JPH0240571A - Diagnosis device for power cable deterioration under live conditions - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Application This invention relates to a power cable deterioration diagnosis device under live power conditions for measuring the insulation resistance of power cables connected to a three-phase ungrounded high voltage system under live power conditions. It is something.

(b) Prior art and problems to be solved by the present invention Generally, a three-phase ungrounded high-voltage bus connected to a three-phase power cable is connected to a grounding transformer (GPT) or star-shaped. There is. Conventionally, the live-line deterioration diagnosing device applied a DC voltage of about 50 V in a superimposed manner to the high-voltage bus from the neutral point of the instrument grounding transformer. but,
Connecting a DC power source to an instrument grounding transformer is extremely difficult, and there are problems that require a great deal of effort to diagnose insulation deterioration.

Also, a method of directly applying DC voltage to each of the three-phase high-voltage buses has been considered; This has not been implemented due to the risk of power outages. Furthermore, when this method is adopted, since DC voltage is applied to each three-phase bus bar, there is a problem that the application equipment becomes large-sized.

The object of the present invention is to provide a live-line deterioration diagnostic device for power cables that can apply DC voltage to a three-phase high-voltage bus bar, prevent the risk of power outage, and reduce the need for application equipment. .

(C) Means for Solving the Problems This invention provides a reactor and a DC superimposition power supply connected in series between one phase of three-phase high voltage buses and a ground point, and the object to be measured. and a measuring device for measuring the direct current flowing between the cable and the ground point, and the voltage value of the direct current voltage source is approximately 3V to approximately 40V or approximately 13V.
It is characterized by being limited to a range of approximately -40V from (2) to approximately -40V.

(d) Approximately 3■ to approximately 40V or 13■ to the high voltage bus of one phase of action
When a DC voltage of approximately -40 V is applied from 1 to 40 V, the insulation resistance of the power cable to be measured can be accurately measured without causing a power outage.

(E) Embodiment FIG. 1 shows an embodiment of this invention, and in the figure, reference numeral 1
is a three-phase power cable, each conductor 1a of which is connected via a cable terminal 2 to a three-phase high voltage bus 3 of an ungrounded high voltage system. The shielding layers 1b of each power cable are interconnected and connected to a ground point 5 via a measuring device 4 for measuring direct current.

The ground capacitance of the high voltage bus 1 is indicated by 6. Further, an instrument grounding transformer 7 is connected to the high voltage bus 3, and its neutral point is grounded.

When saturation of the magnetic flux occurs in the tertiary winding 7a of the instrument grounding transformer 7, a tertiary voltage Vo is generated, which activates the substation relay.
The power supply has been cut off. A high inductance reactor 9 and a switch 10 are connected between one of the three-phase high voltage busbars 3 and the ground point 8. DC superimposition power supply 11
are connected in series. The voltage value of this DC superimposition power supply 11 is adjusted within the range of approximately 3V to approximately 40V.

FIG. 2 shows the relationship between the DC superimposed current measured by the measuring device when a DC superimposed voltage of 3 V is applied in the diagnostic device and the AC breakdown voltage value required for dielectric breakdown of the shielding layer 1b. As can be seen from Figure 2, the insulation deteriorates and the AC
When the breakdown value decreases, a large DC superimposed current is observed, and insulation deterioration can be detected. However, if the DC superimposed current is 3V or less, deterioration may not be detected, and it can be seen that the lower limit of the DC superimposed voltage applied to the high voltage bus is approximately 3V.

FIG. 3 shows the time required for the magnetic flux of the instrument grounding transformer 7 to become saturated when a DC superimposed voltage is applied, as determined by a computer simulation using EMTP.

In this case, the input impedance of the measuring instrument 4 is IOKΩ,
The ground capacitance 6 is set to 0.1 μF. When the magnetic flux of the instrument grounding transformer 7 is saturated, a voltage Vo is generated in the tertiary winding 7a of the instrument grounding transformer 7, which activates the substation relay, leading to a power outage. As can be seen from FIG. 3, the larger the DC superimposed voltage value, the shorter the time required for the magnetic flux of the instrument grounding transformer 7 to saturate, making insulation measurement difficult. It takes about 2 minutes to actually measure the insulation resistance of the shielding layer 1b (in the case of one-line, one-phase measurement), so the DC voltage value applied to the high-voltage bus must be approximately 40V or less. be.

From the results shown in the second UgJ and FIG. 3, it can be seen that the range of the DC superimposed voltage value applied to one phase of the three-phase high voltage bus is approximately 3V to approximately 40V. In this embodiment, a positive voltage is applied to the high voltage bus, but a negative voltage, that is, a voltage of approximately 13V to approximately 140V may be applied to the high voltage bus.

(E) Effect This invention has a configuration in which a DC superimposed voltage is applied to a three-phase high-voltage bus and one-phase high-voltage bus through a reactor.
The device can be connected easily, and the difficulty of connecting to the neutral point of a conventional instrument grounding transformer can be solved. Furthermore, since the superimposed voltage is applied only to the negative phase high voltage bus, the structure is simple and can be manufactured at low cost. In addition, since the applied DC superimposed voltage was limited to the range of approximately 3V to approximately 40V or approximately 13V to approximately 140V, there is no risk that measurement would become impossible, and there would be no power outage during measurement, making it safe. measurements can be taken.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the measured superimposed voltage value with respect to the dielectric breakdown voltage value, and Fig. 3 is the time until magnetic flux saturation of the instrument grounding transformer with respect to the DC superimposed voltage. FIG. 1... Power cable, 1b... Shielding layer, 3...
- High voltage busbar, 4... Measuring instrument, 5.8... Grounding point, 7... Instrument grounding transformer, 9... Reactor, 11... DC superimposition power supply.

Claims (1)

[Claims] A device that measures the insulation deterioration of a three-phase cable to be measured by applying a DC voltage to a three-phase high-voltage bus connected to the cable, the device comprising: one phase high-voltage bus of the three-phase high-voltage bus; The voltage value of the DC voltage source is Approximately 3V to approximately 40
1. An apparatus for diagnosing deterioration under live wire conditions of a power cable, characterized in that the voltage is limited to a range from V or approximately -3V to approximately -40V.