JPH0152691B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for measuring the progress of corrosion in an underground transformer, and is a method suitable for detecting corrosion current in a metal tank of an underground transformer while the transformer is in use. .

In recent years, underground power distribution has become widely used for urban beautification, and transformers are also often buried underground. If the transformer is buried underground, the metal tank housing the transformer is subject to electrolytic corrosion, so it is necessary to constantly monitor the corrosion status of the tank to prevent accidents caused by corrosion.

Potential measurement, which is most used for corrosion monitoring in cathodic protection systems, can detect whether the metal is being corroded or protected by a sacrificial electrode, but cannot evaluate the corrosion rate. . Additionally, a test piece is used to measure the change in weight of the test piece due to electrolytic corrosion, but this is an alternative evaluation to observing or measuring the corrosion status of the test piece itself. There is naturally a difference between this and the corrosion situation of the tank itself, where corrosion is accelerated due to the influence of temperature rise in the tank. The same can be said for measurements using a probe using the electrical resistance method or the polarization resistance method, and since there is a difference between the corrosion of the probe test piece and the tank itself, the reliability of the measurement results is low in either case.

The present invention is based on the viewpoint that the corrosion rate of the tank itself can be accurately evaluated by knowing the corrosion current flowing through the tank, and provides a method for easily measuring corrosion current. Hereinafter, the present invention will be explained along with an embodiment shown in the drawings.

FIG. 1 shows an example of the internal structure of a transformer for measuring corrosion current, and illustrations of the transformer contents, outlet parts, etc. are omitted. FIG. 2 shows an example of a circuit for measuring the electrical resistance of the tank shown in FIG. Figure 3 shows the measurement situation in the buried state.

In FIG. 1, 1 is a metal tank, and 1a is a cooling fin on the outer surface of the tank 1. A terminal chamber 1b is formed in the upper part of the tank 1, and a terminal block 2 having a pair of measurement terminals 2a and 2b is installed in the terminal chamber 1b. On the other hand, a ground terminal 3 is attached to the upper part of the tank 1, and a base terminal 10 is attached to the base 1c which is the lower part of the tank 1. One of the measurement terminals 2a and the ground terminal 3 are electrically connected to each other by an electric wire 4, and the other measurement terminal 2b and the base terminal 10 are electrically connected to each other by a power source 5.

Before burying an underground transformer with such a terminal structure, a power source 11 is connected to the ground terminal 3 and the base terminal 10 as shown in FIG. The voltage E is measured with an ammeter 12 and a potentiometer 9, and the electrical resistance R between the ground terminal 3 and the base 1c is determined in advance using the following equation (1).

R=E/I ...(1) After the above measurements, as shown in Figure 3, install the underground transformer in the underground hole 6 and connect the earth rod 7 to the earth terminal 3 with the earth wire 8 as usual. do.
If corrosion occurs in the installation state shown in Figure 3, the corrosion current i will flow from tank 1 to earth 13 as indicated by the broken line arrow in the figure.
The flow follows the path of → earth rod 7 → earth wire 8 → tank 1. Therefore, a potentiometer 9 is connected between the measurement terminals 2a and 2b.
By connecting and measuring the potential difference between the measurement terminals, that is, the potential difference e between the top and bottom of the tank, the corrosion current i is determined from the following equation (2) using the equivalent resistance R of tank 1 obtained previously using equation (1). .

i=e/R...(2) If the corrosion current i is known, it is possible to monitor the extent to which the material in tank 1 has melted and the progress of corrosion, making corrosion measurement more reliable than conventional methods. . Further, although it is necessary to know the corrosion status after the transformer is buried, according to the method of the present invention, it is sufficient to measure the potential difference e between the measurement terminals 2a and 2b in the terminal room 1b. The progress of corrosion can be easily monitored while the transformer remains in use without being pulled up, and without the need for a person taking the trouble to enter the underground hole 6. Note that the corrosion current i may be measured as needed, or an automatic recorder may be built in the terminal chamber 1b to continuously measure the corrosion current i.

[Brief explanation of drawings]

The drawings relate to an embodiment of the present invention; FIG. 1 is a sectional view showing an example of the internal structure of a transformer for measuring corrosion current in an underground transformer; FIG. 2 is a circuit diagram showing tank resistance measurement; FIG. 3 is a diagram showing an underground transformer in a buried state and a state of corrosion current measurement. In the drawing, 1 is a tank, 1b is a terminal room, 1c is the base of the tank, 2 is a terminal block, 2a and 2b are measurement terminals, 3 is a ground terminal, 4 and 5 are electric wires, 6 is an underground hole, and 7 is a ground rod , 8 is a ground wire, 9 is a potentiometer, 10 is a base terminal, 11 is a power supply, 12 is an ammeter, and i is a corrosion current.

Claims (1)

[Claims] 1 A ground terminal is attached to the top of the metal tank of an underground transformer, and a base terminal is attached to the bottom, a terminal chamber is formed at the top of the tank, and the ground terminal and base terminal are electrically connected to each other within this terminal chamber. Install a pair of measurement terminals, measure the resistance value between the ground terminal and base terminal before burying the transformer, and after burying the transformer, connect the measurement terminals with the ground rod connected to the ground terminal. A method for measuring corrosion current in an underground transformer, comprising: measuring a potential difference; and determining a corrosion current flowing into a tank from the potential difference and the resistance value.