If the cable line is damaged, this is fraught with economic losses during the transmission of electric current; a short circuit may occur, which will lead to breakdown of powered devices or substations. If the insulating material is damaged, there may be a risk of electric shock.

Searching for damage to cable lines

Damage to the line can cause a disconnection from the power supply of residential buildings, business facilities, management and control systems of workshops and enterprises, and vehicles. Finding violations in the cable line is of primary importance.

What are the types of damage?

Underground and above-ground electrical transmission lines can be damaged for many reasons. The most common situations are:

1. Short circuit of one or more wires to ground;
2. Closing several cores simultaneously to each other;
3. Violation of the integrity of the cores and grounding them as if they were torn;
4. The break lived without grounding;
5. The occurrence of short circuits even with a slight increase in voltage (floating breakdown), which disappear when the voltage normalizes;
6. Violation of the integrity of the insulating material.

To establish the true type of power transmission disturbance, a special device is used - a megohmmeter.

Megaohmmeter

The suspected damaged cable is disconnected from the power sources and the working device. The following indicators are measured at both ends of the wire:

• Phase insulation;
• Linear insulation
• There are no violations of the integrity of the conductors conducting electric current.

Stages of identifying locations of cable line damage

Finding problematic areas in a cable involves three main steps, thanks to which the non-working section can be quickly eliminated:

The first stage is carried out using special equipment. For these purposes, transformers, kenotronomes, or devices capable of generating high frequencies are used. When burning for 20 - 30 seconds, the resistance indicator drops significantly. If there is moisture in the conductor, then the necessary burning procedure takes much longer and the maximum resistance that can be achieved is 2-3 thousand Ohms.

AIP-70 installation for burning cables

This process takes much longer in the couplings, and the resistance indicators can change in waves, either increasing or falling back. The burning procedure is carried out until a linear decrease in resistance is observed.

The difficulty in determining the location of cable damage is that the length of the cable line can reach several tens of kilometers. Therefore, at the second stage it is necessary to determine the damage zone. To cope with this task, effective techniques are used:

• Method for measuring conductor capacitance;
• Probing pulse technique;
• Creating a loop between the cores;
• Creation of an oscillatory discharge in a conductor.

The choice of technique depends on the expected type of damage.

Capacitive method

Based on the conductor's capacitance, the length from the free end of the conductor to the core break zone is calculated.

Scheme for determining damage using the capacitive method

Using alternating and direct current, the capacitance of the core that is damaged is measured. The distance is measured based on the fact that the capacitance of a conductor directly depends on its length.

с1/lx = c2/l – lx,

where c1 and c2 are the cable capacitance at both ends, l is the length of the conductor under study, lх is the required distance to the place of the supposed break.

From the presented formula it is not difficult to determine the length of the cable to the break zone, which is equal to:

lх = l * c1/(c1 + c2).

Pulse method

The technique is applicable in almost all cases of conductor damage, with the exception of floating breakdowns, which are caused by high humidity. Since in such cases the resistance in the conductor is over 150 Ohms, which is unacceptable for the pulse method. It is based on applying, using alternating current, a probe pulse to the damaged area and capturing the response signal.

Time sweep of the probing reflected signals using the pulse method for determining damage locations: 1, 2, ..., m – single processes repeating with a frequency of 500 - 1000 Hz.

This procedure is carried out using special equipment. Since the pulse transmission speed is constant and amounts to 160 meters per microsecond, it is easy to calculate the distance to the damage zone.

The cable is checked using an IKL-5 or IKL-4 device.

IKL-5 device

The scanner screen displays pulses of different shapes. Based on the shape, you can roughly determine the type of damage. Also, the pulse method makes it possible to find the place where there is a violation in the transmission of electric current. This method works well if one or more wires are broken, but a bad result is obtained if there is a short circuit.

Loop method

This method uses a special AC bridge to measure changes in resistance. Creating a loop is possible if there is at least one working wire in the cable. If a situation arises where all the cores are broken, you should use the cable cores, which are located in parallel. When a broken core is connected to a working one, a loop is formed on one side of the conductor. A bridge is connected to the opposite side of the cores, which can adjust the resistance.

