WO2006087402A2 - Method for the continuous regulation of voltage ratio in transformers - Google Patents

Abstract

The invention relates to a method of regulating the output voltage from power transformers commonly used in electrical transport and distribution engineering. The inventive method is performed using a single-phase or three-phase power transformer having a series regulating transformer connected thereto and the electronic voltage-regulating device. With said method, a continuously-regulated voltage is obtained at the final output of the aforementioned devices, which is maintained fixed when the existing voltage at the input thereof is within a determined variation range, without incorporating mechanical elements that can generate stress and wear in standard devices, as well as eliminating the problems associated with the electric arc that is produced upon opening circuits mechanically.

Description

Title

Continuous regulation procedure of the ratio of voltages in transformers

Object

The present invention, as expressed in the statement of this Descriptive Report, refers to a procedure that allows to regulate continuously the relationship of voltages in transformers without mechanical elements, based on the use of electronic systems and reducing the number of semiconductor valves.

The present invention finds its scope in the electrical sector, more specifically in the voltage regulation devices of the power transformers. Within this field, it can be applied to any type of power transformer, be it distribution, transportation, generation or other special uses.

State of the art

Historically, in the expansion of electricity transmission and distribution networks, the need has been observed to use methods that can alleviate the different voltage variations existing in the power lines depending on the level of load to which they are subjected. This need is based, not only on maintaining the tensions of the different points of the electric networks within the margins regulated by the different standards and regulations ("Characteristics of voltage delivered by generic distribution networks", European Standard EN50160, 2001 ), but also in reducing the technical losses due to the movement of the electric energy itself. One of the equipment that has most come into play in this area, has been the voltage regulator of power transformers using on-load tap-changers. These equipments allow modifying the relationship of tensions existing in a transformer by means of the variation of the ratio of turns of the same using a mechanical device. On-load tap-changers are the most commonly used devices such as voltage regulators in electric transport and distribution networks, both in high and medium voltage, since the beginning of these networks, as we understand them today, until The present. It is a very robust mechanical equipment that introduces negligible losses in the operation of electrical networks. On the contrary, they have the problem that since they are mechanical switches that open and close circuits, they are slow devices with little capacity to respond to sudden changes in the conditions of the network; In addition, its regulatory possibilities are limited to a series of steps. It also happens that, in order to minimize the effects produced by the electric arc that occurred during the opening of the circuits, these equipments employ a spring system that causes the operating times of the final switching of the circuits to be of the order of 60ms ( the total operating times are of the order of several seconds), causing great mechanical fatigue to the elements that make up the regulators. The combined effect of the appearance of electric arcs and mechanical fatigue due to its own operation cause these equipments to have a high maintenance and be one of the weakest areas of the electric networks.

The tap changers under load have hardly undergone modifications since their inception, almost a century ago; although lately, there are real attempts to improve them trying to reduce or eliminate the electric arcs produced during their operation, as well as their effects. In addition to the different studies on materials that may be little affected by the electric arcs, the use of vacuum switches and semiconductor-based schemes are being used, so that they support the mechanical device, opening operations are performed and closing the circuits inside them (H. Jiang et al. "Fast Response GTO Assisted Novel Tap Changer", IEEE Transactions on Power Delivery, pp 111-115, January 2001). There are also studies on new regulation procedures based exclusively on semiconductors (P, Bawer et al, "Solid State Tap Changers for Utility Transformers", 0-7803-5543- 6/99 IEEE pp 897-902; O. Demirci et al, "A new Approach to SoMd- State On-Load Tap Changing Transformers", IEEE Transactions on Power Delivery, pp 1-10. Jun. 1997). These methods not only eliminate the existing problem due to the electric arc, but also significantly increase the response speed of the regulator by eliminating the mechanical components. On the other hand, the existing restriction regarding the limitation of steps is maintained and a large number of semiconductors is used, implying considerable size and losses that make it impossible to implement it at an industrial level, taking into account the state of the art of The power electronics existing today. In the case of medium to low voltage transformations, tap changers are usually not used under load, but only the possibility of making variations in the relationship of voltages with the transformer without load is used. In these cases, the switch is placed in the position that a priori is considered most advantageous depending on the expected variations in the medium voltage network and the location of the transformer in it.

