JPH08338806A - Gas concentration measuring device in oil - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an apparatus for measuring gas concentration in oil, which enables accurate measurement of gas concentration in oil even if the temperature of insulating oil changes. [Composition] A temperature sensor 25 for detecting the temperature of the insulating oil is provided, and a measuring unit for measuring the concentration of the dissolved gas in the connecting portion 2 from the temperature of the insulating oil detected by the temperature sensor 25 and the gas concentration in the gas cell. 19 was provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-oil gas concentration measuring device for measuring dissolved gas in insulating oil in an OF cable, and more particularly, to an accurate in-oil gas concentration even if the temperature of the insulating oil changes. The present invention relates to an apparatus for measuring gas concentration in oil that can measure.

[0002]

2. Description of the Related Art Dissolved gas in insulating oil is measured for diagnosing deterioration of OF cables. The dissolved gas in the insulating oil is mainly a hydrocarbon-based gas, as well as hydrogen, carbon monoxide, and carbon dioxide. To measure these, the insulating oil in the connection part is sampled. OF for oil collection
Power out the cable line once, open the lubrication hole at the connection, and collect oil from this lubrication hole. The collected insulating oil is brought back to the factory and analyzed by gas chromatography. Deterioration of insulating oil based on the concentration of various gases measured in this way,
That is, the deterioration of the OF cable is diagnosed.

In the above method, since it is necessary to stop the OF cable line once and it takes a lot of time to collect oil because the target OF cable line is long, in recent years, the oiling hole of the connecting portion is filled with oil. A method of mounting a sensor for detecting dissolved gas and constantly monitoring the detection information of the sensor is being studied.

For example, the system shown in FIG. 3 utilizes the optical properties of gas and also measures the dissolved gas concentration in oil remotely using an optical fiber. Specifically, the in-oil gas sensor 3 is attached to the connection portion 2 of the OF cable 1, and the gas data signal detected in the oil-in-gas sensor 3 has a gas data processing unit 13 using the optical fiber 31 as a transmission path. Transmitted to. Gas data processing unit 1
3 obtains the gas concentration from the gas data signal. This gas concentration information is sent to the deterioration diagnosis unit 14, and the deterioration diagnosis unit 14 makes a deterioration diagnosis of the OF cable 1.

The structure of the in-oil gas sensor 3 is simply composed of an oil cell 5 filled with insulating oil 32 and a gas cell 7 through which the gas in the insulating oil permeates. The oil cell 5 and the gas cell 7 are separated by a permeable membrane 6 such as a sintered stainless metal coated with a fluorine resin. The insulating oil of the connecting portion 2 is introduced into the oil cell 5, and the gas dissolved in the insulating oil 32 permeates through the permeable membrane 6 and is separated into the gas cell 7. The concentration of the separated gas is detected on the basis of the amount of absorption of the light that allows light of a specific wavelength to pass through the gas cell 7. Although a light source that emits light of this specific wavelength is not shown, the optical fiber 31 is a transmission line that guides the light of this specific wavelength to the gas cell 7, and the gas data signal detected in the oil gas sensor 3 is transmitted. This is a transmission line leading to the gas data processing unit.

[0006]

In the above prior art, the dissolved gas concentration in oil is measured from the concentration of the gas separated by the permeable membrane, but the speed at which the gas permeates the permeable membrane differs depending on the oil temperature. It was difficult to measure the dissolved gas concentration in oil accurately.

How the permeability of the permeable membrane varies depending on the oil temperature will be described based on experimental results. Here, PF, which is a kind of fluororesin, is used for the sintered stainless steel.
A film obtained by electrostatically coating A was used.

Oil in which gas is dissolved is put into an oil cell so that the gas permeates into the gas cell. At this time,
The permeation equation of gas in oil is represented by the following equation (1).

[0009]

[Equation 1]

Where P ₂ : Gas partial pressure on the gas cell side (P
a) P ₀ : Initial partial pressure in gas cell (Pa) k: Constant (Pa / ppm) N: Gas concentration in oil (ppm) α: Gas permeability coefficient in oil (l · m / m ² · s · P)
a) d: film thickness (m) A: film area (m ² ) τ: permeation time (s) V: gas cell side volume (l).

(A) When A / V is small In the above equation (1), V, N, A and d are constants and P
₂ and P ₀ are obtained experimentally, so the transmission coefficient α is inevitable.
Can be requested. The constant k is a constant determined by the type of gas and the oil temperature, and here, the constant k that has already been obtained by the experiment was used. Since the film thickness d is uncertain, the transmission coefficient is represented by α / d.