Scheme for determining cable damage using the loop method

Finding damage to the power cable using this technique has a number of disadvantages, namely:

• Long preparation and measurement time;
• The measurements obtained are not entirely accurate.
• Short circuits are required.

For these reasons, the method is used extremely rarely.

Oscillatory DISCHARGE method

The method is used if the damage was caused by a floating breakdown. The method involves the use of a kenotron installation, from which voltage is supplied through the damaged core. If a breakdown occurs in the cable during operation, a discharge with a stable oscillation frequency is necessarily formed there.

Considering the fact that the electromagnetic wave has a constant speed, the location of the fault on the line can be easily determined. This can be done by comparing the frequency of oscillations and speed.

Scheme for determining damage using the oscillatory discharge method

Having established the area of ​​damage, an operator is sent to the suspected area to find the point of damage to the power cable. To do this, they use completely different methods, such as:

• Acoustic capture of spark discharge;
• Induction method;
• Rotating frame method.

Acoustic method

This fault detection option is used for underground lines. In this case, the operator needs to create a spark discharge in order to prevent the cable from malfunctioning in the ground. The method works if at the point of damage it is possible to create a resistance of more than 40 ohms. The strength of the sound wave that a spark discharge can create depends on the depth at which the cable is placed, as well as on the structure of the soil.

Scheme for determining damage using the acoustic method

A kenotron is used as a device capable of generating the necessary impulse, in the circuit of which it is necessary to additionally include a ball gap and a high-voltage capacitor. An electromagnetic sensor or a piezo sensor is used as an acoustic receiver. Additionally, sound wave amplifiers are used.

Induction method

This is a universal method for searching for all possible types of cable faults; in addition, it allows you to determine the damaged cable line and the depth at which it lies underground. Used to detect couplings connecting cables.

Scheme for determining cable damage using induction method

The basis of this method is the ability to detect changes in the electromagnetic field that occur when current moves along an electric line. To do this, a current is passed, which has a frequency of 850 - 1250 Hz. The current strength can be within a few fractions of an ampere up to 25 A.

Knowing how changes in the electromagnetic field under study occur, it will not be difficult to find the location where the integrity of the cable has been compromised. In order to accurately determine the location, you can use cable burning and converting a single-phase circuit into a two- or three-phase one.

In this case, you need to create a core-core circuit. The advantage of such a circuit is that the current is directed in opposite directions (one core forward, the other wire backward). Thus, the field concentration increases significantly and it is much easier to find the location of the damage.

Frame method

Scheme for determining cable damage using the frame method

This is a good way to find out-of-service areas on the surface of a power line. The principle of operation is very similar to the induction method. The generator is connected to two wires or to one wire and sheath. Then a frame is placed on the damaged cable, which rotates around an axis.

Two signals should clearly appear at the location of the violation - minimum and maximum. Beyond the intended zone, the signal will not fluctuate without producing peaks (monotonic signal).

Damage in an electrical cable, regardless of whether it is located underground and powers, say, a transformer substation of several residential buildings, or in a wire laid by hidden wiring in an apartment, requires identification and prompt repair. During operation and at the stage of installation of cable lines laid underground, unexpected mechanical damage to the insulation and current-carrying conductors occurs. This may be due to a violation of normal operating conditions, careless installation work on other communications located a few meters from the installation site and not related to the power supply line. In the apartment, they are often damaged during renovations. One of the reasons that unites both situations is a defect in cable and wire products made at the manufacturing stage. But be that as it may, it is necessary to find a fault in the line. We will describe below how to search for cable damage underground and in the wall, providing existing methods and instruments for detecting the faulty area.

Methods for determining cable damage in the ground

To find the location of the cable line damage, you need to understand the specifics and methods of searching. The process must be divided into two stages:

1. Search for problem areas along the entire length of the line.
2. Searching for an accident site on a designated section of the route.

Due to the differences between these two stages, the search methods themselves differ and are:

• relative (remote) - these include the pulse and loop methods;
• absolute (topographic) - acoustic, induction and step voltage method.

