RU2547817C2 - Voltage regulation method at alternating-current traction station - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is used in the field of power engineering. According to the method additional threshold levels for regulation of U_kmin and U_kmax voltage and computation unit for calculation of in-process power losses (loss increment) is introduced in traction energy systems (or in traction and external energy systems) for voltage deviation per ΔU by means of LTC and/or by means of switching the next FM stage on /off and by calculations it is determined how power losses are going to change within limits of additional threshold levels of voltage when voltage is changed per ΔU. At that different combinations of transformer ratios for transformers and switching FM stage on/off are checked. The variant with minimum power losses is accepted.

EFFECT: improved efficiency of voltage regulation.

1 dwg, 1 tbl

Description

The invention relates to the electric power industry for voltage regulation, in particular to a traction power supply system for alternating current of railways for voltage regulation using a voltage regulator under load of transformers (on-load tap-changers) and the installation of transverse capacitive compensation.

Known methods and devices for voltage regulation at traction substations of alternating current using on-load tap-changer transformer and installation of transverse capacitive compensation [1-5]. We accept as a prototype the regulation method in [1, Fig. 1.15]: The voltage regulation method at an alternating current traction substation with three-phase transformers according to the star-delta connection scheme, equipped with a load voltage regulation device (RPN) and a single-phase stepwise adjustable transverse capacitive installation compensation (KU) with voltage transformers and current transformers of 27.5 kV buses, by changing the voltage on 27.5 kV buses with a given time delay when the main threshold level is reached th voltage using on-load tap-changer and switching on (off) the next stage of KU. The disadvantage of this method:

the command to switch on-load tap-changer and to turn on (off) the switchgear is transmitted when the main threshold (limit) voltage levels on the buses 27.5 kV, that is, 21 kV and 29 kV, are reached [8]. However, within the specified threshold (limiting) voltage levels from 21 kV to 29 kV, it is also necessary to regulate, since this leads to a decrease in electric power consumption and an improvement in the operating mode of EPS.

The purpose of the invention: improving the efficiency of voltage regulation at a traction substation.

To achieve this goal, it is proposed to introduce regulation not only on threshold (limit) voltage levels, but also within the entire range of voltage changes.

For this, additional threshold levels of voltage regulation U _kmin and U _kmax and a calculation unit containing a unit for calculating the partial derivatives of power losses (loss increments) in the power supply system to voltage deviations at ΔU using the on-load tap-changer and (or) by introducing ( shutdown) of the next stage of the KU, and the unit for calculating the corrected mode with the definition of new values of power losses, connected to voltage transformers and current buses 27.5 kV and KU, and previously at voltages within additional threshold levels of voltage regulation perform the calculation of power losses of all the corrected variants of new modes for a given voltage increase ΔU by the expression

where ΔP (ΔU) _i is the power loss at a given voltage increase by ΔU when calculating the "i" -th version of the new mode;

ΔP _o - the value of power losses in the power supply system in the initial mode;

S _nj is the coefficient of sensitivity of changes in power losses to changes in the "j" th voltage deviation;

ΔUj - specified for calculations, the "j" th voltage increase,

then choose the corrected mode option with the least power loss ΔP (ΔU) _nm and

if

as well as

then, with the given time delay, the on-load tap-changer is switched and / or turns on (off) the next KU stage, otherwise, either increase the voltage gain and continue calculations, or cancel the on-load tap-changer and (or) turn on / off the KU.

Figure 1 presents the device that implements the proposed method of voltage regulation using the on-load tap-changer of the transformer and a stepwise adjustable installation of transverse capacitive compensation KU.

Designations in the scheme (figure 1):

1 - power transformer 110 / 27.5 kV;

2, 3 - measuring current transformers (CT) of traction load of tires of 27.5 kV;

4 - tires 27.5 kV;

5, 6 - measuring voltage transformers of tires 27.5 kV and KU;

7 - measuring current transformer capacitor stage installation of transverse capacitive compensation KU (8);

8 - single-phase adjustable stepwise installation of transverse capacitive compensation;

9 - unit for calculating the corrected mode with the calculation of power losses in the power supply system ΔP;

10 - block calculation of partial derivatives;

11 - control switch element KU (8);

12 - on-load tap-changer control element;

13 - calculation unit.

Let us explain the formation of formula (1) and the procedure for calculating when the voltage changes by ΔU. Voltage regulation is possible using KU and on-load tap-changer transformer, as shown in the drawing (figure 1).

