|Title of Invention||
"CONTROLLED SHUNT REACTOR OF TRANSFORMER TYPE"
|Abstract||A controlled shunt reactor of transformer type is provided which comprises it circuited magnetic coal (12, 13, 14, 15); a main winding (1); a compensating winding (2) connected as delta and a control windings (3, 4). The control winding is divided into two series connected sections (3, 4). A main thyristor block (8) is connected in parallel to the total control winding (3, 4) and thyristor blocks (5, 6, 7) having series connected chokes (9, 10, 11) are provided in parallel to control winding section (4).|
|Full Text||This invention relates to a controlled shunt reactor of transformer type in the field of electrotechnic and electro power technic and can be used as fast regulated inductive impedance for the regulated compensation a surplus reactive capacity of transmission lines and for the regulation of condenser batteries capacity.
There are known controlled reactor structures for the variable reactors capacity compensation, which are controlled by saturation of their magnetic core by means of special winding with direct current (I.V.DOROZHKO, I.V. Leites, "Comparative analysis of different controlled reactor structures". Electriches tvo, 1990, N.2, p. 18-24).
There are disadvantages associated with the controlled reactor structures.
One of the main disadvantages is that the deficiencies of these structures are a high level of additional power losses because of saturation of main limbs of a magnetic core, the complicated structure of a magnetic core and windings because for each phase the magnetic limb is divided into two separate parts, the increased contents of highest harmonics in the current and very big response time (more than 0.3 sec.).
There is another type of controlled reactor of BBC production with control winding shunted by anti-parallel connected thyristors. The current variation is realized by variation of a firing angle of thyristors.
The main disadvantages associated with such structure is a high level harmonics contents, caused by currents through thyristors and transformed into the main reactors winding (K. Reichert, Y. Kauferle and H. Clavitsch), Controllable reactor compensator for more extensive utilization of high voltage transmission systems. CIGRE-1974, Rep. 3t-04.
Another disadvantages of this structure is that there is a high level of power losses.
To overcome the above disadvantages, the most close technological development as a prototype is a controlled shunt reactor of transformer type in accordance with the international Patent PCT/RV96/00037 having a priority date of 29.11.95.
This reactor eliminates the above-mentioned deficiencies. However, there are disadvantages associated with this structure.
One of the main disadvantages is that the structure of a control winding is complicated because it consists of some series connected layers (as a minimum 4) which are controlled independently.
Another disadvantages is that there are too many taps from each points of series section of a control winding connection.
Yet another disadvantages is that there are too many bushings at the reactor's cover for each tap from the intermediate point of a reactor.
Further disadvantages is that the turns of a control winding are distributed irregular across of total winding.
Yet another disadvantages is that the nominal current for all thyristors in a control circuit is the same and equal to nominal current of a control winding.
Still further disadvantages is that the nominal voltages for each thyristor in the controlling circuits are different; and the potentials at the thyristors are different for each section.
Therefore the main object of the present invention is to provide a controlled shunt reactor of transformer type which is simple and effective and can be used as fast regulated inductive impedance.
An object of the present invention is to propose a controlled shunt reactor of transformer type with a decreasing of a number of control windings upto two.
Another object of the present invention is to propose a controlled shunt reactor of transformer type where the number of intermediate taps decreases till one and number of additional bushings decreases upto one.
Yet another object of the present invention is to propose a controlled shunt reactor of transformer type in which the current in controlling thyristors for the intermediate steps of regulation decreases significantly.
A further object of the present invention is to propose to controlled shunt reactor of transformer type in which the nominal voltage for each thyristor's block for all intermediate steps of regulation is the same and the same is the maximum potential for each thyristor's block for intermediate steps of regulation.
A still further object of the present invention is to propose a controlled shunt reactor of transformer type in which the reactors structure and structure of a controlling system are significantly more simple.
