CA1257902A - Electrical power line parameter measurement apparatus and systems, including compact line-mounted modules - Google Patents

Abstract

Abstract Of The Disclosure The disclosed invention is primarily directed to sensor modules for mounting directly upon energized electrical power lines to monitor parameters associated with operaton thereof, wherein the modules have a more compact lateral configuration than prior art modules designed for the same purpose. The modules include a first, cylindrical housing portion containing the sensing means and other electronic data processing and transmitting elements, and a second housing portion, affixed to the exterior of the first portion and extending not more than about 150° around the periphery thereof, and enclosing mechanical elements of the module mounting means. Also disclosed means for improving the accuracy of voltage measurements made by such modules by compensating for effects of adjacent, energized conductors, means for reducing the number of frequency channels required for RF data transmissions by a large number of sensor modules at a substation, means for acquiring time-synchronized data from multiple modules within a substation for accurate post-fault, sequence-of-events analysis, means for performing high speed sampling and comparison of cyclically variable ii parameters for relaying and harmonic measurement applications, and optical communications links for transmitting data from sensor modules.

Description

79~
BACKGROUND OF THE INVEN'rION
This inventi.on relates to systems for measuring and communicating various operating parameters associated with electrical power conductors; more specifically, the invention relates to systems which include line~mounted sensor modules haviny means for both transmitting signals commensurate with parameter values and optionally for r~ceiving signals to permit time-synchronized data sampling and transmission in a manner allowing highly accurate measurement and analys:is of data from a large number of modules at a single ground sta-tion.
Various power line mounted apparatus for sensing operating parameters of an associated conductor have been disclosed in the prior art. See, for example, U.S. Patents Nos. 3,428,896, 3,633,191, ~,158,810 and 4,261,818, as well as the improved systems disclosed in applicant's U.S. Patents Nos.
4,689,752 and 4,758,962. In yeneral, such systems include line-mounted sensor modules which measure certain quantities associated with operation of overhead power lines, namely, current, conductor temperature and ambient temperature, and transmit such data via a radio link to a nearby ground MLS//~

7~

station. Data from several ground stations is then transmitted to a central control station where it is processed and used to assist in control of the power supplied to the various transmission lines in accordance with the measured parameters.
Prior art systems of this type, while representing a significant improvement over tradi.tional means of measurement and control of power line operati.ng parameters, still have a number of inherent limitations and disadvantayes, some of which are addressed in applicant's U.S. Patent No. 4,758,962, issued July 19, 1988. This patent, for example, provides means for simultaneously measuring current, voltage and phase angle on multiple conductors of a single circuit or of many circuits thereby permitting monitoring of an entire substation. It is possible, however, that the accuracy of measurement of quantities such as voltage on a particular circuit may be adversely affected by adjacent, energized circuits. Also, time synchronized data collection for se~uence-of-events application is not possible. Other drawbacks of the previously discl.osed systems are high speed sampling for relaying and harmonic measurements is not possible for an entire substation installation; and, the use of certain sensor modules on distribution circuits with relatively small conductor clearances, as compared to extra high voltage MLS/~ 2 7Y`3~
transmi~10n c1rouits, 19 difflcult if not prohlbit~ve.
The ob~ects Or the pre~ent lnventlon are addre3sed to providing 1mprovements in power 1lne parameter monitorlng and analy~l~ sy~tems whlch deal with each of the aforementloned disadvantage3 of prlor art system~.
Among the specific ob~ects of the invent10n, all within the context of ~y~tems for collectlng and transmlttlng parameters associated wlth electrical power line operatlon which employ llne-mounted ~ensor modules, are:
to ~mprove the accuracy Or voltage mea~urement in the presence Or adJacent conduotors, irre~pectlve Or whether the latter are energlzed; to reduce the number of freguency channels required for use by a large number of 3ensor modules at a substat10n, thus reduc1ng llcens1n~
con3tra1nts; to provide hot-st1ck mountable, integrated sensor modules whlch can be in~talled on power lines with relat~vely close spaclng between adJacent conductor~; to permit t1me-synchronized data acqu1sit1~n from multiple modules within a ~ubstation ~or accurate po~t-fault, sequence-of-event~ analy~l~; to provide means ~or high speed ~ampling and comparison of cycllcally variable parameters L or relaying and harmonic measurement applications; and, to provide communlcations links other than RF broadca~t qignals ~or transmltting data from sen~or moduleq.
Summary Of The Invention In accordance with the foregolng obJects, the .. . . ,.. ,, . . . . .. ,. . . . . . . ~ . , . . ., .. ~ .... ~ ...... . .

~ 5 7~3~)~
inventlon contemplate~ a hot-stick mountable ~ensor module havlng, Ln a prlnclpal aspeot of the inventlon, a conflguratlon uniquely ~uitable for employment on power lines where ~paclng pre~ents a con~traint. That Ls, modules of the prior art are typlcally toroidal ln .shape and have a diameter on the order of 12", wh~ch ls su1table for mountlng on extra hlgh voltage power tranqmi~ion lines, but not on the more closely spaced, lower voltage (e.g., below 34.5KV) power distribut10n lLnes. In an embodiment partlcularly adapted for use where lateral clearances are constrained, the pre3ent inventlon comprises a compact, generally cyllndrlcal, metallic housing ror the electrical components Or the module, lncludlng the parameter sensing, tran3mlttlng and receivlng equipment, with the mechanical members of the mountLng mean3 positloned outside the cylindr1cal housingO The mounting members are enclo~ed in an arcuate, in~ulated hou~ing portion affixed to the exterior Or the cylladrical hou.qing and extendlng not more than about l50 around the periphery thereo~ in order to avoid clearance problems due to spac1ng o~ the conductor~.
The modules include means for sampl~ng the ~alue~ of voltage and current on the as~ociated conductor at a rapid rate7 i.e., at relatively ~hort, evenly spaced time intervals, e.g., 24 time~ in each cycle of voltage and current. Thls high speed samplLng permits use o~ the monitoring sy~tem for relaying and r~ 3~)~

harmonlc meaqurements for an entlre ~ub~taklon, po~t-fault, sequence-of-events analysls, and storaKe of translent waveforms.
Brief ~
F~gure 1A 1~ a perspectlve view o~ several ~ensor module~ of the inYention attached to the three phaqe conductors of an electric power line showing a fir~t mean3 of data oommunication with a ground ~tatlon;
Flgure 1B i 9 a perspective view, as in Flgure lA J
lo showing a se~ond means for communlcation between the sensor module~ and ground station;
Figure 2 19 a per3pectlve view o~ a sensor module embodying the preqent inventlon belng mounted on a hlgh voltage line;
Flgure 3 19 a diagrammatic lllu3tration of the sensor modules mounted within a substation ~ence;
Flgure 4 is an enlarged, perspective vlew Or a preferred embodiment o~ the sensor module~ oP Figure~
1-3;
Flgure 5 i~ a cro~s-sectional view of the sensor module on the line 5-5 o~ Figure 4;
Figure 6 i~ an end elevational view on the_llne 6-6 of Figure 5;
Figure 7 i~ a diagrammatlc block diagram of the YensQr module subsyste~ components;
Figure ~ i9 an overall ~chematic block diagram oP
the transcelver sensor module electronicq;

Flgure 9 i~ a diagram of the voltage and current waveform ~ampling, atorage and comparison;
Flgure tO illustrate3 the relation~hlp of the ~heet~ bearln~ Fl~ures 10A and lOB to form a sing1e block diagra~;
Flgures 10A and 10B together rorm a block diagram of the Combined Remote Termlnal Unit ground ~tation utilized with the sen~or module~;
Flgure 11 di~playq the transceiver sensor module 10 me99age format;
Figure 12 di~plays the Scale Faotors uAed;
Figure 13A i3 a diagrammatlc lllustration of apparatus used ln fleld voltage calibratlon of the sensor module~;
Figure 13B i9 a schematlc dlagram of` the electrical implementation of the calibration ~ystem of Figure 13A;
Flgure 14 is a compo~ite graphical representatlon related to the explanation o~ error ellmination in voltage measurement:

Figure 15 is a schematic block diagram made up of Pigllres 15A and 15B, of a common 20 three phase transceiver with fiber optio communlcatlon~
lnterface to the tran~ceiver ~en~or module~;
Figure 16 i9 a ~chematic block dlagram ~howing ~ignal generation for di~tribution power line carrier tran~ceiver ~en~or module synchronizatlon with neutral inJection of th~ Power Line Carrier qignal;
Figure 17 iq a ~chematic block diagram of a , .. . .

