HF communication equipment with channel division. OVL equipment for command exchange via HF channels

Digital system HF communication MC04-PLC is designed to organize telemechanics (TM) channels, data transmission (PD) and telephone channels (TF) through high-voltage power lines (PTL) of the 35/110 kV distribution network. The equipment provides data transmission over a high-frequency (HF) communication channel in the 4/8/12 kHz band in the 16-1000 kHz frequency range. The connection to the power transmission line is carried out according to the phase-earth scheme through the coupling capacitor and the connection filter. The connection of the high-frequency end of the equipment to the connection filter is unbalanced and is performed with one coaxial cable.

The equipment is manufactured with a spaced and adjacent location of the transmission and reception bandwidths.

Functionality:

Number of HF channels 4 kHz wide - up to 3;
channel mode: analog ( frequency division) and digital (time division);
low-frequency digital stream modulation - QAM with division into 88 OFDM subcarriers;
HF spectrum modulation - amplitude with the transmission of one sideband of AM SSB;
adapting the bit rate of a digital stream (CPU) to a changing signal-to-noise ratio;
telephony interfaces: 4 ‒ wired 4W, 2 wired FXS / FXO;
the number of telephony channels in each HF channel - up to 3;
conversion of ADASE signaling into subscriber signaling FXS / FXO;
dispatching and subscriber connection under the ADASE protocol over one TF channel;
digital interfaces TM and data transmission: RS232, RS485, Ethernet;
control and monitoring interface - Ethernet;
built-in analyzer of RF path transmission / reception levels, error and temperature meter.
registration of faults and alarms in non-volatile memory;
digital re-reception - transit of channels at intermediate substations without quality loss;
monitoring - MC04 program ‒ Monitor: configuration, setting, diagnostics;
remote monitoring and configuration via built-in HF service channel;
SNMP support - when equipped with the S ‒ port network module;
radial and tree-like monitoring schemes for remote semi-sets;
power supply: mains ~ 220 V / 50 Hz or constant voltage 48/60 V.

main parameters
Operating frequency range 16 - 1000 kHz
Working bandwidth 4/8/12 kHz
Rated peak RF envelope power 20/40 W
Maximum CPU transfer rate in 4 kHz bandwidth (adaptive) 23.3 kbps
The depth of AGC adjustment with an error rate of no more than 10–6 is not less than 40 dB.
Allowable line attenuation (including interference) 50 dB

Power consumption from a 220 V or 48 V power supply network - no more than 100 W.
dimensions block - 485 * 135 * 215mm.
Weight no more than 5 kg.

Operating conditions:

- ambient temperature from +1 to + 45 ° С;
- relative humidity up to 80% at a temperature of plus 25 ° С;
- atmospheric pressure not lower than 60 kPa (450 mm Hg).

Equipment design and composition:

The digital three-channel HF communication system MC04-PLC includes two 19-inch units 3U high, into which the following functional and structural units (boards) are installed:
IP01− power supply, mains input 220V / 50Hz, output + 48V, -48V, + 12V;
IP02– power supply unit, input 36 ... 72V, output + 48V, -48V, + 12V;
MP02 - multiplexer of TM, PD, TF channels, G.729 codec, digital echo canceller;
MD02 - modulation / demodulation of the CPU into an analog RF signal, monitoring and control;
FPRM - linear transformer, attenuator and 4-loop PRM filter, PRM amplifier;
FPRD - 1/2 − x PRD loop filter, high impedance outside the PRD band;
UM02 - power amplifier, digital indication of TRD levels, alarm indication.
TP01 - transit of the content of the HF channel between the blocks, installed in place of the MP02 boards.

Ordering information

The number of MP02 boards corresponds to the number of basic HF channels with a 4 kHz bandwidth, configurable on the MD02 board - from 1 to 3. In case of transit of one of the HF channels between the blocks at the intermediate substation, a TP01 transit board is installed in place of the MP02 board, which provides reception / transmission of HF content channel without conversion to analog form.
The block has two main versions in terms of the peak power of the RF signal envelope:
1P - one UM02 amplifier and one FPRD filter are installed, the RF signal power is 20 W;
2P - two UM02 amplifiers and two FPRD filters are installed, the RF signal power is 40 W.

Block designation includes:
- the number of used HF channels 1/2/3;
- performance according to the peak power of the RF signal envelope: 1P - 20 W or 2P - 40 W;
- types of user joints of each of the 3 x HF channels / boards MP-02 or board TP01;
- supply voltage of the unit - mains ~ 220 V or constant voltage 48 V.
By default, the MP-02 board has digital interfaces RS232 and Ethernet, which are not indicated in the block designation. .

A communication channel is a collection of devices and physical media that transmit signals. With the help of channels, signals are transmitted from one place to another, and also transferred in time (when storing information).

The most common devices that make up the channel: amplifiers, antenna systems, switches and filters. As physical environment a pair of wires are often used, coaxial cable, waveguide, medium in which electromagnetic waves propagate.