According to the present invention there is provided a controlled shunt reactor of transformer type comprising a circuited magnetic core; a main winding; a compensating winding connected as delta; and a control winding; characterized in that said control winding is divided into two series connected sections; a main thyristor block being connected in parallel to the total control winding; and thyristor blocks with series connected chokes being provided in parallel to control winding section.
The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non limiting exemplary embodiments of the invention represented in the accompanying drawing.
Fig. 1 shows the principle electrical scheme of the reactor with parallel connection of control circuits with chokes and thyristor's block's to one section of a control winding.
Fig.2 shows the scheme of reactor's winding arrangement.
Fig.3 shows a second embodiment of the principle electrical scheme of the control circuit reactor with parallel connection of filter circuits, ie. chokes and condensors to one section of a control winding.
Fig.4 shows a third embodiment of the principle electrical scheme of a control circuit reactor with parallel connection of filter circuits to the compensating winding.
In accordance with the present invention the principal embodiment of the control circuit reactor consists of a circuited magnetic core (12,14) with the
main winding (1) at one side (Figs.1& 2) and the compensating
winding (2) and control winding which is divided in two
sections (3,4)' which is series connected. Thyristor blocks
(5,6,7) are shown with series inserted chokes (9,10,11). The main thyristors (5,6,7) alongwith series inserted chokes (9,10,11) are together inserted in parallel to the section of control winding (4). The main thyristor's block (8) is inserted in parallel to total control winding (3,4) and is without a choke.
The detail scheme of the reactor's windings arrangement is shown in figure 2. The main limb of a magnetic core (12) is shown at one end of the control winding (3) and the compensating winding (2) and the main winding (1). The additional limb of the magnetic core (14) is shown on the other side of the main limb of a magnetic core (12). The yoke of the magnetic core (13) is shown supporting the magnetic core (12,13) and the main (1) control (3) and compensating (2) windings.
The decreasing of third harmonic in the current of three phase reactor compensating winding 2 are provided, connected in delta.
The controlled conduction of thyristors (Fig.1) results in the increasing of reactor's current from idle value upto nominal value. When thyristors blocks 5,6,7 are conducting fully the reactor's current comes to 50% from nominal current. When thyristor block 8 is also conducting fully reactor's current comes to 100% from nominal value.
Control winding is a short circuit in the nominal regime of a reactor by thyristor block 8. In this case the main magnetic flux which is produced by a main winding disposes outside of the internal turns of a control winding. The total flux flows through the volume of both windings and in the space between them. That high magnetic flux outside of the magnetic core can produce high additional power losses. For this reason it is necessary to collect this flux and to direct it to the magnetic core. For this purpose additional ring shunts 15 are used fom both sides of windings. Magnetic flux enters into a ring shunt and along its circular path joins the yoke to complete the magnetic path.
The suppression of highest harmonics in accordance with Fig.1 is provided by two different means:
1. In each step of a reactor operation (after the
first) always there is basic sinusoidal current,
provided by previous steps of CSR regulation,
which is bigger than one half of total current.
2. The current, induced in short circuited section
of a control winding, is opposite to the current
produced by the commutated section of the control
winding. For this reason the contents of highest
harmonics and respectively in the current of
the main winding decreases.
The second embodiment of the invention as shown in figure 3 with the control circuit reactor of the same structure with parallel connection of filter circuits,
ie. condensors (19,20,21) to one section of a control
winding (3) instead of thrystor blocks (5,6,7) in series
with current limiting chokes (9,10,11). The chokes (16,17, 18) are of highest harmonics filters and so are the condensors (19,20,21) are of highest harmonic filters.
The third embodiment of the invention the control circuit reactor with simplifiled structure are with parallel connection of filter circuits of chokes (16,17, 18) and condenser (19,20,21) connected to the compensating winding (2). The controlled reactor with simplified structure is without division of the control winding (3) into two sections but with connecting the filters of highest harmonics in parallel to the compensating winding.
The technical result is provided by dividing of control winding of reactor for two series section and by connection of all intermediate regulating circuits in parallel to the first section of a control winding (Fig.1) and special arrangement of magnetic shunts of both sides of winding (Fig.2). Parallel circuits of a controlling device will limit the harmonics to the same permissible level as in the case of a dividing of a control winding for the series connected section.