9~)~

diffe:rential relay protection system incorporating the transceiver sensor modules: and Figure 18 is an elevational view of a transceiver sensor module hub for use on insulated, overhead conductors.

DETAILED DESCRIPTION
Sensor modules 10, shown in Figure lA and in more detail in Figure 4, are of a type suitable for mounting upon energized power lines for sensing various parameters associated with operation of the power line and/or environmental parameters, and have a physical configuration particularly well.
suited for use on power conductors which are spaced more closely to one another than typical E~V power lines. Modules 10 include housing means which enclose the necessary elements for sensing the values of the parameters to be measured, and transmitting signals commensurate with the sensed values to signal receiving and processing means, collectively referred to as Combined Remote Terminal Unite (CRTU) 14, in control house 15 at ground level. Each module normally obtains its operating power from the magnetic field generated by current flowing in the associated conductor, and preferably include power backup means such as rechargeable batteries which provide the necessary operating power when line current is not present, or is below a predetermined value, as descrihed more fully in U.S. Patent No. 4,758,962.

MLS/~d 7 ~ 7 ~
Modules 10 of Flgure 1A each conta1n an RF
transm1tter and antenna for transm1tting data to the ground ~tatlon, whereas modules 10' Or Flgure 1B are each connected by optical fibers 16 termlnating ln male f1ber optlc termlnation ~errules to data concentrator module 18 (with fiber optlc ferrule connectlng ~ocket~
which then transmltq a ~equence o~ coded ~lgnals lndicating the value~ of the various parameters sensed by all Shree module3 10' to CRTU 14 via an RF radio link. In ~ome instances, it may be des1reable to ellminate RF links altogether and provide 1nstead optical flber~ extending dlrectly ~rom the lndlvldual modules 10', or concentrator module 18, to the CRTU.
Flgure 2 illu~trates the manner in whlch module~ 10, 10' and 18, the external conflguratLons and mountlng mechani~m~ of which are es~entially ldentical, are mounted on an energlzed conductor 12 by an indivldual manlpulatlng conventional hot-stick 20. Any ~pecial tool whlch may be required for cooperative engagement with the particular mountlng mechanl~m used in the modules is attach~d to the end of hot-~tick 20, as de~cribed later.
The ~en~or module~ mag al90 be in~talled u~lng in~ulaSed rubber gloves on energized diqtributlon voltage power conductors.
Before proceeding with rurther detail~ of construction and operation o~ the lndividual ~en or module~, a typical power monitoring system employing ~uch module~ will be described with reference to Figure wherein i~ ~ho~n a dia~rammatic representation o~ an ,.. , .. , .. -- .. , ... _ ... ,.. ~ .. . .

57!3~

electrioal power sub~tation enclosed by qtation fence 22. A plurallty of three phase clrcuit~, numbered 1-8, are fed from a common bus comprisLng three phases 24, 26 and 28, each connected through circult breaker 30 to tranqformer bank 32. The latter ls fed by an incoming three-phase power circult comprislng three conductor~
denoted collectively by reference numeral 34. Sensor modules 10 are mounted upon eac:h of the three phases of llne 34, and of llne 36, conneotlng tran~former bank 32 lo to breakers 30. Conductor~ carrying each phase of all circuit~ emanatlng from the sub~tatlon are equipped wlth a line-mounted ~ensor module 10. Conventlonal circuit breakers 38 are lnterposed in cach conductor between its reqpective connection to the common bu~ phase and the assoolated sensor module 10.
Each of module3 10 i~ equlpped to mea~ure the value~ o~ voltage and current, and to determlne the phase relation~hip~ thereoP, of its a~sociated conductor and may, if desired, be further equipped to mea~ure other parameter~ suah a~ frequency, conductor temperature, ambient temperature, vibratlon, etc. The sensed value~ are digitized, encoded and transmitted u~lng an RF ~ignal to the ground ~tation. Transmlq~lons from ea¢h module are controll~d to occur in bursts of predetermined duratlon in such a way that no two module~
are tran~mittlng at the ~ame tlme on the same ~requency.

,. , . .. ,, .. ., .. ,~. . . . .. . . . . .

rrhe previously reEerenced U.S. Patent No. 4,758,g62 describes two means of controlliny the time and intervals at which transmissions begin by each oE the modules in the system.
The first means is self-contained within the modules and involves using a zero crossing of the voltage on one phase of a bus line as a reference signal for timing transmissions by all modules mounted on conductors connected to the common bus.
The second means involved provi.ding each module with a receiver, as well as a transmitter, for receiving messages ~rom a transmitter at the ground static)n; the messages include an address unique to each module and an assigned time slot for transmission oE data by the module transmitter. For example, CRTU 14 may communicate with all modules in the system through transmit and receive antennae 42 and 44, respectively.
Corresponding communication equipment of the sensors is shown and described later. All sensors transmit data on a single frequency channel for reception by antenna 44; signals are transmitted by the ground station from antenna 4~ on a second frequency channel for reception by the sensor receivers.
For example, the system may employ a 950 M~z FM "uplink" (from the ground station to the sensor modules) and a 928 M~lz FM
"downlink". This Time Division Multiple ~ccess (TDMA) technique is useful for controlling the timing of parameter sensing as well as data MLS/,~ lO

transmissions by the various modules and i5 necessary in order to carry out a number of desireable features of the present invention.
Sensor module electronics include a microprocessor, RAM, I/O, and timer components, as disclosed in U.S. Patent No.
4,689,75~. The sampled values of the monitored parameters are digitized, stored in RAM, and communicated to the ground station during the established time interval as a burst of signals. The ground station includes a microprocessor to which signals received Erom modules 10 are supplied for further processing, such as calculation of total circuit and/or substation kilowatts, kilowatt hours, kilovar5, etc. The data is then communicated to a central data receiving and control facility by a data link schematically indicated at ~6, such as radio, land lines or satellite channels. Thus, all parameters necessary for monitoring and control of an entire substation, including relaying and post-fault analysis functions, may be measured, processed and communicated through the present invention, details of construction and operation of which appear in the balance of the disclosure.
Constructional details of module 10 are shown in more detail in Figures ~ and 5. The outer physica]. configuration of module 10 is basically defined by two housing portions, a first, essentially cylindrical portion 48, and a second portion 50 in the form of a MLS/,~ 11 circumferentlally truncated cylinder, afflxed to and extending le~s than half the dl~tance, preferably not more than about 150, around flrqt portlon 48. At least the outer ~kln of ~ir~t housing portion 48 is metallic;
for example, the entlre cyllncler may be a metal casting, or the substructure may be Fibergla~ or other dlelectrlc material with an outer coating of electrioally conduot1ng metal. Second portlon 50 L~ made of heavy duty plastlc or other such non-conducting material.
Fiber optlc receptacles 11 ~or- fiber optic male terminal ferrules for ~nterconnection with the data concentratlon module 18, F1g 1B are also shown in Figure 4.
~ hen module 10 i~ mounted on conductor 12, a~ seen in Flgures 4 and 5, the latter extends along the central axis Or the cyllnder formed by flrst houslng portion 48.
In order to mount the module upon the conductor ~n this manner, the module i3 dlvlded into ri8ht and left halve~, a~ lndlcated by the left and rlght halves of the end of the cylinder seen in Figure 4 and denoted by re~erence numeralq 52 and 54, respectively. The division also extends through qecond houslng portlon 50 and the le~t and right halve~ are coupled for relative movement by a hinge/pivot mechanism housed principally wlthin portlon 50, a~ dlscu~sed later ln more detail.
First hou~lng portion 48 iq further divided lnto front and rear ~ections 56 and 587 respectively, by a plane tranqverqe to the axis of the cylinder. Sections , ",. . . .. ... " . ... . .... .. ... . . . .. . . . .