Experimentally determined methane gas permeability coefficient α / d
The relationship between the oil temperature and the oil temperature T is shown in FIG. From FIG. 4, it can be confirmed that the permeability coefficient differs depending on the oil temperature. For example, the case where the oil temperature is 40 ° C. and 80 ° C. are compared. Bottom diameter 54m
Assuming a cylindrical gas sensor in oil having a thickness of m, a wall thickness of 2 mm, and a length of 10 cm, the film area A is 0.017 m ² , the gas cell side volume V is 0.196 l, and the gas concentration N in oil is 200 pp.
m. Initial partial pressure in gas cell P ₀ = ₀ Pa, 5
The permeation pressure and the gas concentration after 00 hours (1800000s) have been obtained. Oil temperature 40
The transmission coefficient at ℃ is 8.2 × 10 ^-11 l · m / m ² ·
Transmission coefficient at s · Pa, 80 ° C is 2.9 × 10 ^-10
1 · m / m ² · s · Pa. When the permeation pressure is calculated using the formula (1), the permeation pressure is 36.4 P at 40 ° C.
a, the gas concentration is 359 ppm, 5 at 80 ° C
It becomes 7.0 Pa and 562 ppm. 20 in two cases.
It can be seen that 6 Pa (203 ppm) is different.

When measuring the dissolved gas concentration in oil, it is necessary to detect the permeation pressure or the gas concentration and back-calculate from the detection result to obtain the dissolved gas concentration in oil. The formula for obtaining the dissolved gas concentration in oil becomes the following formula (2) by expanding the formula (1).

[0014]

[Equation 2]

Here, the normal oil temperature is 40 ° C., and the oil temperature in the transition period is 80 ° C. If it is not possible to detect the oil temperature, it is not known that the oil temperature had risen to 80 ° C during the transition period. Therefore, even in the transition period, the dissolved gas concentration in oil can be determined under the normal oil temperature of 40 ° C. Will ask. When the oil temperature is 80 ° C and the permeation pressure is 57.0 Pa (562 ppm), the oil temperature 4
When the dissolved gas concentration in oil is calculated by the above back calculation assuming 0 ° C, it becomes 313 ppm. Since the gas concentration in oil N = 200 ppm as initially assumed, it can be seen that the result of back calculation has a value quite different from the actual value.

(B) When A / V is large When the area of the permeable membrane is large and the volume of the gas cell is small,
The denominator of the second term of the equation (2) is 1, and the equation for calculating the gas concentration in oil is as shown in the equation (3).

[0017]

(Equation 3)

The gas concentration in oil can be calculated from the gas partial pressure in the gas cell and k. In this case, it has nothing to do with the transmission characteristic (transmission coefficient) of the permeable membrane itself. However, k is a constant determined by the oil temperature and the type of gas, and in the case of methane gas,
It is given by the following equation (4).

[0019]

[Equation 4]

Here, t: oil temperature (° C.) k: constant (Pa) Therefore, at 40 ° C., k = 0.25027, and at 80 ° C., k = 0.28982. If the gas partial pressure in the gas cell is the same, the calculated gas concentration in oil is 40 ° C.
In the case of, it is 1.2 times that in the case of 80 ° C.

As described above, when the A / V in (a) is small and the A / V in (b) is large, the gas concentration in oil is calculated from the gas partial pressure (concentration) in the gas cell. It can be seen that the oil temperature makes it inaccurate.

Therefore, an object of the present invention is to solve the above problems and provide a gas concentration measuring device for oil which can accurately measure the gas concentration in oil even if the temperature of the insulating oil changes.

[0023]

In order to achieve the above object, the present invention provides a gas cell for separating a dissolved gas from insulating oil in the connection portion at a connection portion of an OF cable, and connecting an optical fiber to the gas cell, In an oil gas concentration measuring device adapted to detect the gas concentration in a gas cell by transmitting light from the optical fiber, a temperature sensor for detecting the temperature of insulating oil is provided, and the temperature of the insulating oil detected by this temperature sensor is set. And a measuring part for measuring the concentration of the dissolved gas in the connection part from the gas concentration in the gas cell.

Further, the optical fiber is used as a temperature distribution sensor for measuring the temperature distribution along itself, and the optical fiber is laid so as to pass around the gas cell, and the same optical fiber is used for gas concentration and temperature of insulating oil. May be detected.

[0025]

With the above structure, the temperature sensor detects the temperature of the insulating oil. On the other hand, the gas concentration in the gas cell is detected by the transmission of light from the optical fiber. As described above, since the temperature characteristic of the permeable membrane is known, the permeation coefficient is obtained from the detection result of the temperature sensor, and if this permeation coefficient is used, the gas concentration in oil can be accurately measured.

