JPS5853777A - Crack detector for field coil of turbine generator - Google Patents

Abstract

PURPOSE:To detect the position and length of cracks by comparing potential differences between lead wires for measuring potential difference which are distributed in plurality at a field coil end with lead wires for supplying direct current. CONSTITUTION:A plurality of measuring terminals 19 are provided at a space 1 from a slot output to the end of a coil. A potential difference V0, the reference potential difference, between the measuring terminals 14 of the end and potential differences V1-V6 between the measuring terminals 19 are switched over sequentially with a scanner 26 according to a command from a computer 24, amplified by passing through a low-pass filter 27, a preamplifier 28 and an amplifier 29 and then inputted into the computer 24 and digitalized with an analog-digital converter 23. The computer 24 calculates V1/V0-V6/V0 by division of the potential differences measured to determine the length of a crack based on a relationship between the length thereof and the ratio of the potential differences. The position and the length of the cracks are displayed on the screen of a CRT 25.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting the length of a crack in a field coil of a turbine generator. This invention relates to a device suitable for measuring.

The methods used to measure crack length are ultrasonic method, AE method,
There are methods such as potential method. The AE method measures the total number of counts, number of documents, Vrms value, etc. of AE that occurs when a crack grows, and compares it with the AE generation behavior during the crack growth process obtained in advance in the laboratory. The crack growth rate is determined from Therefore, it is necessary to conduct experiments under load conditions that simulate the actual machine. The reason for this is A in the case of fatigue cracks, creep cracks, or other types of cracks.
This is because the Ef raw behavior is different. Of course, the AE generation behavior differs depending on the material and is also sensitive to tissue, so there is the inconvenience of having to investigate the two materials actually used. At present, the minimum element for detecting the AE multiplied signal is a diameter of 10111111% and a length of 15 m, making it impossible to measure in a narrow space. Furthermore, A
Since the E times signal corresponds to the crack growth rate, there is the inconvenience of having to measure it all the time. There are various ultrasound methods, but as with the AE method, the ultrasound transmitting and receiving elements are large, making measurement in a narrow space impossible. In the case of the DC potential method, it is only necessary to provide a power supply terminal for inputting DC current into the component and a measurement terminal for measuring the potential difference at two points between the parts where cracks may occur. It has the advantage that it can be measured if there is a gap as thick as . Also, unlike the AE method, since the crack length is detected, there is also the advantage that the cause of crack initiation and growth does not matter.

An object of the present invention is to provide a crack detection device that accurately detects the occurrence and length of cracks in the field coil end portion of a turbine generator without removing the retainer, and predicts the remaining life. There is something to do.

The end of the field coil where cracks occur is covered with retaining, and there is an FRP spacer between the coils, so there is enough room to install a detection element for the AE method or ultrasonic method. Therefore, other methods must be considered.

In the case of the DC potential method, it is only necessary to have the power supply terminal and measurement terminal in contact with the side surface of the coil, and it is sufficient to create a gap large enough to allow the lead wire to pass through. The present invention is a crack length detection method using a DC potential method, in particular, a method in which a large number of lead wires for DC brewing feed and lead wires for measuring potential difference are wired at the end of a field coil, and the potential difference between the measurement lead wires is compared. In particular, it is a crack detection device that makes it possible to detect the location of a crack as well as measure the length of the crack.

An embodiment of the present invention will be described below. FIG. 1 is a diagram showing a field coil end portion of a turbine generator. The field coil is inserted into the slot 2 drilled in the rotor body 1. Many layers are stacked and wound, and then the S pole, N pole
Each pole is wound concentrically a number of times from the first coil. In this case, the top turn 4 of the first coil 3, which is close to the seed stone, may break at the slot exit. If the coil breaks, it will lead to a field grounding accident, so it is necessary to detect crack occurrence and prevent breakage. One method for detecting crack length is the DC potential method.

The principle of measuring crack length using the DC potential method is that the electric field is disturbed by the presence of discontinuities in the conductor, and the measured potential difference depends on the size of the sample being measured, Depends on the shape of the discontinuity. Therefore, the crack length a/
Potential difference V with respect to W.