In the latter case, there is the possibility of including some voltage regulators, based on switches or contactors, independent of the transformers, so that the voltage can be raised with a small number of steps. Some studies about semiconductor-based equipment are also known (O. M. Ruiz, A. Gómez. "Solid-State Voltage Regulator for Dispersed Rural Distribution Systems", IEEE Bologna PowerTech, Jun. 2003). Once evaluated the state of the art in the matter the

"Continuous regulation procedure of the ratio of voltages in transformers" provides the advantage that the electronic systems used in the regulation are coupled by electromagnetic connections that allow reducing the voltages and intensities applied to the semiconductors, minimizing losses and wear of such equipment. Thus, with the application of the electronics to a fraction of the network voltages and the intensities supplied by the transformer, the harmonic distortion that can be introduced into the global currents and voltages is greatly reduced.

On the other hand, by not including mechanical elements, the response times of the voltage regulator can be considerably reduced, increasing the number of operations allowed by the equipment to the point of achieving continuous regulation. Thanks to this possibility, not only is the level of quality of electricity supply increased by facilitating a higher level of control, but voltage fluctuations due to customers with violent variations in their requests for electrical energy can be reduced, such as This may be the case of arc furnaces, high-speed railways, some cogenerators, and so on. It is also possible to ensure adequate voltage levels to customers that are connected at low voltage by reducing, and even eliminating, fluctuations that may exist in the medium voltage supply. An added advantage to the regulator that is proposed with the present invention is that when carrying out an independent regulation by phase it is possible to balance the output voltages, in cases where the network voltages arrive unbalanced or an unbalanced load causes imbalances in the voltage of exit. Finally, it is important to highlight that the technique used in the connection of electronic equipment will not compromise, in the event of a breakdown of semiconductors, the electrical continuity between the networks that connect the transformer. Description of the invention

The "Continuous regulation procedure of the voltage ratio in transformers" is carried out from a single-phase or three-phase power transformer to which a series regulation transformer and the electronic voltage regulation equipment are connected. The objective pursued with this procedure is to obtain in the final output of the equipment a voltage, regulated continuously so that it can remain fixed when the voltage existing in the input of the same, remains within a certain range of variation. Specifically, in the case of single-phase power transformers, it can be carried out according to configuration with regulation in the secondary or primary, making use of an electronic device that, through a series transformer injects a regulated voltage that is added or subtracted from the existing in the secondary or primary of the power transformer respectively, The electronic device can be a chauffeur reducer, although any other configuration could be used. The choice of electronic systems based on the switching of devices, such as the alternating reducer driver, is justified by its ability to ideally generate a continuously controlled output voltage based on the input voltage using a minimum number of semiconductors that allow achieve compact schemes with reduced losses.

The connection scheme used in the regulator transformer is carried out so that the voltages and currents applied to the electronic devices are as small as possible. In addition, if the electronic system is only applied to the regulated voltage fraction, the harmonic components introduced by the use of non-linear electronic elements are applied only to said voltage fraction. Increase of the regulation margin. Investor.

By introducing an inverter system made by contactors, triaos, or any similar operating device, the regulation range of the procedure is increased by double. With the inverter system when performing the change of direction operation, the voltage injected by the series winding is subtracted from that existing in the network. In this way, if we choose suitable turns ratios taking into account this new effect, the possible regulation range is doubled or, failing that, the power to be controlled by the electronics and the harmonic injection due to the Ia is reduced by half use thereof.

Performing the switching of the switches in the moments in which hardly any intensity passes through them, it is not necessary to have devices with a high cutting power, nor systems that help reduce or eliminate the possible electric arcs that usually occur in the use of switches.

Power reduction in the electronic system. Reduction of the harmonic component.

There are cases in which it is possible to use an electronic system with semiconductors of lower nominal power than the one that can circulate due to the regulation, such as cases of high power transformers. Thus, in the case of regulation in the secondary of the power transformer, introducing several primaries, the current existing in each winding is divided between the different semiconductor blocks arranged in the primary of the transformer. By properly crossing the opening and closing moments of the switches that make up each of the drivers, it is also possible to reduce the injected harmonics.

With the proposed configuration if it is desired to divide the intensity by n, it will be necessary to use n chauffeurs and n primary windings in the series transformer. In the same way a configuration can be made with regulation in the primary of the power transformer.

Realization with a single magnetic core. To reduce the size of the equipment, the power and regulation transformers can be mounted on a single magnetic core in both single-phase and three-phase schemes.

Thus, in the case of a single-phase power transformer, the magnetic core consists of a regulation window and another transformation window; so that the transformation window is the one that transforms the power and the regulation window adjusts the output voltage to its desired value, provided that the voltage existing in the secondary is bearable by the electronics. That is, in single phase power transformers with

The configuration of a single magnetic core with regulation both in the secondary and in the primary one, the transformation window corresponds to the power transformer, while the regulation window corresponds to the series regulation transformer. In both cases of regulation, the electronic system is connected directly to the secondary and the amplitude of the input voltage to the regulation window is regulated by the electronic system.

