JPS6066628A - Reactive power compensator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a reactive power compensator capable of suppressing unbalanced voltage fluctuations.

[Background technology and problems]

FIG. 1 shows an example of a conventional reactive power compensator.

In the figure, 1 is an infinite bus, 2 is a power supply impedance, and 3 is a bus.

6 indicates a three-phase unbalanced load connected to the bus bar 3, such as a three-phase arc furnace. Note that the figure only shows one bill. 4 is a CT coupled to an unbalanced load, and 5 is a PT coupled to bus 3.

7 is a series reactor, IO is a thyrisk switch connected in antiparallel, and a thyrisk control reactor (hereinafter abbreviated as TCR) is constituted by the series connection of the series reactor 7 and the thyrisk switch IO. This TC
R is delta, star connected transformer II connected to bus 3
The secondary side phase line of and the capacitor 8 are connected.

9 surrounded by a dotted line indicates a control circuit. 91 is a Q detection circuit, which receives input from CT4 and PT5.

92 is a detection reactive power conversion circuit, and 93 is a pulse generator.

The detected reactive power conversion circuit 92 has a configuration as shown in FIG.

As shown in the figure, a Q detection circuit 91 for each phase detects reactive power Qu, Qv, Qw for each phase, and a detected reactive power conversion circuit 92 detects reactive power Quv+Qvw between lines.

The reactive power is compensated for by converting it into QWu and controlling the steering wheel of each phase.

By the way, when trying to control an unbalanced load on a phase-by-phase basis without being influenced by other phases, the connection on the primary side of the TCR transformer is a delta connection. Therefore, when the energization by the TCR is balanced, the third harmonic circulates and there is no outflow of the third harmonic. If the TCR suppresses unbalanced voltage fluctuations, it will naturally lead to unbalanced operation and the third harmonic will flow out, but it is rare for there to be only completely negative phase fluctuations, and there may be some positive sequence fluctuations. many. Therefore, the outflow of the third harmonic can be suppressed to some extent.

However, the fifth. The seventh harmonic has the disadvantage that it flows out regardless of whether it is balanced or unbalanced. Conventionally, in order to suppress the 3rd, 5th, and 7th harmonics, TCR transformers are connected in delta, neutral line to star connection, star,
It is known that it is possible to operate the TCR unbalanced with a star-connected transformer with a delta or neutral wire.
If the transformer is star, star with neutral wire, or delta connection,
If the CR can be operated unbalanced, even in the present case, the 5th,
7 harmonic generation can be suppressed only during TCR balanced operation, but in star, star with neutral wire, and delta connected transformers, T
CR imbalance'ii! I couldn't control it. The reason is that even if each phase Q can be detected, how to process the obtained Qu, Qv, and Qw will result in a star.

Neutral bound star. This was because it was not known whether the control amount would be the control amount of the secondary side TCR of the delta connection, so there was no way to assemble a control circuit.

[Disclosure of the invention]

The present invention is a reactive power compensator that detects the reactive power of each phase of a fluctuating load and compensates accordingly. The secondary of a star- and delta-connected transformer with a neutral wire is connected with three-phase, four-wire, and the secondary of a star-connected transformer with a neutral wire is also connected with three-phase, four-wire. In equipment that is sensitive to unbalanced and steep loads, such as arc furnaces, the sirisk switch on the side of star, star with neutral wire, and delta connected transformers is equipped with the value of the corresponding phase among the load reactive power detection values. The feature is that the sum of the other two phases is subtracted from 5 times, and the result of the exposure is multiplied by % to obtain the control amount of the cyrisk control reactor of the relevant phase.

Examples will be described below.

FIG. 5 shows an embodiment of the present invention.

+1 is a star connected transformer with delta and neutral wires, and a series reactor (not shown) and an anti-parallel thyristor switch 10 are connected in series between the gonads, and +1'
is a star, star with neutral, delta connected transformer,
A series reactor (not shown) and an anti-parallel thyrisk switch IO are connected in series between each phase on the secondary side of the transformer 11' and a neutral line to form a reactive power compensation circuit. 8 is a parallel capacitor that cooperates with these reactive power compensation circuits. 91 is a CT 4 connected to the variable load 6.
92 is the detected reactive power conversion circuit shown in FIG. 3, which has already been explained, and 92' is the detected reactive power These conversion circuits 9
2.92', the pulse generator 93 generates a control pulse for the thyristor switch 10 to control energization of the reactive power compensation circuit.

(Here, first, we will analyze the relationship between the primary current and secondary current of the transformer 11'.

