# US 5,352,872 A · System of supplying electric power to induction furnace

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- Number: US 5,352,872 A
- Document ID: US5352872A
- Status: Granted
- Kind: A
- Application number: 08/024,289
- Filed: 1993-03-01
- Granted: 1994-10-04
- Earliest claimed: 1992-04-24
- Assignees: Fuji Electric Co., Ltd.
- Inventors: Sadao Tsuji; Takayuki Hira; Shizuo Hayashi
- Web page: https://patentgrep.com/patent/US5352872A

## CPC

- H05B 6/04: Sources of current
- F27D 11/06: Induction heating, i.e. in which the material being heated, or its container or elements embodied therein, form the secondary of a transformer
- F02B 3/06: with compression ignition (compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02)
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- F27D: DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F02B: INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL (gas-turbine plants F02C; hot-gas or combustion-product positive-displacement engine plants F02G)

## Abstract

In a system of supplying electric power to an induction furnace, a required heating power is directly supplied to the induction furnace from an ac synchronous generator driven by a prime mover, such as a diesel engine, via a single-phase coil. At the same time, the voltage to be supplied to the single-phase coil is rendered continuously variable by an automatic voltage regulator of the generator to render continuously variable the heating power corresponding to the voltage to be supplied, and the frequency of the voltage to be supplied is rendered continuously variable by an automatic frequency regulator of the prime mover in accordance with predetermined mutual relationships with the voltage to be supplied. In addition, at the start of power supply, the voltage to be supplied and the frequency thereof are increased with gradients for a predetermined time duration from their predetermined minimum values to their rated values in accordance with the predetermined mutual relationships.

## Claims

### Claim 1

A system of ac electric power supply to an induction furnace for supplying a required heating power to a metal to be heated in the induction furnace, said system comprising:
a single-phase coil mounted in the induction furnace in a location near the metal to be heated;
a generating apparatus, including a prime mover having a rotating portion and an ac generator driven by said prime mover, for generating said ac electric power, said ac electric power generated by the generating apparatus having a predetermined voltage and a frequency corresponding to the required heating power, and said ac electric power being directly supplied to said single-phase coil, wherein said generating apparatus is used as a sole power source for the system;
a speed regulator connected to said prime mover for regulating a frequency of a voltage to be supplied to said single-phase coil so that the voltage is continuously variable, to directly control a rotation of the prime mover.

### Claim 2 (depends on 1)

A system supplying electric power to an induction furnace in accordance with claim 1 further comprising a voltage regulator connected to said ac generator for regulating the ac voltage to be supplied to said single-phase coil so that the voltage is continuously variable.

### Claim 3 (depends on 1)

A system of electric power supply to an induction furnace in accordance with claim 1 further comprising:
a voltage regulator connected to said ac generator for regulating the ac voltage to be supplied to said single-phase coil so that the voltage is continuously variable,
wherein the voltage to be supplied to said single-phase coil and a frequency thereof are rendered continuously variable by said voltage regulator and said speed regulator in accordance with predetermined mutual relationships.

### Claim 4 (depends on 3)

A system of electric power supply to an induction furnace in accordance with claim 3, wherein at a start of supply or power to said single-phase coil the voltage to be supplied and the frequency thereof are increased with gradients for a predetermined time duration from their predetermined minimum values to their rated values in accordance with the predetermined mutual relationships.

### Claim 5 (depends on 1)

A system of electric power supply to an induction furnace in accordance with claim 1, wherein when said ac generator is a three-phase generator, an amount of negative-phase resistance of said generator is a value corresponding to a state of maximum load unbalance in controlling the phases of the three phases.

### Claim 6 (depends on 1)

A system of electric power supply to an induction furnace as claimed in claim 1, wherein said prime mover is an internal combustion engine.