ISSN 10683712, Russian Electrical Engineering, 2011, Vol. 82, No. 9, pp. 455459. Allerton Press, Inc., 2011.Original Russian Text V.V. Khudyakov, 2011, published in Elektrotekhnika, 2011, No. 9, pp. 611.

455

The development of electricity transmission startedwith the construction of the first threephase aerialline (AL) LauffenFrankfurtamMain, Germany,implemented in 1891 with the help of the Russianengineer M.O. DolivoDobrovolskii. The voltage ofthe line was 15 kV, and the length was 170 km.

Only the voltage, length, and transmission capacity, i.e., the only scale, have changed in past 120 years.Despite the considerable progress that has been madein communication, computation, space, and information technologies, there has been no progress in powertransmission with alternating current observed in thelast 120 years.

This is explained by the fact that construction ofelectric stations and electricity transmissions requirelarge expenditures of time and money and a largenumber of specialists and workers involved. As is notedin periodicals, the growth of the load value in energysystems precedes the growth of input power of powerstations, and the authors expect that the worlds needfor electrical power will triple by 2050.

DISADVANTAGES OF EXISTING NETWORKS

The disadvantages of existing networks includelines and equipment aging, insufficient carrying

capacity of lines;deficit of reactive capacity;mistakes with operating material;delay of information on the state of electric sys

tems transferred to the dispatcher, etc.;on the order of 20% of the installed capacity of

the electric power station is used to cover the maximalload and used over 5% of the year; thus, the existingelectric network is not effective in general.

The multiple breakdowns in power systems of different countries in recent years are explained by theseand other reasons. At the end of the previous andbeginning of this century, due to successes in produc

tion of highpower industrial transformers, differentnetworks of transformers were developed; they allowedtotal or partial elimination of the disadvantages ofelectricity transmission of alternating current. Thesenetworks include transformers for transmission andinserts of direct current (TDC) and (IDC) and controlled with thyristors latitudinal and longitudinalcompensating devices of electricity transmission ofalternating current that enhance their qualities andincrease carrying capacity and controllability.

Electricity transmission of alternating currentequipped with thyristorcontrolled buckingout unitsis called flexible electricity transmission of alternatingcurrent (FETAC). These buckingout units are used incases in which they are technically and economicallyjustified. Despite the considerable technical advantages of these devices, they are yet rather expensiveand, thus, they are not in mass production. The existing networks still have disadvantages.

ENHANCEMENT OF POWER SUPPLY NETWORKS

At present, in all countries, the practice of maintaining networks according to instructions is beingreplaced with maintenance in case of need. Substations are equipped with systems controlling the equipments state, allowing one to detect a state close tofailure and repair it on time or replace only equipmentthat may fail quickly. This technique allows one toreduce costs for repair and maintenance of substationsand increase the reliability of electric networks operation. In particular, remote temperature measuringdevices are used that allow one to determine hot pointsat transformer tanks, weak contacts that are heateddue to increased resistance, broken insulators, andother weak points of the equipment and contacts at asubstation.

A delay in obtaining information on the currentstate of the power system transmitted to the dispatchervia communication channels is one of the disadvan

Increasing the Reliability of Electric NetworksV. V. Khudyakov

Received August 22, 2011

AbstractA review of Russian and American periodicals on the reliability of electric networks is carried out.New measures to increase the reliability of electric power supply of consumers are described.

Keywords: phase measuring units, reserve supply sources, distributing generators, satellite communication,micronetworks.

DOI: 10.3103/S1068371211090070

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tages of existing networks. First, this information isbased on calculations of system states carried outaccording to corresponding mathematical modelsbased on the date of the systems design and ratings ofthe equipment provided by manufacturers. The precision of these data is usually higher than 10%. Second,when developing any mathematical model, allowances are made that influence on the precision.

To enable the dispatcher to receive data on theoperation of the system constantly and trace thechanges in the mode promptly, devices for measuringthe amplitude and phase of voltage and current vectorswere developed; they receive a signal from the measuring transformers of voltage and current installed at different substations of the power system. These measuring units, called phase measuring devices (PMDs),have become widely used in different countries. Measuring the amplitude and phase of electric values in thesystem eliminates the mistakes noted above and allowsone to move on from estimation of the systems state tomeasuring its state in real time, excluding time in iterations. At the same time, the real state of the system isreflected online at the display of the dispatcher.