7~:3~3 ~
56 and 5~ are ~eparated by ga~ket 60 of a 9ul table materlal whlch malnta~n~ ~ectlons 56 and 58 electrically ln~ulated from one another. The qections may be bolted together, but the boltq (not qhown) extend through plastic in3erts to avoid completing an electrlcal path between the two qectlonq. This prevents an electrical short circuit, i.eO, a complete conducting path, from extendin~ around the metal housing portion in a direction parallel to the ~urrounded conductor whlch would interfere wlth operatlon Or electrical components which are mounted wlthin hou3ing portion 48 in a manner described later. All qurfaces of houqlng portlon 48, includlng where the cylindrical wall meetq the ends, are rounded and free Or sharp edges to avoid corona condition~ which could occur when the module~ are mounted on lirl e9 carrying hlgher voltage level~.
Module~ 10 are constructed a3 double-~alled cylinder~, the inner wall being ~hown ln Figure 5 and divided in the same manner as the outer wall into ~ront and rear qectlons 56 and 58, respectively. The inner wall i9 al~o divided, of cour~e, lnto right and left halveq, aq previously described in connectlon with the other element~, for openlng and 0109ing mo~ement about conductor 12. A hub ~tructure for engagement of module 10 with conductor 12 i3 prov5ded wlthln both the front and rear end9 of the module. Electrically conductiYe7 ..... . . .. . . . . ... . . . . .. . .

1 ~ ~7~3~)~

annular lnsert~ 66 and 68 preferably of a ~omewhat re~illent material such a~ Neoprene, havlng a central opening Or the same or slightly smaller dlameter a~
conductor l2 are posltioned withln annular rings 70 and 72, respectlvely, al~o of electrically conductive material~ at oppo~lte end~ of module 10~ Ring~ 70 and 72 are ~urrounded by conductive rings 74 and 76, respectively, which are in electrical contact with houslng 48. A layer o~ lnsulating material 78 separate~
lo rlngs 70 and 72 from rlng~ 74 and 76, re~pectlvely, to provlde a portion of the mean~ for ~enslng the voltage on conductor l2, a~ explalned more fully ln the preY1ously referenced, concurrently ~iled appllcation.
Optlonal heavy duty plastic hub caps 80 and 82 are a~fixed to the front and rear ends, respectively, of module 10 to proYlde a protectlve, molsture-proof 3eal for the hub portlon3.
As ~een in Figure 5, Rogowskl coll 84 i5 mounted in the front section of module 10 ~o extend around conductor 12 and provide a means for ~en~ing the current flowing through the conductor when module 10 i~ mounted thereonO Iron core 86 l~ mounted ln the rear ~ectlon of module 10, qurroundlng conductor 12 to provide mean~ ~or obtainlng the power neces~ary for operatlon of the electronic~ of the module ~rom conductor l2 when sufficient current is flowing therethroughl Conductor 12 ~erve~ a~ a ~ingle-turn primary and power pick-off coilq 88 and 90 (Figure 6) on core 86 a~ the ~econdary '`

.. , . , ~ ... , . , .... , .. , " .. .. . . .. .. . . .. . . . . .. . . . . .. . . . .

57~30~

windings o~ a power transformer. Core 86 is divided into riyht and leEt halves for movement with the other portions of the right and left halves of module 10 as the latter is opened and closed for mounting upon conductor 12. The pole faces at the upper end of core 86 are respectively surrounded by a moisture-proof recess 92 and a mating, plastic shroud 94, as also disclosed and claimed in U.S. Patent No. 4,758,962.
~ s previously mentioned, module 10 is divided into two relatively moveable sections for mounting upon an existing power conductor in surrounding relationship thereto. There are, of course, many mechanical systems suited to accomplish such mounti.ng of the module and the present invention is not concerned with details of design of the mounting means. One such means which may be employed, with suitable modifications to take into account the particular configuration of module 10, is the hinge/pivot mechanism disclosed in U.S. Patent No.
4,689,752. In that application, the hinge/pivot mechanism is disclosed in connection with a toroidal module and the mechanical elements are housed within the toroid. Since the present application is concerned in one aspect with providing a module of more compact dimensions, at least in that portion containing the electronic elements and conductive housing surface, most of the mechanical members of the MLS/~ 15 structure providing relative movement of the two sections are contained in second insulated housing portion 50. This permits cylindrical housing portion 48 to have a diameter on -the order of one-half that of the toroidal modules of U.S. Patent No.
~,689,752.
The structure providing relative movement of the left and righk housing sections includes a pair of arms 96 and 98, each pivotally connected at one end by fixed pivot pins 100 and 102, respectively, on base structure lO~ wi.thin second housiny portion 50 and at the other end by moveable pivot pins 106 and 108, respectively, to support members 110 and 112, which are contained within and affixed to the inner walls of housing portion 48. By appropriate mechanical couplings, rotati.on of a socket member within guide member 114 is translated to movement of pivot pins 106 and 108, and thus support members 110 and 112 and to the right and left halves of module 10 away from and toward one another. As discussed more fully in U.S.
Patent No. 4,689,752, this movement is effected by clockwise and counterclockwise rotation, respectively, of a tool carried on the end of a conventional hot-stick.
Turning now to Figure 7, a general block diagram of the electronic subsystem components is shown in connection with an outline drawing of the module housing portions 48 and 50.
In operation of module 10, only MLS/,~,~ 16 ~57~3~)~

cylindrical housing portion 48 serves to collect charginy current for the voltage sensor and for electrostatic charging of rechargeable batteries of subsystem 116, which includes the circuitry for recharging and controlling the use of back-up power as well as the batteries themselves. Power supply 118 received electrical power from pick-off coils 88 and 90 when sufficient current is flowing ~hrough conductor 12, and otherwise from batteries 116, and supplied power at appropriate levels to signal processing subsystent 120. 'rhe elements for sensing the parameters to be measured, indicated collectively as subsystem 122, are connected to provide signals to subsystem 120, which in turn is connected to RF transmitter 124 and to receiver 126 in the embodiments which include the latter.
l~hese features are discussed more fully in U.S. Patent No.
4,758,962.
Referring now to Figure 8, current and voltage on the conductor at a predetermined point in time are sensed simultaneously by Rogowski coil 84 and housing section 48, respectively, in the manner previously described. Rogowski coil 84 is connected to input amplifier 128 through current range select resistors 130. The voltage sensor is connected through capacitor 132 to low impedance operational amplifier 134 with feedback capacitor 136, as previously described, to provide an output signal in phase with the MLS/~ 17 l~S7)~

llne-to-neutral voltage~ A novel means ror improvlng the accuracy of voltage readlngs by compensatlng for the effects o~ adJacent, energlzed conductor~ i~ described later hereln.
Additional ampllfierY such a~ that indicated at 138 may be provided for meaqurement o~ additional parameter~, such as conductor temperature, ambient temperature, conductor vLbrations, etc. The output Or each o~ the parameter-measur.Lng ampllfler~ i~ connected through multlplexer 140 for comparison with the output Or digltal/analog converter means 142, whlch recelve~ an input from voltage re~erence 144, at comparator 146, under the control o~ digltal computer 148. The latter may be, for example, a Motorola CMOS 6805 microprocessor having I/O, RAM and timer component~. Programmable read only memory 150 ls connected to the computer CPU for storing the program.
Current and voltage zero cro~ing detectlon i~
provided by amplifier~ 152 and 154, re~pectively, each having one input connected to the output Or the re~pective current and voltage measuring ampllfier~, and the other input connected to ground. The output~ of both zero crossing detector~ are connected directly to microprocessor 148 ~or phase measurement. In addition to providlng ths signal~ neceqsary ~or mea~urement of pha~e angle and ~requency (whlch 19 the lnver~e of the time between ~ucce~qlve po~ltive golng zero cro~ings) :~'~:3~