Or the potential difference V when there is no crack. If a master curve of the potential difference ratio V/VO is created based on , the crack length can be measured by measuring the solder position difference. Ko(Z)V/L
Except for special materials such as 8U8304f:), the relationship between a and a/WZ) has nothing to do with the material or the thickness of the member, but depends on the shape of the member, the shape of the crack, the current input position, and the potential difference measurement position.

The crack that occurs in the turbine generator field coil is the second
It is a one-sided crack as shown in the figure. When measuring a one-sided crack using the DC potential method, a distance t is placed between the crack 9 and the vicinity of both ends of the member 80. Through the power supply terminal 10 provided at
A stabilized DC current is inputted from the DC power source 11, and the potential difference V between the measurement terminals 12 which are separated by a distance t across the crack 9 is measured by the position difference meter 13. The potential difference V to be measured is hardly affected by to if the distance t0 between the power supply terminals is a little larger than the distance t between the measurement terminals, but it is largely dependent on the distance t between the measurement terminals. Further, the potential difference V is very sensitive to the temperature of the member due to the temperature dependence of specific resistance. Therefore, either investigate the temperature dependence of resistivity and correct it by measuring the temperature with a thermocouple attached to the member, or correct the potential difference V at the part where there is no crack. The crack length must be evaluated by measuring the temperature-independent potential difference ratio V/Vo. In Figure 3, the distance between the measurement terminals is 15m, '45■.

Potential difference ratio V/ when changed to 75mm, 105++on
V.

This is the change in crack length a/W. The increase in impedance due to the decrease in the cross-sectional area in front of the crack becomes relatively small when the distance t between the measurement terminals is large, so V/V
The change in O decreases as t increases, and in order to improve measurement accuracy, it is necessary to make the distance t between the measurement terminals as small as possible.

FIG. 4 shows a crack detection device for a turbine generator field coil. A power supply terminal 10 for supplying a DC current is provided on the side surface of the coil 4 immediately after coming out of the rotor 1, and a DC power supply 11 causes the DC current to flow throughout the coil through this terminal. In order to measure the reference potential difference, measurement terminals 14 are provided at intervals t't at the ends where there is no risk of cracking, and the potential difference V between them is provided. The signal is passed through a low-pass filter 1.5 to pass only the DC component, amplified by a preamplifier 16 and an amplifier 17 to IV order, and then input to an analog divider 18. A measurement terminal 19 is provided at the same distance t as the measurement terminal 14 on the side of the coil between the slot outlet and the end where cracks may occur, and the potential difference V between these terminals is passed through a low-pass filter 20 to the preamplifier 21 and amplifier 22. After being amplified, the signal is input to the analog divider 18, where the amplified potential difference V and vo are divided, digitized by the AD converter 23, and then input to the computer 24. The memory circuit of the computer 24 stores the relationship between the potential difference ratio V/''V O and the crack length a/W corresponding to the distance t between the measurement terminals as shown in FIG. Potential difference ratio V entered from 23
/VOt-By entering this relationship, the crack length a/W
is calculated and displayed on the CRT 25.

Next, we will show how to determine the remaining life until the crack propagates to the critical crack length a/We K. As shown in FIG. 5, the storage circuit of the computer 25 stores the change of the crack length a/W with the number of repetitions N of the stress corresponding to the operating time t and the straddle rotation speed n, that is, the crack growth curve. . Calculate the crack growth rate da/dN up to a certain number of repetitions Ni, and
As shown in the figure, the relationship between crack growth rate d a /d N and crack length a/W is linearly approximated on a logarithmic graph to obtain d a
/d N= (a/W)''.Next, as shown in Figure 7, the crack length a when the number of repetitions N' is
/W+ and the critical crack length a/W are equally divided. a
From /W+, da/dN=(a/W)-+7)+
@ d obtained by substituting the equation ttc a / w I
a/Wl+ with slope of a/d N l.

Draw a straight line until.

