JPH0619538Y2 - Power control device for melting furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a power control device for a resistance melting furnace used for melting glass or the like.

[Prior Art] For example, in a glass melting furnace, the load changes slowly by one digit or more as the molten state progresses due to heating from the initial stage of raw material charging.

FIG. 1 shows an embodiment of the present invention, which explains a conventional power control device.

Constant power control is applied to such power control of the melting furnace.

As shown in the figure, a transformer 3 with a tap is connected to the secondary side via a thyristor 2 which is connected in pure anti-parallel from an AC power source, and one terminal of the tap changer 4 and a return line 15 to the transformer 3 are connected. The electrodes 52 and 53 of the melting furnace 5 are connected between them.

CT6 for load and PT7 between the lines are coupled to the return line 15, and the active power P is calculated by the power converter 9 from these output signals.

The active power P is P = V · Icosφ (W). Where V is the load side voltage and I is the load current. In the case of a glass melting furnace, the power factor co
sφ is cosφ≈1, and P = V · IcosφI ² R.

However, R is the resistance value of the raw material in the melting furnace.

This active power P is the reference power signal Pref in the melting furnace 5.
Is input to the power controller 11 (proportional integrator), and the gate pulse generation circuit 12 generates gate pulses G ₁ and G ₂ for the thyristor 2.

On the other hand, the output signal from the power controller 11 is input to the tap select control circuit 13 to turn on one switch SW of the tap changer 4 and output a signal to turn the other off,
Switch the tap of the transformer 3.

For example, in the initial stage of charging the raw material into the melting furnace 5, the specific resistance value is high, the switch SW ₄ of the tap changer ₄ is turned on to operate the melting furnace 5, and the phase control of the thyristor 2 is performed by this tap voltage. The power consumption in the melting furnace 5 is controlled to be constant, but when the phase control range of the thyristor 2 is exceeded, that is, when the resistance value in the electric furnace decreases and the load current I increases with time, the tap The changer switch is switched to SW ₃ , and control is performed to keep the melting furnace load power constant in this state.

[Problems to be Solved] However, when the above control method is adopted, since the thyristor phase control angle α is not controlled, α = 100 ° or more may occur when the power supply voltage changes or the like. If the thyristor is fired at such a control angle, as shown in FIG. 3, the third, fifth and seventh harmonics are generated in the circuit, so the transformer is designed in consideration of the harmonics. Not only is this expensive, but this power supply will generate more harmonics.

[Configuration of the Invention] The present invention has been made for the purpose of solving the above-mentioned problems, and detects the tap change of a transformer by providing a phase limiting angle for the control phase angle of the gate pulse of the thyristor, and this upper limit, When the lower limit is met, tap switching is performed for each, and the lower limit phase control angle is limited to an angle that reduces the generation of harmonics.

Having already explained a little about FIG. 1, the present invention will be explained with reference to FIG. 2 and FIG. 2 showing a chart of the gate pulse generating circuit.

The gate pulse generation circuit 12 has a block zone for giving a phase limiting angle to the control phase angle of the pulse.

The synchronous power supply device 14 is connected via PT8 on the power supply side, and the synchronous signal is input to the gate pulse generation circuit 12.

In the gate pulse generating circuit 12, as shown in the block zone chart of FIG. 2, the block zone is based on the synchronous power source, for both AC positive and negative waves, and the block angle from the control angle α to the thyristor is 10 ° (upper limit), for example. The pulse is emitted only in the range of 60 ° (lower limit), the energization control of the thyristor 2 is performed, and the voltage is adjusted, but when the upper and lower limit range of α = 10 ° -60 ° is exceeded, no pulse is generated. Is limited to.

As described above, the power signal calculated by the power converter 9 is added to the set reference power signal, and the difference signal is proportionally integrated by the power adjuster 11 and input to the gate pulse generation circuit 12. In this case, if the switch of the tap changer 4 such as SW ₂ is in an appropriate on position, the gate pulse is α = 10 based on the input signal from the power controller 11.
The gate pulse is sent to the thyristor 2 in the range of ° to α = 60 °, the voltage is adjusted on the primary side of the transformer 3, and thus the load power is kept constant.

However, when the output from the power converter 9 greatly increases with the SW ₂ of the tap changer 4 turned on, the control angle α exceeds 60 °, and the control pulse has the lower limit control angle α = 60.
° It will be stuck. Therefore, when it is in this matched state, the gate pulse generation circuit 12 is gated off,
Tap select control circuit connected at the same time
A tap down command signal for stepping down to the lower stage of the tap is sent to 13, and the switch SW ₂ is switched to SW ₁ . Further, when the output power signal from the power converter 9 decreases, the limit angle of the control pulse approaches α≈10 ° in order to compensate for this, and when it still decreases, the upper limit of the gate pulse is α≈.
It will stick to 10 °. Therefore, when this matched state is reached, the gate pulse generation circuit 12 sends a tap-up command signal for stepping up tap switching to the tap select control circuit 13 connected to the gate pulse generation circuit 12, whereby the switch SW ₂ Is switched to SW ₃ .

The switch may be either an electromagnetic mechanical switch or a semiconductor switch such as a transistor.

In the embodiment described above, since the lower limit is set to α = 60 °, it goes without saying that a transformer tap is required accordingly.

Further, although it is not limited to α = 60 °, as is clear from FIG. 3 showing the harmonic components generated by the single-phase antiparallel thyristor, when α exceeds 60 °, the third, fifth, and fifth components are obtained.
Since the amount of generated seventh harmonic becomes large, the above-mentioned problem remains in the phase control of the thyristor having a larger α than this.

[Advantage of the Invention] According to the present invention, in the thyristor power supply device of the Joule heating and melting furnace, not only the generation of harmonics peculiar to the phase control can be reduced, but also the loss due to the harmonic component of the transformer of the main circuit is α = 60.
° can be limited to less than, so the transformer can be economically constructed,
It is possible to reduce the harmonic current flowing out to the grid.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 2 shows the signal waveform of each part in the gate pulse generating circuit of FIG. FIG. 3 shows harmonic components generated by a single-phase pure antiparallel connection thyristor. 1 ... AC power supply, 2 ... Thyristor, 3 ... Tap transformer, 4 ... Tap changer, 5 ... Melting furnace, 51 ...
… Load, 52,53 …… Electrode, 6 …… CT, 7,8 …… PT, 9
...... Power converter, 10 …… Reference power signal, 11 …… Power controller, 12 …… Gate pulse generation circuit, 13 …… Tap select control circuit, 14 …… Synchronous power supply circuit.

Claims (1)

[Scope of utility model registration request] 1. A device for controlling power by a tapped transformer connected to a melting furnace through a thyristor connected to a power source in a melting furnace whose load changes by one digit or more, the tap of the transformer. The detection of the switching, the pulse control phase angle for the thyristor determined by the difference between the melting furnace load power signal and the reference power signal, the upper limit of the phase limit angle also given to the pulse control phase angle for the thyristor, or by matching the lower limit A power control device for a melting furnace characterized by being performed.