JPS6260895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load balancing device, and more particularly to a three-phase load balancing method for an induction heating device.

A coil in an induction heating device for heating a pipe or a metal iron ingot generally includes a plurality of single-phase coils arranged in the axial direction, and each coil is supplied with electric power from a three-phase power source. Therefore, when the object to be heated is gradually heated from the front end of the heating coil of one phase and transferred to the coil of the other phase at the rear end, a large load is placed on the three-phase power supply as the object is transferred. An imbalance occurs. For this reason, conventionally, a converter including a rectifier and an inverter is installed to convert three-phase to single-phase and supply the output to the coil. In this method, the three phases are converted to direct current and then converted to single phase, so the load imbalance described above does not occur, but on the other hand, a converter is required as a power supply for each coil, and each Each converter requires a three-phase full-wave rectifier and an inverter, which has the disadvantage of being expensive.
There is also a conventional method called the so-called balancer method that does not use the above-mentioned conversion device, but in this case, the reactor and capacitor for impedance adjustment are adjusted as the load, which is the object to be heated, passes through the coil. In order to vary the value, the variable means becomes complicated and is more expensive than one in which a conversion device is installed, and even if this means is adopted, sufficient compensation cannot be achieved.

The present invention has been made with the aim of eliminating such drawbacks, and is characterized by the fact that by inserting a dummy bar into the heating coil before turning on the power, the currents flowing into the heating coils of each phase are apparently balanced. This is how it was done.

An embodiment of the present invention will be described in detail below based on the drawings.

In Fig. 1, 1 is a three-phase transformer, 2 and 3 are single-phase (or two-phase) voltage regulators, each of which is composed of a thyristor and a diode, or a switch in which thyristors are connected in antiparallel, and AC output. Control voltage. 4, 5 are power factor adjustment capacitors, 6,
Reference numeral 7 indicates heating coils, and in this embodiment, two heating coils are provided. Therefore, the connections between the coils 6, 7 and the capacitors 4, 5 are as shown in Fig. 2, and the coil 7 is single-phase, but the coil 6 is two-phase. arbitrarily determined. Reference numerals 8 and 9 are control devices for the voltage regulators 2 and 3.

Figure 3 shows the current value flowing into each phase of the three-phase power supply on the vertical axis, and the position of the heating coil on the horizontal axis (in this case, three single-phase coils are arranged) when the object to be heated is inserted. This shows the state of current change. As is clear from the figure, when the object to be heated 10 is transferred from the right side to the left in the drawing, for example, when the tip of the object to be heated 10 is located at a distance L ₁ , the current flowing through the R phase is A ₁ , The S phase is _A3 , the T phase is _A2 , and the currents flowing through each of the three phases are in an unbalanced state.

In the present invention, in order to eliminate this apparent unbalanced state, dummy bars 11 are inserted into the heating coils 6 and 7 before power is supplied from the voltage regulators 2 and 3, as shown in FIG. be. Thereafter, the gates of the voltage regulators 8, 9 are controlled via the control devices 8, 9, and the required power is supplied to the heating coils 6, 7. In this case, the control devices 8 and 9 are configured with a feedback control system that feeds back a current proportional to the load current like a general control function, or a control system that takes temperature signals into account, and controls the set values and these signals. Voltage regulator 2, according to the difference signal between
3 is controlled. When power is supplied to the heating coils 6, 7, the dummy bar 11 has already been inserted into each coil 6, 7, and the load on each coil 6, 7 is shared evenly, so the three-phase power supply is used as in the conventional three-phase power supply. The heating work is started without causing a large imbalance, and the object to be heated 10 is inserted into the heating coil following the movement of the dummy bar 11, and at the time of this insertion, the heating coil has already received a predetermined amount of heat. Since this occurs, the object to be heated 10 is heated in a good condition. When the heating of the continuously heated object 10 is completed, the dummy bar 11 is inserted after the last heated object 10, and the heated object is completely delivered from the heating device, and the dummy bar penetrates the heating device. Turn off the power at this point. Therefore, even when the final object to be heated passes, no unbalance occurs in the three-phase power supply, and the device waits for the next heating operation.

As described above, the present invention inserts a dummy bar into the heating device before and after the power is turned on, and balances the single-phase or two-phase coil load when the power is turned on and when the power is stopped. Since a simple voltage regulator can be used without using a converter, the device has the advantage of being small and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
FIG. 2 is a coil connection diagram for explanation, and FIG. 3 is a characteristic diagram for explanation. 1 is a three-phase transformer, 2 and 3 are voltage regulators, 4 and 5
is a power factor adjustment capacitor, 6 and 7 are heating coils,
8 and 9 are control devices.

Claims (1)

[Claims] 1 In a device in which heating coils are connected to a plurality of single-phase or two-phase branches from a three-phase power source, and the object to be heated is passed through a heating device made up of these coils to heat the object, each of the above-mentioned heating In order to supply power to each of the coils, a voltage regulator consisting of a switch having a thyristor on at least one side and connected in anti-parallel is provided, and a dummy bar is inserted into the heating device, and after this insertion, each of the heating coils is A three-phase load balancing method characterized by supplying and stopping power to.