From the point of view of communication technology, the most important characteristics of communication channels are the distortions to which the signals transmitted through it are subjected. Distinguish between linear and non-linear distortions. Linear distortion consists of frequency and phase distortion and is described by the transient response or, equivalently, the complex channel gain. Harmonic distortion is given by a nonlinear relationship that indicates how a signal changes as it travels through a communication channel.

A communication channel is characterized by a collection of signals that are sent at the transmitting end and signals that are received at the receiving end. In the case when the signals at the input and output of the channel are functions defined on a discrete set of argument values, the channel is called discrete. Such communication channels are used, for example, in pulsed operating modes of transmitters, in telegraphy, telemetry, and radar.

Several different channels can share the same technical link. In these cases (for example, in multichannel communication lines with frequency or time division signals), the channels are combined and disconnected using special switches or filters. Sometimes, on the contrary, one channel uses several technical communication lines.

High frequency communication (HF communication) is a type of communication in electrical networks, which provides for the use of high-voltage power lines as communication channels. The wires of the power lines of the power grids alternating current frequency of 50 Hz. The essence of the organization of HF communication is that the same wires are used as signal transmission over the line, but at a different frequency.

The frequency range of HF communication channels is from tens to hundreds of kHz. High-frequency communication is organized between two adjacent substations, which are connected by a power line with a voltage of 35 kV and above. In order to get to the buses of the substation switchgear, and the communication signals to the corresponding communication sets, high-frequency traps and communication capacitors are used.

HF trap has low resistance at power frequency current and high resistance at channel frequency high frequency communication. Coupling capacitor- on the contrary: it has a high resistance at a frequency of 50 Hz, and at the frequency of the communication channel - a low resistance. Thus, it is ensured that only 50 Hz current reaches the substation buses, and only signals at a high frequency reach the HF communication set.

To receive and process HF communication signals at both substations, between which HF communication is organized, special filters, signal transceivers and sets of equipment are installed that perform certain functions. Below we will consider which functions can be implemented using HF communication.

The most important function is the use of the HF channel in relay protection and automation devices of substation equipment. The HF communication channel is used in the protection of 110 and 220 kV lines - phase-differential protection and directional-high-frequency protection. At both ends of the transmission line, sets of protection are installed, which are connected to each other via the HF communication channel. Due to their reliability, speed and selectivity, protection using an HF communication channel is used as the main for each 110-220 kV overhead line.

The channel for transmitting signals of relay protection of power lines (PTL) is called relay protection channel... Three types of HF protection are most widely used in relay protection technology:

filter directional,

remote with HF blocking,

differential phase.

In the first two types of protection, a continuous HF blocking signal is transmitted via the HF channel with an external short circuit, in phase differential protection, HF voltage pulses are transmitted through the relay protection channel. The duration of the pulses and pauses is approximately the same and is equal to half the period of the power frequency. In the event of an external short circuit, the transmitters located at both ends of the line operate in different half-cycles of the power frequency. Each of the receivers receives signals from both transmitters. As a result, in the event of an external short circuit, both receivers receive a continuous blocking signal.

In the event of a short circuit on the protected line, a phase shift of the manipulating voltages occurs and time intervals appear when both transmitters are stopped. In this case, an intermittent current appears in the receiver, which is used to create a signal acting to open the circuit breaker of this end of the protected line.

Typically, the transmitters at both ends of the line operate on the same frequency. However, on long-distance lines, relay protection channels are sometimes performed with transmitters operating at different HF or at frequencies with a small interval (1500-1700 Hz). Working at two frequencies makes it possible to get rid of the harmful effects of signals reflected from the opposite end of the line. Protection relay channels use a dedicated (dedicated) RF channel.

There are also devices that, using the HF communication channel, determine the location of damage to power lines. In addition, the HF communication channel can be used to transmit signals, SCADA, ACS and other systems of APCS equipment. Thus, through the high-frequency communication channel, it is possible to control the operation mode of substation equipment, as well as transmit commands to control switches and various functions.

Another function is function telephone connection ... The HF channel can be used for operational negotiations between adjacent substations. In modern conditions this function not relevant, since there are more convenient ways communication between the service personnel of the facilities, but the HF channel can serve as a backup communication channel in the event of an emergency, when there will be no mobile or landline telephone communication.

Power line communication channel - a channel used to transmit signals in the range from 300 to 500 kHz. Various schemes for switching on the equipment of the communication channel are used. Along with the phase-to-earth circuit (Fig. 1), which is most common due to its economy, the following circuits are used: phase-phase, phase-two phases, two phases-earth, three phases-earth, phase-phase of different lines. The high-frequency trap, the coupling capacitor and the coupling filter used in these circuits are equipment for processing power lines for organizing high-frequency communication channels along their wires.

