JPS63194315A - Three-phase three-winding transformer - Google Patents

Abstract

PURPOSE:To contrive realizing a three-phase three-winding transformer for SVC by providing the windings of the transformer in the order of a secondary winding, a tertiary winding and a primary winding from the side of the main leg of an iron core. CONSTITUTION:In a three-phase three-winding transformer 11 for SVC, a primary winding 7 and a secondary winding 3 which are star connections and a delta connection stabilizing winding 12 are wound around an iron core and a reactor 13 is connected between the terminals a1, a2 of the stabilizing winding 12. The line terminals U, V, W of the primary winding 7 are connected to an electric power system 1, a neutral point terminal O is directly grounded, the secondary winding 3 is connected to TCR5, TCR6 and a neutral point Q and a neutral point N are also connected. Since the primary winding is the star connection and the neutral point can directly be grounded in this way, the direct connection to an extra-high voltage system is possible, the primary winding can be made graded insulation and reduced insulation, the structure of the primary winding is convenient for an insulating structure since a high voltage line terminal can be drawn from the center of the winding and a low voltage neutral point terminal can be drawn from the upper and the lower ends of the winding easily and the transformer can be made compact for these reasons.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is a three-phase static reactive power compensator b'ffi (abbreviated as SVC) for improving the stability of power systems. It concerns a three-winding transformer.

(Prior Art) In recent years, as the demand for electric power has increased, power transmission voltage has also increased, and the size of electric power systems has also increased. Therefore, fluctuations in the grid caused by changes in the amount of transmitted electricity, changes in the configuration of the power transmission network, switching on and off of lines due to failures, switching on and off of loads, etc. become large, so in order to suppress such fluctuations and improve and increase system stability. SvC is used.

In conventional SvC, in order to remove the 5th and 7th harmonics, a transformer with a primary star connection and a secondary triangular connection is used.

The mainstream is a three-phase 12-pulse system that uses two star-connected transformers for both the primary and secondary, but for example, IEEE Tra
nsaetions on Pouer Appara
tus and Systems.

Vol, PAS-102, Na12. Dece＋＊
ber 1983. According to the description on pages 3728 to 3735, a three-phase 12-pulse system using only one transformer as shown in FIG. 5 is proposed. Adopting this method has the great advantage of reducing not only the cost but also the loss of the transformer.

FIG. 5 shows the main circuit configuration. The power system M1 includes a triangular connected primary winding 2 and a star connected secondary winding 3.
An SvC transformer 4, which is wound around an iron core (not shown), is connected to the secondary side of the transformer 4, and a triangular-connected thyristor control reactor (TCR) 5 and a star-connected thyristor control reactor (TCR) 5 are connected to the secondary side of the transformer 4. TCR6 is connected.

The secondary neutral point σ of the transformer 4 and the neutral point N of the star-shaped connection TCR6 are also connected.

The flow of harmonic current, which is important in SvC, will be explained. For 3rd and 9th harmonics, triangular connection TCR5
The 3rd (I3A) and 9th (1, A) of the generated current are the 5th
As shown in the figure, it circulates within the triangular connection ABC, and the third-order Cl5yL9th-order (I) for the current generated in the star-shaped connection τCR6 becomes a zero-sequence current as shown in FIG. , secondary side neutral point H, secondary winding 3.TCR6 and circulate,
Due to the transformer action, the current in the secondary winding 3 circulates to the primary winding 82 and is canceled, and does not flow into the power system 1. For the 5th and 7th harmonics, connect points A and B between CR5 and TCR6.
, C, the condition is such that the current generated by the triangular connection @TCR5 and the current generated by the star connection TCR6 exactly cancel each other out, so that the current does not flow into the transformer windings 2 and 3 and does not flow into the power system 1.

Therefore, the harmonic current flowing into the power system 1 is the same as in the conventional system using two transformers, and the triangular connection TCR5
and the 11th order (Lzt,
-I, 1Y) and 13th harmonic current (I, 3a*113y).

Regarding the case where the primary winding of the transformer is connected in a star shape, see Chapter 6.
It is easy to imagine what will become of the figure.

FIG. 6 shows a three-phase, three-winding transformer 9 in which the primary winding 7 is star-connected and a triangular-connected tertiary winding 8 is added.
The current I3 Y t II '/ which is the 3rd and 9th harmonic components generated by the star-connected TCR 6 circulates in the tertiary winding 8, and other operations are the same as in FIG.

(Problem to be solved by the invention) As shown in FIG. 6, the neutral point O of the primary winding 7 is located at the arrester 1.
It is necessary to connect the neutral point O or use a method that does not draw out the neutral point O to the outside.

The reason for this is that the impedance of the neutral point 0 with respect to the ground becomes extremely large, increasing the zero-sequence impedance of the primary winding RIA7 and the power system 1, and causing the 3rd and 9th harmonics generated by the star-shaped connection TCR6. This is to prevent the current Lym Lv, which is a wave component, from flowing out to the power system 1.

