COMMUNICATIONS CHANNELS FOR TELEMECHANICS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000600350214-5
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 8
• Document Creation Date: December 22, 2016
• Document Release Date: August 22, 2011
• Sequence Number: 214
• Publication Date: October 6, 1950
• Content Type: REPORT

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r,. CLASSIFICATION coNFIDEr7T ACONFIDENT' '
CENTRAL INTELLIGENCE AGENCY REPORT
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
DATE OF
CO IAITDV
--A-
SUBJECT Scientific - Electricity, telemechanics
HOW
PUBLISHED Monthly periodical
WHERE
PUBLISHED Moscow
DATE
PUBLISHED Mar 1950
LANGUAGE Russian
THIN DOCUMENT CONTAINS INFORMATION AFFICTNS TNR NATIONAL OIFINNI
OF TNl UNITID STATES NITNIN THI NSARIN1 OF RSFIONASS ACT NO
U. ], C.. SI ANN St, Al AMENDED. ITS TRANSNIIIION OR THE NNTILATON
0, 111 ART MANN
A HINITI DC ST TLAIT. 1 NI MODUCTIOMR TO OF 7NIS TORN INI FNONINITID, IS fN0-
Elektricheskiye Stantsii, No 3, 1950.
i
DATE DIST. & Oct 1950
SUPPLEMENT TO
REPORT NO.
THIS IS UNEVALUATED INFORMATION
CO MUNICATIONS CHANNEIS FOR TELEMECBANICS
ZF-igures referred to are appended]
Telemechanics arrangements -- telemetering, telecontrol and telesignal-
ling -- are being introduced more and more as necessary means of improving dis-
patcher control of power systems, long-distance control of automatic hydroelec-
tric power stations and substations. The conditions of using telemechanics,
possibilities and time required for construction, and also the choice of the
type of telemechanical arrangements are determined to a considerable extent by
the avability and character of existing communications channels. The relia-
bility and stability of operation of telemechanics installations depends on the
quality of the communications channel.
Owing to considerations of economy, it is not usual to assign special wires
on communications lines to telemechanics channels. As a rule existing telephone
wires or high-voltage power transmission lines are used to transmit telemechanics
signals simultaneously with the telephoning with the aid of channel consolida-
tion.
The simplest method of consolidating communications lines is a circuit with
a differential transformer (Figure 1). The telephone. circuit terminates at both
ends with differential transformers DT, to the mid-points of which are connected
the transmitting TM-1 and receiving TM-2 telemechanics devices,
When the resistances of the telephone circuit wires and the impedance of
both halves of the differential transformer windings are equal, the currents
Il and 12 from the telemechanics devices are equal and have practically no ef-
fect on the telephone apparatus T. To protect the telephone circuit from higher
harmonics formed when the telemechanics signals are transmitted, and to eliminate
interference on the telephone channel, so-called telegraphic filters are fitted
between the telemecbariic s. device and the mid-points of.the two transformers, as
is shown on Figure 2. The current is 6npplied by the line battery Ln connected
at one end of the transmission: channel,
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yyik tl~ tfl ! IAA
The main advantages of the channel formed by differential transformers are
its simplicity, cheapness, and accessibility in all cases where a communications
circuit already exists.
At the same time, this method has substantial drawbacks. When the resist-
ance of one wire alters, e.g., when a line contact of the insulation deteriorates,
the interference in the principal circuit becomes so great that telephone trans-
mission is impossible. When there is a sharp drop in the wire insulation (in
rain, etc) and the current leaks to ground, the operating current in the windings
of the line relay falls below the permissible value and the relay either ceases
to function or operates erratically. This can be prevented by increasing the
voltage of the line battery, but to do so is often inconvenient or impossible.
In spite of these drawbacks, until recently the devices of the frequency-
pulse telemetering system of Mosenergo operated voverichanwas nels with
transformers. The line battery voltage was ,
cases.