Rice. 1. Structural scheme simple channel communication over the power line between two adjacent substations: 1 - high-frequency interceptor; 2 - coupling capacitor; 3 - connection filter; 4 - HF cable; 5 - device TU - TS; c - telemetry sensors; 7 - telemetry receivers; 8 - relay protection devices and / or teleautomatics; 9 - automatic telephone exchange; 10 - ATS subscriber; 11 - direct subscribers.

Line processing is needed to obtain a stable communication channel. Attenuation of the HF channel along the processed power lines is almost independent of the line switching scheme. In the absence of processing, communication will be interrupted when disconnecting or grounding the ends of the transmission line. One of the most important problems of communication over power lines is the lack of frequencies due to low crosstalk between lines connected through substation buses..

HF channels can be used to communicate with field teams that repair damaged power lines and repair damage to electrical installations. For this purpose, special portable transceivers are used.

The following HF equipment is used, connected to the processed power line:

combined equipment for telemechanics, automation, relay protection and telephone channels;

specialized equipment for any one of the listed functions;

long-distance communication equipment connected to the power transmission line through a connection device directly or with the help of additional blocks for frequency shift and increasing the transmission level;

equipment for impulse control of lines.

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The design of the power transmission line, determined by its main purpose - the transmission of electrical energy over a distance, makes it possible to use it for the transmission of information. The high level of operation and high mechanical strength of the lines ensure the reliability of communication channels, which is close to the reliability of channels over cable communication lines. At the same time, when implementing communication channels via overhead lines for transmitting information, one has to take into account the features of the lines that make it difficult to use them for communication purposes. Such a feature is, for example, the presence of substation equipment at the ends of the lines, which can be represented as a chain of reactance and active resistance connected in series over a wide range. These resistances form a connection between the overhead lines through the substation buses, which leads to an increase in the communication path. Therefore, to reduce the influence between the channels and attenuation, using special barriers, they block the paths of high-frequency currents towards the substations.
The attenuation of the branches from the overhead line also significantly increases. These and other features of the lines require the implementation of a number of measures to create conditions for the transmission of information.
The device of HF channels over 6-10 kV distribution networks is fraught with significant difficulties due to the specifics of the construction of networks of these voltages. On the sections of main lines 6-10 kV between neighboring switching points there are a large number of taps, the lines are sectioned with disconnectors and switches, the primary switching circuits of networks often change, including automatically, due to the greater damage to the lines of these voltages, their reliability is lower than B71 35 kV and above. Signal transmission in distribution networks depends on many factors affecting signal attenuation: the length and number of taps, line wire material, load, etc. The load can vary over a wide range. At the same time, the disconnection of individual taps, as studies show, sometimes not only does not reduce the attenuation, but, on the contrary, increases it due to the violation of mutual compensation of attenuation between adjacent taps. Therefore, even small channels have significant attenuation and are unstable. The operation of the channels is also adversely affected by damage to the insulators, poor-quality wire connection and the unsatisfactory condition of the contacts of the switching equipment. These defects are sources of interference, commensurate with the level of the transmitted signal, which can cause the channel to stop working and damage the equipment. The presence of sectioning devices on the lines leads to a complete cessation of the operation of the HF channel in the event of their disconnection and grounding of one of the sections of the line. The noted disadvantages significantly limit, although they do not exclude, the use of 6-10 kV lines for organizing HF channels. Nevertheless, it should be noted that HF ​​communication has not received wide distribution over distribution networks at the present time.
By designation, high-frequency communication channels over power transmission lines are divided into four groups: dispatch communication channels, technological, special and linear operational communication channels.
Without dwelling in detail on the use and purpose of each group of channels, we note that for dispatching and technological telephone communication channels, mainly the tone frequency band of 300-3400 Hz is used.<300-2300). Верхняя часть тонального спектра (2400-3400 Гц) не пользуется для передачи сигналов телеинформации. Современная комбинированная аппаратура позволяет организовать в этом спектре до четырех независимых узкополосных каналов телеииформации.
Line-operational communication channels are used to organize communication between the dispatcher and the repair crews working on the route of an extended power transmission line or substations, when there is no constant communication with them. For these channels, simplified transportable and portable telephone equipment is used.
According to the degree of complexity, HF channels are divided into simple and complex. Channels consisting of only two sets of RF terminal equipment are called simple. Complex channels include intermediate amplifiers or several sets of terminal equipment (at the same frequencies).

Equipment for high-frequency communication channels over overhead lines.

The connection of the communication equipment to the wires of the power transmission line is carried out using special devices, the so-called equipment for connecting and processing the line, consisting of a coupling capacitor, a trap and protection elements.