Well, let's look at all the methods in order.

Pulse method

This method involves searching for damage using a reflectometer. Work can be carried out, for example, with the REIS-305 device, which is shown in the photo below.

The operation of the device is based on sending probing pulses of a certain frequency, which, when encountering an obstacle in their path, are reflected and returned back to the device. That is, the device is located at one end of the power cable, which is very convenient and practical. To calculate the exact distance to the damage site, you must use the following formula:

Where, according to the formula, L – cable length from the point of connection of the device to the damage, tx – a variable value of the amount of time spent for the impulse to reach the break point and back. υ – the speed with which the pulse travels along the cable (for cable lines from 0.4 kV to 10 kV it is 160 m/µs).

This method can detect not only a break in the power cable, but also a short circuit between the wires. To understand what happened, let's look at the image on the screen during the tests. The pictures will be like this (short circuit on the left, open circuit on the right):

Tests should be carried out on a completely disconnected line. The video example clearly demonstrates how to use a short circuit finder:

Instructions for using the ISKRA-3M reflectometer

Loop method

This method is applicable provided that at least one wire in the cable remains intact, or another conductor with intact cores lies nearby. To find out the distance to the place of damage using the loop method, you need to measure the DC resistance of the wires with the P333 device. This is a DC measuring bridge that looks like this:

Before starting measurements, we connect the end of the intact and damaged core with a short circuit, and connect the other two ends according to the diagram:

You can calculate the distance to the point at which the break occurred using the following formula:

• R 1 - resistance that is connected to the whole core;
• R 2 – resistance that is connected to the wire with a break;
• L – cable length to the point of damage;
• Lk is the length of the entire conductor.

This is perhaps one of the first invented methods used to find the location of the fault, and it is used exclusively for single-phase and two-phase faults. Gradually they stop using it, due to its labor intensity and large error in measurements.

Acoustic method

You can find a break in a cable using the acoustic method by creating a discharge at the site of damage using a high-voltage pulse generator (in the picture below). At the location of the break or short circuit, sound vibrations of a certain frequency will appear. The quality of listening depends on the type of soil, the distance from the surface to the cable line and the type of damage. A prerequisite for the method to work is to exceed the contact resistance value of 40 ohms.

An example of searching for a damaged line using an acoustic method is provided in the video:

Step Voltage Method

The method is based on passing current generated by a generator through a cable. It creates a potential difference between two points located in the ground, which can be judged by the location of the accident. To find a point with reduced insulation resistance, contact probe probes are installed like this - the first one is exactly above the running conductor, the second one is at an angle of 90 0 a meter from the first one.

The point where the cable is damaged is under the first pin, assuming the signal is at its maximum. You can learn more about it from our article!

Induction method

The method very accurately determines the location of the break, but its use is associated with burning the cable. If the transition resistance is high, it is necessary to reduce its value by burning, using special devices, for example, the VUPK-03-25 cable burning installation:

The method is based on passing a high-frequency current through the core, which forms an electromagnetic field above the cable line. In places of mechanical damage to the route, passing the receiving frame, the sound will change. Thus, the absence of sound indicates a wire break.

The video below clearly demonstrates the location of the emergency area by burning:

Burning a cable line

Finding a broken hidden wiring in a concrete wall

A special device - a locator - will help you find the location of a wire break in a concrete wall. It is a combination of a receiver and an oscillator. This method can be associated with the induction method in searching for cable faults underground.

So, determining the location of the break with a route finder is not difficult. The end of the wire in which there is a break is connected to a generator, which sends pulses of a certain frequency into it. By passing the frame over the place where the wiring is laid, the sound that is formed as a result of the influence of impulses will be clearly audible in the headphones. As soon as the sound disappears, mark this place on the wall - this will be the point of damage to the wire.

The device is designed to search for alternating current electrical networks underground and in the channels of concrete and brick buildings, their location and depth.

