Compensation of reactive power electric draft at high-speed movement
The causes of non-symmetric modes in networks. Single-ended and non-sinusoidal modes. Compensation of reactive power. Power factor in the ac electric traction. Installation of the crosswise, longitudinal and transverse-longitudinal compensation.
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Today, the country conducted targeted actions for the further development of the transport capacity of the railway. In his book, "The global financial - economic crisis, ways and measures to overcome it in the conditions of Uzbekistan" President Islam Karimov said further development of industrial and social infrastructure as the most important factor in the country's modernization. Particular attention is paid to the development of a network of railways and roads. As emphasized by the President big tasks this year facing our railroad. In 2011, the need to continue its consistent efforts to improve the transport and logistics systems that will provide reliable domestic and international transit of goods through the territory of Uzbekistan. In particular, it is the construction of new railway lines in the country, is being reconstructed, and the electrification of the main rail transit stations, creation of new routes, taking into account the needs of passengers, short and convenient means of transport, upgrading and modernization of the rolling stock. reactive power electric traction
At the present time in the country introduced the high-speed movement of electric transport.
In connection with this question of reactive power compensation of electric traction at high speed movement was be urgent task.
Reactive power compensation can compensate for reactive power and traction load can be placed on the traction substations, anywhere in the traction network. Better utilization of the installed capacity of compensating devices is achieved when placing them in substations. The greatest economic effect of the compensating device which compensates the reactive power can be obtained by using it simultaneously to improve symmetry and voltage reduction of voltage and current harmonics.
1. The causes of non-symmetric modes
Symmetrical three-phase voltage system is characterized by the same magnitude and phase voltages in all three phases. When unbalanced voltage modes in different phases are not equal. Non-symmetric modes in networks arise for the following reasons:
1) uneven loads in different phases;
2) work unbalance lines or other elements in the network;
3) different line parameters in different phases.
The most common voltage unbalance occurs because inequality Phase load. In urban and rural networks 0.38 kV voltage unbalance caused mainly single-phase lighting and household electric appliances (EP) low power. The number of such single-EP is large, and must be evenly distributed in phases to reduce the asymmetry.
In the area of high voltage unbalance caused, as a rule, the presence of high-power single-EP, and in some cases, three-phase CE with unequal consumption in phases. The latter include the arc steel furnaces. The main sources of asymmetry in industrial networks 0,38-10 kW is thermal installation phase, ore-thermal furnaces, induction melting furnaces, resistance and high heating units. In addition, the asymmetric EP - it welders various capacities.
Unbalance operation of the network elements is called brief interruption of one or two phases of a short circuit (SC) or a longer shutdown in phase segregated repairs. A single line can be equipped with phase segregated control devices that disable the faulty phase line in those cases where the action is not successful because of the AR steady faults. In the vast majority of stable single-phase short circuit. Disconnection of the faulted phase leads to the preservation of the other two phases in the line. In a network with grounded neutral power supply by unbalance line may be acceptable and eliminates the construction of the second line of the chain. Unbalance can occur when disconnecting transformers. In some cases, a group made up of single-phase transformers, during a power failure of one phase may not be valid for two phases of the power supply. In this case, no need to install the backup phase, especially in the presence of two groups of single-phase transformers in the substation.
Inequality line parameters in phase takes place, such as lack of transposition in its elongated lines or loops. Transposition of support and are not reliable sources of accidents. Reducing the number of transposition of supports on-line defect and reduces its reliability. In this case, the alignment deteriorates parametrovfaz line for which usually applies' transposition. The influence of asymmetry of voltage and currents. The appearance of voltage and current feedback and zero-sequence 112, BUT, 12, 10 leads to additional losses of power and energy, and voltage losses in the network, which degrades the regimes and the technical and economic performance of its work. Reverse currents and zero sequence 12, 10 increase losses in the longitudinal branches of the network, and the voltages and currents of the same sequences - a cross branches.
Imposition of W and W leads k'raznym additional voltage deviations in the different phases. As a result, the voltage may exceed the allowed limits. Overlay 12 and 10 leads to an increase in the total currents in the individual phases of the network elements. In this deteriorating condition of their heating and decreased throughput.
The asymmetry of a negative impact on the workers and the technical and economic characteristics of rotating electrical machines. Positive sequence current in the stator produces a magnetic field rotating at synchronous speed in the direction of rotor rotation. Reverse currents in the stator produce a magnetic field rotating the rotor with dual synchronous frequency in a direction opposite to rotation. Because of this double frequency currents in the electrical machine having an electromagnetic braking torque and additional heating, mainly the rotor, resulting in shortened life of the insulation.
