BS 7685:1993 download free.Test methods for direct arc furnaces ( Implementation of CENELEC HD 598 S1 ).
BS 7685 applies to industrial three-phase direct arc furnaces, the rated capacity of which is equal to or greater than 0.5 tonne. The furnaces are suitable both for solid and liquid charges at or near internal atmospheric pressure.
BS 7685 is also applicable to furnaces having one or more electrodes, other than three-phase furnaces, in so far as it applies.
These furnaces are intended for melting of ferrous metals (steel, cast iron) and non-ferrous metals (copper):
they may also be used as holding furnaces for a liquid charge to superheat and maintain the temperature before tapping.
NOTE All the electrical tests exclude the influence of equipment for reactive power compensation and/or voltage stabilization. Should it not be feasible to switch off such apparatus during testing, the terms stated in this standard are applicable in respect of the main electrical circuit (see Sub-clause 3.l6 only with due indication of simultaneous operation of the apparatus. Figures resulting from the influence of such apparatus and valid for the supply network may be additionally shown.
2 Object
The object of this publication is the standardization of arc furnace test conditions and of methods to determine the main parameters and technical operating characteristics.
The scope of this standard does not cover all possible test methods which may be carried out for the technical and economical assessment of arc furnaces.
3 Definitions
For definitions of fundamental and general terms in the electroheating field, the reader should refer to
Chapter 841: Industrial Electroheating, of IEC Publication 50: International Electrotechnical Vocabulary
(I.E.V.).
The following definitions apply for the purpose of this standard.
arc furnace
furnace in which the electric arc is the main source of heat
3.2
direct arc furnace
arc furnace in which the arc is maintained between the charge and one or more electrodes
3.3
arc furnace installation
furnace assembly with complete set of electrical equipment comprising:
— high-voltage equipment (with reactor, if applicable);
— furnace transformer;
rated capacity of furnace –
calculated capacity in tonnes of liquid metal for which the furnace has been designed, built and marked:
this capacity is defined with the specified shell lining, manufactured in accordance with the design, with allowance for the maximum expected slag volume over the liquid metal surface without exceeding the normal sill level. The specific density of the liquid metal used by the manufacturer for the calculations shall be clearly defined
3.7
minimum bulk density of scrap for the single complete maximum charge of the furnace (tIm3,l ratio of the furnace rated capacity to its rated volume
3,8
furnace high-voltage switch
high-voltage switch which serves for switching on and off, under load, the furnace transformer, in accordance with operating requirements
3.9
arc furnace transformer
the transformer feeding the arc furnace from the high-voltage network and providing a voltage range suitable for furnace operation
3.10
power rating of an arc furnace transformer
the maximum admissible continuous power of the arc furnace transformer primary
3.11
melt-down power of an arc furnace transformer
maximum admissible power of the arc furnace transformer with limited on.time during melting (taking into account repetition of the load cycle during subsequent melts)
NOTE The limited on-time of melt-down power shall be at least equal to the net melt-down tiiiw tse Suh-dauae 3.21 i.
3.12
arc furnace reactor
an inductive winding, sometimes connected in series with the primary circuit of the arc furnace transformer in order to limit the short-circuit current and ensure arc stability for each stage of the melting and refining process
3.13
electrode of an arc furnace
a conducting piece, generally of graphite, which is connected to a source of current while one end of the
d) check of the rated capacity of the furnace (see Sub-clause 3.6):
e) carrying out a short-circuit test during normal operation (see Sub-clause 5.5); 1’) determination of the asymmetry factor on primary side (sec Sub-clause 3.17); g) determination of the main operating characteristics during the melt-down period (see Sub-clause 5.6):
— specific electric energy consumption during melt-down period (see Sub-clause 3.19);
— specific melt-down rate (see Sub-clause 3.20);
— power factor (see Sub-clause 3.22);
— net melt-down time (see Sub-clause 3.21);
— specific electrode wear (see Sub-clause 5.7).
NOTI The teats specified in Items a) toe) are recommended to be earned out on all newly installed or reconstructed theae teats give the opportunity not only to check the correct furnace construction. but alao to check the quality of furnace and mounting.
The teats apecified in Items d) to g) need not be carried out if the corresponding data are given in the technical dot-ume arc furnace and arc guaranteed by the furnace manufncturer however, these teats shall be carried out if there is some between the technical data and the actual data obtained during furnace operation,
&2 General conditions of performance of tests
Performance of the tests shall be in accordance with the specifications of I EC Publication 398: Gi Conditions for Industrial Electroheating Equipment.
The furnace shall be prepared for tests and put into operation at the user’s site, in accordance service instructions and the requirements for safe working.
The mains supply to the furnace installation during tests shall ensure a symmetry of voltages separate phases.
The mains supply voltage level at the transformer primary should be within ± 5 % of the furna transformer primary rated voltage. Voltage levels outside these limits may be admitted in test agreement between manufacturer and user. In any case, the test results shall be converted to th. rated voltage value.
5 Principal recommendations on technical tests
5.1 Measurement of electrical insulation of heavy current line
Two tests shall be carried out, in the following order, on the dc-energized furnace with the dec completely mounted and passing through portholes in the roof of an empty furnace:
— in the cold state, on complete furnace installation without water,
— in the hot state, on complete furnace installation with water.
5.1.1 Measurement of elect rical insulation of heavy current line of the furnace in cold The test of the furnace in the cold state shall be carried out by means of a 1 000 V d.c. megohni
a) In the test on the furnace installation without flexible cables the measurement of the insuli is carried out separately between each phase and the eart.hed steel structure of the furnace.
b) In the test on the furnace installation with flexible cables the measurement of the insulatioi out between all three electrically connected phases and the earthed metal body of the furna
5.1.2 Measurement of approximative electrical insulation of the heavy current line of th in hot state
The measurement of the approximative insulation value of the furnace in the hot state shall bei on the arc furnace installation by means of a resistance bridge or equivalent measuring instrui
5.2 Measurement of cooling-water consumption
The purpose of this test is to check the cooling-water consumption as foreseen by the manufactu normal operation.
The test shall be carried out when the fuxnace is in the hot state (see Sub-clause 3.26) during t melt-down period. The pressure, temperature and properties of the cooling-water shall corresp requirements given in the technical documentation by the furnace manufacturer. The tempera outlet water should be measured every 15 mm by means of a thermometer scaled from 0 °C to 100 °C .