UA27875U - Method for electric power supply of melting furnace with direct current - Google Patents

Abstract

A method for electric power supply with direct current of melting furnace with two electrodes relates to methods for melting in electric-slag furnaces with two nonconsumable electrodes and can be used for melting ferro-alloys and for heating and melting different charge materials.

Description

Description of the invention

The utility model relates to a method and a corresponding device for supplying direct current to a melting furnace 2, preferably an electric slag furnace with two non-consumable electrodes and can be used for smelting ferroalloys, as well as for heating and melting various charge materials.

It should be noted that the main requirement for devices for electric power supply of melting furnaces is to ensure a high degree of reliability. Since a sudden stop of melting due to a violation of the operating mode of the power source leads to significant economic losses for every hour of downtime. 70 A known method and device (OA 59489 C2, 15.09.2003) for powering a melting unit, according to which the electric current from the power supply network is distributed to n number of power supply modules connected in parallel. Each module contains an uncontrolled three-phase current bridge, a direct current intermediate circuit and a transistor block.

With the help of the specified method and device, it is possible to continue the melting process without stopping when one or more power supply modules fail, because their number is selected with a margin, which leads to an increase in the cost of the equipment. The consumed reactive power (or power factor) of the device can be kept constant also by increasing the number of modules. The intermediate circuit of each module is a capacitive energy store, characterized by increased starting current (initial charging current) and increased typical (overall) power of the power supply transformer. An additional current-limiting device is required to limit the initial charging current, which also increases the cost of the entire installation.

Thus, the use of this power supply device can be economically justified only in very large units.

The main task of the useful model is to create a method and a suitable device for DC power supply of the melting furnace, which will ensure the necessary reliability of operation while simultaneously reducing the cost and without deterioration of the energy indicators (power factor, distortion factor of the network voltage shape) of the installation.

The task is solved by the fact that in the proposed method of direct current power supply of a melting furnace with two electrodes, in which voltage is supplied from a three-phase supply network to two groups of single-phase rectifiers, linear voltages are applied to the first group of rectifiers, and phase voltages are applied to the second group at therefore, both groups of rectifiers will form three-phase systems, and are made with output current limitation, then switch and regulate the rectified voltage with the help of single-phase alternating voltage regulators, which are included in the primary circuits of each rectifier, and supply the rectified voltage from each rectifier through separate current-carrying devices on the electrodes of the melting furnace, to create on the load a voltage having 3 o ripples, which correspond to a 12-phase rectification scheme. In addition, when adjusting the rectified voltage, the switching frequency of switching on one or two single-phase rectifiers in full-phase mode is changed, followed by the switching on of other rectifiers when the amount of melt in the melting furnace is increased to maintain a constant power factor of the device. "

The proposed method is implemented in a device for direct current power supply of a melting furnace with two electrodes (15, 16), containing at least two single-phase rectifiers with an uncontrolled valve bridge (9) and a control unit (10) connected to a common circuit (12) ), with a current sensor (11) and electronic

With" key (13) at the entrance. At the same time, single-phase rectifiers are combined into two groups, each of which contains three single-phase rectifiers (1, 2, З and 4, 5, 6) with output current limitation, while each rectifier includes a single-phase transformer (7) with by the regulator (8) of the alternating voltage in the primary circuit, and the secondary circuit is connected to an uncontrolled valve bridge (9), and the primary circuits of the rectifiers (1, 2, o З) of the first group are connected to the corresponding linear voltages of the three-phase power supply network, and the primary circuits - And rectifiers (4, 5, b) of the second group are connected to the corresponding phase voltages of the three-phase supply network, the outputs of all rectifiers are connected through separate current-carrying devices (14) in parallel to the electrodes (15, 16) of the melting furnace, creating a twelve-phase system of rectified voltage, and the input of each control unit (10) and 20 is functionally connected via an electronic key to the common unit of the specified influence (17).