Power losses in the initial mode ΔP _{o are} calculated in advance for a given power supply circuit, its parameters and load mode. The calculation is made according to well-known formulas [5, 6, 7]. For the general case with several traction substations, the power losses in matrix form are

- сопряженное значение I; R - матрица узловых активных сопротивлений системы электроснабжения, питающей рассматриваемые тяговые подстанции; К^д - диагональная матрица коэффициентов трансформации трансформаторов. Здесь принято (для упрощения формирования программы расчетов): коэффициент трансформации трансформаторов равен отношению напряжения вторичной обмотки к напряжению первичной обмотки. Поэтому, считая тяговую нагрузку как источник тока, при уменьшении коэффициента трансформации снижаются токи первичной обмотки трансформатора, и, следовательно, снижаются потери в системе внешнего электроснабжения.where I is the matrix of the full currents of the traction load;

- the conjugate value of I; R is the matrix of nodal active resistances of the power supply system supplying the traction substations in question; To ^d - diagonal matrix of transformation ratios of transformers. It is customary here (to simplify the formation of the calculation program): the transformation coefficient of the transformers is equal to the ratio of the voltage of the secondary winding to the voltage of the primary winding. Therefore, considering the traction load as a current source, with a decrease in the transformation ratio, the primary winding currents of the transformer are reduced, and, consequently, losses in the external power supply system are reduced.

It is important to note that power loss calculations are necessary to compare the results of the options. Therefore, only changing traction loads are taken into account here, and a more “calm” non-traction load (which, as a rule, is much less than the traction load) is not taken into account. This circumstance greatly simplifies the device, although it introduces a small error in the calculations, but, as the calculation experiments showed, this does not affect the final results.

It is advisable to determine the active power losses according to the program RAST-05K of the joint calculation of traction and external power supply systems [6, 7]. Depending on the specific tasks under the operating conditions of the control device, the calculation of power losses can only be for the traction power supply system or, in general, for traction and external power supply systems.

If it is necessary to change the voltage (if it is outside the additional threshold levels (boundaries) of regulation), the voltage increase ΔU is set when switching the on-load tap-changer and when switching on the KU; for on-load tap-changer - ΔU on-load tap- _changer (for one switching) and for KU - ΔU _ku1 (for the first stage) and ΔU _ku2 (for the second stage). Are available when the (disconnected) KU consider change of power circuit parameters and the voltage gain set when adjusting the tap changer - ΔU _RPN = ΔU.

The sensitivity coefficients S _{nj are} defined as the partial derivative of active power losses in the traction power supply system (or in the traction and external power supply system) with respect to the voltage deviation (change). Methods of determination are given in [6, 7] for a joint consideration of traction and external power supply systems and are based on the theory of calculation of sensitivity matrices.

The calculation according to formula (1) begins with a task of exhaustive search of all i on-load tap-changers and control devices and each time for a given ΔU we calculate the values of active losses ΔP (ΔU) _i in the power supply system. In other words, for the presented circuit, this is done as follows: ΔU is set when switching the on-load tap-changer of the transformer and we calculate ΔР (ΔU), then KU is turned on (the nodal resistance matrix changes) and ΔU is set again and ΔP (ΔU) is calculated. So several steps are repeated when the voltage gain changes by 2 × ΔU, by -2 × ΔU, etc., and ends when the smallest value of ΔP (ΔU) _nm is selected within the permissible limits of voltage regulation. Similarly, the calculations according to this algorithm are repeated at neighboring traction substations, where the smallest value ΔP (ΔU) _{nm is} also chosen, at which the voltage will not exceed the threshold regulation values.

The threshold voltage levels in the traction network [3] are 21-29 kV. Usually, according to operating experience, to limit the number of on-load tap-changer switchings, the main threshold levels take 24 kV - 28.5 kV.

Given the nominal voltage at the current collector of an electric locomotive of 25 kV, we propose to accept additional threshold levels of voltage regulation on the 27.5 kV busbars of traction substations U _kmin and U _kmax, respectively 25 ... 26 kV and 27.5 kV.

Thus, the considered method of voltage regulation is implemented as follows:

1. If voltage regulation is necessary, when the values of additional regulation thresholds U _кmin and U _{кmax are reached} , the voltage increase ΔU (both positive and negative) is set.