the signals from voltage zero crossing detector 15~ may be used for synchronization of data transmission by transmitter 124 without requiring a receiver in the sensor module and a transmitter at the ground station.
A transceiver system is shown which permits time synchronized, sequential data transmission from a relatively large number of modules, e.g., all modules necessary for monitoring an entire substation, such as that of Figure 3, to a single ground station on a single broadcast frequency. The zero crossing detectors described in ~.S. Patent No. 4,758,962 for controlling the timing of transmissions from the three modules of one circuit may also be used to provide basic synchronization with TDMA coded timing signals transmitted from the ground station and received a the module by receiver 126.
Each module is assigned an identifying number which is selected i.nitially through module 156. The digitized data representing the parameter values is assembled into appropriate messages, encoded in Manchester code by encoder 158 and supplied to transmitter 124 via line 159 for transmission in assigned time slots designated by TDMA data burst control signals received by receiver 126. The timing signals from the ground station are passed on from receive.r 126 to demodulator 160 (which can be part of the receiver 126). The demodulated TDMA signal contains information on the assigned time slot for transmission MLS/~,J 19 790~
by the partl~ular sensor rnodule. The 31gnal i~ passed through CRC check module 162, for error detectLon and the pulse code is detected by module 164, providing the mlcroproce~sor wlth informat~on to control the tranqmitter bur~t timLng.
Sensor modules 10 are in a high voltage environment isolated from ground. It i.3 de3irable~ therefore1 to derive as much information aq possible from the sen~or~
wlthin the sy~tem wlth a minlmum of complexlty and to lo tran9mit thi~ raw data to the ground statlon for prooessing. Varlous derlved quantities can then be calculated by the mlcroprooeq~or CRTU ground ~tatlon.
Becau~e of the hlgh data transmis~ion rates provlded by ths TDMA technlque, lt i9 po3sible to sample and hold both current and voltage values 24 tlme~ per cycle, as indicated ln Figure 9. Fourier co~ponents may be calculated by the sen~or module proceq30r and value~
thereo~ tranqmitted to the ground ~tation sequentlally by pulse code modulation. Alternatively, the values of voltage and current sampled 24 time~ per cycle may be tran~mitted to the ground ~tation and the Fourier component~ calculated therein. The RMS values of voltage, current and the pha3e angle may also be calculated ~ithin each mvdule and the value~ directly r transmitted to the ground station.
When it i9 desired to derive pha~e and harmonic data rather than merely transmltting the fundamental ~ . - .

~ 5 ~30~

Fourier components of the voltage and current to the ground statlon, the shape of the waveforms and thelr relatlve pha~e must be tran~mitted. The ground ~tatlon can then ea~ily compute the quantltles o~ lntere~t, ror example, RMS amplltude o~ voltage and current, theLr relative phase and harmonic content. Since aurrent and voltage are sampled simultaneously, theLr relative pha~e~ are the same as the relative pha~es of the ~ample ~equence. By u~lng zero crossing~ Or the voltaee lo waveform ror aample timing lmproved accuracy and ~tability i~ obtained. Zero cro~sing detectior, of the current waveform and the time difference between the voltage and current zero cro~ing provides a pha~e angle mea~urement check.
The data tran~mis~ion~ take place in e.g, 4.5 mill~3~cond time ~lots at a data rate of approximately 20 kilobits/sec. Time slots of individual senYor modules are ~ynchronized through a 950 MHz ti~ing signal received ~Imultaneou~ly by all qen~or module~ ln a station. This ~lgnal also contain3 addre~ informatlon a~ to the time ~lot allocat~on for the data bur~t from a particular ~en~or module. Wlth this informatlon all voltage, current, pha~e angle, power and energy measurements of the fundamental and harmonic component~
can be calculated by the ground station proce~sor. For example, the ~undamental FourLer componentq of voltage and current VA~ VB and IA, IB are:

~ 21 -, ~, ... . . ... . .. ... . . . ... . ... . . ... . . . . . .

3~];~
ST

VA Sr1~ ~, CO ( ST
B ST ~1= VS 5in ~ .S) ST ~ (ST
IB= 2 ;b~ IS sin ~ , S) Where ST equals the total number of samples; in the apparatus disclosed this is 24. S equals the sample number, and Vs and Is are values of measured voltage and current at sample S. From these RMS voltalge V and current I may be derived from the standard formulas:
V= [ (VA) ~ tVB) ]
I= [ (IA)2 ~ ~IB)2]~
Real Power is:

PR= (VA X IB) ~~ (VAXIB) and Reactive Power is:
QR= ( VAXIB ) ( VBXIB ) Referring to Figure 3, a sinyle large substation 22 may have over 100 sensor modules 10 transmitting data to a single receiver 24. Since frequency spectrum is difficult to obtain, data collisions must be avoided, and synchronized data is required for sequence-of-events applications, it is important that all sensor modules in a substation collect time synchronized data by receiving synchronizing signals through a transceiver conEiguration. This technique also permits high data transmission rates needed for relaying applications and harmonic measurements.
Again referring to Figure 9, the timing diagram is MLS/~ 22 ~ ~ 5 ~30~

shown where the voltage and current ~ine wave~ are mea~ured by the voltage sensor and Rogowsk1 coll. At the PLrst zero cro~sing, labeled t-o, after receipt of the TDMA clocking signal, timing i9 started. Twenty four simultaneous voltage and current waveEorm ~amples are taken succes~ively. The sampl1ng interval i~
defined by equal segment~ withln ~uccesslve voltage zero cross1ngs~ The~e mea~urements are utilized to compute YA, VB, IA and IB, the program load3 shift reg1~ters with the identlficatlon number of the sensor module, auxiliary number, the Fourler components VA, V~, IA, IB, the digit~zed auxlllary parameter~ and the C~C (a check ~um). At the allocated time 910t for each sen~or module establi3hed by the received TDMA ~ynchronlzing s16nal the Fourier componentq of voltage and current, frequency, pha~e angle and auxillary parameter~ are tran~mLtted.
The proce~3 i~ repeated as the program i3 reset at the end of each transmission. All ~ample~ of voltage and current are stored Eor comparison with the next ~et as shown in Table 1.
With the hlgh ~peed qamplin~ afforded by the TDMA
approach the ~ame sensor modules can be u~ed Eor relaylng. Each string of sample~ ~tarting with the voltage zero crossings i3 ~tored in RAM for comparison with the next ~tring of qample~ at the ~ame point in each waveEorm. If the deYiation~ exceed the relay ~ett1ngs ba~ed on a predetermlned initiallzation the ~ ~ ~7~3~)~

data i9 immediately communlcated to the ground statlon CRTU or a separate but simpl1fLed "Relay Ground Station"
on one o~ eLght emergency time ~lot~ provided in the TDMA bur~t stream. An alarm 1~ slmultaneously trlggeredO Alternatively, a second crystal aan be ~witched in to transm1t abnormal data on a second frequency channel available to all sensor module~ on a random acce~s basi~.
Referr$ng agaLn to Flgure 8, the data oommunlcated on line 159 from encoder 158 to transmltter 124 19 that data required to perform the normal metering funct1Ons.
A second line 161 may be provided for communicating data to perform r0laying functlons. In thi~ case, both llnes 159 and 161 are connected to logic module 163 which i9 adapted to dl~able the metering channel whenever a slgnal 19 present on relaying data line 161. Flr~t and second crystal~ 165 and 167 allow transm1tter 124 to transm1t meterin~ and relaying signals on two, mutually exclusive channels, whereby the relaying data will always be received at the ground station even though another module may be transmitting at the same tlme on the metering channel. Preferably, a te~t slgnal ~9 periodically tran~mitted on the relaying channel to en~ure constant operability.
Abnormal condition~ may be deflned in a number of ways, e.g.
If: 0.8~Vtp/V(t ~)porVtp>1.2 pu ,~ ~