Phasemeasuring units are produced as individualdevices or are integrated into existing relay and automatic units. The phasemeasuring unit receives a signal from the measuring voltage transformer, which iscompared to basic cosine voltage ub of standard frequency f = 50 Hz (or 60 Hz) that has zero initial phaseand is used in any point of the network. At the sametime, the frequency must be nominal and time mustcorrespond to standard international time. In the process of measuring the voltage phase, the amplitude ofthe voltage in any point of the network is conditionallyassigned to be equal to the amplitude of basic voltageUm and the shift angle relative to basic cosine curve isdetermined by phase measuring unit and its soughtvalue. The true effective value of the measured voltageis also measured and is given to the dispatcher [1].

The basic cosine curve is

(1)

or in vector form,

(2)

The instantaneous value of the voltage in somenode A of the network can be determined relative tothe basic voltage as

(3)

or in vector form,

(4)

where is the initial phase of the cosine curve of voltage uA.

This will be the voltage vector at the currentmoment of time measured with a phasemeasuringunit (Fig. 1). The individual voltage vector uA is not ofinterest. To estimate the state of the system, a voltagevector in another point of the system is required; i.e.,the angle between vectors in different points of the system is required. Each phasemeasuring device canusually control up to eight different parameters: voltages, currents, frequencies, and moment of measuring. All these data must be synchronized with international standard time.

Let us consider a method of measuring voltage atsubstations of transmission line with the use of phasemeasuring units by Schwitzer Engineering Laboratories Inc. (SEL, United States) [2] (Fig. 2). At eachsubstation of the transmission line, the phasemeasuring devices PMD1 and PMD2 are integrated into theunit of automatics and transmission protection P1 andP2 (Fig. 2a). A voltage signal goes to the automaticsunit from a voltage transformer. A signal of precisestandard international time (SIT) arrives at an electronic clock via a communications unit and is transferred to the phasemeasuring device. The precision ofthe electronic clock is 0.1 s. The error of the phasemeasuring voltage vector with a phasemeasuringdevice is less than 1%.

In the United States, a standard IEEE Synchphasor Standard C37.1182005 of measuring phases ofvoltage and current vectors has been developed,according to which the precision of measuring phasesof vectors relative to the true value must be above 1%[1]. A sinusoidal signal received from a measuringvoltage transformer (VT) is processed using discreteFourier transformation in several periods at a normalfrequency of the network. With deviations of frequency of nominal value, corresponding errors indetermining phase of vectors are adjusted, whichallows one to obtain results with the required precisionand use them in the system of measuring electric values (SME) over a large area.

ub Um tcos=

Ub Umej90

.=

uA Um t +( )cos=

UA Umej 90 ( )

,=

5

Umub

t, s

+j

90

+l

u

uA UA

Fig. 1. Determining phase of voltage vector in node Aof the network with use of a phase meter ( [2008] IEEE).

UA

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INCREASING THE RELIABILITY OF ELECTRIC NETWORKS 457

Measuring the phases of vectors is carried out witha frequency from 6 to 60 measurements per second. Tocompare, the existing system of automatics and dataprocessing (SAP) updates data every 25 s. Units ofautomatics and transmission protection P1 and P2carry out measuring and controlling functions. Theycan be programmed to control such events as increasing the deviation of voltage at a substation below orabove the normal value, deviation of frequency, poweroscillations, unbalanced of loading in the system, etc.Together with signals from transformers of current andvoltage, measured values of active and reactive powerat branches of the network can be received, i.e., resultsof measuring states of the system at the currentmoment of time: voltages in nodes and power inbranches.

In Fig. 2b, vector diagrams of voltages at the transiting and receiving ends of the transmission linereceived with the use of phasemeasuring devices areshown. They allow one to determine phases 1 and 2of voltage U1 and U2 relative to the basic cosine curveUb. Angle of shift = 2 1 between these two vectorsis an important characteristic of transmitted activepower via a line, and it determines the limit of thispower based on static stability.

Figure 3 shows curves of changes in phases 1 and2 of voltage U1 and U2 vectors in time and the warningalarm signal given to the dispatcher if the angle grows

and reaches a critical value cr after which the breakdown of the system is possible [2]. If we take a specificsubstation as a basis to calculate the shift angle of thevoltage vector, then phases of voltage vectors at othersubstations of the system can be determined relative toa certain substation and the basic cosine curve of voltage, which allows the dispatcher to see the state of theentire system at each moment of time with a certainprecision and in certain intervals of time, there is asimilar situation for currents in lines of the network orloads.

In Fig. 4, an example of a power system consisting ofpower supply network C1 and substation s/st 1s/st 3connected with transmission lines of 500 kV withphasemeasuring devices PMD1PMD3 integratedin each substation is shown. Each phasemeasuringdevice receives an SIT signal via communications satellite SC, an electronic clock determines the phase ofvoltage of substation where it is installed, and thisinformation is transmitted to a receiving and dataprocessing unit (RDPU) located at dispatcher centerDC1. The RDPU processes the received informationin a form convenient for the dispatcher. This information arrives at the display of the dispatcher and is usedfor operation. Part of this information is transferred toarchive and part to another dispatcher center DC2 viachannels of the local Internet connection for dataexchange.