In asynchronous motors there are additional losses in the stator. In some cases it is necessary for the design to increase the nominal motor power, if not to take special measures for voltage balancing. In synchronous machines except the additional heat losses and the stator and rotor can start dangerous vibrations. Because of the asymmetry of reducing the life of isolation transformers, synchronous motors and BC decrease the production of reactive power.
The total damage caused by the asymmetry in industrial networks, including the cost of additional energy losses, increase allocations for the renovation of the capital cost, technological damage, damage caused by the decrease of luminous flux of lamps installed in phases with reduced voltage, and reduced lamp life, set in phases with a higher voltage, the damage due to the reduction of reactive power generated by the IC, and synchronous motors.
Voltage unbalance factor is characterized by negative sequence voltage
K2U = (U2 (1) / U NOM) Ч 100
coefficient of residual stresses K0U = (U0 (1) / U nom) Ч 100 normal and maximum allowable values, which according to GOST 13109-87 are 2 and 4%.
Balancing stress on the network is reduced to compensate for the current and the negative sequence voltage. With stable systematic reduction of load voltage unbalance in the network can be achieved by balancing load phases by switching the current load from congested phase in unloaded. Rational redistribution of loads does not always reduce the rate of voltage unbalance to an acceptable value (for example, when part of the high-power single-phase CE operating under the terms of technology is not all the time, as well as preventive and overhaul). In these cases it is necessary to use special baluns. A large number of schemes baluns, some of them performs a control depending on the nature of the load curve.
For single-phase load balancing scheme is used, consisting of inductance and capacitance. Load and connected in parallel to her capacity are included in the line voltage. On the other two line voltages includes inductance and another capacitance.
For the balancing of two-and three-phase unbalanced load scheme is applied with unequal capacities BC, included in the triangle. Sometimes using baluns with special transformers and autotransformers. Since baluns contain BC, it is advisable to apply such schemes, in which both Baluns mode and generates an orthogonal view to compensation. Device for the simultaneous balancing regime and compensation 0 are in development.
2. Single-ended and non-sinusoidal modes
The asymmetry of three-phase voltages and currents, any asymmetric system of three vectors (U and, Uvv and Uc or UVA, U AU and USV) can be decomposed sodium symmetrical systems: direct sequence U1
Fig. 1. The decomposition of the asymmetric system into symmetrical components phase rotation which coincides with the initial phase sequence of the reverse sequence U2 which is the opposite phase sequence and zero sequence U0, all the vectors that have the same direction (Fig. 1).
The impact of unbalanced voltages on the electrical system is the same as the three symmetric systems. The essence of this effect on the single-phase and three-phase EP different. For single-phase EP matters is the voltage of the phase to which they are connected. As means for controlling the voltage change at the centers of supply voltage the same in all three phases, the ratio between the voltage remains unchanged. As a result, the voltage range in all the phases can not be maintained in an acceptable range. Fig. 1 shows the case where the voltage UA - is at an acceptable level, UB-below, and (Uc - higher than acceptable.
For three-phase EP (for example, three-phase motors) the impact caused by the reverse phase sequence the negative sequence voltage. Given that typically U1 »U2, the motor rotates in accordance with the alternation of the positive sequence vector and the inverse has a braking effect on it. It is known that the resistance depends on the sliding motor rotor relative to the stator 5 and expressed by the relation shown in Fig. 2. In normal operation, the induction motor slip a little (s «1), and for simultaneous, s = O, so the resistance of the motor HD close or equal to Xc Stalled. S = 1 and the resistance drops abruptly to XK ratio XC / XK defines the multiplicity of inrush current (usually KP = 4/7).
With an increase in slip to s = 2 (field of the stator rotates in one direction and the other in the rotor, which is the case for the negative sequence currents) xA value remains almost unchanged compared to the s = 1, so you can take the feedback resistance of the motor sequence x г = x к .
Fig. 2. The dependence of the resistance Fig. 3.
Open loop phase
Motor slip vectors (a) and closed linear vectors (b)
This means that for the negative sequence currents in the resistance of the motor gearbox times smaller than a straight line. Therefore, for example, when an input to the motor gearbox 7 = negative sequence voltage (U2 = 5% reverse current in its windings is 35% positive sequence current, causing them additional heat.