Rice. 21. Scheme of a high-frequency communication channel for overhead lines
In fig. 21 shows a diagram of the formation of a communication channel over the overhead line. Signal transmission by high-frequency currents is carried out by the transmitters of the compaction equipment J, located at both ends of the overhead line at substations A and B.
Here, in the composition of the compaction equipment 1, there are receivers that receive modulated RF currents and convert them. To ensure the transmission of signal energy by HF currents through the wires, it is sufficient to process one wire at each end of the line using a trap 5, a coupling capacitor 4 and a connection filter 3, which is connected to the sealing equipment 1 using an HF cable 2. To ensure the safety of personnel working on the connection filter when the RF channel is operating, the grounding knife is used 6.
Connecting high-frequency equipment according to the diagram in Fig. 21 is called phase-to-earth. Such a scheme can be used to form single-channel and multi-channel information transmission systems. Other connection schemes are also used.
If it is necessary to connect the equipment installed on the line route to the power transmission line (mobile telephone equipment of repair crews, equipment of a remotely controlled VHF radio station, etc.), as a rule, antenna connection devices are used. Sections of insulated wire of a certain length or sections of a lightning protection cable are used as an antenna.
A high-frequency (linear) trap has a high resistance for the operating frequency of the channel and serves to block the path of these currents, reducing their leakage towards the substation. In the absence of a suppressor, the channel attenuation may increase, since the small input impedance of the substation shunts the RF channel. The trap consists of a power coil (reactor), a setting element and a protection device. The power coil is the main element of the minelayer. It must withstand the maximum operating line currents and short-circuit currents. The power coil is made of coiled copper or aluminum wires of the appropriate cross-section, wound on wood-laminated plastic (delta-wood) or fiberglass rails. The ends of the rails are fixed on metal crosspieces. A setting element with protective arresters is attached to the upper crosspiece. The tuning element is used to obtain a relatively high resistance of the trap at one or several frequencies or frequency bands.
The tuning element consists of capacitors, inductors and resistors and is connected in parallel
power coil. The power coil and setting element of the trap are exposed to atmospheric and switching overvoltages and short-circuits. The role of overvoltage protection, as a rule, is performed by a valve arrester consisting of a spark gap and a non-linear power resistor.
In electrical networks of 6-220 kV, minelayers VZ-600-0.25 and KZ-500, as well as minelayers with a steel core of the VChZS-100 and VChZS-100V types, differing from each other in rated current and inductance, stability and geometric parameters power coil, as well as the type of setting element and its protection.
The arresters cut into the phase conductor of the power line between the line disconnector and the coupling capacitor. High-frequency traps can be mounted suspended, on supporting structures, including coupling capacitors.
Coupling capacitors are used to connect HF equipment to the overhead line, while the power frequency leakage currents are discharged through the coupling capacitor to ground, bypassing the high frequency equipment. Coupling capacitors are designed for phase voltage (in a network with a grounded neutral) and for a line voltage (in a network with an isolated neutral). In our country, two types of coupling capacitors are produced: СМР (communication, oil-filled, with an expander) and SMM (communication, oil-filled, in a metal case). For different voltages, capacitors are assembled from individual elements connected in series. Coupling capacitors can be installed on reinforced concrete or metal supports with a height of about 3 m. To isolate the lower element of the СМР type capacitor from the support body, special porcelain supports with a circular cross-section are used.

The coupling filter serves as a link between the coupling capacitor and the RF equipment, separating the high voltage line and the low current setting, which is the sealing equipment. The connection filter thus ensures the safety of personnel and protection of the equipment from high voltage, since when the lower plate of the coupling capacitor is grounded, a path is formed for leakage currents of industrial frequency. With the help of the connection filter, the wave impedances of the line and the high-frequency cable are matched, as well as the compensation of the reactance of the coupling capacitor in a given frequency band. Connection filters are made according to transformer and autotransformer circuits and together with coupling capacitors form band-pass filters.
The most widespread in the organization of high-frequency communication channels through the power transmission lines of the enterprise is the connection filter of the OFP-4 type (see Fig. 19). The filter is enclosed in a steel welded casing with a bushing for connecting a coupling capacitor and a cable funnel for entering an RF cable. An arrester is mounted on the wall of the housing, which has an elongated pin for connecting the grounding bus and is designed to protect the connection filter elements from overvoltage. The filter is designed for connecting RF equipment according to the phase-to-ground scheme, complete with coupling capacitors with a capacity of 1100 and 2200 pF. The filter is installed, as a rule, on the support of the coupling capacitor and is bolted to the support at a height of 1.6-1.8 m from the ground level.
As noted, all switchings in the connection filter circuits are performed with the grounding knife turned on, which serves to ground the lower plate of the coupling capacitor during the work of personnel. A single-pole disconnector for a voltage of 6-10 kV is used as a grounding knife. Operations with the grounding knife are carried out using an insulating rod. Some types of connection filters have an earthing knife mounted inside the housing. For safety reasons, a freestanding earthing blade must be installed in this case.
The high-frequency cable is used for electrical connection of the connection filter (see Fig. 21) with the transceiver equipment. When connecting the equipment to the line according to the phase - earth scheme, coaxial cables are used. The most common is a high-frequency coaxial cable of the RK-75 brand, the inner conductor (single-core or multi-core) of which is separated from the outer braid by high-frequency dielectric insulation. The outer braided shield serves as a return conductor. The outer conductor is enclosed in a protective insulating sheath.
The high-frequency characteristics of the RK-75 cable, like ordinary communication cables, are determined by the same parameters: wave impedance, kilometric attenuation and the speed of propagation of electromagnetic waves.
Reliable operation of HF channels on overhead lines is ensured by high-quality and regular implementation of scheduled preventive work, which provides for a whole range of work on the equipment of HF communication channels over overhead lines. To perform preventive measurements, the channels are taken out of service. Preventive maintenance includes scheduled checks of equipment and channels, the frequency of which is determined by the condition of the equipment, the quality of maintenance, taking into account preventive maintenance, and is set at least once every 3 years. Unscheduled channel checks are performed when the RF path is changed, equipment is damaged, and when the channel is unreliable due to violation of the regulated parameters.