The task of the dispatcher of the power system is tocontinuously trace the mode of the systems operationand provide a balance of active power in the system incoordinate system P, f, U and the balance of reactivepower in the system with coordinates Q, f, U. In theemergency mode, the dispatcher must take measuresto bring the system back to the preemergency mode asfast as possible. As both the circuit and modes of system change continuously, the use of phasemeasuringdevices with data updated up to 60 times per secondwith high precision allows the dispatcher to carry outits responsibilities much more effectively than whenusing SAP to secure a mode of operation close to the

SC

PMD1 Ch

P1 P2

VT1 VT2

C1 C2

PMD2Ch

A A

(a)

(b)

U11

U2

2

Ub

S1 S2

Ub

U2

U1

U1

U2

Fig. 2. System of the phasemeasuring unit (PMU) atreceiving (C1) and transmitting (C2) substations of thetransmission line for measuring the shift angle between

voltage and at ends of the line: (a) the circuit of the

system (A is clock antenna, Cl is clock); (b) vector diagrams of voltages in the line ( [2008] IEEE).

U1 U2

3011:00

50

70

90

110

11:15 11:30 11:45 12:00 12:15

Alarm

cr

Time, h : min

signal

1

2

Fig. 3. Measuring phases of voltages and (1 and 2)at the ends of the transmitting line and determining limit shiftangle cr between them (http://www.seline.com).

U1 U2

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KHUDYAKOV

limit of static stability and increase the reliability ofelectricity supply to consumers.

METHODS OF PROTECTION OF DISTRIBUTIVE NETWORKS

FROM BREAKDOWNS IN THE POWER SUPPLY NETWORK

The considerable growth of load of consumers anddelay in implementing new power units lead to areduction of static stability reserves in power systems.Thus, any, even insignificant, overloads in networkscause breakdowns, frequently cascade breakdowns,according to the domino principle. As, to date, systemautomatics has been introduced only to a level of 1520% in distribution networks, they appear to be theweakest link of the power system. At present, measuresare being taken to equip distributive networks withrequired automatics and new power sources, distributive generators, energyaccumulating devices, and, insome cases, reserve power supply sources in particular.

Domestic loads and small industrial enterpriseswith power of up to 10 MW are the main consumers ofthe distributive network. Thus, reserve supply sourcesusually have a power of up to 10 MWt and are locatedin different points of the distributive network. In the

case of distributive networks, there is a return to thebeginning of development of power systems: a sourceof electric power is installed at the consumer. A newfactor is the sources; these are mainly generators withrenewable energy sources (RESs) using water, wind,solar, and new types of accumulators and other meansof electricalenergy accumulation. These sources ofpower located in different points of the distributive lineare called distributive generators (DGs). In somecases, DGs are used as reserve power sources that areswitched on automatically when the distributive line isdisconnected with the stepdown substation. Eithercold or hot reserves are used.

It is well known that the load of consumers of anelectric network is subject to occasional changes. Thediagram of load is nonuniform and usually has twopeaks: morning and evening. In the existing network,the dispatcher of the system can only provide for thischanging load, covering peaks of load by increasingthe power of generators or switching on the reserves.

The transition to controlled changes in load withfeedback dispatcherconsumer (requestresponse) isa new approach. The dispatcher does not simply provide the power required to the load, but also has thepossibility of limiting consumption of electric power inmaximal load hour by either notifying the consumer orcontrolling the release price for electric power, whichis considerably higher at the maximal load hour. Thedispatcher now can shift the load over the day, depending on the available power of the system, which allowsone to smooth the peaks of the load diagram.

The consumer can receive information on powerconsumption over time past and the price of this electricpower via the Internet. Newgeneration electricitymeters allow one to change the price of electric powerdepending on the time of day and available power in thesystem. If the consumer has personal power sources,e.g., solar batteries, then it can sell excess power to thepower system and the new electricity meter will takeinto account the price of the sold power in its bill.

MICRONETWORKS OF SMALL CONSUMERS

Micronetworks are electric networks of small consumers. These may be networks of moderate voltage(169 kV) or low voltage (up to 1 kV). They may beprivate houses, commercial industries, educationalinstitutions, etc., with power of up to 10 MW. Micronetworks are supplied from the distributive networks,but they have their own reserves, which provide electricity supply to all or some of consumers whenmicronetworks are disconnected from the distributiveline; i.e., these networks are totally or partially autonomous.