Further, a temperature distribution sensor, for example, an optical fiber distribution type temperature sensor utilizing Raman scattered light may be used, and the optical fiber and the gas concentration detecting optical fiber may be used in common. That is, the optical fiber is laid so as to pass around the gas cell, and the temperature at the position of the gas cell is extracted from the temperature distribution along the optical fiber.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the OF cable 1 has connection portions (JB) 2 spaced apart along the longitudinal direction thereof.
Is provided. Since two connecting portions 2 are shown in FIG. 1, a and b are added to the reference numerals such as 2a and 2b when differentiating them below. The in-oil gas sensor 3 according to the present invention is attached to the oil collection hole 4 of the connection portion 2. Gas sensor 3 in oil
Is an oil cell 5 communicating with the connecting portion 2, a gas separation membrane 6 such as a membrane made of a stainless sintered metal coated with a fluororesin,
Gas cell 7 separated from the oil cell by a gas separation membrane
The gas cell 7 is provided with an entrance window 8 and an exit window 9 facing each other so that light for measuring gas concentration can be transmitted.

On the other hand, the central monitoring station 1 remote from the connection unit 2
0 is provided with an optical switch 11, an oil temperature measuring unit 12, a gas data processing unit 13, and a deterioration diagnosing unit 14, and the oil temperature measuring unit 12 and the gas data processing unit 13 are optically coupled to the optical switch 11. ing. Transmission optical fiber 15 (15a, 1
5b) is laid from the optical switch 11 to the entrance window 8 of each gas cell 3, and the receiving optical fiber 16 extends from the gas data processing unit 13 to one output end of the optical switch 17 provided on the exit window side of each gas cell 3. It has been laid. An optical fiber 18 coupled to the emission window of each gas cell 7 is spirally wound around the in-oil gas sensor 3 and then coupled to the input end of the optical switch 17. The other output end of the optical switch 17 is coupled to the transmission optical fiber 15 for the connection portion 2b on the downstream side thereof.

The oil temperature measuring section 12 includes an optical fiber 15 for transmission.
The temperature distribution along the transmitting optical fiber 15 is measured from the Raman scattered light generated therein. Oil temperature measuring unit 12
Is performing a measurement operation, the optical fiber 18 serves as a temperature sensor 25 that detects the temperature of the insulating oil. The gas data processing unit 13 uses the light received from the optical fiber 15 for transmission via the gas cell 7 and the optical fiber 16 for reception to detect the gas cell 7
It measures the gas concentration inside. Although not shown, the oil temperature measuring unit 12 and the gas data processing unit 13 each have a built-in light source. The deterioration diagnosis unit 14 has a measurement unit 19 that measures the concentration of the dissolved gas in the connection unit 2 by adding the temperature of the insulating oil to the gas concentration, and the deterioration of the OF cable 1 is determined from the measurement result of the concentration of the dissolved gas. To diagnose.

Next, the operation of the embodiment will be described.

The light emitted from the light source in the gas data processing section 13 is transmitted through the transmission optical fiber 15a to the gas sensor 3 in oil.
It is transmitted in a and used for detecting gas concentration information. The gas concentration information detected here is the optical fiber 16 for reception.
Is transmitted to the gas data processing unit 13. Optical switch 11
It is possible to obtain information of the other in-oil gas sensor 3b by switching between.

On the other hand, the temperature information detected by the optical fiber 18 wound around the oil gas sensor 3 is also transmitted to the gas data processing unit 13 through the receiving optical fiber 16 at the same time. The temperature information and the gas concentration information together with the deterioration diagnosis unit 14
Sent to

When the gas concentration in one gas sensor 3a is obtained, the light source in the gas data processing unit 13, the optical switch 11, the transmission optical fiber 15a, the optical fiber 18,
The receiving optical fiber 16 and the gas data processing unit 13 operate, and at this time, the optical switch 17 shuts off the transmission path to the other gas sensor 3b in oil. Therefore, only the information detected by one gas sensor 3a in oil is transmitted to the gas data processing unit 13 via the receiving optical fiber 16, and the gas data processing unit 13 obtains the gas concentration in the gas cell 7.

At this time, the permeability of the gas separation membrane 6 differs depending on the oil temperature as described in the conventional example. Therefore, after detecting the gas concentration, the temperature is detected as follows.