If the neutral point O is directly grounded, the zero-sequence impedance of the primary winding 7 and the power system 1 will be small, and the current IY
A portion of w IsY will flow into the power system 1. If a large amount of harmonic current I3 Y v Is Y were to flow into the power system 1, the harmonic current would cause problems in generators and loads connected to the power system 1, causing problems in system operation. Therefore, such systems are generally not electrokinetic.

On the other hand, the voltage of power systems is often insulation class 170 or higher, and the neutral point 0 of the primary winding of a transformer used in the system is often directly grounded. If the primary neutral point O is not directly grounded, the insulation of the primary winding cannot be reduced, resulting in the transformer being larger in size, weight, and price, so direct grounding is generally used.

Further, even if the primary winding is triangularly connected as shown in FIG. 5, this is disadvantageous in terms of insulation of the primary winding, and is not normally used in transformers that are directly connected to the power system.

The present invention takes the above-mentioned points into account, and even if the primary neutral point O is directly grounded, the current I3 Y e II 1. The amount flowing out is very small and does not pose a problem in practice.
The purpose is to obtain a three-phase three-winding transformer for SvC.

[Structure of the invention]

(Means for solving the problem) The winding arrangement of the transformer 9 in Fig. 6 is normally arranged in the order of the tertiary winding, the secondary winding g, the primary winding from the iron core main leg side, but 1 In the present invention, the secondary winding, the tertiary winding,
Place them in the order of the primary winding.

(Function) By changing the winding arrangement as described above, the zero-sequence impedance distribution between the winding groups is changed, and the zero-sequence reactance of the tertiary winding becomes a negative value.

If this negative reactance value is canceled by connecting a reactor in series with the tertiary winding, the zero-sequence reactance to the tertiary winding can be made zero. When the zero-sequence reactance to the tertiary winding becomes zero, the zero-sequence impedance to the tertiary winding also becomes small, and even if the primary neutral point 0 is grounded, the zero-sequence to the primary winding and the power system Even if the impedance circuit is configured, the tertiary
The current L'l p I! is the ninth harmonic component. l Y is 3
Circulate within the next winding.

It will no longer flow into the primary winding and will not flow into the power system.

(Embodiment) An embodiment of the present invention shown in the drawings will be described below.6 In Fig. 1, a Sanwa three-winding transformer 11 for SYC according to the present invention has a star-connected primary winding 7 and a secondary The winding 3 and the stable winding 12 having a triangular connection are wound around an iron core, and the reactor 13 is connected between the terminals 81982 of the stable winding 12.

The line terminals U, V, and W of the primary winding 7 are connected to the power system 1.
The neutral point terminal 0 is directly grounded.

The secondary winding 3 is connected to TCR5 and TCR6, and the neutral point α
and the neutral point N are also connected.

FIG. 2 shows the winding arrangement of the transformer 11 of the present invention, with the secondary winding 3. Stable winding 12
and each winding of the primary winding 7 is wound in sequence.

The dimensions of those windings are shown below.

The zero-sequence reactance between each two windings in the core type concentric winding shown in FIG. 2 can be approximately calculated by the following equation.

Between the primary winding 7 and the secondary winding [3] % IXo, p-s = K X Qp-s [%]...
...01st volume, t! 7 and stable winding 12 %IXa tP-T= K X QP-T [%]
-・-■ Between the secondary winding 3 and the stable winding 12 %IXo ts-r= K X Qs-t [%]・
・・・・・・ C Tsudashi = 4.961P/(3e2H
) −...G4) f: Rated frequency [H
z, I); Rated capacity lit [MVA] e; 1 turn volt [V/turn.

H; axial height of the winding shown in Fig. 2 [IIWI
I Cor〇,・B, D6・B, D,・8゜Q
p-s −−+ −+□ ・・・・・・■QP−
T ” ””50 1000.0 B1-Bs, D, ~
D6: The radial dimension of the winding shown in 6th [m1] Next, the equivalent circuit of the zero-sequence impedance seen from the secondary winding 3 of the transformer 11 is shown in Figure 3, and the zero-sequence impedance of each branch is 2゜Py Each zero phase reactance% of Zase ZIIT
IXaPe%IXoBe%IXaT is determined by the following formula.

%IXop=' (%IX+wP-3+%IX.,P-
7-% IX. ,3-T)-...<8)%IX,s=
'(%IXneP-8+%lX5sP-T+%Ixo
, 8-7)...(9)%IXoT=↓(%
orP-3+%IX. , P-7+%IX. , 5-t)
- (10) By substituting equations (1) to (10), and further substituting equations (0) to (2), the result is that %IXOT becomes a negative value.

The zero-sequence reactance including each resistance becomes the zero-sequence impedance 2゜P+zos+ZaT,
Z o L is the zero-sequence impedance of power system 1, ZR
is the impedance of the reactor 13.

The current shunt in FIG. 3 is determined by the following equation.

Since %IXoT is a negative value in equation (11), if the reactance value (%IXR) of reactor 13 is set to KxD, - the value of (ZllT+ZR) is only the resistance, which becomes small, so equation (12) The IP represented can be small.