Before searching for the route, an audio frequency voltage of sufficient power should be applied to disconnected cable lines, and the end of the line should be temporarily closed; this should also be done in case of possible mechanical damage; the electromagnetic field in the damaged area is always several times higher than in a healthy section of the line.

The principle of operation of the device is based on the conversion of the electromagnetic field of the electrical network with a frequency of 50 Hz into an electrical signal, the level of which depends on the voltage and current in the conductor, as well as on the distance to the radiation source and the shielding factors of soil or concrete.

The device circuit consists of an electromagnetic field sensor BF1, a pre-amplifier on a transistor VT1, a power amplifier DA1 and an output control device consisting of a sound analyzer on headphones BA1, a light peak indicator HL1 and a galvanic power indicating device - PA1. To reduce distortion of the electromagnetic field signal, negative feedback circuits are introduced into the amplifier circuits. The use of a powerful low-frequency amplifier at the output allows you to connect a load of any resistance and power.

Installation resistors and regulators are introduced into the circuit to optimize the operating mode of the device circuit. The device can estimate the depth of the electrical network from the surface of the earth.

To power the device circuit, a current source of the Krona type at 9 volts or a KBS at a voltage of 2 * 4.5 volts is sufficient.

To eliminate accidental discharge of batteries, the circuit uses double shutdown: by opening the positive power bus of the power bus when the BA1 headphones are turned off.

The BF1 electromagnetic sensor is used from high-impedance telephone headphones of the TON-1 type with the metal membrane removed. It is connected to the pre-amplifier on transistor VT1 through the coupling capacitor C2. Capacitor C3 reduces the level of high-frequency interference, especially radio interference. The amplifier on transistor VT1 has voltage feedback from the collector to the base through resistor R1; when the voltage on the collector increases, the voltage on the base increases, the transistor opens and the collector voltage decreases. Power is supplied to the amplifier through load resistor R2 from filter C1, R4. Resistor R3 in the emitter circuit of transistor VT1 mixes the characteristics of the transistor and, due to the negative voltage level, slightly reduces the gain at signal peaks. The pre-amplified electromagnetic field signal is supplied through galvanic isolation capacitor C4 to the gain regulator R5 and then through resistor R6 and capacitor C6 to input (1) of the analog power amplifier chip DA1. Capacitor C5 reduces frequencies above 8000 Hz for better signal perception.

The audio power amplifier on the DA1 chip with an internal device for protecting against short circuits in the load and overload allows you to amplify the input signal with good parameters to a value sufficient to operate a load of up to 1 watt.

The distortion in the signal introduced by the amplifier during operation depends on the value of the negative feedback. The OS circuit consists of resistors R7, R8 and capacitor C7. With resistor R7 it is possible to adjust the feedback coefficient based on the quality of the signal.

Capacitor C9 and resistor R8 eliminate self-excitation of the microcircuit at low frequencies.

Through the isolation capacitor C10, the amplified signal is supplied to the load BA1, the level indicator PA1 and the LED indicator HL1.

Electrodynamic headphones are connected to the output of the amplifier via connector XS1 and XS2, the jumper in XS1 closes the power supply circuit from battery GB1 to the circuit. The HL1 indicator light monitors the presence of output signal overload.

Galvanic device PA1 indicates the signal level depending on the depth of the electrical network and is connected to the output of the amplifier through an isolation capacitor C11 and a voltage multiplier on diodes VD1-VD2.

There are no scarce radio components in the power grid search device: the BF1 electromagnetic field receiver can be made from a small-sized matching transformer or an electromagnetic coil.

Resistors type C1-4 or MLT 0.12, capacitors type KM, K53.

Reverse conduction transistor KT 315 or KT312B. Pulse diodes for current up to 300 mA.

A foreign analogue of the DA1 chip is TDA2003.

The PA1 level device is used from the recording level indicator of tape recorders with a current of up to 100 μA.

HL1 LED of any type. Headphones BA1 - TON-2 or small-sized ones from players.

A correctly assembled device begins to work immediately, by placing the electromagnetic field sensor on the power cord of the switched-on soldering iron, set resistor R7 to the maximum volume of the signal in the headphones, when

middle position of the R5 “Gain” regulator.

