Josifs Survilo

A Ringed Non-Uniform Network: How to Raise its Efficiency

A Ringed Non-Uniform Network: How to Raise its Efficiency As distinct from radial electric power lines, in closed loops the consumers are fed from two sides. This is advantageous from the viewpoint of supply reliability, power quality and its losses; however, these are the least only when a loop is uniform, which is not always met in practice. In a non-uniform loop a circulating current flows, and the losses increase proportionally to its square. To reduce losses in such a non-uniform loop, the circulating current should be eliminated. For this purpose a booster transformer can be used. The voltage of such a transformer is known to be in quadrature to the phase voltage; the present consideration has shown that such orientation of the opposing voltage gives the best results only when all loads in the loop are active, otherwise the angle of opposing voltage should be regulated. The voltage value should also be regulated depending on the load. Another technique consists in introducing a complementary reactance into the terminal branches. Such reactance should be regulated if loads are changing in time disproportionately with respect to each other. The best results are achieved when all loop node loads have the same cosφ. If the complementary reactance calculated at one end of the loop is positive, then that calculated at the second end of the loop will be negative, and vice versa. The appropriate choice can be made, in particular, involving both loop terminals. Slēgtie Gredzenveidīgie Tīkli, to Efektivitātes Paaugstināšana Atšķirībā no radiālajām elektriskajām līnijām slēgtajā gredzenveidīgā tīklā patērētāji tiek baroti no divām pusēm. Priekšrocība ir tā, ka ir lielāka elektroenergijas piegādes drošība un labāka elektroenergijas kvalitāte, kā arī mazāki elektroenergijas zudumi. Bet zudumi ir mazāki tikai tad, ja tīkls ir homogēns, kas ne vienmēr īstenojas praksē. Nehomogēnajos tīklos ir cirkulējošā strāva, un zudumi palielinās par lielumu, proporcionālu cirkulējošās strāvas kvadrātam. Lai samazinātu zudumus nehomogēnajā gredzenā, ir jānovērš cirkulējošā strāva. Šim nolūkam lieto būstertransformatoru. Ir pieņemts, ka būstertransformatora spriegums ir vērsts taisnā leņķī pret fāzes spriegumu. Šie pētījumi parādīja, ka šādi var iegūt vislabākos rezultātus tikai tad, kad visas līniju gredzena slodzes ir aktīvas, citādi leņķis ir jāregulē. Arī sprieguma vērtība jāregulē atkarībā no slodzēm. Cirkulējošo strāvu var arī novērst, ieslēdzot sākuma zaros papildus reaktīvo pretestību. Šī pretestība ir jāregulē, ja slodzes mainās laikā neproporcionāli savā starpā. Vislabākais rezultāts ir sasniegts, kad visām gredzena mezglu slodzēm ir vienāds cos φ. Ja papildus pretestība, rēķināta pie viena gredzena gala, ir pozitīva, tad papildus pretestība, rēķināta otrā gredzena galā, būs negatīva un otrādi. Jāizvēlas labākais variants, tai skaitā izmantojot abus gredzena galus.

Determination of reciprocal current by electricity delivery to more than one consumer

To determine the payments for delivered electricity and the power losses arising from the supply of electricity, the amount of electricity delivered from a power station to a certain consumer (reciprocal power) should be known. This to be realized requires tracing the flow of electricity. The superposition principle can be applied. The network is represented by generator nodes and consumer nodes connected by transmission line or by network branches. Generator nodes are fed by generator currents, consumer admittances determined at normal power flow mode are connected to consumer nodes. This circuit is energized by all generators in turn sending to their nodes currents equal to those in normal operation mode. Reciprocal current of a specific consumer node and a given generator is determined out of voltage across this consumer and its admittance. Reciprocal power loss then is determined by method of reciprocal current increments.

Transformer design according to criteria and load profile

Transformer efficiency, which has an impact also on the environment, involves minimum of transformer power losses. The losses are main factor also in transformer owning cost. They are minimal when ratio κ of load loss to no-load loss assumes a certain value. This value depends on how transformer load changes when operating a transformer. However, for minimum of transformer losses and its owning cost minimum, the ratio κ is different. The owning cost (total) of a transformer is determined more accurately; for this, to optimization is brought not only transformer loss price but the price of transformer active materials as well.

Optimal territory of renewable fuel collection for cogeneration plant

Secure and long-term supplies of low-cost feedstocks are critical to the economics of biomass power plants. Provided that the distribution of electricity and heat infrastructure already exists, cogeneration plant (CHP) costs depend mainly on the investment, biomass distribution density and price as well as biomass transportation cost. On sufficiently large space it is possible to operate with the average values of biomass density. The cost of transportation depends on the size of biomass collection territory, which monotonically increases with collection territory growth. The benefit index - ratio of CHP income to expanses - is the maximum at some optimum value of the territory. Proposed model of transportation cost allows optimizing the size of territory feeding the cogeneration plant with biomass.