2. consider all possible voltage regulation: using tap changer _(OLTC with a gain ΔU), KU (increasing _ku ΔU), etc.

3. The partial derivatives (loss increments) and the new corrected modes in block 13 are calculated for all options and the option with the smallest power loss is selected, and this voltage regulation option is considered below.

Essentially, when items 1, 2, and 3 are fulfilled, what would be the power losses in the power supply system if control were performed according to the intended voltage increase in item 1, that is, the well-known problem from the theory of sensitivity is solved here: “what would happen , if…".

4. If the considered option with ΔP (ΔU) _nm satisfies conditions (2) and (3), then with the specified time delay the on-load tap-changer is switched and (or) the next KU stage is switched on (off).

5. Otherwise, they either increase the voltage gain and continue calculations, or cancel the on-load tap-changer and (or) switching on (off) the control unit.

Let us explain the operation of the circuit. Current transformers 2 and 3 with a given time interval measure the input values of the traction load current on the 27.5 kV 4 buses, and transformer 7 - the KU current, and transfer them to the calculation unit 13, voltage transformers 5 and 6 connected between the 27.5 buses kV (4) and the rail, also transfer the measured values to the calculation unit 13. In the block for calculating the partial derivatives 10, the calculation of the growth of power losses relative to the specified "j" -th voltage deviation ΔU is calculated, and in the block for calculating the corrected mode 9 according to the deviation ΔU calculation of new loss values begins and if power ΔP (ΔU) _nm <? P _o, and _kmin U ≤U≤U _Kmax, then at a predetermined time delay calculated by block 13 is instructed to switch the tap changer 12 and (or) switch (disconnect) the next step 11 KU. If (2) and (3) is not satisfied, then the following deviations are set: 2 × ΔU, 3 × ΔU (-2 × ΔU, -3 × ΔU), etc. and the calculations for determining ΔP (ΔU) _{nm are} repeated. If this time (2) and (3) are not performed, then the on-load tap-changer switching and switching on (off) of the control unit are canceled.

Switching is performed with a time delay, which is determined by experimental operational testing. The time delay is chosen so as not to exceed the specified operating life of the on-load tap-changer and the drive of the KU switch [1] (the KU switch is not indicated in the diagram).

Appendix 1. Calculation of the sensitivity coefficient of power losses to voltage changes

In the situation under consideration, it is advisable to use the coefficient of sensitivity of power losses to a change in the transformation coefficient — Snj (ΔP / К _Т ) for calculations.

1. Calculation of the sensitivity coefficient of total power losses in the external and traction power supply system Snj ((ΔP _Σ / Kt) to a change in the transformation coefficient.

We change the transformation coefficient at the traction substation i at node m, that is, at this substation, a transformer connected to node m will have a transformation coefficient K _m . Then, taking in a first approximation the immutability of the currents of the traction load when the voltage changes, we obtain the value of the sensitivity coefficient

where R _Σ is the matrix of nodal active resistances for the jointly considered systems of traction and external power supply. The subscript m indicates that in the matrices under consideration only those elements that depend on K _m are taken into account. Having completed transformations (5), we finally obtain

The accepted notation in (6) is as follows.

There are n nodes in total, in the transformer of node m we change the transformation coefficient Km, the remaining nodes p (from 1 to n). The intrinsic nodal resistance of the node m is Rmm, and the mutual resistances Rmp (p varies from 1 to n). Loads at node m - Im, at other nodes - Ip.

It is important to note here that the matrix of nodal active resistances R _Σ is determined for the entire network as a whole, taking into account the connected contact network. In addition, since the voltage mode of the substation under consideration is affected only by neighboring substations, the matrix dimension R _Σ can be limited to 3n × 3n, where n = 3 - three substations (and 3n indicates taking into account the three phases of the external power supply system).

Accepted in the calculations of the voltage premium ΔU must be consistent with the resulting premium when you change K _T.

2. Now define the power loss in the sensitivity of the coefficient of traction network at change? P _mc K - Snj (ΔP _mc / Km)

We use formula (4) and apply it for the case when the nodal resistance matrix R is determined taking into account (R _Σ ) and without taking into account (Rin) the connected traction network.

Then the losses in the traction network will be determined

where ΔP _Σ and ΔР _int are power losses taking into account and without taking into account the connected traction network.

therefore

When the transformation coefficient changes at traction substations, the surge current in the traction network changes. Therefore, the nature of the change in the specified sensitivity coefficient will correspond to the nature of the change in the coefficient of sensitivity of the surge current to the change To _t .