The system of linear zero-sequence voltage can not be present, as opposed to the system of phase voltages, the amount of which is equal to three times the value of the residual voltage (Fig. 2a), the system of linear voltage necessarily closed (Fig. 3b) and the sum of their vectors is zero. To the original system of vectors UA, UB and UC get symmetrical components, it is necessary first of all to ask the location of the coordinate axes. Usually, the real axis is directed through
Then UA vector coordinates [1, j] voltage symmetrical components is determined by the following formulas:
U1 = 1/3 (UA + + aUv a2Uc)
U2 = 1/3 (+ UA + a2Uv AUC) (1)
U0 = 1/3 (UA + UB + Uc).
Can be similarly defined for U1 and U2 of phase voltages. The real axis directed along the vector of Uva, and in (1) is replaced by Ul Uva, UB on Usb and Uc at Uas. Determination of UQ for line voltages from (1.15) in view of the above, does not make sense, because the result of this calculation is always zero.
In practice, the operation of electrical networks and linear-phase voltage is measured with a voltmeter. However, they have the form of real numbers, not complex, as provided. There's also describes the technical specifications, special instruments which can measure current and voltage symmetrical components, and phase coals ^ 2 ^ 0 and directly (without calculations).
Sources of unbalance currents and voltages. Non-symmetric modes are determined by the three groups of reasons: 1) the operation of the equipment unbalance caused by the brief interruption of one or two phases of a short circuit (SC) or a more permanent shutdown in repairs per phase, the presence of cross-reactors is not at all phases of the ultra-high-voltage lines, etc.; 2) phase of the line parameters inequality (due to, e.g., lack of transposition line or its extended cycles), 3) uneven phase loads.
In general, the relationship between the voltages at the nodes in the line currents and resistances of different sequences expressed by the formulas:
Where Z11, Z22i Z00 - own resistance sequences, and Z12, Z10, and so on - the mutual resistance.
For symmetrical phase system parameters ZA = ZB = ZC mutual resistance sequences are absent, then (2) becomes:
Zn I11 = ДU1; Z22I2 = U2; Z00I0 = U0 (3)
and in the absence of currents I2 and Io voltage at the nodes are determined only by direct sequence mode, as
U2 = Uo = 0.
When you disable one of the phases of the phase line equation parameters is broken and there are mutual resistance sequences. Thus, even in the case of a symmetrical three-phase load (I2 = I0 = 0) having voltage
U2-Z21 I1 and UQ = Z01
Equality of phase parameters is violated, although to a lesser extent, in the absence of transposition line. The unbalanced system voltages occur on the tires and consumers, fed from sites located within a full cycle of transposition.
The most common cause of voltage unbalance, in practice, is the inequality of current loads phases. | The system distinguishes between two types of asymmetry: the systematic and probabilistic. A characteristic feature of a systematic asymmetry is constant overload of one of the phases. In this case, the load balancing phase produced by switching the current load from an overloaded on underused phase. The probability is characterized by asymmetry
Phase load variability, and usually alternating overload of one or the other phase (intermittent asymmetry). In this case it is necessary to apply automatic baluns.
Fig. 4 Decomposition of non-sinusoidal curve on the sinusoidal components
3. Compensation of reactive power
When connected to the mains active-inductive load current IH lags the voltage U on the corner shift cosine of the angle ц (sovц) is called the power factor.
Power-consuming equipment with a load consume both active P, Q and reactive power. Reactive power
Q = Ptgц
Active energy consumed by power consumers is converted into other forms of energy: mechanical, thermal, energy, compressed air and gas t.p.Opredelenny percentage of active energy consumed by the loss.
Reactive power Q is not associated with EA and useful work is spent on the creation of electromagnetic fields in electric motors, transformers, lines. Of course TFE is known that the reactive power can be inductive or capacitive. We agree consider the inductive reactive power QL load or consumption, and capacitive reactive power generated by Qc.
Passage in networks reactive currents causes additional losses of active power lines, transformers, generators, power plants, an additional voltage drop, demand higher nominal capacity or the number of transformers, reduces the capacity of the entire SES.
active power losses
where P, Q, S-, respectively, active, reactive and apparent power;
R and X-, respectively, resistance and reactance elements electrical power supply;
-Rated supply voltage.
The main consumer of reactive power inductive nature in industrial plants are asynchronous motors in blood pressure (60-65% of total energy consumption), transformers, including welding (20-25%), the valve converters, reactors and other EP.
Additionally loaded with reactive power supply and distribution networks of enterprises, respectively, increases the overall power consumption. Measures to reduce the consumption of reactive power: natural compensation (natural COSц) without the use of compensating devices (ky); Artificial compensation, often simply referred to as compensation.