A better method is to transmit telemechanics systems with currents of carrier
frequencies in the 6.0-7.0 kc range. The transmitting device is a vacuum tube
oscillator with a frequency of 6,500 kc. To the telemechanics device is connected
a relay whose contacts switch on the output amplifier of the transmitter. The re-
ceiver consists of a one-tube amplifier and a tube detector whose plate circuit
contains the receiving relay. The method of connecting the device is shown on
Figure 3. The communications circuit contains standard line filters consisting
of the choke filter D which passes frequencies below 2.8 kc and the condenser
filter K which passes all frequencies above 2.8 kc, connected in parallel. To
the former are connected the telephones T or the switches; to the latter, the de-
vices for transmitting telemechanica signals.
To limit the output of high harmonics from the transmitter and to increase
the selectivity of the receiver, special band filters P, passing frequencies in
the 6.0-7.0 kc band only, are fitted between the filter K and the transmitter
(receiver). A diagram of the filter link is shown on Figure 4.
The diagrammatic circuit of the transmitter shown in Figure 5 consists of
a parallel-fed master oscillator using a 6L6 tube and designed for a frequency
of 6.5 kc. The output cascade uses two 6L6 tubes in a push-pull circuit and
operating in Class A.
The cascade is controlled.by the relay contacts which connect the negative
plate voltage. The push-pull amplifier circuit and the inclusion of resistors
between the plates and cathodes of the amplifying tubes reduce distortion of the
carrier-frequency current curve. The transmitter power is about 4 w.
The receiver (Figure 6) consists of two stages. The first, the voltage
amplifier, uses a 2K2M tube; the second, a power amplifier and, at the same time,
a plate detector, uses a TO-?.':. tube. The biases on the tube grids are obtained
from the filament circuits, which are DC-fed. The receiver sensitivity can be
seen from the following table:
Level of reception,
nepers
Current in receiving
relay, ma
-CIO -2.7 -2.0 -1.4 -1.0
0 0.05 0.1 0.2 0.275
CONFIDENTIAL
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Level of reception,
nepers
-0.8
-0.65
-0.4
+ 0.05
+ 0.3
Input voltage
0.35
0.4
0.5
0.8
1.0
Current in receiving
relay, ma
6
6.25
6.75
7.25
7.5
The device under discussion was designed by TsLEM fentral Laboratory for
Electric Machines?7 of Mosenergo in 1947 and is now operating successfully on
a bimetallic circuit over 200 km long with a cable insert 15 km long. There was
no interference in the voice-frequency telephone channel. When the device was
switched on, it was noticed that the transmitting station had a considerable ef-
fect on the high-frequency telephone channels (SMT-34) working on the same com-
munications line, especially at the near end.
After replacing the code line relay by a polarized relay, the sensitivity
of the device increased considerably which enabled the receiving level to be
lowered, and it has now been reduced to -1.3 nepers. The margin of reliability
is about 0.5 nepers, i.e., the receiver level can be reduced to -1.8 nepers.
The radius of action of the system is determined by the lire attenuation and is
300 km along nonferrous wires and 50-70 km along steel wires.
In recent years a start has been made on introducing special high-frequency
stations for transmitting telemechanics signals along 110 and 220 kv power trans-
mission lines. These stations are connected to the power transmission lines with
the aid of high-voltage condensers similar to stations for high-frequency communi-
cation or high-frequency protection.
Figure 7 is a block diagram of the transmitting and receiving stations.
The station for high-frequency telemechanics channels contains a high (carrier)-
frequency oscillator GVCh, from 3 to 8 low (voice)-frequency oscillators GNCh
for the telemechanics channels, a filter system, and a power supply unit.
