Youngstown Sheet & Tube Bulletin, Volume III, Issue 6

              VOL.   III.
JANUARY 15, 1922.
NO. 6
THE MANUFACTURE OF STEEL
ARTICLE XXVL
The Use of Electrical Power in Driv¬ ing Machinery in the Mills- Large and Complicated Installations Are Required to Generate and Transmit This Power to Points Where it is Needed.    Provisions for Safety.
(By A. G. PLACE)
Electricity is an important factor in all the mills of The Youngstown Sheet & Tube Company, because it is a form of power that is easily transmitted, controlled and applied to almost all operations. There is no other form of power that is so gen¬ erally used in so many different oper¬ ations from the time the incoming ore is unloaded by a car dumper until the finished product is loaded on an out¬ bound car.
All of this electric power is generated in the plant, most of it by steam driven turbo generators, and some by steam engines. There is a total of 21,000 KW of 6600 volt, 3 phase, 25 cycle generating capacity, mainly located at the Blast Furnace Power House and the Struthers Power House. In addition to the 6600 volt generators, there are four 250 volt direct current engine driven generators of a total capac¬ ity of 2400 KW, and three 1500 KW, 250 volt direct current geared turbine driven generators. The total generating capacity at the Main Plant is, therefore, 27,900 KW, which is equivalent to 37,000 horse power.
It is possible to transmit power at 6600 volts over a distance of several miles, but power at 250 volts cannot be economically transmitted in quantities a distance of more  than   1500  feet.   The  highest prac¬
tical transmission voltage today is 220,000 volts, which will enable large blocks of power to be transmitted 350 miles. For mill purposes, 6600 volts is high enough to transmit our power over the distance necessary between the East and West ends of the plant, but in using the electricity in the mills, it is reduced to 250 volts in order to make it easier to handle and control in small quantities. It is also safer, for, with 250 volts, an accidental contact usually will not be fatal, although a bad burn will result from the heavy current flowing, in case of a ground or short circuit.
In   order   to   distribute   the   power   re-
as possible from lightning and switching surges by electrolytic lightning arresters, and are carried as high as possible over tracks to prevent short circuits, and grounds from steam cranes. Every effort is made to keep power continuously flow¬ ing to the distribution centers so that no interruption will occur in the mill oper- tions, perhaps resulting in a furnace full of steel that cannot be rolled, or a full ladle hanging  in  the  air  waiting for  power.
The power coming in to the distribution points at 6600 volts is changed to 250 volt direct current through motor genera¬ tor sets, or reduced to 250 volts alternating current through transformers, and is sent out to the mills over feeders. These feeders are protected by circuit breakers, so that in case of local  trouble,  only a
Switchboard   at  a  sub-station—a  point  from  which  current  is distributed  to
various mills.
quired to the mills at 250 volts, without carrying any part of it too great a distance, there are eleven points in the Struthers and East Youngstown plants where either alternating or direct current is supplied at the low voltage. These distribution centers are connected together with 6600 volt lines supplied by the main generators and by one emergency generator. This latter unit is in a strategic position to supply power to the pumps for the Open Hearth, and some 250 volt direct current, in case of any serious  trouble on  the  lines.
The 6600 volt lines are protected as far
small section of the mills will be without power at one time.
The 250 volt aher- nating current is the easiest to furnish to all operations, as it requires only trans¬ formers to reduce the voltage. These trans¬ formers are similar in all respects, except size, to the trans¬ formers hanging on the poles to supply city light to resi¬ dences. Alternating current does not have the same flexibility of control as direct current, and the al¬ ternating current tbo- tors have a smaller air gap between the rotating part and the stationary frame, resulting in more bearing trouble on heavy duty mill drives. The A. C. motor is also a constant speed motor, because of the nature of its design, and has no commutator, which is liable to give trouble and cause delays, as is the case with direct current motors.
(In the next article Mr. Place will dis¬ cuss the manner in which electric current is used in many different operations throughout the plant. Two additional illustrations of electrical equipment will be found on page 3.)
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