~ ~ S 7~3~)~

or itp/i(t l)p> 3pu an alarm 19 transmltted to the ground ~tatlon, Where~ tp i9 the peak voltaKe for a sample set V( t 1 )pi9 the peak voltage for the prev~ou~
~ample set itpis the peak current for a ~ample set i(t 1)pi~ the peak current for the previous ~ample set.
Data may be tran~mltted ln Manche~ter code or other oonventlonal encoder~. Eaoh mes~age comprlses the latest mea~ured Fourier component~ o~ voltage and current and another measured auxillary parameter wlth a number identifying it. Thus, each mes~age format for the fundamental and lts harmonlc3 would be repeated a~

rOllOws:
Sen~or Module Iden~lficationl~,blt3, Auxiliary Parameter No. 4 bits Voltage Sine Component 12 bits Voltage Cosine Component 12 blt~
Current Slne Component 12 blt~

Current Co~ine Component 12 bitq Auxillary Parameter 12 bit~

Cyclic Redundancy Check 12 bits The auxlllary parameter rotate3 among each one on ~uccessive tran~misqion~3 e.g.

, .

,; _. ,.. , , , ._, .. , ......... . .... . . ~ ..

~L~ rj79();~

Paramet_r No. Parameter O Check Ground (zero volts nominal) l Check Voltage (1.25 volts nominal)

2 Sensor Module Interior Temperature A block diagram of CRTU 1~ of the present invent:ion is shown in Figures lOA and lOB. It is important to note that CRTU 14 combines the non-metering functions of a conventional utility Supervisory Control And Data Aquisition (SCADA) system with the Remote Terminal Interface (RTI) capability of U.S.
Patent No. 4,689,752. Tha-t is, a conventional SC'ADA system is employed at a power substation to monitor alarm status, receive control signal inputs from a central SCADA master computer or Energy Management System (ÆMS) computer, record the sequence in which substation relays operate, monitor analog signals associated with power transformer banks or underground cable (temperature, pressure, etc.), and other pulsed inputs and outputs. The RTI disclosed in U.S. Patent No. 4,689,752 provided signal processing means for performing metering functions in conjunction with the line-mounted sensor modules, and/or form analog signals associated with underground power cables through existing current and potential transformers.
Lower overall system cost is achieved by combining these separate functions in the CRTU of the present invention, as will now be explained.
In addition to receiving transmissions from MLS/~ 26 ~ 3~
multlple ~ensor module~ 10, via 928 MHz rece1v~nK
antenna li4 and radio receiv~r 166 the CRTU syatem 14 can reoelve analog data from multiple current tran~formers 168 and potentlal tran~formers 170 not a~oclated w~th the overhead 11ne~. CRTU 14 i9 a m1croprocessor-based 9y9tem operated by Central Processlng Unit (CPU) 172, ~uch as a type 68000 mlcroprocessor or an 8386 Intel mi¢roprooessor. The ¢oded transml~10ns from sensor modules 10 received by receiver 166 are transmltted through a CRC error oheok 174 be~ore belng proce~ed by CPU 172. The input from current and potentlal transformers 168 and 170 are condltloned by condltlonlng ampllfler~ 176, 3ample and hold clrcui~ry 178, multlplexer 180, and A/D converslon circu1ts 182, under control o~ analog meterlng control board 184~ The digitlzed data i9 supplied on data bus 18fi to CPU 172~
CPU 172 is provided with RAM 188, PROM 190 ~or storing its progra~, and an Electronlcally Erasable Read Only Memory 192 for storing ~cale factors and personality tables.
CPU 172 is provided with keyboard 194 and a 16 character ~ingle line d~splay 196. It i8 also~provided with an RS232 port 198 for loading and unloadlng personality tables comprisln~ ~cale ~actors and the like for the sensor modules and the input~ from transformers t68 and 170. CRTU 172 ~upplle3 data via current loop 200 from an RS232 communlcationq port 202 on 1~ 5~3~
communlcation~ board 204 to a substation SCADA
telemeterlng link, or for local dl~play of data directly on an IBM XT or Compaq mlcrocomputer screen. Complete, conventional non-metering SCADA ~unctlon capabillty i9 provlded by scannlng lnput~ from ~ub~tation pulse, analog, oontrol (Select-Before--Operate), Sequence-of-Events, and Alarm Status ~ignals, indlcated collectively by reference numeral Z06. These lnputr~
are connected directly to I/O interraoe 20B Or cpu 172, wlth circult breaker control performed through interpo~ing relays operated by the Select-Before-Operate control port. CPU 172 13 further connected, through I/O
20~, to ~pread 3pectrum satelllte controller 210 for two-way data communicatlon to an EMS Master Control Center or SCADA Di~patch Center.
CRTU 14 also ~end~ ~ TDMA coded synchronlzlng message, vla pulse code modulator 212, Tran~mitter 214 and 950 MHz transmit antenna 42. Thi~ ~ignal i9 recelved by all ~ensor module~ and serYe3 to synchroniz~
transml~ion of data, a~ de~cribed ln the concurrently flled applicatlonJ
Flgure 11 indicate~ the type of data included in individual messages whieh are perlodically received~rom each of ~ensor modules 10 at CRTU 14. Th~s representq the data temporarily ~tored in an individual burfer, one Or which i9 provided for each ~ensor module in the ~ystem. Thi~ data i~ then used to calculate desired .,, ~
- 28 ~

... . , ,., .... . ... . . ... .. ~

~'~ 5'7~

output parameters lncludlng voltage, current, temperature, rrequency, kllowatt hour~, kllowatt~, kVA, and KVAR I 3 ( Reactive Power). Each sensor module supplles the Fourler oomponents Or voltage and current which are used for ¢alculatlng power, reactive power and energy related quantities. Items indlcated ln the word column are u3ed to ~dentlfy the proce~alng ~tatus of data from thc lndlcated sen~or module.
Figure 12 di3play~ the scale ractor table for each sensor module, ~uch tables beln~ 3tored in EE P~OM 192.
Note that there are 4 voltage scale ~actors, ln order to enhance accuracy o~ voltage measurement dependlng on the qtatus of ad~acent clrcuit3, l.e., whether ad~acent conductor~ are energlzed.
In analog meterlng board 184 the analog lnputs from current and potential tran3formers 168 and 170, re~pectlvely9 are ~ampled In turnO After lt~ condltion has been converted to d~gital form, an Interrupt i3 generated, and the data lq suppll~d to data bus 186. It should be noted that analog board 184 cause~ the lnput~
from the current and potentlal trans~ormer3 16~ and 170 to be sampled 24 tlmes per cyole, ~u t as current and voltage are sampled in ~ensor ~odule~ 10~ Data ~upplled to data bus 186 from analog board 184 comprl~e~ 24 ~ucces~ive values over one voltage and current cycle.
A~ter all 24 value~ have been ~tored in Random Acoess Memory 188, and appropr~ate correc~lon ~actor~ applied, .. . . . .. .

