JPS60185171A - Measurement of dielectric dissipation factor - Google Patents

Abstract

PURPOSE:To always monitor an insulating state by enabling the accurate measurement of dielectric dissipation factor even in the live wire state of a power cable, by measuring the phase difference of a voltage wave form and the current wave form of the vector current difference thereof. CONSTITUTION:The voltage wave form from an AC power source 10 is measured by a voltage divider 12 and, at the same time, current wave forms are measured by current transforms 13, 14 in a transmitting terminal side and a receiving terminal side to be inputted to a subtractor circuit 15 through an optical fiber 17 and the current wave form of the vector current difference of said wave forms is calculated to obtain the real straight-through current of an insulator. The wave form of this straight-through current and the voltage wave form from the voltage divider 12 are inputted to a phase meter 16 to measure the phase difference of both wave forms. By this method, dielectric dissipation factor tandelta is measured.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for measuring dielectric loss tangent, and in particular, the present invention relates to a method for measuring dielectric loss tangent, and in particular, the current is measured by the difference between both ends of a power cable in a live state, and the current waveform and voltage waveform are This invention relates to a method of this kind for measuring the dielectric loss tangent with a phase difference of .

[Technical background of the invention] The dielectric loss tangent (t
an δ) has been measured as a powerful index.

When an alternating current voltage is applied to a dielectric and no power loss occurs, the phase of the charging current generator 0 is 90" than the voltage ■
It's progressing. However, in an ordinary dielectric material which causes electric conduction or absorption phenomenon due to direct current, the current advance under an alternating electric field is smaller than 90° as shown in FIG.

This angle δ smaller than 90° is called a loss angle, and 90°−δ=O is called a phase angle, and in such a case, dielectric loss occurs.

Also, the dielectric power factor is cos of phase angle O or s of loss angle δ
Since δ is usually extremely small, the dielectric power factor = cos θ = sin δ = tan δ, and the dielectric power factor can be expressed as an δ, which is called dielectric voltage junction.

When monitoring the insulation of power cables, there are cases in which the insulation performance is measured in a live line state, and cases in which tan δ, partial discharge, etc. are measured in a power outage state. Measurement while the line is live is highly desirable in terms of constant monitoring, but it has not yet been put to practical use.

Generally, all δ is measured under a power outage condition as shown in FIG. That is, an AC power source 2 is connected to the power transmission end side of the power cable 1, and a voltage divider 3 is further connected to observe the voltage waveform. The electric power cable 1 is jointed at a connecting portion 4, and the cable sheath is grounded at multiple points. In addition, a current transformer 5 is installed to measure the waveform of the ground point current at a predetermined position on the power transmission end side, and the phase difference (0) is determined by the voltage waveform of the voltage divider 3 and the current waveform of the current transformer 5. A phase meter 6 for measurement is installed.

In this way, the phase difference (0) between the voltage waveform by the pressure reducer 3 and the current waveform at the grounding point of the current transformer 5 is measured by the phase meter 6, and from this phase difference (θ), tan δ (906-〇=δ ).

[Problems with the Background Art] However, the above conventional example is only for power outages, and there is no problem in itself because the conductor current and the grounding point current are equal.However, if you try to measure tanδ in a live line state, the load current Because there are multiple grounding points in the power cable, branch currents occur, and furthermore, induced currents from the ground phase and other circuits flow to the grounding point.

For this reason, it becomes impossible to detect the true current passing through the insulation of the power cable, and therefore the correct and an δ
The problem is that it cannot be measured.

[Purpose of the Invention] The present invention has been made in view of the above-mentioned difficulties, and aims to provide a method for measuring dielectric loss tangent that constantly monitors the insulation state by measuring the Lan δ of the power cable sheath in a live state. It is something.

[Summary of the Invention] A method for measuring a dielectric loss tangent (L, an δ) according to the present invention to achieve such an object measures a voltage waveform at the end of a power cable in a live state, and The current waveforms at the power transmitting end and the power receiving end of the cable are measured respectively, the vector current difference is calculated to detect the true current passing through the insulator, and the voltage waveform and the current waveform of the vector current difference are calculated. The phase difference (a) is measured and finally the cyan δ is measured.

[Embodiments of the Invention] A preferred embodiment of the present invention will be described below with reference to FIG.

The method for measuring dielectric voltage junction (an δ) of the present invention is realized by the system configuration shown in FIG. That is, in FIG. 3, when power is being transmitted from the AC power supply 10 through the power cable 11 jointed by the connection part 11', a voltage divider 12 and a transformer are connected to the power transmission end side in parallel with the AC power supply 1.0. A current transformer 13 is provided, and a current transformer 14 is also provided on the power receiving end side. The current from the current transformers 13 and 14 is passed through the subtraction circuit 15.
The output of the subtraction circuit 15 is input to the phase meter 16 along with the voltage from the voltage divider 12. Incidentally, voltage divider 12
For signal transmission of the current transformers 13 and 14, for example, an optical fiber 17 is used, and the signals are input to the subtraction circuit 15 and the phase H (16).

To measure the dielectric loss tangent using such a system configuration, first, the voltage (voltage waveform) supplied from the AC power supply 10 is measured by the voltage divider 12. At the same time, current transformers 13 and 14 installed at the power transmission end and power reception end generate a current (current waveform).
is measured. The current waveforms measured by the current transformers 13 and 14 are input to the subtraction circuit 15 through the optical fiber 17, and the current waveform of their vector current difference is calculated. That is, the current measured by the current transformer 13 is
This includes both the through current of the sheath (insulator) and the load current, and the current measured by the current transformer 14 is only the load current, so these are input to the subtraction circuit 15. By calculating the vector current difference, the true through current of the insulator can be obtained.

Then, the true through current waveform of this insulator and the voltage divider 12
The voltage waveform sent from the optical fiber 17 through the optical fiber 17 is input to the phase meter 16, and the phase difference (0) between them is measured. Since the phase difference (θ) is 90°−δ, from this, δ
The dielectric loss tangent tan δ is measured.

[Effects of the Invention] As is clear from the embodiments described above, according to the present invention, the difference in current between both ends of the power cable, that is, the level between the true through-current waveform of the insulator and the voltage waveform at the terminal portion, can be reduced. Measure the phase difference and
By measuring , and δ, the influence of load current on power cables is removed, so accurate t can be obtained even in live line conditions.
An δ of 811 can be maintained, and since the current is measured at a location other than the power cable, it is not affected by induced current and is always connected to the cotton I.

Green status can be monitored.

[Brief explanation of drawings]

Figure 1 is a vector diagram of dielectric voltage and current, and Figure 2 is a conventional system 4M for measuring dielectric loss tangent (tan δ).
FIG. 3 is a system configuration diagram in the method for measuring dielectric loss tangent of the present invention. 11 ...... Electric cable 12 ...... Voltage divider 13.14 ...... Current transformer 15 ...... Subtraction circuit 16・・・・・・・・・Phase side lθ Agent Patent attorney Moritani-Yu 1 Figure 2 Gate 3

Claims (1)

[Claims] Measure the voltage waveform at the end of the power cable in a live state, measure the current waveforms at the sending end and receiving end of the power cable, calculate the vector current difference, and calculate the difference between the voltage waveform and the vector current. A method for measuring dielectric loss tangent, characterized by measuring the phase difference between the difference and the current waveform.