs may be set according to the magnitude of the predicted insulation resistance RT of the entire line of the high-voltage distribution line 2, but the value of the output current ls also varies according to that value. Needless to say, it is necessary to select an ammeter Ms having a different sensitivity each time.
To further explain with a numerical example, if the 1/2 scale of the current meter is selected to indicate 50KQ, the maximum insulation resistance value corresponding to the 1'20 scale, that is, the normal minimum scale, is 95.
Since it is 0KQ, the scale range of the insulation resistance value is from 0 to IMQ. In this case, the value of Rs + Rv is set to 50KQ in the standard state, but to be more specific, if the voltage of the DC power supply 8 fluctuates between 1050V and 900V, RS will be 4 arcs and RV will be 0. ~7. Set the arc to 0, and use a 2 hA full scale output ammeter Ms. By the above operation, when the DC voltage ET is applied to the high voltage distribution line 2 in the live line state and the circuit is activated, the insulation resistance RT to earth of the entire line of the high voltage distribution line 2 will be determined by the output ammeter Ms on the insulation resistance scale. In the case of a current scale, it can be read directly, and in the case of a current scale, it is calculated from the formula RT=Er/IS.

Next, to explain the insulation resistance measurement of each power cable of the power cable group connected to the high voltage distribution line 2, for the power cable C in FIG. If the value of the DC leakage current IXI flowing in the power cable C is read with the ammeter Mx,
The value of the insulation resistance Rx, of , can be calculated from the formula Rx,=ET/lx. In the figure, only the power cable C is shown to simplify the explanation, but for each of the other power cables, the above power cable Each insulation resistance value can be determined in exactly the same manner as in the case of C. After determining the respective insulation resistance values of the entire line of the high-voltage distribution line 2 and each of the power cables running therethrough, if the DC power supply 8 is de-energized and the switch 5 is opened, the insulation resistance value is relatively large. The charges charged in the high-voltage distribution line and the capacitor 4, which have a capacitance to the ground, are discharged through the resistor Ro. If the resistance value IKQ and the power capacity are set to 25W to discharge a charging voltage of 1000V, it is possible to prevent the contacts of the switch 5 from burning out and the generation of discharge noise, and moreover, most of the charge is absorbed within a short time. is converted into heat loss. Thereafter, the switch 6 is closed, and the neutral point 0 of the grounding transformer 3 is completely returned to the grounded state, returning to the normal state. Since the present invention has the configuration and operation described above, according to the present invention, the complicated insulation state of a high voltage distribution line in a housed line state is determined from the DC power value actually applied to the line. The insulation resistance value is highly accurate and reliable, and the value can be read directly by using the scale of the meter as the resistance value, so the insulation resistance value can be easily and quickly determined, and it can also be used to measure the insulation resistance of power cables. Since it is possible to read the DC voltage value that is actually applied, the measured value is not affected by fluctuations in the voltage generated by the DC power supply or voltage drops due to circuit resistance, making it possible to obtain highly accurate and reliable insulation resistance values. Furthermore, after the measurement is completed, the charges charged in the high-voltage distribution line and the capacitor, which have a relatively large capacitance, are short-circuited and discharged through a resistor having an appropriately set resistance value and lightning capacitance. Burnout of switch contacts and generation of loud discharge noise are eliminated, and there is no longer any concern that the neutral point potential will oscillate during short-circuit discharge and cause dielectric breakdown at local insulation failure points on the distribution line. The industrial effects of implementing the invention on distribution line maintenance are significant.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a wiring diagram for explaining a conventional method of applying DC voltage to a high-voltage distribution line for measuring insulation resistance in a live line state, and Fig. 2 is a wiring diagram for explaining one embodiment of the present invention. It is.

1...Power transformer, 2...High voltage distribution line, 3
・・・・・・Grounding transformer, 4, 9, 10, 11...
...Condenser, 5, 6, 12...Switch, 8
...DC power supply, 13...Choke coil,
C.・・・・・・Power cable.

Aoi no zu diagram 2

Claims (1)

[Claims] 1. In order to measure the insulation resistance of the entire high-voltage distribution line and each power cable connected thereto, the entire high-voltage distribution line and the power cable are connected to the grounding transformer installed on the high-voltage distribution line in a live state. A capacitor, a short-circuit circuit for the capacitor, and a DC voltage application function from the DC power source consisting of a DC power source, a resistor, and an output ammeter are connected in parallel to the neutral point, and the DC voltage is applied via the neutral point. The method for applying DC voltage is characterized in that a function is provided to measure the DC voltage value actually applied to the high-voltage distribution line and the power cable between the neutral point and the ground, and the DC voltage is applied. Method of applying DC voltage to high voltage distribution lines.