~ ~ 7 the fundamental 31ne and coslne Fourler components ar~
calculated, ~u9 t as ~or Bensor roodule~ 10. From these all oth~r quantlties required are calculated and stored ln RAM 188.
When CRTU 14 is lnltlally ~et up, appropriate ~en~or module scale factor~ are loaded through RS232 port 202 into the Electrlcal Era~able Read Only Memory 192. The output personallty table may ba displayed on di~play 196 and entered by keyboard 194 or entered or lo read out through RS232 port 198. A common power supply ls used for the integrated CRTU 14, thereby reduclng c03t and space requirements.
In order to en~ure that the ~lgnal indicatlve of llne volta~e tran~mltted to the ground ~tatlon by the ind1vidual sen30r module~ accurately reflect~ the actual line voltage, it is necessary to callbrate the module3 wlth a known callbration potentLal transformer.
Depending upon clr¢uit YolSage, a ground potential transformer, ~uch aR indlcated generally by reference numeral 215, Fig 13A or, for volta~e~ below 35KV, by a transformer mounted in an in~ulated bucket truck, as indicated at 217. Such callbratlon may convenlently be performed utilizing a line-mounted senqor module Or the pre~ent invention ~ith ~ome very ~imple modiflcatlonq.
Sen~or module Z16 include~ all physical and electrical feature~ of module~ 10 a~ previou31y de~cribed and, ln addition, i~ provlded with a threaded ~ocket 21a in ~ 3C)~

houslng portlon 50, connected by lead 220 to the circultry withln houslng portlon 48. Rod 222 i3 threaded into ~ocket 218 at one end, and carrie~
spherical probe 224 at the other end. Probe 224, rod 222 and socket 218 are all of eleotrically conductlng materlal, whereby probe 224 1~ in electrlcal communication with ons o~ termlnals 226 (Fig. 13B) of range select re~i~tor~ 228. Common reference numerals are used in Flgure 13~ to denote clrcuit element~
lo prevlou~ly described in connectlon wlth Flgure 8.
When concave probe 230 i9 ralsed, by mean~ o~
telescoplc mount 232, operated manually or by radlo controlled servo-motor 234; lnto ¢onductln~ contact with spherical probe 224, the current flow through probe 230 to the winding of tran~former 215 i9 dlrectly proportlonal to the actual voltage on the llne upon ~hlch module 216 i~ mounted. This current also i9 made to flow through the appropriate re~istor 228 to the preYlously mentioned ~pare operational ampli~ier 138.
The outpuS slgnal o~ amplifler 138 iq thu~ proportional to thi~ current, and hence to the line voltage. The sen~or module 216 electronic~ beyond the mu~tiplexer 140 i9 ~dentical to ~en~or module 10 electronlcs ~hown in Fig. 8. The normal voltage ~ensing mean~ of sen~or module 10 i~ provided by operational amplifier 134.
Thu~, the voltage measurements of the ~en~or module and of the calibratlon potentlometer ~rom ampllfiers 134 and .
~ 31 -.. .... .. . ... . . . ..

~ ~ tlt7~3~

13~ respectlv~ly, are proce~ed through multiplexer lllo and the re~t of the previously described c~rcuitry.
Zero crossings of the callbratlon voltage ~ignal determlned by operatlonal amplifler 154 and the current sensed by the Rogowskl coil 84 are used to provide an accurate mea~urement o~ the l~ne power factor angle through phase angle detector 236, provided for thls purpose in calibratlon module ~'16. Thl3 is also prooeqsed and transmltted to the ground receiver in the same fa3hlon as the other sl6nals. Both voltage and phase angle mea~urement i9 repeated for each phass, by mountlng module 216 on each individual line, and the calibration factor~ are entered lnto the per~onallty table for the partlcular circult at the ground statlon.
An alternative voltage callbratlon procedure iq descrlbed below with respect to Flgure 14. Due to the proximity Or the other conductors, each sen~or module colleots charging current~ rrom adJacent phase~. For example, the ~en~or module mounted on pha~e 1, in addition to oollecting the desired phase one oharging current iol, collects phase two and three char~lng current~ lc2 and 1c3. The ef~eot3 of these unwanted oharging current~ mu~t be mea~ured and ellminated in the calibratlon procedure. Wlth the transcelver ~ensor module and the TDMA synchronizlng slgnals this is efriciently achieved by meaquring the total charglng ~L~579~
current (the vectOr 9um ~ ~c1, lc2, and c3) on given conductor at preclse time interval~, a~ lndlcated below. After the frequency l~ determined through meaqurement o~ ~u¢ceqsive æero cros~ings o~ the voltage waveform, as previously deqcrlbed, the total charglng current of ~enqor module 10 i~ measured at t1=60~ 2 ~f, t2=90~ 2 ~f and t3-120~ 2 ~ f. The total charging current measured at theqe tlmes (wlth r0~erence to the zero croqslng) i3 held in RAM by the proce~sor when the coded TDMA ~lgnal received by She ~en~or module proces~or put~ the proce~sor ln thl~ callbration mo~e.
The total charglng current due to the phase one voltage alone, denoted c1 i9 obtalned by solving the ~ollowLng equatlon~:
lc1m/wt=60- c1 qin 60_Ic2 ~in 60~
iC1m/wt=90=Icl- c2 sLn 300_Ic3 ~in 30~ (2) i~1m/wt=120=Ic1 3in 120-Ic3 3in 60~ (3) c1m i~ the phase one charging current measured by the voltage ~en~or. From the 3 3ampled measurement3 Ic the charglng current due to voltage V1 alone ls calculated. From the relatlon~hiP V1(actual)=I V1~

Ic1m, e c1 ~ obtalned by ~olv~ng equation (1)~ (2) and (3). The calibration factor kV -I

1' clm By calculating IC2 and IC3 above data the voltagç phase angle error lntroduced by the charglng currents ic and ic on pha~e 1 can al~o be e3tabli3hed. ~he actual voltage then relate~ to the .. ,. , . ~ .. ,, .. .... ~ . . _ , . . . .. .. . . .. .. . ... . .

36`)~::

measurecl voltclge by the equAtion:

V . For ultimate accuracy ln Vl(actual)= kV1. lm voltage measurement~ under all clrcult condltlons, all adjacent circuit data must be recorded in the CRTU 14 a~
such. When there are two ad~acent circu~ts there are 4 scale factors for voltage whlch are applied based on deteetlon of whether:
1. both ad~acent clrcuit~ are energlzed, 2. only pha~e 1 ad~acent clrcuit 19 de-energlzed, lo 3. only pha~e 2 ad~acent clrou~t i9 de-energLzed, or 4. both adJacent clrcults are de-energlzed~ These ~actors are stored in the CRTU 14 electronlcally eraseable PROM a~ ~hown ln Flgure 12 for each sen~or module voltage measurement, and the appllcabls scale factor ls appl~ed to each voltage mea~urement dependlng on the qtate of ad~acent conductor~.
Overall oo~t~ and complexlty Or indlvldual dl3tr~butl0n reeder tran3celver ~en~or module~ aan be reduced through the use Or flber optl¢ communlcatlons between indiv~dual tran~ceiver ~en~or modules and a common electronlcs slgnal proc¢~ing, ~ynchron~zation pulse code detector, tlmlng, storage, program control and transmitter/re¢e~ver bur~t control ~ystem common to all 3 phases. Thls optlon was prevlo~ly mentloned and a physical de~cription Or the sen~or module ~ountlng glven in connection with Flgure 1Bo A block dlagram Or , ... .. .. .. ... .. .... ... .... . . . .. . . . . ... .. . .