To simplify the determination of the coefficient Snj (ΔP _TC / K _T ), you can use the graphoanalytical calculation method using a computer model using the RAST-5K program [6]. It is known that power losses in the traction network are determined independently of power losses from the traction load. Therefore, for average operating conditions of the traction substations under consideration (for medium loads), according to the RAST-05K program, power losses in the traction network from the surge current are determined for different transformer transformation ratios before one substation and then another. The ratio of power losses from the surge current to the change in the transformation coefficient will correspond to the desired sensitivity coefficient - Snj / (ΔР _mc / К _т ). The calculation results are presented graphically and are used in the considered problem.

Appendix 2. An example of the implementation of the algorithm on a mathematical model for calculating traction power supply taking into account the external power supply system.

The calculation is performed using a mathematical model (MM) according to the program RAST-05K [6, 7]. At the substation installed single-stage KU according to the scheme in figure 1. We accept additional levels of voltage regulation within 25 and 27.5 kV.

The initial data for the model was taken from a real site: a matrix of nodal resistances of the external power supply system was used, the load of the traction network was reduced to the tires of traction substations. Since in the calculations all the initial data are reduced to a voltage of 27.5 kV, the nominal transformation ratio of the transformer is 1.

For some instantaneous scheme of the real section, the initial data for the MM are as follows: on the lagging phase of the UA bus 27.5 kV, the voltage is 24.84 kV, K _t = 1, the one-stage KU is disabled.

For the specified source data, the total power losses in the considered power supply system are calculated by the RAST-05K program - 1807 kW.

Due to the fact that according to the source data, the voltage at the substation is 24.84 kV (which is lower than the value of the additional control threshold of 25 kV), the automatic control algorithm will come into effect and the calculation unit 13 will start working.

Using the on-load tap-changer, K _t can be changed in increments of 1.78% of the rated voltage, and a single-stage KU can either be switched on or off. A change in K _{t of} 1.78% corresponds at a given load to a change in voltage by ΔU = 0.3 kV, which is obtained by preliminary calculations on the mathematical model PACT-05K. Enumeration of all options for the operation of the power supply circuit will be as follows: the transformation ratio of the transformer is changed step by step with the switch off and then with the switch on.

According to the available source data, block 13 will begin calculating the sensitivity coefficient Snj [7], and for each new mode that is created by switching on-load tap-changers, it will be different, since the circuit parameters (nodal resistance matrix) change with K _t . Further, according to the formula (1), we calculate the possible values of power losses. For the source data, the total power loss in the considered system of traction and external power supply by calculation, as indicated, is equal to 1807 kW.

The calculation will be repeated for each step of the change of K _t until a control option is found that satisfies conditions (2) and (3). The results of calculations on a mathematical model are summarized in table 1. Let us explain the formation of table 1 during the operation of the algorithm at the substation.

We carry out step-by-step enumeration of the transformation coefficient K _t , at each step j we decrease (increase) the transformation coefficient - by 0.0178. In this case, at each step j on the model, we measure the voltage of the phase U _A supplying the contact network from the TPA and set the voltage change by 0.3 kV (which corresponds to the calculation on the model when K _t changes by 0.0178 at given loads).

Table 1 Calculations on a mathematical model according to the program RAST-05K KU Off KU Included K _t U _A , kV ΔU, kV Snj ΔР (ΔU), kW U _A , kV ΔU, kV Snj ΔP (ΔU), kW 1,0356 25.44 0.3 193.3 1865 26.28 0.3 203,335 1796 1,0178 25.14 0.3 86.69 1833 25.98 0.3 93,331 1763 one 24.84 0 0 1807 25.68 0 0 1735 0.9822 24.54 0.3 -66.69 1787 25.38 0.3 -73,336 1713 0.9644 24.24 0.3 -113,327 1773 25.08 0.3 126,676 1697 0.9466 23.94 0.3 -143.35 1764 24.78 0.3 -163,345 1686

We begin the calculation, taking K _t = 1 (initial mode). With an increase in voltage by ΔU = 0.3 kV, we calculate the sensitivity coefficient by the formulas from [7], we obtain 86.69, then we perform the calculation ΔP (ΔU) = 1807 + 0.3 × 86.69t = 1833 kW. The same losses (with an error of no more than 10%) were obtained on the mathematical model according to the program RAST-05K. Similarly, the calculation is performed and when the voltage is reduced by ΔU = -0.3 kV.