All radio components of the circuit are located on the printed circuit board except for the BF1 sensor, which is installed in a separate metal box. Battery – KBS is fixed outside the case with a bracket. All housings with radio components are mounted on an aluminum rod.

You can start testing the power grid search device without leaving your home; just turn on the light of one of the lamps and clarify the route in the wall and ceiling from the switch to the lamp, and then proceed to search for routes underground in the courtyard of the house.

Literature:

1. I. Semenov Measurement of high currents. "Radiomir" No. 7 / 2006 p. 32

2. Yu.A.Myachin 180 analog microcircuits. 1993

3. V.V.Mukoseev and I.N. Sidorov Marking and designation of radioelements. Directory. 2001

4. V. Konovalov. Device for searching electrical wires - Radio, 2007, No. 5, S41.

5. V. Konovalov. A. Vanteev Search for underground power networks, Radiomir No. 11, 2010, C16.

I remind you that all articles from the previous competition, as well as the rules and results, can be seen.

The topic of the article is similar to the previous one:

High-voltage pulse generator for searching for a break in a power transmission line

This device allows you to determine the location of a break in the electrical wiring line at home. This way, you can easily repair the electrical wiring in your home if it breaks.

In electrical engineering this method is called acoustic. It is based on listening to sound vibrations (pops) caused by a spark discharge at the site of damage. Typically, the gap in electrical wiring ranges from 0.5 ... 2 mm. Such a gap easily breaks through a voltage of 1 ... 3 kV DC. Simplified diagram in Fig. 1.

Uu is a source of boosting voltage until breakdown.

Ru is the internal resistance of the voltage source.

If there is low resistance at the breakdown site, there will be no pop. The source will discharge and the voltage will not increase. To avoid this, you need to install a spark gap in the circuit circuit (Artificial gap is about 1 mm). And in order for the breakdown to be clearly audible and visible, add a high-voltage capacitor. Device diagram in Fig. 2.

Typically, a wiring break is located at a depth of 1...2 cm in the plaster or in the junction box. The location of damage is easily detected by the light flash and the sound of the discharge pop.

Before searching for a break in a section of the electrical network, you need to turn off all electrical consumers. High voltage of the device can damage the insulation of the electrical windings. motors and other electronic devices. And it is imperative to follow electrical safety precautions (3).

It is useful to first use a high-frequency generator and a finder and approximately determine the location of the damage (2). And also measure the wiring capacitance to the point of cable damage APPV 2*2.5, the capacitance of 1 m is approximately equal to 80-100 pf. Then connect the ~220 V power supply to the high-voltage device (see device diagram Fig. 4.) and the open line to the output terminals “0” and “1” or “2”. Press the SA1 button and hold for about 3 seconds. Until discharge. If you hold the button longer, the discharges will be repeated as the voltage accumulates on capacitor C2.

The device itself consists of not scarce parts. Transformer Tr1 from a horizontal scanning black-and-white TV. The P35 arrester can be replaced with a homemade one.

It is made from a piece of foil fiberglass laminate measuring 30*30 with a round hole in the center with a diameter of 15 mm. The foil has been removed in the middle. There are 2 holes at the edges for connecting wires, see Fig. 3.

From each pad, 2 pieces of copper wire with a diameter of 1 mm are soldered towards each other with a gap of 3 mm. A breakdown will occur in the gap, with a calculation of 1 mm = 1 sq. Such a spark gap P1 is installed in the circuit to protect the high-voltage transformer Tp1. When discharged in the factory P35, the sound is very weak and does not interfere with listening to the discharge in the electric. house wiring.

Device diagram

The device is a high-voltage pulse generator based on a thyristor. Capacitor C2 K75-53 1 µF for a voltage of 5 kV. It can be replaced with several capacitors of smaller capacity, but the total capacitance should be about 1 µF, the operating voltage should be at least 5 kV.

The ST1 thyristor control circuit is taken from (4). The ratings of the circuit parts are indicated on the circuit diagram. The device is assembled in a small plastic case, see photo. Neon lamp L1 is needed to signal the 220v network voltage to power the device.