The telemechanics devices (frequency-pulse telemetering, time-division tele-
control, and telesignalization), by means of the contacts of the TM transmitting
relays, act on the corresponding voice-frequency oscillators, switching them on
when a signal is sent and switching them off when there is no signal. The voice
frequencies, controlled by the transmitting_.relays,---are--applied_to the modulator
M in which modulation of the high-frequency currents takes place. The process
of modulation is reduced to altering the amplitude of the carrier frequency in
time with alterations in the instantaneous values of the modulating voice frequen-
cies. The carder. ftequency,'modulated,by, all the voice:frequencies, passes through
the: amplifier iU ?:and' the; ;linaeci?rcuit 7LK``and .re+ ched .the ~ power transmission li.rie -
tl'bug?3~ -the; coupli ngi.cgnd nser 1 C. ~,The power transmission' line=.contains. high.
frequency blockirgechokes VChZ, which prevent leakage of carrier-frequency currents.
At the receiving end, having reached the station, the carrier-frequency cur-
rents are amplified and transformed in the detector D into the sum of the voice
frequencies. Subdivided by means of the filters F1 - F8, these frequencies reach
their individual receivers U/D, where they are transformed into telemechanics
signals whose form and duration coincide with the signals of the transmitting
end. In view of the great diversity of control station circuits and their in-
dividual components, it is not feasible to jive a detailed description.
Like the high-frequency communication. station, the telemechanics stations
operate in the 40-300 kc band. Each station, depending on its type, contains
k from three to eight individual telemechanics channels worki on voice frequenc-
ies, e.g., 420, 540, 660, 780 cycles and. so on through 120 Li] cycles. A defi-
nite frequency ratio is selected to decrease interference between channels and
which night be in the tone of higher harmonics of channels
c {cc w n ...-o.._
iCi..luuc frcqu2,. ~u.~
lower in the frequency scale.
Laii dE Al.
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1
The receiving and transmitting relays are polarized telegraptic relays
with high sensitivity (1-3 ma) and low time lag (3-5 milli sac).
Depending on the carrier frequency, the installations operate stably'at
a distance of up to 300 km without intermediate amplifiers with a station
power of 2-4 w, depending on the type.
A comparison of the above methods of obtaining telemechanics channels
undoubtedly favors high-frequency channels along power transmission lines.
The decisive factors should be stability, reliability, and economy.
Practice has shown that the number of technical hitches on high-frequency
channels is considerably fewer than on channels working on overhead communica-
tions lines. During a comparison period, for each high-frequency channel in
the Mosenergo system there were 1.2 stoppages, 0.9 of which were along one chan-
nel due'to the power transmission line being shut off for repair work on the
line itself.
For each communications circuit during the same period there were 1.7
breakdowns, i.e., the susceptibility of high-frequency channels is one sixth
of that for communications channels. In the vast majority of cases, damage
to high-frequency channels is located in the stations, whereas channels along
communications lines fail due to damaged circuits (line damage).
A considerable drawback of high-frequency channels is that, at present
they go out of order whenever the power transmission line is switches off,
accompanied by grounding (in 75% of cases).
The merits and drawbacks of various methods of transmitting telemechanics
signals may be formulated in the following manner:
Along Channels with Differential Transformers
Advantages: cheapness and simplicity of installation; availability for
all cases where there is a communications line, irrespective of the material
of. the wires; possibilities of transmitting signals by polarized code with DC.
Disadvantages: high sensitivity to the state of the line, weather, and
quality of insulation; necessity for large voltages of the line battery when
the length of the circuit is considerable; distortions introduced into the
transmission channel; dependence on the intactness of the communications line;
possibility of transmitting telemechanics signals only with a signal frequency
of up to 40-60 pulses or periods per sec, according to conditions affecting
telephone transmission.
Along Carrier Channels is the Audio Band
'Advantages: comparatively simple apparatus; possibility of carrying it
out even under power system conditions; stability and comparatively small de-
pendence on the state of the communications line; suitability for transmitting
signals in any practical telemechanics installations.