The natural power factor correction does not require high material costs and should be carried out by companies in the first place. To compensate for the natural include: streamlining and automation of the process leading to the alignment of the load curve and improve the energy regime of the equipment (even distribution of loads on the phases, the time offset lunchtime individual shops and sites, transfer of energy-intensive large-scale EP to work outside the hours of peak energy, and vice versa , output in the repair of high-power EP in peak hours in the power grid, etc.), the establishment of a rational scheme of power supply by reducing the number of stages of transformation, replacement of transformers and other electrical equipment of the old structures with new, more advanced with smaller losses on reversal, replacement of transformers malozagruzhennyh transformers and motors and engines less power and full load, use of LEDs instead of blood pressure when it is permitted under the terms of the process, limiting the duration of the XX engine and welding transformers, reducing the duration and dispersion during the start-up of major EP, improving the quality of repair of electric motors, reduction of transient resistance contact connections, disconnection at low load (for example, at night, on weekends and public holidays) of power transformers.
For artificial reactive power compensation, sometimes called the "transverse" compensation, special compensation arrangements, which are sources of capacitive reactive power. Until 1974 the main regulatory indicator of the consumption of industrial enterprise reactive power, average power factor was COSц CP, B3B
The average power factor at time t
where W at W pt-and accordingly consumption of active and reactive power in the reporting period vremeni.
Industrial companies made payments for electric power is given SOSц CP, B3B, electricity supply company requirements were such that on the inputs of the enterprise value SOSц CP, B3B had to be in the range 0.92-0.95.
However, under the old guidelines for compensation of reactive power companies were not interested in disabling the installed CHP in the hours of minimum load. In this regard, the feed is often observed overcompensation grid reactive power.
Overcompensation - is the excess reactive power generated by the installation of a compensating reduction in periods of stress (at night, in obedennyepereryvy, at weekends and public holidays, etc.) and transmitted to the grid network. The result of overcompensation was to increase the total power and energy losses in electric networks and complexity, and the increased cost devices for voltage regulation.
To stimulate the activities of reactive power compensation Energy installed a new scale of discounts and allowances to the tariff for electricity, depending on the degree of reactive power compensation for consumers.
A visual representation of the essence of reactive power compensation yields (Fig. 5). Na (Figure 5 a) shows a diagramcircuit. Let the user had to compensate the active power P, respectively, the current Ia(Segment OB in Figure 5b) and reactive power from the inductive load current of Q1 with the corresponding IL12(VA interval). S1 corresponds to the total power vector IH (segment OA). Power factor compensation
Fig. 5 Vector diagram of compensation of reactive load capacity COSц.
Vector diagram of compensation is presented in (Figure 5 c).
After payment, ie after connecting in parallel to load CG (condenser) with a capacity of Qx (current IC), total reactive power of the consumer is already Q1 - Qkh (mokIL ~ Ic) and sootvetstvennosnizitsya phase angle with ц1 and ц2 to increase the power factor COS with ц1 to COS ц2. Total power consumption for the same consumption of active power P (current Ia) will decrease from S1 (current IH) to S2 (current I2) (segment OA ')
Consequently, as a result of compensation can be in the same section of wires to increase network capacity in active power. The technical means of reactive power compensation include the following types of compensation devices: capacitor bank (CB), synchronous motors, the valve static reactive power sources (RPS).
4. Power factor in the ac electric traction
4.1 Crosswise compensation
The main purpose of setting a transverse capacitance compensation (LOC) to compensate the reactive power traction load. KU can reside on traction substations, anywhere in the traction network. Better utilization of the installed capacity of KU reached at their location in substations. The greatest economic effect of DF compensating reactive power can be obtained when it is used simultaneously for balancing and voltage rise, reducing current and voltage harmonics. For reactive power compensation of the positive sequence currents does not matter on which phase included KU.
However, to compensate for the negative sequence currents and balancing the currents and voltages depending on the ratio of the average supply current shoulder, CHP should be included at certain phases. On the traction substations, usually should be applied single-KU, and install them on the lagging phase. KU single-phase are most effective in balancing for the same load on the shoulder cord (see ris.ba). When a significant difference between mean current supply shoulders pas substation appropriately set KU into two phases: in the lagging and advanced (ris.66) when the load exceeds the load of the leading phase lagging, otherwise (under load lagging phase) KU should include a backward and free phase (ris.bv).
Circuits for KU to pull the transformer into phases: a, b, -, respectively, lagging, lagging and anticipatory; lagging, and free. On electrified with large fluctuations traction load is advisable to use adjustable shunt compensation setting. In its simplest form, this single-stage and multi-stage adjustable KU (Fig. 7). Power of KU depending on the monitored parameters (power factor, voltage, unbalance, etc.) regulate the activation and deactivation steps (or sections) KU. Perhaps the use of more advanced CG regulated using controlled reactors with a rotating magnetic field (ris.76). A feature of these reactors is a sinusoidal current in all normal operating conditions, despite the saturation of the magnetic circuit and the associated curvilinear current-voltage characteristics. In another scheme (ris.7v) Power CG can be adjusted by varying the voltage on the capacitors through deep control transformer Tr.