Using a break detection device

Now two examples of using the device from my practice.

1. Reducing the cable from the VHF antenna. The resistance between the screen and the central core according to the tester is 100 Ohms. It should be about 5...10 ohms. When connecting the device to the cable, one person pressed the SA1 button, and I watched the antenna and cable in the evening. Sparks were visible under the right bolt connecting the cable to the antenna cable. The right bolt was tightened more. The transition resistance dropped to 8 ohms.

2. It was necessary to repair the electrical wiring in the house. The electric lamp in the room went out. The lamp is intact and in good working order. I turned out the lamp. I shorted the ends in the cartridge. The wires coming from the device “0” and “1” were connected to a separate line going to the lamp socket. When the SA1 button of the device was pressed, discharges were heard at the site of a break in the wiring coming out of the ceiling. Closing the gap is easy.

Photo of the device.

Literature:

• Radio amateur No. 2 1997 Art. 24.
• Radio world No. 7 2014 Article 27 and amendment Radio World No. 9 2014 Article 32.
• Radio No. 5 2015 Article 54.
• Radio No. 1 2008 Article 27.

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Third Eye (Part 3)

Devices for searching and diagnosing underground utilities

Thanks to multi-directional antennas, the sensitivity of devices is increased and the likelihood of errors is reduced. The operator no longer needs to zigzag around the area under study - he just has to press the power button and select the type of route he needs, and the device itself will find it and display it on the screen. This approach allows the locator to be used even by workers with low qualifications and virtually no special training.

Acoustic leak detectors (locators)

A number of methods for locating underground communications based on acoustic location are widely used. Often such methods are used to search for water and gas leaks in pipelines made of any metallic and non-metallic materials. That’s why leak detection devices are called leak detectors.

Acoustic inactive method

As liquid or gas flows out of a pipe, it makes noise that can be detected by an acoustic leak detector with a passive detection function, in other words, an inactive acoustic detector. Acoustic microphone sensors, which can be contact, applied directly to the ground, or non-contact, pick up sound waves propagating along the ground. As the operator approaches the leak, the noise becomes louder. By identifying the point where the sound is strongest, you can determine the location of the leak. This method works when the pipeline is located at a depth of approximately 10 m.

If you have access to the pipe through manholes, you can listen to the noise by attaching a microphone to the pipe or valve handle, since sound waves travel better through the pipeline material. Using this method, you can identify the section of pipe between two wells where there is a leak, and then, based on the sound strength, which of the wells it is closer to. The accuracy of the method is low, but it can detect leaks at a much greater depth than when listening from the surface. If the device has a pseudo-correlation function, it can calculate the distance to the leak site based on the difference in sound intensity and refine the search result.

The device usually includes headphones, a powerful sound amplifier (gain up to 5000–12,000 times), an interference filter that passes sounds only of the frequency that are stored in its “memory,” as well as an electronic unit that processes and records the results and can be reports. Some devices are compatible with a computer.

It is believed that the use of leak detectors can reduce the cost of eliminating accidents on utility pipelines by up to 40–45%.

However, acoustic leak detectors have a number of disadvantages. The research results are highly dependent on the presence of noise interference, so they work best in quiet conditions when examining shallow pipelines - up to 1.5 m. However, modern instruments are equipped with digital signal processing microprocessors and filters that filter out noise interference. It is necessary to know exactly the route of laying the pipeline under study in order to pass exactly over it and listen to the noise from the leak at different points.

Acoustic active method - using a shock generator

In a situation where it is necessary to find a non-metallic pipe and therefore an electromagnetic locator cannot be used, but some part of the pipe is accessible, one alternative is the sonic active method. In this case, a sound pulse generator (impactor) is used, which is installed in an accessible place on the pipe and, using the impact method, creates acoustic waves in the pipe material, which are then picked up from the surface of the earth by the device’s acoustic sensor (microphone). This way you can determine the location of the pipeline. Of course, this method can also be used on metal pipes. The range of the device depends on various factors, such as the depth and material of the pipe, as well as the type of soil. The strength and frequency of the blows can be adjusted.

