Frequency Converter For Steel Melting Furnace

Frequency Converter For Steel Melting Furnace

The proven 'Parallel Resonant Current Fed' topology is employed to ensure highest degree of reliability and efficiency besides ensuring constant power tracking in a variable impedance load as commonly encountered in an induction Melting cycle. The result is improved load factor and maximum productivity per kVA of utility demand. The converter houses a controlled rectifier converting fixed 50/60 Hz AC voltage to variable DC voltage followed by a DC link reactor that acts as a current source of an inverter, which in turn converts DC to AC of desired frequency. The parallel capacitor Bank that supplies the reactive power demand of inductive load is either separately built or integrated within the converter housing. Deionised water cooling is employed to cool the power source by using Plate Heat Exchangers that separates if from the electrically conductive primary cooling water source.

Technical Characteristics

Megatherm's Static Frequency Converters mainly consist of Rectifier, DC link and Inverter. The rectifier consist of one or more fully controlled three phase bridges employing the latest semi-conductor technology and digitally controlled special phase locked loop synchronization enabling power source to operate with mains as well as Gas/Diesel generator sets easily. This design allow infinitely variable adjustment of converter output between 5% to 100% of its rated power capacity. The DC link circuit consists essentially of water cooled reactors with special type of winding. The DC link circuit smoothens the current from rectifier which is fed to the inverter. Moreover, the smoothing choke prevents an excess rise of current in the DC link circuit in the event of a short circuit on the load. On each switch off, the flow pattern in the rectifier is reversed, so that magnetic energy stored mainly in the DC link circuit is feed-back into the mains. High speed semi-conductor fuses are fitted to protect the power thyristors.

Inverter consists of one fully controlled single phase bridge employing the latest high speed distributed gate Thyristor or Insulated Gate Bipolar Transistor (IGBT). By alternate switching on/off of the inverter device, an alternating current is produced in a load circuit. The inverter electronics control ensures that inverter runs at the frequency determined by the natural resonance created by the load.

Power conversion efficiency of Megatherm panels is very high. At 500Hz. frequency the efficiency is 97% and between 10 Hz. to 50 KHz. is 91%. The main advantage is that efficiency together with instant readiness for operation and reliable starting offer excellent possibility of controlled energy savings on different type of parallel compensated resonant load circuits.