JP2008220140A - Transformer and controller of flicker suppressing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase response speed of a flicker suppressing apparatus for an electric furnace, and reduce the number of harmonics as well as the capacity of a reactor. <P>SOLUTION: A reactor connected with SCR in series is connected to two pairs of three-phase power supplies having a phase difference of 30 degrees or less, respectively, each of which is controlled independently. An ignition phase delayed by 30 degrees or more from an ignition phase which causes a 180-degree conduction state is defined as a maximum ignition phase of SCR. When no power is supplied to SCR when 30 degrees are exceeded, data is acquired again, ignition phase is recalculated and the next ignition phase is determined. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a device that suppresses voltage fluctuation (flicker) caused by an electric furnace using a reactor and a thyristor (SCR).

  A conventional apparatus uses a set of a three-phase power source in which a reactor and an SCR are connected in series. (For example, see Patent Document 1)

Patent Publication 2000-234875 Patent Publication 2000-2222053

Since the conventional apparatus uses one set of the reactor and the SCR, the response speed is delayed by more than 1/2 cycle, the harmonics are large, and the price of an ultra-large apparatus such as an electric furnace becomes high.
An object of the present invention is to reduce the number of harmonics by utilizing the overlapping of each set of harmonics.
The ignition angle at the time of maximum energization of the SCR is delayed to perform a high-speed response, and the capacity of the reactor is reduced.

The timing for determining the ignition phase of the SCR is conventionally determined by determining the DC control voltage at the phase angle at which the maximum energization current is obtained, and comparing with the voltage delayed by 90 degrees from the power supply voltage applied to the SCR.
According to this, since the determination of the ignition timing is once per ½ cycle, a high-speed response is not obtained.
The problem with the present invention is to do this several times.

  Two or more reactor and SCR pairs were used in the past (using two pairs has a large cost-effective ratio, and in the case of three or four groups, the effect is less effective in a complicated ratio. Therefore, this text mainly explains the case of 2 sets.) In the case of 2 sets, each set is connected to a power supply whose phase of the three-phase power supply is different by 30 degrees, and in the case of 2 sets or more, each power supply phase has the same angle. Just connect to a different power source.

In the case of two sets, the firing angle at the time of maximum energization of the SCR is delayed by 30 degrees or more in the case of two sets from the firing position at the time of full-arc energization (180-degree energization).
Even if this delay is small, it is possible to make a device, but the smaller the delay, the slower the response speed and the less the reactor capacity saving effect.
The determination of the ignition phase is performed at this delayed point (for example, a point delayed by 30 degrees),
If ignition is not performed at this point, the ignition phase is determined again.

The flicker suppression apparatus of the present invention calculates the ignition phase just before the maximum ignition phase once per cycle for one SCR, whereas the flicker suppression apparatus of the present invention does not start many times when the ignition does not start. But the ignition phase is calculated.
This increases the control speed because the data up to the last moment is taken in and fired without determining the firing phase until just before firing.

  In addition, when the conventional device is fully energized, all ignition is performed (180-degree energization), while in the present invention, when maximum energization is performed, energization starts slowly and ends as early as 120 degrees energization. Compared to the above, a high-speed response becomes possible.

Since two or more reactors and SCRs connected in series are connected to power supplies having different phases, harmonics cancel each other.
If the phase angle of maximum energization is further reduced, for example, 120 degrees or less, the capacity of the expensive reactor can be further reduced, and the response speed is increased.
However, since the current waveform passing through the SCR has a short energization time, the SCR and the reactor are burdened.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a single-line diagram showing a main circuit of the present invention.
In this figure, the three-phase power supply has a high voltage of 66 KV, 110 KV, 220 KV, etc., and the main transformer 1 reduces this voltage to, for example, 22 KV.
The electric furnace transformer 2 further reduces the voltage and supplies electricity to the electric furnace 4.

The flicker transformer 3 is a self-winding transformer and produces a three-phase power supply with a minimum capacity and a 15-degree advance and 15-degree delay based on the power supply phase of the main transformer 1.
Reference numeral 5 denotes a process of connecting the flicker transformer 3. The primary winding is a small capacity delta connection, and there are secondary windings as shown on the secondary side of the delta winding.
If the central part of the secondary winding is connected to the tip of the delta of the primary winding, the flicker transformer 3 is connected.

FIG. 2 is a three-line diagram of the connection between the flicker transformer 3 and the main transformer 1, and since the flicker transformer 3 is a single-turn transformer, the secondary winding of the main transformer 1 Combined and works as one transformer, the neutral point uses the neutral point of the main transformer 1.
FIG. 3 is a connection diagram in the case where the electric furnace transformer and the flicker transformer are combined into one unit to form the flicker and electric furnace transformer 6.
This reduces the number and capacity of transformers, but is inconvenient for inspection, testing, etc.

FIG. 4 shows the case where the reactors 7 and 8 and the SCRs 9 and 10 are connected to the flicker transformer 3, and the actual SCR is connected in reverse parallel, but only one side is written in the drawing.
Reactor 7 and SCR 9 are connected to a secondary winding that is advanced by 15 degrees, and reactor 8 and SCR 10 are connected to a secondary winding that is delayed by 15 degrees.
Since the main transformer 1 has a neutral point, it is grounded and one end of each of the SCRs 9 and 10 is connected.