Acoustic electric - by the sound of an electric discharge

If a spark discharge can be created at the site of cable damage using a pulse generator, then the sound from this discharge can be listened to from the ground surface with a microphone. For a stable spark discharge to occur, it is necessary that the value of the transition resistance at the point of cable damage exceeds 40 Ohms. The pulse generator includes a high-voltage capacitor and a spark gap. The voltage from the charged capacitor is instantly transmitted through the spark gap to the cable, the resulting electromagnetic wave causes a breakdown at the site of cable damage, and a click is heard. Usually one pulse is generated every few seconds.

This method is used for locating cables of all types with a burial depth of up to 5 m. It is not recommended to use this method to search for damage in cables in a metal sleeve laid openly, since sound travels well through the metal sheath and the accuracy of localizing the location will be low.

Ultrasonic method

This method is based on the registration of ultrasonic waves that are inaudible to the human ear. When a liquid or gas under high pressure (or vice versa - suction at high vacuum) exits the pipeline through cracks in welds, leaks in shut-off valves and seals, friction occurs between the molecules of the leaking substance and the molecules of the medium, as a result of which ultrasonic frequency waves are generated. Due to the short wavelength nature of ultrasound, the operator can accurately locate leaks even in high noise environments, in above-ground gas lines and underground pipelines. Ultrasonic devices are also used to detect faults in electrical equipment - arc and corona discharges in transformers and distribution cabinets.

The ultrasonic leak detector includes a sensor-microphone, an amplifier, a filter, and an ultrasound converter into audible sound, which is broadcast by headphones. The closer the microphone is to the leak, the louder the sound in the headphones. The sensitivity of the device is adjustable. The LCD screen displays the scan results digitally. The kit may include a contact probe, with which you can also listen to vibrations. To actively identify leaks, the device includes a generator (transmitter) of ultrasonic vibrations, which can be placed in the object under study (for example, a container or pipeline), the ultrasound emitted by it will come out through leaks and cracks.

Advantages. The method is simple; searching for leaks does not require a complex procedure; training to operate the device takes about 1 hour, and the method is very accurate: it allows you to detect leaks through the smallest holes at a distance of 10 m or more against the background of strong extraneous noise.

Correlation method

In this case, two (or more) vibroacoustic signal sensors (piezoelectric sensors) are installed on the pipe on both sides of the leak (for example, in two wells or on a shut-off valve on the surface of the earth). The signal from the sensors is transmitted to the device via cables or radio. Since the distance from the sensors to the leak location is different, the sound from the leak will arrive at them at different times. Based on the difference in the time of signal arrival at the sensors, the electronic correlator unit calculates the cross-correlation function and the location of the damage between the sensors.

This method is used in noisy areas that are difficult for acoustic scanning, such as urban and factory areas.

The accuracy of the calculation depends on the accuracy of measuring the travel time of signals by the device, the accuracy of measuring the distance between the sensors and the accuracy of the speed of sound propagation through the pipe. According to experts, when these measurements are carried out correctly, the reliability, sensitivity and accuracy of the correlation method significantly exceeds the results of other acoustic methods: the deviation is no more than 0.4 m and the probability of detecting leaks is 50–90%. The accuracy of the result does not depend on the depth of the pipeline. The method is very resistant to interference.

The disadvantage of the correlation method is that the results are distorted in the presence of inhomogeneities in the pipes: blockages, bends, branches, deformations, sudden changes in diameter. Correlation leak detectors are expensive and complex devices that can only be operated by specially trained specialists.

Gas detectors

Gas detectors are used to detect gas leaks from pipelines. The micropump, which is part of the device, pumps an air sample from the location being tested. The selected sample is compared with reference air (for example, using the heating coil method: when heating a sample with gas and air, the temperature of the coil will be different), and the device records the presence of gas in the sample. There are also gas detectors (comparing sample and reference air) based on different principles. Such equipment is capable of capturing gas or other dangerous volatile substances even if the air contains only 0.002% of it!