Thus, the transformation window, with ni and n-turns, and the regulation window, with n _s1 and n _s2 turns, act as separate power transformers with magnetic fluxes Φ _t and Φ _r , respectively. In the magnetic column that belongs to both windows, the magnetic flux that circulates through it is obtained from Φt - Φr, Description of the figures

Next, in order to facilitate a better understanding of this descriptive report and forming an integral part thereof, some figures are attached in which the following has been represented by way of illustration and not limitation:

• Figure 1, - "Continuous regulation procedure of the ratio of voltages in transformers" with secondary regulation.

• Figure 2 - "Continuous regulation procedure of the ratio of voltages in transformers" with regulation in the primary.

^« Figure 3a -" Procedure of continuous regulation of the ratio of voltages in transformers "with connection of the electronic equipment from an outlet of the power transformer.

^« Figure 3b -" Procedure of continuous regulation of the ratio of voltages in transformers "with connection of the electronic equipment from the primary of the power transformer.

^» Figure 3c -" Procedure of continuous regulation of the ratio of voltages in transformers "with connection of the electronic equipment from the secondary of the power transformer. "Figure 3d -" Procedure of continuous regulation of the ratio of voltages in transformers "with connection of electronic equipment from the output line.

• Figure 4a - Reducing drivers according to a triangle connection for three-phase transformers. ^» Figure 4b - Reducing drivers according to star connection for three-phase transformers.

^« Figure 4c - Reducing drivers according to v-connection for three-phase transformers.

• Figure 5a - Switch scheme that allows the realization of the inverter system in the deactivated position. ^« Figure 5b - Switch scheme that allows the realization of the inverter system in activated position.

• Figure 6 - Two drivers and two primary windings in the series transformer. • Figure 7a - Example of making connections using a two-window core with secondary regulation.

• Figure 7b - Example of making connections using a two-window core with regulation in the primary.

¹ Figure 8 - Example of making connections using a two-window core with primary regulation for three-phase transformers

The following details are numbered in them: 1. Power transformer consisting of three windings. 2. Transformer regulation series consisting of two windings.

3. Electronic voltage regulation equipment.

4. Regulation window.

5. Transformation window.

Preferred Embodiment Example

By way of example of a preferred embodiment of the invention, the "Continuous regulation procedure of the ratio of voltages in transformers" can be carried out according to regulation in the secondary, as shown in the diagram represented in Figure 1 or in its symmetric according to regulation in the primary, represented in Figure 2. The power transformer (1) is composed of three windings. The winding n, defines the primary of the transformer and has no turns; the n ₂ defines the secondary with n ₂ turns and the n _r defines the winding of regulation of the power transformer, with n _r turns.

The aim with this method is to obtain at the output of a voltage equipment, Uzwnea, regulated continuously so that it can remain fixed when the voltage existing in the inlet, Uu¡ _line, remains within a given range variation. For this, an electronic device will be used that, through a series transformer (2), formed by two windings, n _s1 and n _S2 , with n _s1 and n _s2 turns respectively inject a regulated voltage that is added or subtracted from Ia existing on one side of the transformer.

Looking at Figure 1, it is necessary that the voltage that arrives on the line, U ₁ | [ _ne a ⁼ U ₁ traffic, the power transformer (1) is transformed according to the ratio of turns to _t , resulting in a secondary voltage of the transformer U _2t ra _f o-

U ° Itrafo ~ --J ^or J

As shown in Figure 1, of the same power transformer, a voltage U _{re is taken} that is to be introduced into an electronic device (3) that acts as a transformer with an easily adjustable voltage ratio.

U re ~ ^~ U \ trφ ~ ^ Urafo H ₁ u _r The electronic device represented in the figures by a reducing chauffeur, although any other configuration can be used, will modify the amplitude of the input voltage so as to provide an output voltage U _rs .

U _n = DU _n with De [0,1]

The series transformer (2) modifies the regulated voltage U _rs to the necessary regulation values in the secondary of the transformer by:

^ ₂ , = - U _n = -U _rs

The voltage U _2r is added to the secondary voltage of the power transformer, obtaining the desired voltage U ₂ [ _ín ea, verifying that said value depends on the regulation of the electronic system, D.