As can be seen from the results: when KU is switched off, conditions (2) and (3) are satisfied by the situation at K _t = 1.0178 (since this mode has minimal losses during regulation). But since KU is also involved in the regulation, it is possible to achieve better results: when KU is turned on, the greatest effect on power losses is achieved at K _t equal to 0.9644, where conditions (2) and (3) are also satisfied. Therefore, the automation device gives a signal to switch two tap-changers in the direction of decreasing K _t and a signal to turn on the KU.

Thus, they simulated the real work of the regulation algorithm by the proposed method.

So, the result of the calculations: it is necessary to switch on the control unit, as well as switching the on-load tap changer to minus 2 soldering, which corresponds to K _t = 0.9644, the voltages are within the additional control threshold values (25.08 kV, which is above the threshold of 25 kV), and power losses are reduced by 110 kW.

Literature

1. German L.A., Serebryakov A.S. Adjustable capacitive compensation systems in railway traction power supply systems: monograph. - M.: MIIT, 2012 - 211 p.

2. Patent No. 102435. Transformer voltage regulation device / German L.A., Yakunin D.V., Kurov D.A. Published on February 27th, 2011.

3. German L.A., Sinitsyna L.A. Automation of regulation of asymmetric voltage of traction substation of alternating current // Central Research Institute of Engineering and Technology. Railroad trance. Ser. "Electrification and energy economy." Issue 1, 1981. - p. 1-12.

4. German L.A., Eisenstein L.S. Management of transverse capacitive compensation installations for electrified railways. CRI TEI. Railroad trance. Ser. "Electrification and energy economy." Express inform. No. 6, 1987, pp. 7-12.

5. Borodulin B. M., German L. A., Nikolaev G. A. Condenser installations of electrified railways. - M .: Transport, 1983. - 183 p.

6. German L.A., Morozov D.A. Calculation of typical tasks of traction power supply of alternating current on a computer. Uch. pos. - M .: MIIT 2010. - 59 p.

7. German L.A. Matrix methods for calculating the traction power supply system. Uch. pos. 4.1. - M.: RGOTUPS, 1998, 36 p. and part 2. M .: RGOTUPS, 2000, 38 p.

8. Rules for devices of the traction power supply system of the railways of the Russian Federation CE-462. - M .: MPS, 1997, 79 p.

Claims (1)

The method of voltage regulation at an alternating current traction substation with three-phase transformers according to the star-delta connection scheme, equipped with a load voltage regulation device (RPN) and a single-phase stepwise adjustable transverse capacitive compensation (KU) installation with voltage transformers and bus current transformers 27.5 kV and KU, by changing the voltage on the 27.5 kV buses with a given time delay when the main threshold voltage levels are reached with the on-load tap-changer and on (off) of the next KU stage, characterized in that additional threshold levels of voltage regulation U _kmin and U _kmax and a calculation unit containing a unit for calculating the partial derivatives of power losses (loss increments) in the power supply system to voltage deviations by ΔU using on-load tap changer and (or) by switching on (off) the next KU stage and the corrected mode calculation unit with determining new values of power losses in power supply systems, connected to voltage transformers and t ok of buses 27.5 kV and KU, and previously, at voltages within the boundaries of additional threshold levels of voltage regulation, the power losses of all the corrected versions of the new modes are calculated according to a given voltage increase ΔU by the expression:
ΔP (ΔU) _i = ΔP _o + S _nj ΔUj,
where ΔP (ΔU) _i is the power loss at a given voltage increase by ΔU when calculating the "i" -th version of the new mode;
ΔP _o - the value of power losses in the power supply system in the initial mode;
S _nj is the coefficient of sensitivity of changes in power losses to changes in the "j" -th voltage deviation;
ΔUj - specified for calculations, the "j" th voltage increase,
then choose the corrected mode option with the least power loss ΔP (ΔU) _nm and
if ΔP (ΔU) _nm <ΔP _o , as well as U _kmin ≤U <U _kmax ,
then, with a given time delay, the on-load tap-changer is switched and / or turns on (off) the next stage of the switchgear, and otherwise either increase the voltage increase, or cancel the switch-on switch and (or) turn on / off the switchgear.