A method for node prices formation

Proposed by producers price is a major factor in determining the nodal price, next transport losses, congestion costs and other paying. In the paper, main attention is paid to accounting producer prices and losses to the node in question. Each producer sends its share of power (reciprocal power) in the considered node while on the road he needs extra energy (reciprocal losses) to reach the node. Thus consumer which feeds from the node is to pay for received energy and the losses of its transportation to the node. The reciprocal power is defined by proposed node voltage method but reciprocal losses are defined by node current increment method. Reciprocal losses can rarely be also negative, that is caused by redistribution of the branch currents in a closed network. Nodal price takes into consideration all suppliers by calculating an average value. If congestion is expressed by current limitation in a line, then there is additional condition that causes recalculation of reciprocal quantities.

Factors affecting the value of network medium voltage

In distribution network low voltage nominal is defined by consumer but medium voltage nominal can be selected at discretion which is different in various countries. If the costs of network is not sensitive to medium voltage nominal, then, obviously, the lower the voltage the better. The studied model showed that costs abruptly diminish with load density and/or sizes of fed zones growing (up to certain limit), cost and voltage losses are little sensitive to voltage nominal at uniform load density, cost only slightly growing with medium voltage. While at non-uniform load density (when thick load alternates with sparsely populated area) the network costs are critical to medium voltage due to voltage loss, the latter strongly diminishing with medium voltage growing, making it possible to increase medium voltage fed zone. AH the above is dominated by equipment prices and other economic indices.

Delivery of electricity to cluster-like consumers

To decide how to deliver electricity to cluster-like consumer, the cost of two options should be compared. In the first option, transformerless one, the cluster is connected by LV line (stem) to the central MV/LV transformer; if conductance of all conductors is the same, minimum annual cost is secured when current densities in stem and in cluster lines are equal. Cost minimization is made considering the derivative of curtailed costs observing that maximum voltage drop and current densities do not exceed admissible values. In the second option, MV/LV transformer located at the cluster is connected by MV stem to the center and cross-sections of the MV stem line and of the cluster lines are defined in a usual way. Most of the annual cost falls on the cluster transformer.

Extra Losses in Imperfect Closed Grids

Extra Losses in Imperfect Closed Grids Closed grids consist of two-terminal power lines or/and of rings (loops). In non-uniform two-terminal lines, equalizing and circulating currents appear, in rings - circulating current. These currents cause extra power losses. Those losses are equal to the product of summary resistance and squared said extra currents and are independent of the direction of said currents. Equalizing current causes considerable losses by phase discrepancy of terminal voltages even when voltage magnitudes are equal. Equalizing current losses do not exceed 1/4 of load losses when terminal voltage difference is equal to maximum load voltage loss. The degree of non-uniformity of inhomogeneous rings can be estimated by inhomogeneous factor. The increased reliability and higher electricity quality in distribution grids can be attained by use of uniform or ameliorated ringed grids but the reservation can be implemented by controllable links between adjacent rings.

Compensation for Non-Uniformity in a Meshed Electrical Network

Compensation for Non-Uniformity in a Meshed Electrical Network Non-uniform electrical networks (meshed included), providing more reliable supply of electric energy to consumers, have greater losses than uniform ones. To upgrade such a network by reducing losses, special measures are provided, which should be done at the least cost. An effective measure of the kind would be introduction of opposing voltage or complementary reactances in some branches of the network. In this case, to determine the required parameters, a non-uniform meshed network should be disintegrated into separate cells - closed loops with equivalent node loads, which are the sum of node loads and the flows not belonging to a given cell. Then the circulating power of all cells is calculated, and the cell with the maximum circulating power is selected to be upgraded. For this purpose, in this cell the pre-defined opposing voltage or complementary reactance is brought. If the total power loss in the network after the first step of upgrading is not satisfactory, a next similar step should be taken, and a next cell singled out for upgrading. Such cell upgrading should be continued until the total losses stop decreasing. Slēgto Elektrisko Tīklu Nehomogenitātes Kompensācija Slēgtiem elektriskiem tīkliem ir lielāks elektroapgādes drošums. Turklāt nehomogēniem slēgtiem tīkliem ir lielāki jaudas zudumi nekā homogēniem. Izstrādāti nepieciešamie tehniskie pasākumi, lai tos mazinātu. Tīkla dažos zaros ir nepieciešams ievadīt pretī vērstus eds avotus vai ieslēgt reaktīvo pretestību. Parametru noteikšanai nehomogēnie elektriskie tīkli jāsadala atsevišķās šūnās - cilpveida shēmās ar ekvivalentiem mezglu punktu slodzēm. Katrā no šīm slodzēm ietilpst reālā mezglu punkta slodze un incidentu zaru plūsmas. Pretēji vērsto eds lielumu vai reaktīvo pretestību ievada šūnā ar vislielāko cirkulējošo jaudu. Gadījumā, ja pēc pirmā aprēķinu soła tīkla summārie jaudas zudumi pietiekoši nesamazinās, tiek veikts nākamais aprēķinu solis un uzlabojumam izvēlēta cita šūna. Šūnu uzlabojuma process jāturpina tik ilgi, kamēr tīkla summārie zudumi turpina samazināties.