The gas detector is a lightweight and compact, convenient and easy-to-use device. However, it is very sensitive to the ambient temperature: if the temperature is too high or low, its performance decreases and may even become zero, for example, at temperatures below –15 and above +45 ° C.

Complex devices

As we can see, each type of locator has certain limitations and disadvantages. Therefore, for services operating underground communications, modern locating devices are often complex, consisting of equipment of different types, for example, together with an electromagnetic locating device, they may include an acoustic locator, ground penetrating radar and pyrometer, and the acoustic receiver may also have a channel for receiving electromagnetic signals. The search can be carried out simultaneously at the frequencies of electromagnetic and radio waves, or the device can switch to modes of receiving magnetic, radio or acoustic waves. Moreover, the modular design of the devices allows the complexes to be completed individually for each client company, depending on its specific tasks. The use of complex instruments increases the likelihood of accurately finding the location of an object, facilitates and speeds up work on maintaining underground communications.

Innovations in the equipment industry for searching underground communications

Recording coordinates of search objects in GPS/GLONASS

Some modern route-finding devices have the ability to determine the coordinates of a detected object using GPS/GLONASS and record them (even online) in a database of a digital site plan created by computer-aided CAD design, indicating the identified utilities there. In parallel, the data is sent to a computer at the company's head office. The information can be presented in the form of simple labels to help the excavator operator visually navigate the layout shown on the machine's display. It will be even easier for the operator if the excavator control is partially automated and connected to GPS/GLONASS - the automation will help avoid damage to communications.

New line-finding equipment

Leading developers of this equipment offer scanners that scan a construction site and, based on an analysis of the characteristics of the local soil and other conditions at the construction site, automatically indicate the optimal frequency at which it is recommended to locate underground utilities. To achieve the best sensitivity, some locators are equipped with a function for automatically selecting the optimal signal frequency - this is convenient in “dirty” air conditions and when several routes pass underground at once.

Devices with two outputs have appeared, which can now be connected and conduct research simultaneously on two utilities.

The devices are equipped with a high-contrast liquid crystal display, the image on which is visible even when illuminated by direct sunlight, the information content of the displays increases: all the necessary parameters are displayed in real time: the depth of communication, the direction of movement towards it, signal intensity, etc. The device screen can even a visual diagram of the location of communications is formed, the route finder is able to simultaneously “see” up to three underground communications, “drawing” a map of their location and intersections on a large display.

Ground Penetrating Radars (For more information about ground penetrating radars, see Part 1)

The operation of GPR is based on emitting an electromagnetic pulse into the ground and recording the reflected signal from underground objects and environmental boundaries with different electrophysical properties.

The areas of application of ground penetrating radar are enormous: it allows you to determine the depth of communications, the location of voids and cracks, waterlogging zones and groundwater levels, the nature of geological boundaries, decompaction zones, illegal cuttings, defects in the subgrade, the presence of reinforcement, mines and shells, as well as other objects .

GPR has become widespread in the field of searching for underground communications, largely due to the fact that this method detects communications made of any material, including non-metallic ones.

To search for underground communications, a georadar with antennas having an average central frequency (200–700 MHz) is selected. Searching at such frequencies provides a probing depth of up to 5 m, and also allows you to find cables and pipes of small diameter.

If it is necessary to survey large areas, ground penetrating radar systems with an array of antennas installed on a vehicle are used. Such systems scan up to several hectares per day.

Modern georadars can find underground communications in real time and can be used together with GPS equipment, which allows them to be tied to the area and, using the obtained coordinates, transfer georadar data to CAD systems, as well as plot detected communications on existing diagrams.

For a long time, it was believed that ground penetrating radar is a difficult technology to understand and control, but with the advent of modern technologies and advanced software, the situation has changed radically. GPRs from leading manufacturers have maximum automation of data acquisition and interpretation, which eliminates errors associated with the human factor. Thus, today GPR is an indispensable assistant in searching for underground communications and can rightfully be considered the “third eye” of a survey engineer.