In the figure shown in Figure 2, 1 indicates the primary side and 2 indicates the secondary side.

However, the primary and secondary voltage ratio of the transformer 11' is considered to be I:l. On the other hand, if the positive-phase and negative-phase components of the transformer primary current are set as II and I2, respectively, the following equation (2) holds true.

Further, the transformer secondary current can be expressed as shown in the following equation (3).

Next, from equations (1), (2), and (3), transformer primary current Iu.

1v11. By eliminating , the following equation (4) is obtained.

Here, II, 12 is decomposed as shown in the following equation (5).

At this time, the following equation (6) is obtained from equations (4) and (5).

Now, let the magnitude of the bus voltage be Vs, and consider the variables set in the following equation.

From equations (6) and (7), equation (8) holds true.

As described above, Q1+ p2. on the primary side of the transformer. The Q22nd order is expressed by the secondary side Qu, Qv, and Qw components.

(2) Next, analyze the output signal from the Q detection circuit 910.

The voltage of the power source 41 can be expressed by the following equation (9).

The line current of the load is expressed by the following equation (10).

(10) Next, equation (9) is delayed by 90 degrees (to obtain equation 0.

The Q detection circuit 91 first calculates the following 0 from (10) and formula 00.
2) Calculate the formula. However, by removing the ripple component by some means, the output becomes a signal expressed by the following equation (+a).

On the other hand, Ip++ expressed by equation (5) ■p2+ lQl+
IQ2 can be expressed by the following formula (+4).

Equation (15) is obtained from Equations (18) and (+4).

As described above, the outputs QU, Qv, QW of the Q detector 9I are the loads Ql, p2. Q2 Expressed by J component.

(3) Next, from equations (8) and (15) obtained above the transformer secondary side control amount and the output of Q detector 91, Q+, P21
When Q2ft is eliminated, the following equation 〇6) is obtained.

The equation θ6) can be summarized as the following equation (r7).

Equation (7) is a calculation equation that calculates the transformer secondary side control amount from the output of Q detection W+91, and can be obtained from a circuit as shown in FIG.

As shown in the figure, among the load reactive power detection values from each Q detector 91, the Q value of the corresponding phase is multiplied by 5, the sum of the other two phases is subtracted from this, and the result is further calculated. An operation of multiplying by % is performed.

〔effect〕

In the device of the present invention shown in Fig. 5, TCR-A is of the conventional type, but TCR-B as described above is operated in parallel with this circuit, and TCR-A and B are sensitive to the same load. let

Of course, when TCR-A and TCR-B are in balanced operation, the 3rd degree 5.7th harmonic current is canceled out, but even for an unbalanced load such as an arc furnace, only the unbalanced amount flows out to the power source.

In this method, the larger the compensation device, the greater the economic effect. In other words, if the capacity becomes large, the devices will be divided into multiple groups, but conventionally the TC as shown in No. 514
This is because although only R-A types are operated in parallel, it is possible to make about half of the multiple groups TCR-B types.

[Brief explanation of drawings]

FIG. 1 shows a conventional reactive power compensator. FIG. 2 is an explanatory diagram for calculating the transformer circuit current used in the device of the present invention. FIG. 3 shows a detection reactive power conversion circuit applied to the device shown in FIG. ' Figure 4 shows a star in the present invention, a star with a neutral wire. 1 shows a detection reactive power conversion circuit for a si-risk switch connected to a delta-connected transformer. FIG. 5 shows an embodiment of the invention. l...Infinite bus bar, 2...Power supply impedance, 3.
b'+ti, 4...CT, 5...PT, 6...Unbalanced load, 7...Series reactor, 8...Parallel capacitor, 9...Control circuit, lO/Sirisk switch, 11
．． 11'...Transformer, 91...Q detection circuit, 92.
92'...Detection reactive power conversion circuit, 93...Pulse generator. B. Ini - Attorney Patent Attorney Hide Aoki 4 eyes on 1 figure 2 Sekicho chopsticks 3 figures

Claims (1)

[Scope of Claims] (A reactive power compensator that detects reactive power of each phase of a fluctuating load and compensates accordingly. The secondary of a star/delta connected transformer with star/neutral wire is connected with three-phase, four-wire, and the secondary of a star-connected transformer with delta/neutral wire is also connected with three-phase, four-wire. In devices that are sensitive to unbalanced and steep loads such as arc furnaces, the star and the star with a neutral wire are used. The control amount of the five-stage reactor is the value of