Third

Second

First

Transformer protection circuit, in which there is differential and gas protection (DZ), responding to the disconnection of the transformer on both sides and the maximum current protection (CZ), which should disconnect only on one side.

When drawing up a schematic diagram of relay protection in a minimized form, the electrical connection of the tripping circuits of two switches may not be detected. From the expanded scheme (Scheme 1) it follows that with such a connection (cross-circuit), a false circuit is inevitable. Two auxiliary contacts are required at the protective relays (Diagram 2) acting on two switches or an isolating intermediate relay (Diagram 3).

Rice. - Transformer protection circuit: 1 - wrong; 2,3 - correct

Unseparated high and low voltage circuits transformer.

Figure (1) shows the impossibility of independently disconnecting one of the sides of the transformer without disconnecting the other.

This situation is corrected by turning on the intermediate relay KL.

Rice. - Transformer protection circuits: 1 - wrong; 2 - correct

The protections of the generator and transformer of the unit at the power plant act, as required, to turn off the circuit breaker and the field extinguishing circuit breaker through the separating intermediate relays KL1 and KL2, but the relays are connected to different sections of the power bus, i.e. through different fuses.

The false circuit, shown by the arrows, was generated through the HL fuse control lamp due to blown fuse FU2.

Rice. - Formation of a false circuit when a fuse blows

1, 2, 3 - relay contacts

Circuits with power supply of circuits of secondary connections with operational direct and alternating current

When the poles of the power supply are well isolated from earth, an earth fault at one point in the secondary circuit is usually not harmful. However, a second earth fault may cause false activation or deactivation, incorrect alarms, etc. Preventive measures in this case can be:

a) signaling of the first earth fault in one of the poles; b) two-pole (two-way) separation of control circuit elements - practically not used due to complexity.

With insulated poles (Fig.), Grounding at a with open NO contacts 1 will not yet cause a false action of the coil of the command body K, but as soon as a second insulation fault to ground appears in the branched network of the positive pole, false operation of the apparatus is inevitable, since the contact 1 turns out to be shunted. That is why a ground fault signaling is necessary in the operating circuits, and above all at the poles of the power supply.

Rice. - False operation of the device at the second earth fault

However, in complex circuits with a large number of operational contacts connected in series, such an alarm may not detect an earth fault that has occurred (Fig.).

Rice. - Ineffectiveness of insulation monitoring in complex circuits

When grounding appears between the contacts at the point a signaling is not possible.

In the practice of operating automatic installations with low-current equipment (up to 60 V), they sometimes resort to deliberate grounding of one of the poles, for example, the positive one (it is more dusty and susceptible to electrolytic phenomena, i.e. it already has weakened insulation). This facilitates the detection and elimination of the emergency source. In this case, it is recommended to connect the control circuit coil at one end to the pole that is grounded.

All that has been said about the supply of circuits with a direct operating current can also be attributed to an operating alternating current with a supply of circuits with a linear voltage. In this case, the likelihood of false operation (due to capacitive currents) and resonance phenomena should be taken into account. Since it is difficult to provide conditions for reliable operation in this case, sometimes auxiliary isolating intermediate transformers are used with grounding of one of the terminals on the secondary side.

As can be seen from the diagram, in this case, if the insulation to ground at point 2 is damaged, the fuse FU1 blows and an earth fault at point 1 does not cause a false switch on of the contactor K.

Connection diagram of capacitors with isolation diodes

High-frequency (HF) communication over high voltage lines has become widespread in all countries. In Ukraine, this type of communication is widely used in power systems to transmit information of a different nature. High-frequency channels are used for transmission of signals for relay protection of lines, tele-disconnection of switches, remote signaling, telecontrol, telecontrol and telemetry, for dispatching and administrative telephone communications, as well as for data transmission.

Communication channels through power transmission lines are cheaper and more reliable than channels through special wire lines, since no funds are spent on the construction and operation of the communication line itself, and the reliability of the power transmission line is much higher than the reliability of conventional wire lines. The implementation of high-frequency communication over power lines is associated with features that are not found in wire communication.

To connect the communication equipment to the wires of power transmission lines, special processing and connection devices are required, which allow separating high voltage from low-current equipment and implementing a path for transmitting HF signals (Fig. 1).