FIG. 5 shows the secondary side star voltage of the main transformer 1 with a 15 degree lead and 15 degree winding added. The main transformer 1 has two types of power supply for the electric furnace and flicker. Supply.
In addition, there are various possible connections for a transformer having a phase difference of 15 degrees advance and 15 degrees delay, but it is the same that the voltage of 15 degrees advance and 15 degrees delay is extracted and applied to the reactor and the SCR.

Here, the reason why a transformer with a lead of 15 degrees and a delay of 15 degrees is used will be described from another viewpoint.
In the case of such a flicker suppressing device, 6-phase than 3-phase, 12-phase than 6-phase, and 24-phase than 12-phase can respond at high speed, reduce harmonics, and become closer to inverter control performance.

However, the more the number of phases, the more complicated it becomes. If 12 phases are used here, a vector as shown in FIG. 6 is obtained.
As seen from FIG. 6, the solid line vector and the dotted line vector are 180 degrees different from each other. Therefore, when viewed from the three-phase power source side, the same result is obtained regardless of whether the solid line vector is loaded or the dotted line vector is loaded.
Therefore, even if the dotted line vector is omitted as shown in FIG. 7, the result is the same as when 12-phase control is performed.

Since the solid line vectors have three sets having a phase difference of 30 degrees, the connection shown in FIG. 4 can be obtained by allocating 15 degrees forward and 15 degrees from the 30 degree intermediate point.
In this case, the neutral point is the neutral point of the main transformer 1.
For the connection advanced by 30 degrees, a form in which a winding is added to the delta connection in addition to a form in which a winding is added to the star connection is conceivable, but a star connection is good in that the ground voltage is stable.
FIG. 8 shows the current of the SCR at the time of maximum energization of the present invention (energization with a delay of 30 degrees).
In this way, the current waveform flowing through one SCR has many harmonics.

FIG. 9 shows that the harmonic current is reduced by adding the advanced SCR current (9) and the delayed SCR current (10).
FIG. 10 is an SCR current waveform diagram for explaining that the response speed changes depending on the ignition phase.
In this figure, P1... P7 are the points explained in the drawing. When firing at P1 (0 degree), the current continues to flow through the SCR until P7 (180 degrees) after firing, and cannot be controlled.

When firing at the point of P2 (30 degrees), the control decision phase is delayed, so that the controllable range is increased accordingly, resulting in a high-speed response.
When the SCR is ignited at P2 (30 degrees), the energization is completed at P6 (150 degrees), so that it is ignited at P1 (0 degrees) and ends at P7 (180 degrees) and ends 30 degrees earlier.
The end of energization 30 degrees earlier means a quick response of 30 degrees.
Further, since the delayed SCR 10 can be controlled 30 degrees after the leading SCR 9 is energized, the response speed is increased.

Single line connection diagram showing an embodiment of the main circuit of the present invention 3 wire connection diagram of a 15 degree forward and 15 degree flicker transformer of an embodiment of the present invention Wiring diagram in the case where the transformer for flicker and the transformer for electric furnace with 15 degree advance and 15 degree delay of the embodiment of the present invention are combined with one transformer 3-wire connection diagram when reactor and SCR are connected to a transformer for flicker Single-line connection diagram when main transformer and flicker transformer are combined 12 is a vector diagram of a 12-phase power supply for explaining the principle of connection of a transformer having 15 degree advance and 15 degree delay vectors according to an embodiment of the present invention. Same as Fig. 6 The figure of the SCR current waveform at the time of maximum energization in the device of the embodiment of the present invention Waveform diagram showing that the current of the advanced SCR and delayed SCR is summed to reduce the harmonic current The figure which shows the energization waveform of the half cycle of one SCR

Explanation of symbols

1 Main Transformer 2 Electric Furnace Transformer 3 Flicker Transformer 4 Electric Furnace 5 Transformer Winding Before Connecting Flicker Transformer 6 Flicker / Electric Furnace Transformer 7, 8 Reactor 9, 10 SCR
11 Flicker power supply 12 SCR current at maximum energization 13 SCR current at low energization

Claims (3)

In a large-capacity flicker suppression device that requires a high-speed response, such as an arc furnace, two sets of three-phase power supplies are used that use two sets of three-phase control units connected in series with an SCR connected in antiparallel. The transformer of the flicker suppressing device is characterized in that a phase difference of 30 degrees is set. In the above flicker suppressing apparatus, the flicker suppressing apparatus is characterized in that an ignition phase that is delayed by 30 degrees or more from an ignition phase in which the SCR is energized 180 degrees is set as a maximum ignition phase. In the above flicker suppression device, when the SCR exceeds 30 degrees and does not become energized, the data is collected again and the ignition phase is calculated again from the beginning to determine the next ignition phase. The control unit of the flicker suppressing apparatus, wherein if the arc is not reached, the data is obtained again and the calculation of the ignition phase is performed again to determine the next ignition phase.

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