According to the useful model, the voltage from the three-phase network is supplied to six single-phase rectifiers with sl output current limitation, which are included in two groups. The first group of rectifiers is powered by linear, and the second by phase voltages of the three-phase supply network.

Each rectifier contains a single-phase transformer with an alternating voltage regulator in the primary circuit 25 and an uncontrolled valve bridge in the secondary circuit, as well as a control unit connected to a common circuit with a current sensor and an electronic key at the input. The output voltage from all rectifiers is fed through separate current-carrying devices to the melting furnace electrodes, creating a twelve-phase rectified voltage system. The input of each control unit is functionally connected through an electronic key to the general unit of the specified influence. 60 When adjusting the heating power, the power factor of the device is kept constant by changing the frequency of inclusion of one or two single-phase rectifiers in full-phase mode, followed by the inclusion of others when the amount of melt in the melting furnace increases.

In order to automatically distribute power between groups or individual rectifiers, each rectifier includes a limiting element and a second electronic key functionally connected to it, and the input of the limiting element is connected to the common circuit of the current sensor and the control unit. The output of the second electronic key is connected in parallel to the first electronic key of the next rectifier.

As an AC voltage regulator in each rectifier, two thyristors connected in parallel (single-phase thyristor regulator) can be used, which allows you to switch a single-phase AC network and regulate the voltage on the load by the phase method.

The second electronic key must be not fully controlled, that is, such that it turns on when there is an opening signal and remains turned on when it is removed. An opto-thyristor can be used as an electronic key, for example.

The proposed useful model provides the necessary reliability of work while simultaneously reducing the valuable 7/0 indicators. The elements used in it (thyristors, diodes) have a lower cost than the elements (transistors, storage capacitors) in the prototype.

The use of separate current-conducting devices instead of one common one leads to an improvement in valve commutation, which increases their reliability, and to a reduction in the effect of rectifiers on each other due to the presence of the current-conducting devices' own inductance, the value of which depends on their location and /5 LENGTH.

Figure 1 shows the structural electrical diagram of the new device for powering the melting furnace, which can be divided into three main blocks:

A1 - two groups consisting of three single-phase rectifiers (1, 2, C and 4, 5, 6) with output current limitation. Each rectifier includes a single-phase transformer 7 with a voltage drop regulator 8 2o In the primary circuit and an uncontrolled valve bridge 9 in the secondary circuit, as well as a control unit 10 with a current sensor 11 and an electronic key 13. The current sensor 11 performs the function of a measuring element and forms from control unit 10 common circuit 12 (feedback circuit), which is designed to limit and stabilize the output current of each rectifier.

A2 - electric melting furnace with electrodes 15 and 16, which are connected by separate current conduits 14 to the corresponding INPUTS of rectifiers 1-6.

АЗ - the general unit of the specified influence 17, which is functionally connected to the control units 10 of each t rectifier, through the electronic key 13 and serves to set the required value of the output parameter (voltage, current) of the power source.

Fig. 2 shows the structural electrical diagram of the control of the new power source. In this case, an additional block A4 is introduced into the control scheme, which is designed for automatic switching on of rectifiers and distribution of power (load) between them. Block A4 contains the limit element 19 and is functionally connected to it - the second electronic key 20. The input of the limit element 19 is connected to the common circuit 12, and the output of the second electronic key 20 is connected in parallel to the first electronic key 13 of the next rectifier, that is, the electronic key 20 of the first of rectifier 1 is connected in parallel to key 13 of the second yz5 of Rectifier 2, key 20 of the second rectifier to the first key 13 of the third rectifier Z, etc. The second electronic key 20 of the last rectifier is connected in parallel to the electronic key 13 of the first rectifier (Fig. 2 shows the structural diagram of control of only one group of rectifiers 1-3).