Rice. - Connection of high-frequency communication equipment to high voltage lines

One of the main elements of the circuit for connecting communication equipment to power lines is a high voltage coupling capacitor. The coupling capacitor, connected to full mains voltage, must have sufficient electrical strength. For a better matching of the input resistance of the line and the connecting device, the capacitance of the capacitor must be large enough. The coupling capacitors produced now make it possible to have a connection capacity on lines of any voltage class not less than 3000 pF, which makes it possible to obtain connection devices with satisfactory parameters. The coupling capacitor is connected to the coupling filter, which grounds the lower plate of this capacitor for power frequency currents. For high-frequency currents, the coupling filter together with the coupling capacitor matches the resistance of the high-frequency cable with the input resistance of the power line and forms a filter for transferring high-frequency currents from the high-frequency cable to the line with low losses. In most cases, a coupling filter with a coupling capacitor forms a bandpass filter circuit that passes a certain frequency band.

The high-frequency current, passing through the coupling capacitor along the primary winding of the connection filter to ground, induces a voltage in the L2 secondary winding, which through the capacitor C1 and the connecting line enters the input of the communication equipment. The power frequency current passing through the coupling capacitor is small (from tens to hundreds of milliamperes), and the voltage drop across the coupling filter winding does not exceed several volts. In the event of an open or poor contact in the connection filter circuit, it may be under full line voltage, and therefore, for safety reasons, all work on the filter is performed when the lower plate of the capacitor is grounded with a special grounding knife.

By matching the input impedance of the HF communication equipment and the line, the minimum energy loss of the HF signal is achieved. Matching with an overhead line (OHL) with a resistance of 300-450 Ohm is not always possible to complete completely, since with a limited capacitance of the coupling capacitor, a filter with a characteristic impedance on the side of the line equal to the characteristic impedance of the overhead line can have a narrow bandwidth. In order to obtain the necessary bandwidth, in some cases it is necessary to admit an increased (up to 2 times) characteristic impedance of the filter on the side of the line, reconciling with somewhat larger losses due to reflection. The connection filter, installed at the coupling capacitor, is connected to the equipment with a high-frequency cable. Several high-frequency devices can be connected to one cable. To weaken the mutual influences between them, crossover filters are used.

Channels of system automation - relay protection and interconnection, which must be especially reliable, require the mandatory use of crossover filters to separate other communication channels operating through a common connection device.

To separate the HF signal transmission path from the substation high voltage equipment, which may have a low resistance for high frequencies of the communication channel, a high frequency trap is connected to the phase conductor of the high voltage line. The high-frequency trap consists of a power coil (reactor), through which the operating current of the line passes, and a tuning element connected in parallel with the coil. The power coil of the minelayer with a tuning element form a two-pole, which has a sufficiently high resistance at operating frequencies. For a power frequency of 50 Hz, the trap has a very low resistance. The minelayers are used, designed to block one or two narrow bands (one- and two-frequency minelayers) and one wide frequency band of tens and hundreds of kilohertz (broadband minelayers). The latter are most widespread, despite the lower resistance in the obstacle strip compared to single and dual-frequency ones. These barriers make it possible to block the frequencies of several communication channels connected to the same line wire. The higher the resistance of the trap in a wide frequency band can be provided the easier, the greater the inductance of the reactor. It is difficult to obtain a reactor with an inductance of several millihenries, since this leads to a significant increase in the size, weight and cost of the minelayer. If the active resistance in the band of cut-off frequencies is limited to 500–800 Ohm, which is sufficient for most channels, then the inductance of the power coil can be no more than 2 mH.

The trap is produced with an inductance of 0.25 to 1.2 mH for operating currents from 100 to 2000 A. The operating current of the trap is the higher, the higher the line voltage. For distribution networks, minelayers are produced for 100-300 A, and for 330 kV lines and above, the maximum operating current of the minelayer is 2000 A.

Various tuning circuits and the required range of cut-off frequencies are obtained using capacitors, additional inductors and resistors available in the trap tuner tuning element.

Connection to the line can be done in various ways. With an unbalanced circuit, the HF equipment is connected between a wire (or several wires) and ground according to the "phase-to-earth" or "two-phase-to-earth" circuits. With symmetrical circuits, HF equipment is connected between two or more wires of the lines ("phase - phase", "phase - two phases"). In practice, the "phase-phase" scheme is used. When you turn on the equipment between the wires of different lines, only the "phase-phase of different lines" scheme is used.

To organize HF channels along high voltage lines, a frequency range of 18–600 kHz is used. In distribution networks, frequencies ranging from 18 kHz are used, on trunk lines 40–600 kHz. To obtain satisfactory parameters of the HF path at low frequencies, large values ​​of the inductances of the power trap coils and the capacitances of the coupling capacitors are required. Therefore, the lower frequency limit is limited by the parameters of the processing and connection devices. The upper limit of the frequency range is determined by the acceptable value of the linear attenuation, which increases with increasing frequency.