Consumers of micronetworks can buy electricpower from the distributor or sell excess power. Themicronetwork has a personal system of automatic control and protection and retains the voltage level, distri

SC

PMD1 C1

s/st 1

PMD2

s/st 2 s/st 3PMD3

DC1 RDPU archive

DC2

Fig. 4. Circuit of the power system consisting of power supply network C1 at the substation s/st 1s/st 3 connectedwith lines of electricity transmission of 500 kV with phasemeasuring devices PMD1PMD3 installed at each of thesubstations. is a communication channel(http://www.selinc.com).

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INCREASING THE RELIABILITY OF ELECTRIC NETWORKS 459

bution of load between consumers, control of frequency, and active power of autonomous generators.In the case of emergency disconnection of themicronetwork from the power supply, it automaticallyswitches to a mode of autonomous operation so thatconsumers do not lose voltage.

The United States, Germany, and Japan havestarted using micronetworks for supplying houses. InFig. 5, a future micronetwork of a house is shown thatcan be implemented at present [3]. The house is supplied from a reducing transformer connected to thedistributive line and has a number of personal supplysources, allowing not just supply to all the loads, butalso reversing the power flow to the power supply network. All supply sources and loads are controlled witha system of control and automatics that provides uninterrupted power supply to the house independently ofthe power transformer.

The concept of the micronetwork may be related tothe reducing substation of distributive network andradial distributive line. In Russia, micronetworks canbe used for both individual small consumers and forgroups of consumers, e.g. villages, educational institutions, hospitals, etc. Diesel or gasolineelectricequipment is usually used as the reserve supplysources, and their energy is very expensive. In theLenin VEI, sliver microHESs are being developedthat can be used at any natural water channels andwater reservesLuch1 with a power of 1 kW and

Luch2 with a power of 2 kW [4]. These microHESsare simple to control and reliable in exploitation; theirinstallation and starting up can be carried out by people without special qualifications. The payback periodof microHESs with a power of 1 kW relative to gasoline equipment is less than 3 months.

CONCLUSIONS

In respect to the conditions of Russia, the followingconclusions can be drawn:

(1) Wide use of phasemeasuring devices isrequired to provide dispatchers with operating information on the powersystem operation, which hasbeen implemented in Russia for a number of substations.

(2) In Russia, hydroelectric power engineering hasbeen undeservedly held back, Russia has huge hydropower resources in the form of large rivers. Siberia andthe Far East alone have resources of more than 700 billion kW h. Undoubtedly, under conditions of worldwide financial crises, the development of hydropowerengineering is complicated, but the development ofsmall HESs, and even microHESs, is quite possibleaccording to the designs of the Lenin VEI, which willfurther develop dispersed generators.

(3) In connection with ineffective heat generationwith multiple boilers, it is required to increase theireffectiveness by means of electric power generationand also develop construction of ATETs.

(4) New achievements in development of convertertechnology allow one to use inserts of direct current asbuffer devices for asynchronous communicationbetween individual joint power systems and betweenformer republics of the Soviet Union, which not onlyincrease the reliability of power supply, but also simplify arrangements for power exchange between thenew countries.

REFERENCES

1. Martin, K.E. and Carroll, J.R., Phasing in the Technology, IEEE Power Energy Mag., 2008, vol. 6, no. 5,pp. 2433.

2. Complete Synchrophasor System: SEL Sinchrophasors. Flyer (3). A New View of the Power Systems,Available from: http://www.selinc.com

3. Kroposki, B., Margolis, R., and Ton, D., Harnessingthe Sun, IEEE Power Energy Mag., 2009, vol. 7, no. 3,pp. 2233.

4. Mavlyanbekov, Yu.U., Alekseenko, V.N., andSimakin, V.V., Analysis and Prospects of Developmentof Renewable Sources of Power in Russian Federation,in Sbornik nauchnykh trudov VEI im. V.I. Lenina (AllRussian Electrotechnical Institute Named afterV.I. Lenin. Collection of Scientific Papers), Moscow,2006, pp. 181188.

12

3

4

5

67

8

9

10

11

12

~=

Fig. 5. Micronetwork of a house or commercial enterprise: is a power cable, is a communication

channel, 1 is dispatcher of the system, 2 is a distributionnetwork, 3 is a power supply reducing transformer, 4 is aphoto cell on the roof of the house, 5 is a meteorology station, 6 is a unit of control, communication with dispatcher,and maintenance, 7 is a panel of automatic and control ofthe house micronetwork, 8 is a computer in the house, 9 isan accumulator, 10 is an inverter, 11 is a load of the house,and 12 is a hybrid electric vehicle in the garage ((2009,IEEE)).