The device for powering the melting furnace (Fig. 1) works in the following way. When the three-phase mains voltage is applied to the input terminals of the power source, the linear voltage of phases AB, BP and CA is supplied, respectively, to the inputs of Rectifiers 1, 2, C of the first group, the phase voltage of the three-phase network AM, VM, and CM is supplied, respectively, to the inputs of C rectifiers 4, 5, b of the second group. When the supply voltage is applied to the control circuit and when all are switched on. of electronic keys 13, bulging signals corresponding to the full-phase switching mode are applied to и? regulators 8 of each rectifier, the latter open and at the output of the power source and at the electrodes 15, 16 of the furnace, a rectified voltage with twelve-phase pulsations appears (because both rectifier groups

They are powered by two three-phase systems, the voltages of which are shifted relative to each other by an electrical angle equal to 302). ka Direct current flows through electrodes 15, 16 and provides heat generation in the furnace. In the initial period of melting, the process is carried out with a small input electric power, which is regulated due to the inclusion of one, two or one group of rectifiers. At the same time, the output voltage will be ОО 9-0.945, О Ор-1.2705 and О0-1.3505 (where О2 is the current value of the voltage of the secondary winding of a single-phase transformer) with 5r number of output phases (the number of pulsations during the period tho) to-2 , then-4, then-6 - respectively. Smooth voltage regulation

If necessary, it is carried out by the phase method with the help of thyristor regulators 8 depending on the 4 control signal coming from the general unit 17 of the influencing factor. The presence of the current sensor 11 and the feedback circuit 12 puts each rectifier into current limiting (stabilization) mode.

Stabilization occurs when the current reaches the nominal value.

The power source in automatic mode (Fig. 2) works as follows. The initial state for the start of work is taken as when one (of each group) rectifier is turned on during the initial phase of melting, let’s say 1. With the increase in the electrical conductivity of the melt, the current in it increases, when the current reaches the nominal value of rectifier 1, the latter goes into the current stabilization mode , at the same time the limit element 19 is activated (the voltage of the limit elements is chosen such that they are activated when the output signal of the sensor 11, proportional to the current of the working rectifier, reaches its nominal current), after which the second electronic key 20 is activated and the second rectifier 2. In this case, the load current is distributed between rectifiers 1 and 2 and the current value in the first rectifier becomes less than the nominal value. The connection of other rectifiers is carried out automatically as the conductivity of the melt increases, as indicated above, and the load current (introduced b5 power in the furnace) will be distributed evenly among all working rectifiers. When the current in each rectifier decreases, the electronic keys 20 remain on and the rectifiers do not turn off until the end of melting.

Thus, when adjusting the melting parameters, the power factor remains practically constant, because the heat generation in the furnace is regulated by changing the switching frequency of one or more single-phase rectifiers in full-phase mode, followed by the inclusion of other rectifiers when the amount of melt in the furnace increases.

The economic effect of the useful model is achieved by ensuring the necessary reliability of the equipment without deteriorating its energy performance, reducing the cost and capital costs of spare parts and maintenance, which reduces the payback period of the entire unit, especially with the capacity of the melting furnace 70 0.6-1.5MW.

Claims (2)

The formula of the invention 1. A method of direct current power supply of a melting furnace with two electrodes, in which voltage is supplied from a three-phase supply network to two groups of single-phase rectifiers, which differs in that the first group of rectifiers is supplied with linear voltages, and the second group is supplied with phase voltages, and both groups rectifiers form three-phase systems, and are made with output current limitation, then switch and regulate the rectified voltage with the help of single-phase alternating voltage regulators included in the primary circuits of each rectifier, and supply the rectified voltage from each rectifier through separate current-carrying devices to the electrodes of the melting furnace, for creating a voltage on the load that has ripples corresponding to a 12-phase rectification scheme. 2. The method according to claim 1, which is distinguished by the fact that when adjusting the rectified voltage, the frequency of inclusion of one or two single-phase rectifiers in full-phase mode is changed, followed by the inclusion of other rectifiers when the amount of melt in the melting furnace is increased to maintain a constant power factor of the device. - IF) in (ee) in the village - and? ime) -i (ee) -i sl 60 b5