Figure 7 Scheme adjustable KW: a - multi-b-controlled reactor with c-adjustable transformer.
Adjustable KU set for traction substations, reach at the same time reactive power compensation a significant stabilization of the voltage unbalance reduction to acceptable values, and generally improve the economy mode of traction substations. Currently, traction substations (TS) AC 25 kV equipped with "non-regulated" means of compensation of reactive power (CHP), ie, their compensating power is constant and involves a certain amount of load in the power train.
As a result, when the load is consumed or the generation of reactive power, In either case, you must pay both for reactive power flows, and for the loss of active energy. Adjustable KU set for traction substations, reach at the same time reactive power compensation a significant stabilization of the voltage unbalance reduction to acceptable values, and generally improve the economy mode of traction substations.
Operation capacitors are prohibited:
- At the voltage on the tires in excess of 110% of rated voltage capacitors;
- Ambient temperature in excess of the highest and lowest temperature allowed for the applicable type capacitors;
- If there is a leakage of impregnating liquid droplet and, finally, in case of damage of the porcelain insulators.
After disconnecting the capacitor units from 27.5 kV bus capacitors discharge should occur through the winding specifically for the connected voltage transformer. Therefore, grounding systems is virtually capacitors are discharged and discharge currents are insignificant. Interlocks capacitor units must be configured so that the open enclosure door Capacitor ground only after the installation. Before working on the capacitors due to possible residual charge even when grounded capacitor bank with two sides should make sure to check digit, while carefully holding the bar to the terminals of the capacitor. This discharge is due upon each connected in parallel row (group) capacitors. Rod for controlling the discharge manufac poured from the operational bar for 25 kV, which reliably reinforce metal rod cross-sectional area not less than 25 mm2.
The discharge is carried out between the terminals of the capacitor, and between terminals and case, special care and caution must be under the control of capacitor discharge emergency shutdown of compensation because due to possible breakage or damage to the main circuit capacitors common ground installation can not lead to the category of individual capacitors . When testing capacitors with high voltage megger or from other sources should be used with discharge resistor rod, specially made of metal wire or glass or polyvinylchloride tubes filled with water and a bit of built-in bar. The discharge of the rod first produce a resistor, and then the metal core rod connects both terminals of the capacitor. In testing one of the conclusions and the capacitor must be connected to ground. Electromagnetic lock must be capable of disconnecting switches to operate the capacitor bank only if the circuit breaker.
To work in a chain reactor permitted only after disconnecting the capacitor bank. Care should be properly connected to the rail condenser units are located in positions partitioning. In place of connection must be established and enforced labeling cylindrical nut. Capacitor units must be provided with fire-fighting equipment: fire extinguishers, sand box. In addition, the mobile units to provide smoke alarms at the same time acting on the off-voltage installation. Begin to extinguish surrounding fire only after proper grounding capacitors.
4.2 Unregulated and controlled utility shunt compensation
Non-adjustable settings. The main purpose of setting a transverse capacitance compensation (LOC) to compensate the reactive power traction load. The features of KU on electrified railways are their AC single-phase to single-ended switching the phases for traction load balancing and availability of the reactor, the main purpose is to limit the dangerous-resonance phenomena Be placed at KU may traction substations, anywhere in the traction network, as well as locomotive.
When placing the locomotive on the KU reactive power is compensated directly by the consumer (electric), but the installed capacity of CHP is used very badly, as not all electric all the time are in the works. Better utilization of the installed capacity is reached at KU p.ch location in substations. The greatest economic benefit of KU compensating reactive power can be obtained when using it at the same time for balancing and voltage increase, reduce current harmonics and reactive power compensation napryazheniya.Dlya outflows of direct sequence does not matter on which phase included KU. However, to compensate for the negative sequence currents n balancing the currents and voltages depending on the ratio of the average supply current KU shoulders should be included on certain phases.
On the traction substations are usually used single-KU and establish their pas lagging phase (Fig. 8a). KU single-phase are most effective in the balancing of power with the same load on the shoulders of supply. In the case of a significant mean difference currents arms supply pas substation load appropriately lagging phase) KU should include a backward and a free phase (Fig. 8.б)
When a large load with low power factor of regional consumer KU can be installed on the district winding. If KU provided for compensation of reactive power and traction load, they perform single-ended (ie, with different power phase) and can include both the district and on the traction transformer windings. On a number of traction substations on orders powerful grid KU (50 MVAR n more) include the tires of 110 kV.