Disadvantages: necessity for.special sources to feed the plate circuits
of the installation; complication of the telephone transmission channel; de-
pendence on ti.-.:e intactness of the communications line.
Along High-Frequency Channels on Power Transmission Lines
Advaritaaes: high sensitivity and reliability of transmission; small dis-
tortion of signals; large (up to eight) number of simultaneous one-way trans-
missions.
CONFIDENTIAL v'Tl??.
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Disadvantages: high cost (up to 150,000 rubles for one amplifier section);
possibility of failure in service if there is a breakdown in the power trans-
mission line of the point controlled.
In comparing the reliability of transmission of telemechanics signals along
power transmission lines and along the wires of communications lines, the fol-
lowing points must also be taken into consideration:
1. In the case of channels along power transmission lines, there are still
considerable possibilities of reducing the number of breakdowns. Switching off
and grounding a three-phase line behind line blocks fisolating switches?7, and
also grounding the line on the repair site through portable blocks would enable
high-frequency transmission to be preserved in the vast majority of cases of
breakdown and disconnection of the high-voltage lines. At the same time, break-
downs are considerably more frequent on communications lines, take a considerable
time to fix, and there is no possibility of preserving telemechanics transmission
during the breakdown period.
2. In cases where provision is made for switching the telemechanics trans-
mission to another circuit in the event of damage (other communications.wires,
a parallel power transmission line), this switching over is-more effective for
high-frequency channels along high-voltage communications lines. For the latter,
the probability of simultaneous damage to both circuits is considerably less'than
for communications lines with their great dependence on severe meteorological
conditions (ice crust, strong wind, etc).
The foregoing enables one to lay down certain conditions for selecting a
system and method of forming channels. It is quite obvious that the decisive
factor should be reliable operation of the telemechanics channel depending, of
course, on concrete conditions. It can be assessed correctly only by taking
into account both the significance of the actual telemechanics installation and
the responsibility and role in the power system of the telecontrolled or con-
trolled object (station, substation, transmission line), But it is incontest-
able that in a very large number of cases, there are no grounds for making the
requirements extremely severe and thereby incurring superfluous expenditures on
equipping more expensive channels.
Channels with differential transformers should be used for transmitting tele-
mechanics signals over short distances (50-70 kin) along nonferrous wires and
steel circuits in the numerous cases of lesser importance. These channels can
also be used if it is necessary to transtit signals of only one telemeasurement
or only telecontrol, for which the method has special advantages (possibility
of two-way operation without supplementary arrangements.)
For large distances (over 100 km) and in the absence of a channel along
power transmission lines, it is advisable to use the installation for. "compress-
ing" the communications 3-ne in the voice-frequency-carrier band. In this case
it is possible to establish the two systems des-ribed on the communications line -
a channel with` differential transformers for telecontrol (telesignalization), and
a channel on a frequency of 6.0-7.0 kilocycles for telemeasurement.
To ensure dispatcher control of, the most important units in a system which
is connected in a 110 or 220 kv network, the use of high-frequency channels along
power transmission lines must be considered obligatory.
Further development of high-frequency channels along transmission lines de-
mands solution of a number of long-standing technical problems in our labora-
tories, among which are:
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1. Completion of work (begun mere
grounding choke (reactor), necessary to
frequency links during repair and other
than once) on designing a portable
ensure uninterrupted operation of high-
work on power transmission lines.
2. Design of special simplified stations with
for high-frequency communications and telemechanics
voltage transmission lines (20 and 35 kv).
a small number of channels
to work on intermediate
3. Design of the corresponding apparatus for connecting to 20 and 35 kv
transmission lines -- coupling condensers, etc.
[Appended figures follow
Cornmunicaf/on Line
Figure 2
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e
Figure 4
Figure 5
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J Communication
7 Linc J T
l~ 1
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CONFIDENT) U N Fi DEN TiA L
50X1-HUM
.(NV Transmission Line)
VChZ LEPv/N _ {
- END -
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