The problem here is how the current I>YtIsY, which is the 3rd and 9th harmonic components generated by the star-connected TCR6, flows, so the reactance component is proportional to the frequency,
The current ICY is tripled, and the current LY is 9x, and since the resistance component hardly increases depending on the frequency, IP expressed by equation (12) approaches zero more and more. The fact that ip becomes zero means that the second volume vA
3, the currents I, Y w 1. 'l does not flow towards the primary winding 1m7.

On the other hand, in equation (13), 1 gun is equal to ■s, which means that the secondary volume #! 3, the current r flowing through the stable winding 12 cancels the current r, Y s I9 Y, and the current Ii Y
All of s I9 'f is stable winding 12 and reactor 1
It means to cycle through 3.

As a design example, consider a transformer with a rated capacity (P) of 300 MVA, and if its winding arrangement is shown in Figure 2, the zero-sequence reactance between each winding is (1)2~(■). (8) Obtain from equations 2 to (10).Reactor 1
The capacity of 3 is %IX, value of t - C), 2% or 30
0MVA (7) Since it is sufficient to set it to 0.6MVA corresponding to 0.2%, its capacity can be extremely small.

Note that the role of the stabilizing winding 12 is to circulate the third harmonic current included in the excitation current in the same way as a normal transformer, and also to lower the zero-sequence impedance seen from the primary winding side.

As explained above, the primary winding has a star-shaped connection, and its neutral point can be directly grounded, so it can be directly connected to an ultra-high voltage system, and the primary winding can be stage-insulated or reduced-insulated. The configuration of the primary winding is convenient in terms of insulation structure, as the high-voltage line terminal can be easily pulled out from the center of the winding, and the low-voltage neutral point terminal can be easily pulled out from the upper and lower ends of the winding. ,
The transformer can be made more compact accordingly.

Since the stable winding is placed between the primary winding and the second winding,
The electrostatic transition voltage from the high voltage primary winding to the secondary winding l\ becomes smaller. Since the TCR thyristor connected to the secondary winding is a semiconductor, its insulation properties are much worse than that of the transformer winding.

A small transition voltage also helps reduce the number of thyristors used.

In Fig. 1, the case where the reactor 13 is configured with one single-phase generator was explained, but as shown in Fig. 4, the reactor 13
There is also a method in which three 5 are connected in series with the tertiary winding 16, and they are connected in a triangular connection, and the effect is the same as in the case of FIG.

However, in the method shown in Figure 4, since the two phases are symmetrical, terminals a, b, and c are pulled out to the outside and used as tertiary side terminals, and a capacitor for power factor improvement or harmonic absorption as a tertiary load is used. You may also connect a load for use.

In this case, the capacity of one reactor 15 is one-third of the capacity of the single-phase converter shown in Fig. 1, and the configuration can be freely configured to include three single-phase converters or one Sanwa converter. , just choose the one that is convenient for you.

(Effect of the invention) It has half the rated capacity of the conventional method, and the connection is star-shaped.
Two units, one triangular and one star-shaped, are used, but in the present invention, only one unit is required, although the rated capacity is twice that of those units. The advantage of combining two transformers into one is that the total weight of the transformer is approximately 75% lower than that of one transformer.
It is to become. Reducing the total weight means that the material cost and processing cost can be reduced, the losses that occur can be reduced, and the installation area for installing the transformer can also be reduced.

Therefore, it is possible to provide a three-phase, three-winding transformer for SvC, which can be used by directly grounding the neutral point of the primary winding, is inexpensive to manufacture, and has low loss.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram showing the main circuit configuration using the three-phase three-winding transformer for SvC according to the present invention, FIG. 2 is an explanatory diagram showing the winding arrangement in the transformer shown in FIG. 1, and FIG. The figure is an equivalent circuit diagram showing the zero-sequence impedance of a three-winding transformer, Figure 4 is a wiring diagram showing the connection of the tertiary winding and reactor in another embodiment of the present invention, and Figure 5 is a conventional method. Main circuit configuration diagram, Fig. 6 is a main circuit configuration diagram when three windings are used, which can be easily imagined from the conventional method.6 1...Power system 2.7...Primary winding 3... Secondary winding 4... Sanwa two-winding transformer for SvC 5... Triangular connection TCR 6... Star connection TCR 8.12... Stable winding 9, 11... SvC Sanwa two-winding transformer 10...Arresters 13, 15...Reactor 14...Iron core main leg 16...Third winding Agent Patent attorney Noriyuki Chika Yudo Hirofumi Mitsumata Figure 3 Figure 4 Figure 6

Claims (1)

[Claims] On at least three main legs of the core, each winding is sequentially wound from the inside: a secondary winding with a star connection with a neutral point, a tertiary winding with a triangular connection, and a primary winding with a star connection with a neutral point. A three-phase three-winding transformer, characterized in that one or more reactors are connected in series with the tertiary winding within the triangular connection of the tertiary winding.