JPH0456096A - Power control method for direct current arc furnace - Google Patents

Abstract

PURPOSE:To prevent reverse tidal current by changing a set value of the self- generation side power in response to a real value of an arc furnace load power to make initial power receiving constant in outline when power fluctuation more than a constant is detected in the output of a control unit. CONSTITUTION:When generation of power fluctuation more than a constant by a comparator 16 is detected, arc furnace load power is given from a power converting unit 10 to a setting unit 2 as an instantaneous value through a contact 18 and an adder 93. The initial power receiving is made to be constant in outline. Consequently, an instantaneous value of the arc furnace load power is outputted from the power converting unit 10 at this stage, and a set value to be set by a setting unit 22 is set at an appropriate level, in which power fluctuation can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power control method in a DC arc furnace that is supplied with power from a power supply facility in which a commercial power source and a private power source are operated in parallel.

[Conventional technology]

Conventionally, when supplying electric power to a DC arc furnace while operating a commercial power source and a private power source in parallel, it is common to supply a constant amount of power from the private power source.

[Problem to be solved by the invention]

Incidentally, in an arc furnace, arc breakage occurs due to depression of molten steel, etc., and the load power of the arc furnace may become substantially zero.

FIG. 5 is a schematic diagram showing a conventional general power source equipment for an arc furnace.

In the figure, 5 is a generator, 13 is a DC arc furnace, PG
is the private power generation power, PS is the received power (commercial power), PLI is the arc furnace load power, and PL2 is the other equipment load power, and the following relationship holds true.

PG 1 PS = PL 1 + PL2 Here, when arc breakage occurs and the load power of the arc furnace becomes substantially O (PL1 = O), PS = - (PC, -P
L2), and the amount of (PG-PL2) flows in the opposite direction to the power receiving side (this is called a reverse power flow).

In general, such reverse power flow is regulated in power systems by electric power related laws and the like, so it is necessary to prevent such reverse power flow from occurring.

Furthermore, the occurrence of reverse power flow also means that power is wasted.

Therefore, this invention does not cause reverse flow;
The aim is to make effective use of private power generation.

[Means for solving the problem] A predetermined adjustment calculation is performed to supply a constant current to a DC arc furnace that is supplied with power from a power supply facility in which a commercial power source and a private power source are operated in parallel. Provide a regulator,
If it is predicted that the arc will burn out by comparing the output with a predetermined set value, either increase the received power by subtracting a fixed amount proportional to the power of the arc furnace from the private power set value, or A DC arc furnace is supplied with power from a power supply facility in which a commercial power source and a private power source are operated in parallel, and a regulator is installed to perform predetermined adjustment calculations to supply a constant current to the DC arc furnace, and its output is adjusted. When a power fluctuation of a certain level or more is detected compared to a predetermined set value, the received power is kept approximately constant by changing the private power generation side power set value according to the instantaneous value of the arc furnace load power.

[Effect]

By detecting an unstable arc before arc breakage in an arc furnace load with severe load fluctuations, and using this detection signal to reduce the power on the in-house generator side and increase the received power, the electric power after arc breakage is reduced. or when the output of the tAwJ device is compared with a predetermined set value and a power fluctuation of more than a certain level is detected, the in-house power generation side power set value is adjusted according to the instantaneous value of the arc furnace load power. By changing the , the received power can be kept almost constant.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the invention. In the figure, 1.10 is a power converter, 2°21, . 22
is the setting device, 3 is the governor (GOv), 4 is the prime mover, 5 is the generator (G), 6,61°62 is the breaker, 7
, 71 is an instrument transformer, 8° 81.82 is an instrument current transformer, 9, 91.92 is an adder, 11 is a transformer, 12 is a rectifier, 13 is a DC arc furnace, 14 is a current regulator ( ACR)
, 15 is an ignition regulator, 16 is a comparator, 17 is a relay (coil), 18 is a relay contact, 19 is a computing unit,
20 is a subtracter, and D is a diode.

On the private generator side, the output power of the private generator side power converter 1 determined by the voltage detected via the transformer 7 and the current detected via the current transformer 8 is approximately equal to the setting value from the setting device 2. to match, i.e. output from setter 2 and power converter 1.
The generator 5 is controlled via the governor 3 and the prime mover 4 so that the output from the adder 9 is given to the adder 9 with the polarity shown, and the difference between the two becomes O.

On the other hand, current is supplied to the arc furnace 13 connected to the breaker 61 and the transformer 11 via the rectifier 12, and the rectifier 12 is controlled by the ACR 14. That is,
The ACR 14 matches the DC component of the input current of the rectifier 12 provided via the current transformer 82 and the diode D with the value from the setter 21, that is, the set value from the setter 21 and the current transformer 82 and the diode D. By applying the current value given through the adder 91 with the polarity as shown in the figure, a predetermined adjustment calculation is performed so that the difference between the two becomes O, and the switching element in the rectifier 12 is adjusted according to the calculation output. By controlling the rectifier 12 via an ignition regulator 15 that performs ignition control, a substantially constant direct current is supplied to the arc furnace 13. Here, the current flowing to the arc furnace 13 is controlled by detecting the current on the input side of the rectifier 12, but it may be controlled based on the current on the output side of the rectifier 12.