By switching the optical switch 11,
The light emitted from the light source in the oil temperature measuring unit 12 is guided to the oil gas sensor 3a via the transmission optical fiber 15a.
This light passes through the gas cell 7a and reaches the optical switch 17 via the optical fiber 18. At this time, the light is guided to the in-oil gas sensor 3b by the optical switch 17. The light passes through each gas cell 7. Raman scattered light generated by gas molecules in each gas cell 7 is transmitted to the oil temperature measurement unit 12 via the transmission optical fiber 15a. The oil temperature measuring unit 12 obtains a temperature distribution along the transmission path, and measures the temperature of each gas cell 7, that is, the temperature of the insulating oil of each in-oil gas sensor 3 according to the distance between each gas cell 7. The distance between the in-oil gas sensors 3 is obtained from the time when the light emitted from the oil temperature measuring unit 12 reciprocates.

As described above, both the oil temperature and the gas concentration are obtained using the same optical fiber. Degradation diagnosis unit 14
Then, the deterioration diagnosis of the OF cable 1 is performed based on the oil temperature and the gas concentration.

Next, another embodiment of the present invention will be described with reference to FIG.

In this example, three connecting portions 2 of the OF cable 1 are shown. The in-oil gas sensor 3 attached to each connecting portion 2 is composed of an oil cell 5, a gas separation membrane 6 and a gas cell 7 as in the above-mentioned embodiment. However, the gas cell 7 is provided with a reflecting portion 20 facing the entrance window 8. The optical fiber 22 coupled to the entrance window 8 of each in-oil gas sensor 3 is coupled to one concentration measuring optical fiber 21, and the concentration measuring optical fiber 21 is laid up to the gas data processing unit 13 of the central monitoring station 10. ing.

On the other hand, one oil temperature measuring optical fiber 23 is laid from the oil temperature measuring section 12 of the central monitoring station 10 so as to penetrate the oil cell 5 of each in-oil gas sensor 3. In the oil cell 5 of each in-oil gas sensor 3, the optical fiber 2 for oil temperature measurement is used.
3 is formed in a loop to accommodate a predetermined fiber length.

In this example, the gas data processing unit 13 obtains gas data of each gas cell 7 via the optical fiber 21 for concentration measurement. The gas data processing unit 13 obtains the gas concentration in each gas cell 7, and these are sent to the deterioration diagnosis unit 14. The oil temperature measuring unit 12 measures the temperature of the insulating oil in each oil cell 5 at regular time intervals by using the oil temperature measuring optical fiber 23. These are also sent to the deterioration diagnosis unit 14. The measurement unit 19 in the deterioration diagnosis unit 14 measures the concentration of the dissolved gas in each connection unit 2 by adding the temperature of the insulating oil to the gas concentration. Then, the deterioration diagnosis unit 14 performs deterioration diagnosis of the OF cable 1.

[0042]

The present invention exhibits the following excellent effects.

(1) The gas concentration in oil can be accurately measured even if the temperature of the insulating oil changes.

(2) The gas concentration and the oil temperature can be measured with the same optical fiber, which is economical.

(3) Since the optical fiber is used, the measurement can be performed without being affected by the electromagnetic field.

[Brief description of drawings]

FIG. 1 is a block diagram of a deterioration diagnosis system for an OF cable showing an embodiment of the present invention.

FIG. 2 is a block diagram of a deterioration diagnosis system for an OF cable showing another embodiment of the present invention.

FIG. 3 is a block diagram of a deterioration diagnosis system for an OF cable showing a conventional example.

FIG. 4 is a graph showing the relationship between methane gas permeation coefficient and oil temperature.

[Explanation of symbols]

 2 Connection part 7 Gas cell 19 Measuring part 25 Temperature sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akiyuki Nakamura 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Cable Co., Ltd.

Claims (2)

[Claims] 1. An OF cable is provided with a gas cell for separating dissolved gas from insulating oil in the connection portion, an optical fiber is connected to the gas cell, and the gas concentration in the gas cell is adjusted by transmitting light from the optical fiber. In the gas concentration measuring device for oil to be detected, a temperature sensor for detecting the temperature of the insulating oil is provided, and the temperature of the insulating oil detected by this temperature sensor and the gas concentration in the gas cell are used to measure the dissolved gas in the connection portion. An in-oil gas concentration measuring device comprising a measuring unit for measuring the concentration. 2. The optical fiber is used as a temperature distribution sensor for measuring a temperature distribution along itself, and the optical fiber is laid so as to pass around the gas cell, and the gas concentration and the temperature of the insulating oil are the same with the optical fiber. 2. The apparatus for measuring gas concentration in oil according to claim 1, wherein