To reduce the higher harmonic (harmonics) set KU can be divided pas three sections and adjust accordingly on the 3rd, 5th and 7th harmonics. These units compared to conventional CG configured only on the third harmonic, with the same net power are 13% lower installed power [M |. CHP installation, performing the role of traction load balancing and filter harmonics, called filtroenmmetriruyuschimi units (FSE).
CG placement in appropriate traction network primarily to increase the voltage on the stretch-limiting and generally to an electric current collector for the stroke on the feeder zone, as well as to reduce the power losses in the power train. In the forced mode when disconnected substation Tse-l consistent with KU place at the end of the feeder zones using KU off the substation or mobile CG
Setting compensation included in a power train has disadvantages compared with CG at the substation. First, the limited opportunities in the cross of balancing the current and voltage. Bol with that at the substation, feeder feeder zone KU advanced phase can be lazhe increase in asymmetry. Second, the reduced efficiency of CHP because of possible significant reduction of tension in the traction network. In the power train KU usually plug into the fast partitioning of PS (Figure 9).
In this case, the post partition can be performed pas-breakers and disconnectors for, install, ie dead time include (disable) or in the latter case provided be locked with a switch disconnectors KU that when sectioning off the post capacitive current from turning off a switch. In areas electrified by 2x25 kV system installation KU may be included in the traction substation 77 / and in the traction network at between auto transformer LT contact. Circuit of the CG at full network CN and the rail / '. partitioning between the supply wire PP and rail and between the COP and PP (Fig. 10). In design practice the option of switching between the COP and the KU rail.
Adjustable settings. These KU performed single-stage (when turned on and off the whole installation) or multi-stage (Fig. (11.) In some cases the first step in a multi-KU running unregulated. Schemes in multi significant time last stage KU is not in use. This disadvantage is eliminated in a stepwise switching circuit KU (Fig. 11, a). better here and capacitors are used, the reliability of their work, although the complicated process of switching steps. Due to the hazardous switching processes that occur when connecting the next stage of capacitors, power control is carried out at switch off all the switches PI stage, P2, RP, and then include the entire unit with izmenennoymoschnostyo switchB(see Fig.11)
So it is advisable to regulate the power switches with a limited number (no more than 1-2 times a day), for example, to perform a task to disable the power system in KU night minimum system load, seasonal regulation under forced conditions, etc. More frequent switching require special measures to dampen the surge voltage and current. For this purpose, first of all use a vacuum circuit breaker (contactors), safely disable the capacitive currents and have a long service life. To limit the surge when the single-stage CG quite effective is to connect a resistor in parallel reactor through a vacuum contactor or thyristor varistor arrestor TP (Fig. 11.6 in).
When the voltage at the reactor R while turning the vacuum circuit breaker is triggered spark gap in the TR and connects resistor K. After switching process thyristors are closed, and the resistor is switched off. Arrester TR connected to the capacitor bank at which the fundamental frequency of the network voltage in the steady state minimum (ie at the point where the natural frequency is equal to the mains frequency 1S2). As a threshold element in theTPapplied Ristori all-Hb(see Fig.11,c).
In a multi-KU require more effective measures of damping. In particular, the inclusion of a three-stage process (Fig. 9 g) is included B2, then B1, B2, and then turned off. Such a scheme with two capacitor banks of various capacities (eg, 3 and 5 MVAR) can implement the 'PH power levels (3, 5 and 8 MVAR). For the first stage of a two-step can be performed by a single-stage scheme of the LOC (see RNS. 11.6) or be unregulated. In this case, reduction of harmonics and limit the inductance of the reactor self-resonant frequency of the second stage is performed at 250 Hz.
The minimum power level is limited to a typical inductance of the reactor Frome and the number of capacitors connected in parallel in a row and is 3 Mvar. Reduce the power stage can reduce the voltage on the capacitor bank with pomoshyo transformer or autotransformer AT (Figure \ 2a). In this case, to limit the resonance phenomena using conventional reactors tokoogrannchivayuschis R for networks 6 and 10 kV, and to reduce the switching overvoltage used resistors and vacuum switches in 6 (10) kV. In step adjustable KU promising application of thyristor switches to significantly reduce the inrush current and voltage by switching on and off of capacitors in a voltage phase. In the presence of voltage regulators in the transformer (autotransformer) Power CG changes smoothly.