^ - 'Hlπea ~ ^ ilrafo ⁺ ^ Go

U TT _{2! Mea} = ^ U _Wnύa with * ₂ = 1 + - * -; 2> e [θ, l] a, a _r a _í

In the alternative embodiment of Figure 2, it can be seen that the regulated voltage obtained at the output of the electronic equipment (3), U _rs , is added or subtracted from the voltage that arrives on the line, Uni _ne a, once modified to the regulation values required by the series transformer (2), U _n . In this way there is an input voltage to the power transformer (1), already regulated, U-i tra _f o, so that the output voltage U ₂ i _fπea = U ₂ trafo is set at its value of reference varying the regulation of the electronic system, D.

one

^ lllnsa ^' * -' Minea with K; From [OA] to, D

1- ar ° s In Figures 3a, 3b, 3c and 3d a series of alternative variations to the connection systems of the electronic equipment shown in Figure 1 are shown. These variants can also be applied to modify the configuration of Figure 2. In the cases of Figures 3c and 3b the proposed connection system also offers the possibility of regulating voltages in a line, regardless of the existence or not of a power transformer.

For the electronic regulation of tensions, the use of systems capable of reducing the tension has been preferred, presenting as a basic possibility the use of an alternating reducer driver (3) which in its single-phase version is represented in Figures 1 and 2, while that preferred examples of three-phase assembly are introduced in Figures 4a, 4b, 4c.

The use of electronic systems based on the switching of devices has been chosen, as is the case with the alternating reducer chauffeur, due to their possibility of offering, ideally, a continuously controlled output voltage depending on the input voltage using a minimum number of semiconductors that allow to achieve compact schemes with reduced losses.

The connection scheme used in the regulating transformer to power the electronic system is justified, among other reasons, because it is required that the voltages and intensities applied to the electronic devices be as small as possible. It can be verified that (at the power that semiconductor valves have to control, S _e ι _eo , it is, at most, percentage equal to the desired regulation range if we refer to the nominal power of the transformer, S _traf o. Thus, if we define the unit regulation range, Δreg _pu , as:

Δreg _pu = - a ', U _2n U. linάx for secondary and primary regulation cases: max {S _tltc ) U _hnáx -U _x \ _¡ min = Are 'ü o: pu

S _1n -a / or U-linάx

A second characteristic, also fundamental, that motivates the choice of this connection scheme is that when applying the electronic system only to the fraction of regulated voltage, the harmonic components introduced by the use of non-linear electronic elements are applied only to said fraction of tension. In this way, when the voltage coming from the network is added, the percentage harmonic components injected into the network are greatly reduced, the quality indices of the generated electric wave are significantly improved.

Increase of the regulation margin. Investor.

A technique that makes it possible to increase the regulation margin of the procedure, by folding it, is the alternative use of an inverter system made by contactors, triacs, or any similar operating device, following the scheme shown in Figure 5a and 5b.

The idea of using the inverter is based on the fact that when performing the change of direction operation, the voltage injected by the series winding is subtracted from that existing in the network. In this way, if we choose suitable turns ratios taking into account this new effect, the possible regulation range is doubled or, failing that, the power to be controlled by the electronics and the harmonic injection due to the Ia is reduced by half use thereof. Thus, in the case of secondary regulation, there is:

y para el caso de regulación en el primario: U, —Ir TT lllnea ^Λl/m ^u llínea con £e[θ,l]

La conmutación de los interruptores se realiza en los momentos en los que D es prácticamente cero, por Io que apenas pasa intensidad por los mismos. Este efecto provoca que no sea necesario disponer de dispositivos con un elevado poder de corte, ni de sistemas que ayuden a reducir o eliminar los posibles arcos eléctricos que suelen producirse en Ia utilización de interruptores.

and in the case of regulation in the primary: U, —Go TT line ^Λ l / m ^or line with £ e [θ, l]

Switching of the switches is carried out at times when D is practically zero, so that hardly any current passes through them. This effect causes that it is not necessary to have devices with a high cutting power, nor systems that help reduce or eliminate the possible electric arcs that usually occur in the use of switches.

Power reduction in the electronic system. Reduction of the harmonic component.

There are cases in which it is possible to use an electronic system with semiconductors of lower nominal power than the one that can circulate due to the regulation, such as cases of high power transformers.

Figure 6 shows an alternative connection method capable of reducing the intensity that circulates through the semiconductors, dividing it by the number of windings arranged in the primary of the series transformer with the advantage of allowing to reduce the injected harmonics if the moments are properly crossed opening and closing of the switches that make up each of the drivers. The idea is that, by introducing several primaries, the current in each winding is divided between the different semiconductor blocks; Thus, for n windings, in the case of regulation in the secondary of the power transformer there is a power to be controlled, Seiec, for each block of:

windings ^

In the same way it is obtained for regulation in the primary:

* -T TT - ^Aregp " ^u ^ _x Specifically, in figure 6 two chauffeurs and two primary windings have been represented in the series transformer, so that the intensity that is necessary to regulate is divided between both chaupers,

As already indicated, the harmonic injection in the networks will be reduced because if a pulse width control is used in each of the electronic systems so that the switching of the different equipment is alternated, it can cause the cancellation of harmonics introduced at the lowest frequencies.