Ring shunts from both sides of a windings collect the magnetic flux from the volume, occupied by winding and from the space between winding and direct it to yokes. For this reason the power losses caused by leakage flux decreases significantly.
In the next variant of the technical result providing the highest frequency component in a reactor current, filters of highest harmonics are connected in parallel to one section of control winding (Fig. 3) instead of some parallel circuit with thyristors and current limiting chockes. In this case control system is significantly easier, because it is necessary to provide the control of only one thyristor's block.
In the next variant of the technical result providing all parallel filters are connected with the compensating winding for each phase of a reactor (Fig.4). In this case the reactor structure is simplier because it is not necessary to divide the control winding into two sections and to arrange the additional tap from a control winding. Thus compensating winding provides the limitation of all highest harmonics (3-rd, 5-th, 7-th ).
A simple reactor's structure allows to determine reactor's parameter's by means of a formula
where Ush.c%is the short circuit voltage in the percent of the nominal phase voltage Uph ;
f is the nominal frequency;
N1 is the number of turns in the main winding; a12 is the radial gap between main and control windings;
a1 and a2 are radial dimension of these windings corespondingly;
d12 is the average diameter of a gap between the main and control winding;
1o is the distance between upper and lower ring magnetic shunt (see. Fig.2)
All values in this formula are given in the SI system of units. In accordance with this formula it is possible to increase of the short circuit voltage till 100 per cent by increasing of a number of turns, radial dimensions of windings and by decreasing of the magnetic core window too.
The suppression of highest harmonic in accordance with Fig.3 and Fig.4 with filters is provided only by second means (by induction of opposite current in the corresponding filter circuit). But in these cases the suppression is more effective because there are no current limiting chokes and for each highest harmonic corresponding filter provides the effective short circuit for the winding connected in parallel (in Fig.3-part 4 of control winding; in Fig.4-compensating winding).
In order to provide this condition for each K-th harmonic it is necessary to select the parameters Lk and Ck of filters in accordance with the relation
It is necessary to take into consideration that the Power frequency curent is flowing through each filter because the filter impedance for Power frequency is equal
It can be seen from (3) that the current is capacitive because K >1.
The calculation shows that the optimum value of Power frequency current, corresponding to the minimum capacity of all filter components, is equal to (4).
where B, is the ratio of the maximum current of f "•
K th harmonic to the nominal current,
^5 is the ratio of short circuit impedances between the main winding and that winding which is in parallel to the filter to the nominal short circuit impedance of the CSR, which is always less than one Fig 1.
Respective value of CSR parameters are
In order to provide the effective operation of compensating winding for suppression of all highest harmonics, it is necessary to dispose it outside the control winding which produces highest harmonics.
The distinctive peculiarity of the controlled reactor of transformer type is the fact, that in the nominal regime when short circuited control winding 3 the magnetic flux is almost completely displaced from the volume, arranged inside the control winding 3, into the space between the main winding 1 and the control winding 3, and also into the area, occupied by these windings. In order not to let big additional losses, in particular, in the reactor's tank, it is necessary to collect this flux and direct it into the magnetic core. This problem can be solved in the following way.
The face parts of windings and the gap between the windings are covered on the top and the bottom by spiral circle shunts 15 with radial cut, which excludes the laying currents along the shunt 15, abutting to the upper and lower
yokes of reactor (Fig.5). The magnetic flux in the circle shunt 15 is directed to the yoke 13 and then along the yoke 13 it is directed either to the additional limbs when phase-by-phase type of reactor, or is circuited round the flux paths of other phases.
In the regime of maximum content of the third harmonic about 70% of the magnetic flux is displaced from the main limb of the magnetic core. For this reason in order to exclude the third harmonic in a known way by connecting into a triangle the special compensation winding 2 it is necessary to place the compensation winding 2 outside of the control winding 1, which is the generator, of the highest harmonics in the current wave form of the reactor.