A common drawback of these schemes yavlyaegsya complication compensation systems caused by the need to use a transformer (autotransformer), which creates an additional loss of active and reactive power, and the power of the transformer is equal to the power of corporate governance.
In the areas of 2X25 kW two-stage adjustable KU simply do: if stage 1 is connected between the COP and the rail P, the 2nd stage - between the P / R 7 and rail (see Fig. 12) - In this case, the connection process easier stage 2, and CG can be made simplified.
In the scheme with a booster transformer (Figure 12.6) Power CG is proportional to the square of the voltage applied to the capacitor. In the simplest case, when the booster transformer VDT fixed by switching the polarity of the secondary transformer winding receive two stage power regulation. Power ratio of the 1st and 2nd stages
Qil Qt - K - *) (! + *).
where i; = UilUi - the ratio of the voltage of the secondary and primary windings of the transformer Polish todobavochnogo.
The power of the transformer S = KQ2 / (\ + k) and is K) -15% of the installed capacity of CHP.
Include the 1st stage power switch KU B1 pas low voltage (see Fig. 12.6). For stage 2 turns B2, B1 and then turned off and the voltage of the capacitor increases. When switching the reactor limits the current transformer VDT. Accepted order of switching vacuum switches B1 and B2 provides ("excess inrush current and voltage tolerance.
Power control is possible without KU switches B1 \ \ B2, but then the primary winding is connected in parallel VDT adjusting winding power transformer load voltage regulation (ARPN). When working ARIN varies power KU 1.5-2 times or more.
In the scheme with two capacitor banks C1 and C2, and VDT (Fig. 12a) can achieve the five stages of power regulation KU corresponding switch switches B1 and B2. In particular, the inclusion of counter-VDT (included CF and BI and B2 and disabled VZ) power KU Q = (U1-U2) and Ds at the circuit breaker 'B1 and B2 include power KU 0 = (u> u2) 1 (XC1 Hs2 +). (Here * ci) and a resistance-capacitor cells C1 and C2).
Adjustable KU can be included in the traction substations and directly into the power train. On the traction substations by connecting adjustable according to KU developed, at the same time achieve a significant reactive power compensation voltage stabilization, reduction of unbalance to acceptable values ??willows generally more economical modes of traction substations. In controlled KU collected under the scheme of two open triangles (Fig.. 12d), depending on the ratio of the currents through the power switch shoulders A capacitor connected to the battery with a deep adjustable transformer TR1 and Tr2 or TRZ. Thus, the value of the current capacitor bank and its phase changed by regulating the voltage transformers TP1, TP2, TRZ and under the influence of the switch P. Due to the complexity of the transformers, the scheme has not yet found application.
For electrified section is promising centralized power control all the CG located at traction substations and power train. It should be guided primarily by the more easily performed single-stage adjustable KU.
Turning (Off) setting shunt compensation should be based on the task grid, as well as on the voltage and load "their" feeder zone adjacent substations and other KU and energy supply networks. In such a setting, the problem of regulation is extremely complex and does not yet have a final decision. So the more simple but less effective methods of regulation. First of all, KU switched on and off at times due to power system operational duty personnel energodispetcherom fire by remote control system. This may also be done automatically by means of a timer. In the rest of the day to increase the efficiency of the control regime KU made depending on the current and voltage values.
On the DC traction substations KU is controlled by, the minimum power loss in the step-down transformers with a voltage correction. On the AC traction substations, depending on the load of both arms supply KU regulate the minimum power loss and current unbalance in traction transformers for voltage correction.
For QA in the traction network, you can pass a law regulating the minimum power losses in the power train between the substation area. In this case, the value and location of traction loads appropriate to determine at higher harmonic voltage power train with off K.U or higher harmonic current KU. Naturally, the reduced voltage to the traction network automation system is to work on the inclusion of KU even during the minimum load power system.