1. HIGH FREQUENCY PROTECTORS

Tunnel configuration schemes... High-frequency traps have a high resistance for the currents of the operating frequency of the channel and serve to separate the elements (substations and branches) shunting the HF path, which, in the absence of traps, can lead to an increase in the attenuation of the path.

The high-frequency properties of the trap are characterized by an obstacle band, i.e., a frequency band in which the trap resistance is not less than a certain permissible value (usually 500 Ohm). As a rule, the barrage is determined by the permissible value of the active component of the resistance of the trap, but sometimes by the permissible value of the impedance.

The barriers differ in the values ​​of the inductances, the permissible currents of the power coils and in the tuning schemes. One- and two-frequency resonant or blunted tuning circuits and broadband circuits are used (according to the full-link and half-link of the band-pass filter, as well as according to the half-link of the high-pass filter). Suppressors with single- and dual-frequency tuning schemes often do not provide an opportunity to block the desired frequency band. In these cases, minelayers with broadband tuning schemes are used. Such adjustment schemes are used when organizing protection and communication channels that have a common connection equipment.

When current flows through the coil of the trap, electrodynamic forces arise, acting along the axis of the coil, and radial, tending to break the coil. The axial forces are uneven along the length of the coil. Great forces are generated at the edges of the coil. Therefore, the step of the turns at the edge is made larger.

The electrodynamic resistance of the minelayer is determined by the maximum short-circuit current that it can withstand. In the KZ-500 minelayer at a current of 35 kA, axial forces of 7 tons (70 kN) arise.

Overvoltage protection of setting elements... An overvoltage wave arising on the overhead line hits the trap. The wave voltage is distributed between the tuner capacitors and the input impedance of the substation busbars. The power coil is a large impedance for a steep wave front and can be ignored when considering overvoltage processes. To protect the tuning capacitors and the power coil, an arrester is connected parallel to the power coil, limiting the voltage on the elements of the trap to a value that is safe for them. The breakdown voltage of the spark gap, according to the conditions of deionization of the spark gap, should be 2 times higher than the accompanying voltage, i.e., the voltage drop across the power coil from the maximum short-circuit current U res = I short-circuit. ωL.

With a long pre-discharge time, the breakdown voltage of the capacitors is much higher than the breakdown voltage of the arresters; at low (less than 0.1 μs), the breakdown voltage of the capacitors becomes less than the breakdown voltage of the spark gap. Therefore, it is necessary to delay the growth of the voltage across the capacitors until the spark gap is triggered, which is achieved by connecting an additional inductor L d in series with the capacitor (Fig. 15). After the breakdown of the spark gap, the voltage across the capacitor rises slowly and an additional spark gap connected in parallel with the capacitor protects it well.

Rice. - High-frequency minelayer circuits with overvoltage protection device: a) single-frequency; b) dual-frequency

2. COUPLING CAPACITORS

General information... Coupling capacitors are used to connect HF communication equipment, telemechanics and protection to high voltage lines, as well as for power take-off and voltage measurement.

The resistance of a capacitor is inversely proportional to the frequency of the voltage applied to it and the capacitance of the capacitor. The reactance of the coupling capacitor for industrial frequency currents, therefore, is significantly higher than for the frequency of 50 - 600 kHz of telemechanics and protection communication channels (1000 times or more), which allows using these capacitors to separate high and industrial frequency currents and prevent the ingress of high voltage on electrical installations. Power-frequency currents are diverted to ground through coupling capacitors, bypassing the HF equipment. Coupling capacitors are designed for phase (in a network with a grounded neutral) and line voltage (in a network with an isolated neutral).

For power take-off, special take-off capacitors are used, connected in series with a coupling capacitor.

In the names of capacitor elements, the letters denote sequentially the nature of the application, the type of filler, design; numbers - rated phase voltage and capacity. СМР - connections, oil-filled, with an expander; SMM - ties, oil-filled, in a metal casing. Coupling capacitors for different voltages are composed of individual elements connected in series. Elements of capacitors СМР-55 / √3-0.0044 are designed for normal operation at a voltage of 1.1 U uhm, elements СМР-133 / √3-0.0186 - for 1.2 U uhm. The capacitance of capacitors for insulation classes 110, 154, 220, 440 and 500 kV is accepted with a tolerance of -5 to + 10%.

3. CONNECTION FILTERS

General information and calculated dependencies. High-frequency equipment is connected to the capacitor not directly through the cable, but through a connection filter, which compensates for the reactance of the capacitor, matches the wave impedances of the line and the high-frequency cable, ground the lower plate of the capacitor, which forms a path for industrial frequency currents and ensures the safety of work.

When the linear winding circuit of the filter is broken, a phase voltage appears with respect to the ground on the lower plate of the capacitor. Therefore, all switching in the linear winding circuit of the connection filter is carried out with the grounding knife turned on.