Because the reactor's voltage is practically constant independently of its operation regime, the flux coupling with the main winding of the reactor should be constant. The displacement of the magnetic flux from the main limb leads to the fact, that its part does not couple with all the turns of the main winding 1 . This circumstance determines the necessity of total flux increasing in the air comparatively with the flux in the main limb. The factor of the flux increasing in the air in the normal regime comparatively with the flux in the main limb in the idle regime is determined by the formula (7).
where d12 and a12 are the average diameter and the width (radial size) of the gap between the main winding 1 and the control winding 2; a1 and a2 are the widths (radial sizes) of the main winding 1 and the control winding 2.
Correspondingly the cross-section of the magnetic shunts, which collect the magnetic flux and the direct it to the yokes, should be selected with the consideratin of
the magnetic flux in the air.
The magnetic flux in the yokes is less than the magnetic flux in the air, but more than the magnetic flux in the main limb. The factor of the magnetic flux increasing in the yokes in the nominal regime comparatively with the flux in the main limb in the idle regime is determined by the formula (8).
Correspondingly it is necessary to increase the cross-sections of the yokes comparatively with the cross-section of the main limbs in consideration of this factor.
The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims.
1. A controlled shunt reactor of transformer type comprising:
- a circuited magnetic core (12,13,14,15);
- a main winding (1);
- a compensating winding (2) connected as delta; and
- a control winding (3,4);
characterized in that
said control winding is divided into two series connected sections (3, 4); a main thyristor block (8) being connected in parallel to the total control winding (3,4); and thyristor blocks (5,6,7) with series connected chokes (9, 10,11) being provided in parallel to control winding section (4).
2. A controlled shunt reactor as claimed in claim 1 wherein the said circuited
magnetic core comprises a main limb (12) with a yoke (13) and an
additional limb (14) with a pair of ring magnetic shunts (15).
3. A controlled shunt reactor as claimed in claim 1 wherein the said
compensating winding (2) is connected in delta for decrease of third
harmonic in the current of the three phase reactor.
4. A controlled shunt reactor as claimed in claim 1 wherein the said
thyristors blocks (5, 6, 7) inserted in parallel to control winding section
(4) and the said main thyristor's block (8) which is inserted in parallel to
the total control winding (3, 4) and both conducts 50 % from nominal
current each and together comes to 100 % from nominal value.
5. A controlled shunt reactor as claimed in Claim 1
wherein a pair of said ring magnetic shunts (15) are provided
from both sides of windings for the high magnetic flux
outside the magnetic core to enter and pass along the said
ring shunts (15) along its circular path to join the yoke
to complete the magnetic path.
6. A controlled shunt reactor of transformer type as
claimed in Claim 1 comprising of circuited magnetic core
(12,13,14,15), the main winding (1), compensating winding
(2) connected as delta, and control winding (3), divided
into two series connected sections (3,4) wherein condensers
(19,20,21) of highest harmonics are connected to one section
of control winding (4) instead of thyristor blocks (5,6,7)
in series with current limiting chokes (16,17,18).
7. A controlled shunt reactor of transformer type as*
claimed in Claim 1 comprising of circuited magnetic core
(12,13,14,15), the main winding (1), compensating winding
(2) connected as delta and the control winding (3) which
is not divided into two sections wherein chokes (16,17.18)
in series with condensors (19,20,21) are inserted in
parallel to the compensating winding (2) and a thyristor's
block (8) inserted in parallel to the control winding (3).
8. A controlled shunt reactor of transformer type as
herein described and illustrated.
|Indian Patent Application Number||1092/DEL/1998|
|PG Journal Number||03/2008|
|Date of Filing||27-Apr-1998|
|Name of Patentee||ALEXANDROV GEORIGIY NICOLAEVICH|
|Applicant Address||BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.|
|PCT International Classification Number||H02H 007/04|
|PCT International Application Number||N/A|
|PCT International Filing date|