~ 7~3(J~
the 1.1terconnectlon and operation Or a sy~te~ employlng flber optlc l1nk~ hown in F'lgure 15 where1n individual ~ensor modules 238, 239 and 240 are shown for each pha3e. These modules contaln the ba~ic Rogowskl ¢oll current and insulated hous1ng voltage ~ensor~. The individual current and voltage analog q1gnals are converted through co~merically available electro-optlc aircuitry 241, 242, 243, ln modules 238, 239 and 240, respectively, to optical ~i6na~.s which are tran~mitted vla optical ~1bcr cable~ 24~, 245 and 246 to opto-electronlc rece1vers 248, 250 and 252. These opto-electronlo receiver~ are housed ln a separate ~ensor module 18 (Flg. 1B) whlch carr1es zero cro~lng ourrent and ~oltage detect op-amps 254, 256, 258, 260, 262 and 264. The latter are all connected to the common multiplexer and remalning circultry whlch i~ the same aa that of the lndiv~dual ~ensor module~ prev10u~ly described and ~hown in Figure 80 For each pha~e, current and voltage analog signal~ are mea~ured by the Rogow~ki and ~oltage sensor coils, converted lnto optlcal signal~ and transmitted as analog signals to the common 3-pha e transceiver module 18 via flber o~tlc termlnatlon ~errule receptacle~ 11. The power supply ~odule for the individual pha~e sen~or module~ and the common tran3ceiver module 19 as de~cribed in connectlon with the module coa~lguratlon of Flgure lA. In common

3-pha3e sensor module 1~ the optlcal ~lgnal~ are ~ ~ 7~3(~

converted to electronlc ~lgnal~. The zero cro~lng~ ror current and voltage measurement~ are monltored by the re~pective op-amp~ and fed to the multlplexer. All of the 3-phase ~lgnals are tran~mittcd through the comparator to th~ mioroprocessor ln common module 18, and processed as prevlously descrlbed. Voltage zero crosslng~ are used to control ~3ampling ln conJuctlon wLth the transmit burst control signal which is enabled upon recelpt of the data burst control TDMA signal.
lo Alternatlvely, analog electrlcal slgnal~ from individual clrauit phase sensor modules can be communicated as analog optical ~ignals through Plber optic cables to the CRTU 14 that is located ln the 3ub~tatlon control house, thereby eIimlnatln~ all radio llnk~. Here, the optlcal slgnal~ are converted to electronic ~lgnals and proceYsed In the manner previously dlsclo~ed.
An alternative to FM (950 MHz) or broadcast FM
subcarr~er synchronizatlon would be the in~ection of a 7-30 khz power llne carrier (PLC) signal Flg. 16. The PLC signal is pulse code modulated, for example, by mode 3 coupllng, as shown, through the trans~ormer bank neutral 266 feeding the substation bu3es and hence the circuits to be monitored. The PLC signal i~ detected by an lnductive pick-up 268 on the ~pllt core 86 Or the sensor module 10. The ~ignal i9 flltered by a hl6h-pas3 ~ilter 270, to remove 60Hz components of the power line, demodulated by demodulator 272 and the ~ynchronizlng ~ 7~3~)~
slgnal detected by PCM detector 274. The sensor module prooessor tlmlng ~equenoe l~ inltlated upon detectlon Or the ~ynchronlzlng 31gnal message. The remaining operatlon of the ~ensor module 19 the ~ame a~ for the FM
synchronizing approach.
Wlth thl~ technlque the FM recelver on the ~ensor module iq not required7 If th~ optlcal data transmls~ion technlque is utlllzed for the 11nk to the CRTU 14 from the ~ensor ~odule, the need for an FCC
lo license ls e1imlnated.
It 19 ~urther polnted out that the compact sen~or modu1es 10 diso10~ed hereln may be synchronized wlth reqpect to lnLtiation of transmlssion o~ 405 milllsecond slgnal bur~ts by the mean~ dlqc103ed In the related appllcatlon fi1ed concurrently herewlth. That 1~, ~ynchronlzatlon may be ef~ected by us~ng the voltage ~ero cros~ings and inherent pha~e shl~t wt=120 ~or voltage zero cro3~ings o~ ad~acent pha~es. Ad~acent ~ ircuits can then transmit every 7th, 11th, 13th, 17th and 19th cycle, with reference to the voltage zero crossing of cirucits connected to the same bu3. This ellminate~ the need for a receiver in the ~en~or~
module~, and a transmitter at the ground tation.
The transcelver ~en~or moduleq can be applled ror differentla1 relay protection; as indlcated in Flgure 17, ~ince all the voltage and current ~amp1es are collected in on~ cycle with thi~ approach. Sen~or ~ 7~30~
module3 lO indicated by the notatlon~ RDT ~n~ RDT

(ln accordance with conventlonal difrerent1al transformer b~nk relay protectlon notatlon) are mounted on the primary and secondary sldes o~ tran~former bank 276. The~e modules replace the current tran~ormer 1nputs of a power tran~former bank dif~erent1al relay.
The ¢urrent slgnal~ o~ sensor modules DT~A and DT
are recieved by CRTU 14 and compared in the miaroproces~or. If there i9 a need to provide a lo separate relaying ground statlon due to utillty operatlng practlces, the CRTU for the relaying functlon alone may be s1mpllr1ed to the form ~hown in Flgure 17.
The differential ourrent ~ignal mea~ured, lr above the relay ~ettlng, 1~ u~ed to dr~ve a digltal relay.
Alternatively, the digital signal i3 converted in D/A
converter 278 and u~ed to actuate an analog relay. The RF signals to and from the lndividual ~en~or module~ can be replaced by an optical cable, and converted to analog electrical ~ignals that driv~ a di~ferentlal op-amp which provides a driving signal ~or a dirferential relay clrcult above a pre-determined thre~hold. A~ al30 ~hown in Figure 17, bu~ dif~erentlal relay protectlon can be perrormed in a similar manner by communicatin~ the current signals from ~en30r module~ RDT1~, RDT2B and RDT3B (and other 9en90r module~ connected to the same bus) to the ~ame ground stat10n and comparing the signal~ digitally to determlne 1~ the dif~erence exoeed~
a pre-~et thre~hold.

,. ., . .. ~.. . . . . . . .. ., ..... . ~ . . .. . . . ... . .

~ 7~3~

If the transcelver sensor modules are to be mounted on lnsulated dL~trlbutlon conductors, a special hub i9 used. Such a hub i9 ~hown ln Figure 18, having 3harp metal protrusions 280 extendLng Yrom hub inner rlng 70, 72 (Flg. 5), through insert 66, 68 to pierce the conductor lnsulatlon 282 and to provida a conducting path between the lnner rlng 70, '72 and tho conductor.
Alternatively, a bucket crew using rubber ~loves could mount the sensor module over a ~tripped portlon of the 10 aonduotol~.

Claims (29)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A compact system for installation on and removal from energized AC power conductors and accurately measuring the voltage on each of a plurality of AC power conductors, said system comprising:
(a) a plurality of sensing means one of which is mounted upon each of said conductors and including means to measure said conductor voltage simultaneously by all of said sensing means at a plurality of predetermined times;
(b) signal transmitting means associated with each of said sensing means to transmit signals commensurate with said conductor voltage at each of said predetermined times;
and (c) signal receiving and processing means for receiving said transmitted signals and calculating therefrom the true value of said voltage on each of said conductors after correcting the received signal for any influence of adjacent conductor on said measured voltage.

2. The invention according to claim 1 wherein said sensing means includes a metallic housing mounted in surrounding relation to and conductively isolated from the associated conductor, upon which it is mounted whereby a charging current is present on said housing due to the electrostatic field of said associated conductor, and said conductor voltage is measured by sensing said charging current.

3. The invention according to claim 2 wherein said influence of adjacent conductors comprises the charging current present on said housing of any one of said sensing means as a result of the electrostatic field of any conductors adjacent to said associated conductor.

4. The invention according to claim 3 wherein said energized conductors have at least one adjacent conductor which may be energized or deenergized and said processing means includes scale factor storage means responsive to the state of energization or deenergization of each of said adjacent conductors.