The OFP-4 filter (Fig.,) Is designed to operate on 35, 110 and 220 kV lines according to the "phase-to-ground" scheme with a coupling capacitor of 1100 and 2200 pF and with a cable having a characteristic impedance of 100 Ohm. The filter has three frequency ranges. There is a separate air transformer for each range, sealed with insulating compound.

Rice. - Schematic diagram of the OFP-4 filter-connection

6. PROCESSING OF LIGHTNING PROTECTION CABLES, ANTENNAS

Lightning protection cables of high voltage lines can also be used as information transmission channels. The cables are isolated from the supports in order to save electricity; in case of atmospheric overvoltages, they are grounded through breakdown spark gaps. Steel cables have a high attenuation for high frequency signals and allow information to be transmitted only on short lines at frequencies not exceeding 100 kHz. Bimetallic cables (steel cables with aluminum coating), alumoveld cables (made of twisted steel-aluminum wires), single-thread cables (one layer - aluminum wires, the rest - steel ones) make it possible to organize communication channels with low attenuation and noise levels. The interference is less than in the communication channels along the phase wires, and the HF processing and connection equipment is simpler and cheaper, since the currents flowing through the cables and the voltages on them are small. Bimetallic wires are more expensive than steel ones, so their use can be justified if HF channels on phase wires cannot be made. This can be on ultra-long-distance, and sometimes on long-distance power transmissions.

The cable channels can be switched on according to the "cable - cable", "cable - ground" and "two cables - ground" schemes. On AC overhead lines, the cables are interchanged every 30 - 50 km to reduce the induction of industrial frequency currents in them, which introduces an additional attenuation of 0.15 Np for each crossing in the "cable-cable" schemes, without affecting the "two cables - Earth". On DC transmissions, the cable-to-cable scheme can be used, since crossing is not necessary here.

Communication via lightning protection cables is not interrupted when the phase conductors are grounded, and does not depend on the line commutation scheme.

Antenna communication is used to connect mobile HF equipment to the overhead line. The wire is suspended along the wires of the overhead line or a section of the lightning protection cable is used. Such an economical way of connection does not require suppressors and coupling capacitors.

The division of the vertically integrated structure of the post-Soviet electric power industry, the complication of the control system, an increase in the share of small-generation electricity generation, new rules for connecting consumers (reducing the time and cost of connection), while increasing requirements for the reliability of power supply entails a priority attitude to the development of telecommunications systems.

In the energy sector, many types of communication are used (about 20) differing in:

• appointment,
• transmission medium,
• physical principles of work,
• the type of transmitted data,
• transmission technology.

Among all this diversity, high-frequency communication stands out through high-voltage power lines (HVL), which, unlike other types, was created by power specialists for the needs of the electric power industry itself. Equipment for other types of communication, originally created for public communication systems, to one degree or another, is adapted to the needs of energy companies.

The very idea of ​​using overhead lines for the distribution of information signals arose during the design and construction of the first high-voltage lines (since the construction of a parallel infrastructure for communication systems entailed a significant increase in cost), respectively, already at the beginning of the 20s of the last century, the first commercial HF communication systems were put into operation.

The first generation of HF communications was more like radio communications. The connection of the transmitter and receiver of high-frequency signals was carried out using an antenna up to 100 m long, suspended on supports parallel to the power wire. The overhead line itself was a guide for the HF signal - at that time, for the transmission of speech. Antenna connection was used for a long time to organize communication between emergency crews and on railway transport.

Further evolution of HF communication led to the creation of HF connection equipment:

• coupling capacitors and coupling filters, which made it possible to expand the bandwidth of transmitted and received frequencies,
• HF traps (barrage filters), which made it possible to reduce the influence of substation devices and overhead line inhomogeneities on the characteristics of the HF signal to an acceptable level, and, accordingly, improve the parameters of the HF path.

The next generations of channel-forming equipment began to transmit not only speech, but also telecontrol signals, protective commands of relay protection, emergency control equipment, and made it possible to organize data transmission.

As a separate type of HF communication, it was formed in the 40s and 50s of the last century. International Standards (IEC) have been developed, guidelines for the design, development and manufacture of equipment. In the 70s in the USSR, the forces of such specialists as Shkarin Yu.P., Skitaltsev V.S. Mathematical methods and recommendations for calculating the parameters of HF channels were developed, which significantly simplified the work of design organizations in the design of HF channels and the choice of frequencies, and increased the technical characteristics of the introduced HF channels.

Until 2014, HF communication was officially the main type of communication in the electric power industry in the Russian Federation.

The emergence and implementation of fiber-optic communication channels, in the context of widespread HF communication, has become a complementary factor in the modern concept of the development of communication networks in the electric power industry. Currently, the relevance of HF communications remains at the same level, and intensive development and significant investments in the optical infrastructure contribute to the development and formation of new areas of application of HF communications.

The indisputable advantages and the presence of a huge positive experience in the use of HF communication (almost 100 years) give reason to believe that the direction of HF will be relevant both in the short and in the long term, the development of this type of communication will allow solving both current problems and contributing to the development of the entire electric power industry. industry.