Electric system of vacuum self-consuming arc furnace
Vacuum since arc furnace is mainly used for power consumption under the vacuum state, melting qin, fault, lead, tungsten, key, bear, and lively and refractory metals and their alloys, and metal can also be used to heat resistant steel, stainless steel, tool steel and bearing steel vacuum melting. The electrode of the device itself is the molten metal. During the melting process, the electrode gradually consumes itself. After melting, the electrode drops into the crystallizer and condenses into ingot. The vacuum self-consuming arc furnace is mainly composed of furnace body, vacuum system, dc power equipment and electrode automatic regulator. Electrical system refers to vacuum control system, dc power equipment and electrode automatic regulator. The system has been used to update the electric system of ozH- 0.2 type 200kg vacuum self-consuming arc furnace. The low voltage distribution panel is compressed into one piece.
The new electrode lifting control system adopts SCR 1-d system. In addition to the original electric motor, the control of crystal gate tube is used instead of the ac magnetic magnifier.
(3) dc power compared with the original system, the new system improve the most part is the dc power supply. The new power supply adopted high-pressure magnetic saturation reactor, of high pressure controlled transformer with high voltage transformer and the power supply into high voltage switchgear, control transformer, rectifier cabinet three components, compact structure, covers an area of less than the original equipment required for l / 2. Especially the rectifier, only 6 4 oooA six phase rectifier rectifier components, compared with the original equipment, the consistency of the performance of rectifier requirements is greatly reduced, at the same time adopted five pillar type three-phase transformer, thereby eliminating the flow reactor.
2. Compared with the original equipment, the new and old systems have many disadvantages, which are not suitable for the current technical development. Therefore, it is decided to carry out technical transformation. The differences between the old and new systems are mainly reflected in the following three aspects:
(1) vacuum control system of original equipment, USES the relay contact logic control system, the new system is still a similar scheme, only using the new type of relay, contactor, instead of the old heavy electrical appliances, and simplify the circuit was made, the original two pieces of 3 electrical system Vacuum since the working characteristic of arc furnace power consumption is shown in figure 1. Before striking, between the upper and lower electrode voltage is equal to the no-load voltage U0 of dc power supply, top and bottom electrode short circuit arc, arc voltage will immediately drop to zero, the current increases quickly along the abscissa, F features as shown in figure l.
3. The power of the dc outputs allow short circuit, the short circuit current is not more than 000 ^ 13. Three phase 10 kV power supply through vacuum switch, controllable transformer and rectifier form no-load voltage 70v dc power supply. The controllable transformer is equipped with a three-phase magnetic saturation reactor and a five-column transformer. Magnetic saturation reactor is used to obtain constant current characteristics, limit short circuit current, and continuously adjust arc current. The arc current of the furnace can be adjusted to the left by adjusting the dc control current of the magnetic saturation reactor according to the requirements of the smelting process. Five pillar type transformer secondary side has two sets of three-phase windings, a double star, in order to save both flow reactor can still meet general with flow under the condition of the performance of the reactor of the six phase half-wave rectifier. Figure 3 shows the measured characteristics of the dc power supply. This property is measured by using steel tube as simulated load. The electrode automatic regulator is used to control the electrode lifting mechanism to control arc length and stabilize the melting power. This is based on two SCR - D speed control systems, superimposed arc voltage automatic adjustment links. Both adjustment systems use constant setting excitation to change the control mode of armature voltage. They are taking the armature voltage feedback signal after filtering, and the speed for a given value (i.e. voltage, given by VR. Or VRZ setting), the difference between the speed regulator to control the output of the trigger pulse phase after the operation, and then change the thyristor conduction Angle, to regulate the armature voltage, that is the purpose of adjusting the motor speed. The SCR a D added to the feedback of the river closure in the speed control system, when the armature current is more than a given value, the current amplifier output voltage polarity changes, the diode D into the speed regulator, thyristor trigger pulse phase ward, armature voltage drop, the armature current limit value in river closure. When working normally, the armature current is less than the given value of current, the output of the comparison amplifier is negative, and the diode D is cut off due to the reverse bias, so as to compare the output operation of the amplifier.