JPS5854845Y2 - 3-phase load compensation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compensation device for a three-phase circuit, and more particularly to a compensation device for a load in which each phase varies irregularly.

As a conventional three-phase circuit compensation device, there is one shown in FIG. 1, for example.

That is, a variable load 2 is connected to the secondary side of the three-phase transformer 1, and a capacitor 3 is connected to the primary side of the transformer 1.
, and a circuit in which the reactor 4 and the thyristor 5 are connected in series.

Then, the inflow current of the transformer 1 is given to the phase control circuit 8 through the current transformer 6 and the auxiliary current transformer 6', and the line voltage is given to the phase control circuit 8 through the potential transformer 7. controls the firing of the thyristor 5.

This device is used as a flicker compensator in, for example, arc furnaces for steel manufacturing.

When the arc furnace load is turned on and connected, each phase of the arc fluctuates irregularly.

In this case, a furnace I lance is inserted between the arc furnace and the power receiving point, but when looking at the load side from the power receiving point, each line is fluctuating independently and irregularly.

Therefore, in order to comprehensively and most effectively compensate for load fluctuations at the power receiving point, the compensation device must be connected to control each line independently.

Generally, current is detected by a current transformer on each line, and voltage is detected by line voltage.

However, this detection method cannot directly detect reactive power between lines.

Conventionally, the voltage between each relative ground is detected by an instrument transformer, the reactive power and active power of each phase are detected using this and the line current, and this is further converted into line-to-line reactive power. A method is used to detect reactive power.

However, this method naturally causes a time delay in detection.

Particularly in the case of arc furnaces, this detection delay can be fatal, so the amount of variation must be detected as instantaneously as possible.

The present invention was developed in view of the above points, and aims to provide a device that instantly detects the reactive power of irregularly fluctuating loads in a polyphase circuit and compensates for load fluctuations based on this detected amount. .

To achieve this objective, the present invention detects the line current and line voltage of the load and performs predetermined calculations to detect the line reactive power, and controls the reactive power source based on this detection signal. This constitutes a device that performs compensation by

Here, only the reactive power is detected because the voltage fluctuation in the power supply system caused by the fluctuating load is extremely small compared to the reactance of the resistance bone of the power supply system.

In order to compensate for voltage fluctuations in the power supply system, it is only necessary to compensate for the reactive power of the variable liability.

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4.

FIG. 2 shows the relationship between line current and phase current in a three-phase circuit.

That is, when the I-lance has two windings, the phase current can be determined if the line current is given.

Here, the line current is IR, Is. IT and the phase current I
If R5, IST, ITR, then.

Therefore, by subtracting equation (2) from equation (1), we can calculate
From B=3"RB-C"RFl+, T"TR) can be obtained.

Since within the four windings, IR5+ISR+ITR=O, the phase current IR5 can be found.

Similarly, the phase currents IST and ITR are also obtained.

Figure 3 a, l) shows that when the IR phase is a resistive load, the R3 phase and the S
It shows the flow of current within the four windings of the T phase and IR phase, and the current waveform.

If the turns ratio of the transformer is set to 1:l, the load R will have I
When (A) flows, a current will flow in the transformer winding.

The power between each line is VH2I R5, Vs□■5□; "'V"rRI□ for each line of R3, ST, and TR.

Therefore, the power VI (W) applied to the TR phase load R is the power between the transformer primary side and the miter wire VR5I R5 (VA)
, Vsll ST (VA).

VTRI TS (Equivalent to VAII.

As shown in FIG. 3a, when there is a resistive load on the IR phase, the power between each line as seen from the transformer primary is as follows.

Figures 4a and 4l) show the active power and reactive power between each line as seen from the transformer primary when the phase angle ψ of the IR phase load is changed.

Regarding this, the same holds true even if the IR phase is replaced with the R3 phase or the ST phase.

In this way, the line current can be determined from the line current by using two windings.

To instantly detect reactive power from voltage and current, proceed as follows.

That is, reactive power is proportional to the instantaneous value of current when the instantaneous value of voltage becomes zero.

There, becomes.

As shown in Fig. 4, when the power factor of the load changes from 0 to 1, the reactive power compensation between each line is determined by the phase advance capacity CV
to lagging capacitance VI are required.

However, when compensating for reactive power fluctuations due to arc short circuits (R=O) in a steady state with a power factor of about 75%, such as in an arc furnace, very little phase advance capacity is needed, as can be seen from Figure 4. do not.

Therefore, when used as a countermeasure against flicker in a steelmaking arc furnace, it is sufficient to provide only a delay capacity as a compensation device.

Further, as an application example of the present invention, there is also a case where a three-phase unbalanced load is balanced.

In other words, it is known that a single-phase load can be balanced into three phases using inductance and capacitance, and in this case, if each line load is compensated to have a power factor of 100%,
Three-phase balancing can be achieved by inserting GKW inductance or capacitance between the other two lines.

For example, when the R3 phase is P (KW), the ST phase has P /v
'3 (KVA) capacitor, TR phase has P/, /
``Insert the m (KVAR) glue acdle.

In this way, if the reactive power between each line can be detected, the necessary accelerator or capacitor between each line can be detected immediately.
Three-phase balance can be achieved.

As described above, the present invention detects line current and line voltage, performs predetermined calculations based on the detected amount of electricity, detects line reactive power, and uses this detection signal as a source of reactive power. Since the system is controlled, it is possible to respond to load fluctuations extremely smoothly.

Moreover, since this detection is carried out instantaneously, although some error is involved, it is possible to respond quickly to load fluctuations.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional reactive power compensator; Figure 2 is an explanatory diagram showing the relationship between line current and phase current in a three-phase circuit; FIGS. 4a and 4b are diagrams showing an example of the change characteristics of reactive power and active power between each line. ■・・・Current, ■・・・Voltage.

Claims (1)

[Claims for Utility Model Registration] A device for detecting load line currents (IR, IS, IT), a device for calculating phase currents IR5, IS□, and ITR based on formulas from these currents,
A three-phase load comprising a device for detecting load phase voltage, a device for determining line reactive power based on the phase current and phase voltage, and a device for compensating the reactive power of the load based on the line reactive power. compensation device.