4.3 Installation of the longitudinal and transverse-longitudinal compensation
The main purpose of setting the longitudinal capacitance compensation (CCP) is to improve and stabilize the voltage in the traction network in conditions of continuous change traction load. At the same time the CCP. effectively balancing, voltage and reactive partially offset moschnost.Na traction substations for the purpose of stabilization and voltage balancing of the CPC included in the 27.5 kV side in one, two or three phases. According to the "technical-rational economic indicators are the four schemes include: single phase of the CPC in the suction wire, two-phase wire of the CPC in the suction and trailing in the suction phase and wire and advanced phase, three-phase of the CPC, in general, with different resistances in phases (asymmetrical CPC) .. The inclusion of a symmetrical three-phase CPC compensating inductance supply power lines and substations, almost completely offset the loss of voltage and symmetrize it. A similar effect can be achieved with a single phase of the CPC in the suction with a wire-to-phase transformer coupling (Fig. 13a). When the ratio Lt. transformation is 0.73 and the degree of compensation for each section of the Code of Criminal Procedure, equal to 1.86, obtained full compensation of voltage drops on all phases. Also, this scheme works without transformer Tr2 and with modified parameters: um = 2:1 in the transformer TR1, / c = 0.5 in section C1, k = 1.5 in the section C2. In this case, the same effect for balancing and stabilizing the output voltage is reduced in the transformer 3 times and 20% power capacitors. TP1 As can use Two suction transformer, connecting two coils in series, and two others - in parallel using a similar transformer connection between the phases of traction and traction transformer windings of the district, you can use the CPC symmetrize voltage ua and traction, and the windings of the district. On traction substations with large loads include the second transformer, bringing the total inductance power lines and transformers decreases 1.4-1.9 times. Consequently, to maintain the desired degree of compensation when the number included in the installation work of transformers CCP should change their basic parameters (capacitance and rated current ), that is to be controlled (switchable). At the most simple scheme controlled by the CCP connect a second transformer is connected battery kondensatorop C2, resulting in increased current rating and reduce the total capacitance of the Code of Criminal Procedure (see Figure 13.6). disadvantage of this scheme is that when one turned on battery power transformer C2 is not used, so the schemes of the CPC with the best use of power capacitors
At one switched isolator transformer included P1 and P2 off, and when the two transformers, disconnectors included P1 disabled and P2 is on. In such a rated current of the CPC changes of 1.33 times, and the capacitance-to 1.78-fold. You can create a CCP with any number of branches and groups within it. The choice of a scheme of the CPC is determined by the desired ratio of nominal currents and capacitances of the CPC in the operation of one and two transformers.
Therefore, for the CPC in the suction applied wire circuit with switching capacitors (see Fig. 14.6), and for the CPC in the shoulder should use the power to connect additional capacitors (see Fig. 14a).
In the case of large losses in the power train, which is usually feeder zones with single feed, the CCP has to be connected directly to the power train, offsetting its inductive reactance. The simplest is the inclusion of the CPC in the partitioning of contact network, such as the partitioning of posts in the SS (Fig. 15a). In this case, the performance decreases and the air gaps AM (insulating interfaces) contact system due to arcing when passing an electric current collector, the intensity of which increases with increasing power UG1 K. To improve the reliability of the CAP used known methods of protection VP of burnout. But the most effective bypass switch on the VI controlled valves, which included prior to passing the susceptor when the instantaneous voltage of the CPC is zero.
Scheme of the Criminal Procedure Code with additional wire (Fig. 15.6) DP does not affect air gaps, as well as on the cross current in the power train between substations. Loss of voltage to the electric, located near the CCP depends on the compensated resistance DP.
A way to incorporate the CCP to offer DP applied in areas with regenerative braking. In this case, the area of contact network-intensive recovery is shunted by an additional wire and the contact portion of the network is partitioned, and connects to the AP through the Code of Criminal Procedure (rns. 15c). This helps improve the power factor of electric recovered.
At sites with very different load on the even and odd ways of using the CPC scheme included between the catenary ways. Here, the voltage on the way with intensive load increases, while the other path, by the same value decreases. It should be noted that due to the load transfer path rising power loss in the traction network and, in addition, it is necessary to take measures for the protection of section insulators between the catenary ways when passing them on the susceptor.
In the presence of a contact network of suction transformer from the installation of the CPC can be included on the secondary winding of the transformer (Fig. 15d). Thereby compensating for the inductive resistance of the secondary winding of the transformer and wiring ETA inverse addition to reducing voltage loss, CCP reduces suction power transformers (about 2 times) or increase the distance therebetween.
The main disadvantages of unregulated KU (no voltage regulation) and the Code of Criminal Procedure (lack of reactive power compensation) are eliminated by applying a combined installation of longitudinal-transverse capacitance compensation (UPPK). This combination unit is a promising and should solve the complex problem of improving power quality, although the optimal parameters and strategies to incorporate UPPK not yet fully defined.
In one of the options KU compensate reactive power and current balun, and the Code of Criminal Procedure in the suction wire balancing, voltage regulation, and partly compensates the reactive power. Due to the presence of stabilized voltage in this circuit work effectively and KU2 KU 1 (Fig. 16).
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2. Бизнинг бош ма?садимиз - жамиятни демократлаштириш ва янгилаш, мамлакатни модернизация ва ислох этишдир. - Т.: Ўзбекистон, 2005 й. -94б.
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