Similarly, from “/Wl +1, da/dNl+t
(Draw a straight line up to a/Wl+2 using D, and repeat this to extend the crack growth curve to the critical crack length a/W.

The number of repetitions N at the critical crack length a/W, , minus the number of repetitions N1 at the time of the last measurement, is N, =N, - the tooth is the remaining life. After a/Wl, each time the crack grows, the computer repeats the operations shown in FIGS. 5 to 7, and the remaining life N is determined each time.

Correct and display. When the remaining life N1 becomes extremely small, or when the critical crack length a/WK is reached, a warning is displayed on the CRT screen, the generator is stopped, and the coil is replaced.

FIG. 8 shows a second embodiment. As shown in FIG. 3, the accuracy of crack length measurement is better as the distance between the measurement terminals is shorter. Therefore, a large number of measurement terminals 19 are provided at short intervals t from the slot outlet to the end of the coil. Here, an example is shown in which the 4-position difference at 6 locations is measured by providing measurement terminals at t-8 locations. The potential difference V between the measurement terminals 14 at the end portion is the reference potential difference. and the potential difference between the measurement terminal 19 v1~
v6 is switched in accordance with instructions from the computer 24 in the scanner 26, amplified through the low-pass filter 27, preamplifier 2B, and amplifier 29, and then sent to the AD converter 2.
3 and is digitized and input to the computer 24. The computer 24 divides the measured potential difference to obtain Vs/Vo to Vs/vo, and calculates the crack length a/Vo from the relationship between the crack length a/W and the potential difference ratio V/Vo as shown in FIG. Find the crack occurrence position and crack length on the CRT 25 screen, and if the crack grows, calculate and display the remaining life N according to the steps in Figures 5 to 7. .

According to the present invention, there are two lead wires for supplying direct current and four to ten lead wires for measuring potential difference.
By pre-wiring several wires to the generator field coil end, the crack occurrence position and crack length can be detected, so there is no need to measure the field coil temperature.

It has the effect of being able to detect cracks without removing the glyph.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the area around the generator field coil end. Figure 2 is a wiring diagram for crack length measurement using the DC potential method, Figure 3 is a diagram showing the relationship between potential difference ratio and crack length when the distance between measurement terminals is changed, and Figure 4 is a diagram showing the relationship between the potential difference ratio and crack length when the distance between measurement terminals is changed. Figure 5 shows the relationship between crack length and number of repetitions. Figure 6 shows the relationship between speed and crack length for crack propagation. Figure 7 shows how to create a predicted crack growth curve. The figure shown in FIG. 8 is a crack detection device for a field coil end portion. V/VO...Potential difference ratio, a-...Crack length, W...
・Plate width, t... Distance between measurement terminals, 10... Power supply terminal, 11... DC power supply, 14.19... Measurement terminal, 1
5,20°27...Low pass filter, 16,21
．． 28... Preamplifier, 17, 22. 29... Amplifier, 18... III IE device, 23... AD converter, 24... Computer, 25 2... CRT, 26
···scanner.

Claims (1)

[Claims] 1. Turbine power generation [DC/- current is passed from the slot outlet of the field coil, and the potential difference between measurement terminals placed at a certain interval at the end is passed through a scanner, a low-pass filter, and amplified by an amplifier. AD convert it and input it to the manipulator, use this as a reference potential difference, and measure several sets at intervals equal to the interval between the measurement terminals of the end section from the slot exit section where cracks may occur to the end section. The terminals are arranged, and the potential difference between the several sets of measurement terminals is passed through the scanner linked to the computer, passed through the low-pass filter, amplified by the amplifier, AD converted, inputted into the computer, and inserted into the slot. A potential difference ratio is obtained by dividing the potential difference between each terminal of the outlet section by the reference potential difference of the end section, and the area between the measurement terminals where the value is greater than 1 is indicated as a crack initiation point. A crack detection device for a turbine generator field coil, characterized in that the crack length is determined and displayed from the relationship between the potential difference ratio and the crack length stored in the computer.