Power frequency furnace load sales
Power frequency furnace
At 50/60 Hz, most inductors have a rather low power factor due to the low frequency. Values are generally 0.4 (non-ferrous metals) to 0.5 (magnetic steel heated below the Curie point). When the steel is heated to the Curie point, the impedance and voltage of the inductor are equal to those of the power supply directly to the inductor. Standard 440 volt air-cooled or water-cooled capacitors are used.
For high-power industrial frequency heaters, high-voltage power supplies (3000 and 6000 volts, three-phase, 50/60 Hz) are usually used. Since the number of turns of the inductor at this voltage is very large and there are considerable insulation problems, transformers are almost always used.
Power frequency furnace load sales
Power factor compensation capacitors are standard models like low-voltage capacitors. The dielectric is chlorinated biphenyl or similar, and the electrodes are aluminum foil separated by resin-impregnated paper. The rating of each capacitor is standard, between 50 and 150 kvar. Recent advances in capacitors include the use of plastics instead of paper and new fluids (such as “Dielektrol”), which are safer.
In smaller systems, individual capacitors are mounted in an operating cabinet or sensor cabinet. Larger systems use a separate capacitor rack that also includes a cabinet for mounting the circuit breaker and measuring and controlling the circuit breaker circuit.
Each capacitor bank is connected to the busbar separately through a fuse. The safety device includes a short-circuit grounding switch that grounds the main power busbar when the cabinet door is opened. The cabinet door is interlocked and cannot be opened unless a special master control key is used. Only when the circuit breaker is tripped and locked in the open position can the master control key be disengaged from the main circuit breaker and the cabinet door opened.
For loads with varying power factors, additional capacitors can be automatically connected by increasing the current. This method is often used when heating steel parts. After reaching the Curie point, the increased current sends a signal sufficient to operate the circuit breaker coil.
The power control and matching of the transformer is similar to the design of the welding transformer. The secondary coil is generally water-cooled due to the high current and KVA values. For very high power installations, air-cooled dry distribution transformers are used, in which case space is not an important factor. In most systems, it is desirable to keep the size of the equipment to a minimum. The transformer is often mounted directly under the inductor to minimize the inductor wire and thus minimize wire losses. The secondary winding is made of pressed thin-walled copper tube or solid copper strip with water-cooled copper tube brazed on the outer wall. The current can be increased to 10,000 or 15,000 amperes, and only water cooling can remove the heat loss of the resistor. The primary winding is made of copper strip in a flat form, and the distribution of taps depends on actual requirements.