Realization with a single magnetic core.

Alternatively, it is possible to reduce the size of the equipment, by mounting the power and regulation transformers on a single magnetic core as shown in the single-phase diagrams of Figures 7a and 7b or three-phase in Figure 8. Thus, the embodiments of Figures 7a and 7b are based on the use of a magnetic core composed of a regulation window (4) and a transformation window (5), so that the transformation window (5) is the one that transforms the power and the window of regulation (4) adjusts the output voltage to its desired value, provided that the existing voltage in the secondary is bearable by the electronics.

In the case of regulation in the secondary figure 7a, the regulation window (4) will be dedicated to providing a variable voltage (U ₂₁ -) that will be added to the voltage obtained in the secondary of the transformation window ( U ₂ tra _f o) to obtain the regulated output voltage (U ₂ ) _line ). In the case of regulation in the primary figure 7b, the regulation window (4) will provide a voltage (U _1r ) that, added to the voltage of Ia (A _f πea), provides the regulated voltage (U _1traf o) that feeds the primary winding of the transformation window (5). In both cases, the amplitude of the input voltage to the regulation window (U _rs ) will be regulated by the electronic system. It is not considered necessary to make this description more extensive so that any expert in the field understands the scope of the invention and the advantages derived from it. The materials, shape, size and arrangement of the elements, as well as the equipment itself Electronic voltage regulation are susceptible to variation as long as this does not imply an alteration in the essentiality of the invention.

Claims

1.- Procedure for continuous regulation of the voltage ratio in transformers characterized by being carried out from a series transformer or regulation transformer (2) in the secondary (figure 1) that will allow adding a certain voltage, U _2r to that obtained from the secondary winding of the power transformer (1) U ₂ transformer. 2.- Procedure for continuous regulation of the voltage ratio in transformers according to claim 1 characterized in that the voltage that feeds the regulation transformer (2) U _rs is regulated by electronic equipment. (3) that allows the voltage received at its input U _re 3 to be varied, - Procedure for continuous regulation of the voltage ratio in transformers according to claims 1 and 2, characterized in that, alternatively, the regulation transformer (2) can be mounted. in the primary (figure 2). 4.- Procedure for continuous regulation of the voltage ratio in transformers according to claim 1, 2 and 3, characterized in that, alternatively, in a seral regulation transformer in the secondary, the power supply of the electronic system can be carried out according to the intermediate outlet of the secondary of the power transformer (figure 3a), according to an independent transformer fed by pumps from the primary of the power transformer (figure 3b), according to an independent transformer fed by pumps from the secondary of the power transformer (figure 3c) or from the output of the equipment transformer-regulator (figure 3d) and equivalently in a series regulation transformer in the secondary. 5.- Procedure for continuous regulation of the voltage ratio in transformers according to claim 1, 2, 3 and 4, characterized in that, alternatively, and in the case of three-phase transformers, the electronic voltage regulation equipment can be carried out according to reduction choppers. with delta connection (figure 4a), star connection (figure 4b) or V connection (figure 4c). 6.- Procedure for continuous regulation of the voltage ratio in transformers according to claim 1, 2, 3, 4 and 5, characterized in that, alternatively, use can be made of the switch scheme according to the inverter system (figure 5a and 5b) increasing the regulation range of the equipment, or reducing the power to be controlled by the electronics and, consequently, the harmonic distortion that the electronic equipment can inject. 7.- Procedure for continuous regulation of the voltage ratio in transformers according to claim 1, 2, 3, 4, 5 and 6, characterized in that, alternatively, an intensity division system can be used (figure 6) that incorporates several pieces of equipment. electronics implies a reduction of the power to be controlled by each of them, as well as a reduction of the harmonic injection of the set for regulation carrier signals of each of the chosen electronic equipment. 8.- Procedure for continuous regulation of the voltage ratio in transformers according to claim 1, 2, 3, 4, 5, 6 and 7, characterized in that, alternatively, the power and regulation transformers can be mounted on a single magnetic core. in single-phase systems with regulation in the secondary or primary according to figures 7a and 7b respectively, or in three-phase systems according to figure 8.