Electrothermal installations. Installations of arc furnaces of direct, indirect action and resistance arc furnaces

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 7. Electrical equipment of special installations

Electrothermal installations. Installations of arc furnaces of direct, indirect action and resistance arc furnaces

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Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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7.5.44. The power supply system of enterprises with installations of arc steel-smelting furnaces of alternating current (AAF) or (and) direct current (DSMFS) should be carried out taking into account the mandatory provision of the values of power quality indicators normalized by GOST 13109-97 in the general-purpose supply network to which these installations will be connected .

In order to limit the content of voltage harmonics in the general-purpose supply network, it is recommended to consider the technical and economic feasibility of using converters with a large number of rectification phases in DSMET installations, and with an even number of converter transformers, half of them should have HV windings according to the "star" scheme and the second half - "triangle".

Furnace step-down or converter transformers of arc steel-smelting furnaces may be connected to general-purpose electrical networks without performing special calculations for voltage fluctuations and the content of higher harmonics in it, if the condition is met:

where STi is the rated power of the furnace step-down or converter transformer, MVA;

Sk - short-circuit power at the point of connection of the installation of arc furnaces to general-purpose electric networks, MVA;

n is the number of connected installations of arc furnaces;

D is the coefficient for installations of arc steel-smelting furnaces: alternating current (DSP) equal to 1, and direct current (DSPT) - 2.

If this condition is not met, it should be checked by calculation whether the values of voltage fluctuations and (or) the content of harmonics in it are not exceeded by the current standard for power receivers powered by an electrical network connected to a given point.

If the requirements of the standard are not met, the steel arc furnace installations should be connected to a network point with a higher short circuit capacity or appropriate measures should be taken, for example, use of power filters and / or a fast thyristor reactive power compensator. The option is selected in accordance with the feasibility study.

7.5.45. In arc furnace installations where operational faults can occur, it is recommended that measures be taken to limit the current surges they cause. On such installations, short-circuit current surges should not exceed 3,5 times the rated current. When using reactors to limit the currents of operational short circuits, it is recommended to provide for the possibility of their shunting during melting, when they are not required to be constantly switched on.

7.5.46. For furnace transformers (transformer units) of arc furnace installations, the following shall be provided:

1. maximum current protection without time delay against two- and three-phase short circuits in the winding and on the terminals, detuned from operational short circuit currents and magnetizing current surges when the installations are turned on;

2. gas protection against damage inside the tank, accompanied by the release of gas, and from lowering the oil level in the tank;

3. protection against single-phase earth faults in the winding and at the outputs of furnace transformers connected to an electrical network with an effectively grounded neutral;

4. overload protection for installations of all types of arc furnaces. For installations of arc steel furnaces, it is recommended to provide protection with a current-dependent time delay characteristic. The protection must operate with different time delays for signaling and tripping.

Characteristics and time delays of protection, as a rule, should be selected taking into account the speed of lifting the electrodes during the operation of the automatic current (power) controller of the arc furnace, so that operational short circuits are timely eliminated by lifting the electrodes and the furnace switch is turned off only in case of failure or untimely work from the regulator;

5. protection against rising oil temperature in the furnace transformer cooling system using temperature sensors with an effect on the signal when the maximum allowable temperature is reached and on shutdown when it is exceeded;

6. protection against violation of oil and water circulation in the furnace transformer cooling system with signal action - for oil-water cooling of a furnace transformer with forced circulation of oil and water.

7.5.47. Arc furnace installations must be equipped with measuring devices for monitoring the active and reactive electricity consumed, as well as devices for monitoring the technological process.

Ammeters must have appropriate overload scales.

On installations of resistance arc furnaces with single-phase furnace transformers, as a rule, devices must be installed to measure the phase currents of transformers, as well as to measure and record currents in the electrodes. On installations of arc steel furnaces, it is recommended to install devices that register a 30-minute maximum load.

7.5.48. When arc furnaces are located on work sites above the floor level of the workshop, the space under the sites can be used to place other equipment of furnace installations (including furnace substations) or to place a control room (with reliable waterproofing) without permanent human presence.

7.5.49. To exclude the possibility of a short circuit during the bypass of the electrodes of arc resistance furnaces, in addition to the insulating coating on the working (bypass) site (see 7.5.40), installation of permanent separating insulating shields between the electrodes should be provided.

See other articles Section Rules for the installation of electrical installations (PUE).

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