In an unstable arcing state where the arc is broken, the ACR 14 that controls the rectifier 12 reaches a limit voltage in an attempt to maintain the arc current. If the arc current still cannot flow stably even after reaching this voltage, the current will eventually decrease, the arc current will stop, and arc breakage will finally occur. Therefore, we monitor whether or not the rectifier limit voltage has been reached, and when it does, it is predicted that the arc will break, so we reduce the amount of electricity on the in-house generator side by a predetermined amount of power, and increase the amount of electricity on the receiving side by that amount. This prevents reverse power flow.

For this reason, in the embodiment, a comparator 16 is provided, which monitors the difference between the output of the ACR 14 and the limit voltage setting value from the setting device 22 through an adder 92, and operates the relay 17 when the difference becomes less than a certain value. and close the contact 18. This contact 18 is connected to the voltage from the transformer 71 and the current transformer 8.
Since the arc furnace load power, which is determined by the current from Then, by lowering the setting value of the setting device 2, the amount of electric power on the private generator side is lowered. Note that from the relationship of calculating the average value of the output of the power converter 10,
At least the arithmetic unit 19 is provided with a memory function.

FIG. 2 is a waveform diagram for explaining the operation of FIG. 1.

In the same figure, (a) is the received power PS, (b) is the private power generation power PC, and (c) is the combined load power PL (PL1+P
L2) are shown, and each left side shows the conventional method, and each right side shows the method according to the present invention (this method).

In other words, in the past, even if an arc breakage occurred, the private power generation power P
Since G is kept almost constant as shown in the figure (b), the figure (
As shown in (a), there was a reverse power flow for (PC-PL2), but according to this method, this amount becomes O, and the reverse power flow can be eliminated.

FIG. 3 is a block diagram showing another embodiment of the invention.

This means that when the comparator 16 detects that a power fluctuation above a certain level has occurred, the arc furnace load power is directly supplied as an instantaneous value to the setting device 2 from the power converter 10 via the contact 18 and the adder 93. This allows the received power to remain almost constant. Therefore, at this time, the instantaneous value of the arc furnace load power is output from the power converter 10, and the setting value set in the setting device 22 is different from the case shown in FIG. 1 and can detect power fluctuations. It will be set at an appropriate level.

Figure vJ4 shows its operation. As is clear from the figure, by making the private power generation power PG shown in the figure (b) follow the arc furnace load power instantaneous value PLI, the received power PS can be kept almost constant as shown in the figure (a). You can see that Note that (c) in the same figure shows the combined load power. Also, in this example, only the output from the adder 93 is set in the setting device 2, but it is also possible to set a predetermined value here and lower the received power PS by that amount. be.

〔Effect of the invention〕

According to this invention, an unstable arc before arc breakage is detected in an arc furnace load with severe load fluctuations, and this detection signal is used to reduce the private power generation side and increase the received power, or When a power fluctuation above a certain level is detected by comparing the output of It is possible to prevent reverse power flow, which is regulated by electricity-related laws, and to suppress wasteful power consumption.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of this invention, Fig. 2 is a waveform diagram for explaining its operation, Fig. 3 is a block diagram showing another embodiment of this invention, and Fig. 4 is its operation. FIG. 5 is a schematic diagram showing a general example of power supply equipment for an arc furnace. 1.10... Power converter, 2.21.22... Setting device, 3... Governor, 4... Prime mover, 5...
... Generator, 6,61.62 ... Breaker, 7.71
... Instrument transformer, 8,81.82... Instrument current transformer, 9゜91.92.93... Adder, 11... Transformer, 12... Rectifier, 13.・・Arc furnace, 14・
... Current regulator (ACR), 15... Ignition regulator,
16... Comparator, 17... Relay (coil)
, 18... Relay contact, 19... Arithmetic unit, 20...
・Subtractor, D...diode.

Claims (1)

[Scope of Claims] 1) Adjustment that performs predetermined adjustment calculations to supply a constant current to a DC arc furnace that is supplied with electric power from a power supply facility in which a commercial power source and a private power source are operated in parallel. If it is predicted that the arc will burn out by comparing its output with a predetermined set value, the received power will be increased by subtracting a certain amount proportional to the electric power of the arc furnace side from the electric power set value of the in-house generator side. A power control method in a DC arc furnace characterized by: 2) A regulator is installed to perform predetermined adjustment calculations to supply a constant current to the DC arc furnace, which is supplied with power from a power supply facility in which a commercial power source and a private power source are operated in parallel. When a power fluctuation of more than a certain level is detected by comparing the power with a predetermined set value, the incoming power can be kept almost constant by changing the private power generation side power set value according to the instantaneous value of the arc furnace load power. Characteristic power control method in DC arc furnace.