5. A system for monitoring the rate of change of a cyclically variable parameter of an energized electrical power conductor and for actuating ground station control means in response to a predetermined abnormal rate of change of said parameter, said system comprising:
(a) a sensor module for mounting upon and removal from said energized conductor, and carrying means for sampling the value of said parameter at each of a plurality of evenly spaced times within each cycle of said parameter, and for storing the sampled values;
(b) means carried by said module for comparing said stored values with the sampled values at corresponding points in successive cycles of said parameter and determining whether the difference between said sampled values and said stored values indicates said predetermined abnormal rate of change;
(c) means carried by said module for transmitting an alarm signal in response to said abnormal rate of change; and (d) ground receiver means remote from said module for receiving said alarm signal and actuating said control means in response thereto.

6. The invention according to claim 5 wherein said transmitting means includes means to transmit signals on either of first and second transmission channels, and means responsive to said comparing means to cause said transmitting means to transmit on said first and second channels when said difference indicates the absence and presence, respectively, of said abnormal rate of change.

7. The invention according to claim 6 wherein said transmitting means comprises an RF transmitter having at least two crystals for respective transmissions on said first and second channels.

8. The invention according to claim 7 wherein said remote means includes means for receiving and processing signals transmitted on each of said first and second channels and for actuating said control means in response to signals received on said second channel.

9. The invention according to claim 8 and further including means to disable transmission on said first channel, thereby permitting immediate transmission on said second channel, in response to said abnormal condition.

10. The invention according to claim 5 wherein said module further includes means for varying the duration of said evenly spaced times, and thereby the interval of said sampling, to sample at shorter intervals in response to said parameter varying at said predetermined abnormal rate of change.

11. The invention according to claim 10 wherein the number of samples within each cycle is variable in response to a predetermined rate of change of said parameter within a cycle.

12. The invention according to claim 11 wherein the number of samples within each cycle is increased by a pre-determined multiple in response to a predetermined increase in the rate of change of said parameter.

13. The invention according to claim 10 wherein said sampling means is constructed and arranged to sample at least one harmonic of said parameter, and said sampling interval is proportionate to the frequency of the harmonic being sampled.

14. The invention according to claim 5 wherein said control means comprises means for actuating operator alarm means.

15. The invention according to claim 14 wherein said operator alarm means comprises a remote telemetering interface for communicating said alarm signal to a location remote from said ground receiver means.

16. The invention according to claim 5 wherein said control means comprises a relay actuable to interrupt the circuit including said power conductor.

17. The invention according to claim 5, wherein said transmitting and receiver means comprise a fiber optic communications link.

18. A system for wireless sensing of current differen-tial across the primary and secondary windings of a power transformer bank to provide differential relay protection of said power transformer bank, said system comprising:
(a) a sensor module for mounting upon and removal from each of the energized conductors which are connected to said primary and secondary windings, said modules carrying means for measuring the current flowing through its associated conductor;
(b) means for causing said modules to measure the current on its associated conductor simultaneously;
(c) means for transmitting signals from said modules commensurate with the value of current measured thereby;
(d) means remote from said modules for receiving and comparing said signals all within the time constraints required for effective differential relay protection; and (e) means for operating a differential relay in response to the difference between said compared signals exceeding a predetermined threshold level.

19. The invention according to claim 18 wherein said time constraints comprise a time period not greater than that of 3 successive cycles of said current.

20. The invention according to claim 19 wherein said remote means further includes means for transmitting time-synchronizing signals, and said modules include means for receiving said time-synchronizing signals and for measuring said current and transmitting said signals commensurate with the value of current at times established by said time-synchronizing signals.

21. The invention according to claim 20 wherein said time-synchronizing signals are transmitted through the air.

22. The invention according to claim 20 wherein said means for transmitting said time-synchronizing signals comprise means coupling said remote means with said power conductors and said time-synchronizing signals are transmitted using power line carrier injection.

23. The invention according to claim 20 wherein said means for transmitting and receiving at least one of said time-synchronizing signals and said signals commensurate with the value of current comprise fiber optic communication links.

24. A system for wireless sensing of current differen-tial on first and second pluralities of electrical conductors carrying current to and from, respectively, a singled bus to provide differential relay protection of said bus, said system comprising:
(a) a sensor module mounted upon each of the conductors of said first and second pluralities, said modules carrying means for measuring the current flowing through its associated conductor;
(b) means for causing all of said modules to measure the current on its associated conductor simultaneously;
(c) means for transmitting signals from said modules commensurate with the current measured thereby;
(d) means for receiving and comparing said signals from modules on said first plurality of conductors with signals from modules on said second plurality of conductors; and (e) means for operating a differential relay in response to the difference between said compared signals exceeding a predetermined threshold level.

25. An integrated system for performing metering functions by both wireless and hard-wired sensing means at an electrical power substation, said system comprising:
(a) a plurality of individual sensor modules each mounted upon one of a first plurality of power conductors at said substation, each of said modules including means for simultaneously measuring each of a plurality of variable parameters, including d voltage and current, associated with operation of said first conductors;
(b) means for time-synchronizing the measurement of said parameters by said plurality of modules, whereby each of said modules measures the value of the same parameter at the same time on its associated conductor;
(c) means for transmitting first metering signals commensurate with the values of said parameters from said modules;
(d) a ground station having means for receiving and processing said signals from said modules;
(e) said ground station further including means for receiving substation analog signals, and conditioning signals from existing current and potential transformers, processing the values of current and voltage on a second plurality of conductors and generating second metering signals in response thereto;
(f) means for multiplexing said second metering signals for processing at said ground station; and (g) means at said ground station for integrating in a single processor the processing of said first and second metering signals.

26. The invention according to claim 25 wherein said ground station further includes means for monitoring alarm status, sequence-of-events, and performing select-before-operate control functions through interposing relays, pulse control and means for processing non-metering analog and pulse/digital signals.

27. The invention according to claim 25 wherein said ground station further includes means for establishing from said first metering signals whether each of the conductors of said first plurality is energized, and means for selecting an appropriate scale factor to be applied to the voltage reading of each of said sensor modules in accordance with the state of energization of adjacent conductors.

28. A system for monitoring a plurality of parameters associated with each of a plurality of energized electrical power conductors of a power delivery network over the full operating range from minimum to maximum conductor current, said system comprising;
(a) a plurality of sensor modules for complete install-ation and removal while said conductors are energized, one of said modules being mounted upon each of said energized con-ductors;
(b) means carried by each of said modules for sensing values of a plurality of parameters of the associated power conductor;
(c) means carried by each of said modules for identify-ing, processing and storing said sensed values;
(d) means carried by each of said modules for periodi-cally transmitting a sequence of encoded signals in data bursts of predetermined duration from each of said plurality of sensor modules commensurate with each of said sensed values;

(e) means carried by each of said modules for controlling the starting times of said data bursts by said transmitting means of each of said modules to avoid simultaneous transmission, with consequent data collisions, by any two of said modules;
(f) means remote from said modules for receiving said signals from each of said plurality of modules and decoding said signals to provide said parameter values at said remote means, and to derive from said values operational status information, including normal, abnormal and transient operating conditions,about said power conductors; and (g) means for controlling said power delivery network over said full operating range during all of said normal, abnormal and transient operating conditions, in accordance with said operational status information.

29. A method of monitoring and controlling a power delivery network having a plurality of power conductors over the full operating range from minimum to maximum conductor current, said method comprising;
(a) mounting upon each of said conductors a sensor module;
(b) measuring a plurality of parameters of each of said conductors by the module mounted thereon;
(c) transmitting from each of said modules to a remote receiver a sequence of encoded signals in data bursts of predetermined duration indicating the values of said measured parameters and module identification;

(d) controlling the starting times of said data bursts to avoid simultaneous transmission by any two of said modules;
(e) deriving from said values operational status infor-mation, including normal, abnormal and transient operating conditions, about said power conductors; and (f) controlling said power delivery network over said full operating range during all of said normal,abnormal and transient operation conditions, in accordance with said operational status information.