closing of the oil circuit breaker completes the closing circuit of the star oil switch, if the brushes on the con­verter are raised. When the converter has attained synchronous speed a relay bridges a gap in the tripping circuit of the star oil switch, and this circuit is com­pleted by another relay which closes at a definite value of the field current after the field switch has been thrown over to self-excitation. The star oil switch on opening completes the closing circuit of the delta oil switch, provided the oil circuit breaker continues closed. The oil .circuit breaker is trip-free during these opera­tions so that full protection is assured. The d-c. switches and circuit breakers are electrically operated, but before the positive switch can be closed the delta oil switch must be closed, brushes lowered, equalizer switch closed, and positive circuit breaker closed.

The oil circuit breaker will open on over-current or low voltage and, by interlock control, automatically opens either the star or delta oil switch and the d-c. circuit breaker. The d-c. breaker opens on over current, reverse current, over speed, or under voltage, and upon opening, opens the positive switch and the equalizer switch.

In the event of a converter flashover, a ground relay opens both the oil circuit breaker and the d-c. breaker; thus it may be seen that many of the operations are automatic, the operator performing only the initial movement of a sequence. The design also assures speed of operation and prevents an operator from making mistakes in putting a converter on the line. At the time of an unexpected failure of the power supply to a substation, the operator was able to clear all feeder circuits and auxiliaries, ordered power on again, started up the station, and established full d-c. feeder service in three minutes.

These three substations have been in operation for over two years and all equipment has functioned very satisfactorily. The converters have flashed over oc­casionally but have not averaged more than two or three per year per machine; and when they do occur, the damage is slight and usually the machine does not have to be left out of service. The flashovers generally occur a t times when a heavy load is suddenly cut off, particularly where a limited short circuit occurs which does not open the high-speed breaker but clears itself or is cleared by a subway air circuit breaker. Ap­parently the flashovers are due to large synchronizing currents caused by angular displacement of the arma­ture after heavy momentary load.

One operator and a helper are on duty in each station a t all times.

• • •

Electrolysis Survey at Louisville, Ky.

Cooperative commit tee finds that electrical drainage is only a partially effective measure in the protection of pipe systems.

By W. C. White S o u t h e r n B e l l T e l . & T e l . C o .

A t l a n t a , G a.

P1

Section through a converter substation where ventilation and sound-proofing must both be

assured

PREVIOUS to 1926, no concerted action in respect to the electrolysis of underground metallic structures

in Louisville had been taken, although the individual action of the water, gas, and electric and railway companies had served to mitigate specific cases of trouble. Realizing that the electrolysis problem could be solved only by securing complete data on all of the underground metallic structures, a conference of the public utility companies was held which resulted in the formation of the Louisville Electrolysis Committee in which all of the public utilities were represented. A citywide electrolysis survey and test procedure were planned the expense of which was prorated among the interested utilities.

A potential survey was made of the entire city, tests being made a t over 600 points. I t was found advan­tageous to use recording meters, and twelve of the smoked chart types were mounted on a truck with suitable switching arrangements for connecting them

F r o m " A C o o p e r a t i v e E l e c t r o l y s i s S u r v e y i n L o u i s v i l l e , K y . , " p r e s e n t e d a t Α . I . Ε . E . S o u t h e r n D i s t r i c t m e e t i n g , L o u i s v i l l e , K y . , N o v . 1 9 - 2 2 , 1930 . ( N o . 3 0 - 1 8 9 . )

100 Electrical Engineering

between various structures and between structures and earth.

A current survey of sub-surface structures supple­mented the potential survey in determining probable hazardous conditions and furnished valuable data for consideration in the application of remedial measures.

Specially equipped truck typical of those used in Louisville, Ky., electrolysis survey

A current survey of cable systems is a relatively simple procedure and in a great many cases will indicate hazardous conditions where they would not otherwise be located. Approximately 72 such test stations were established on the underground systems of Louisville

A graphical method of presenting electrolysis survey data for joint study

and 24-hr. records were made of the stray currents. Numerous measurements were also made of track-potential drop and track-potential gradients.

Soil resistivity tests were made on 180 samples which differed widely, bu t averaged about 5,000 ohm/cm.

Test data were assembled on cards a t the time when current or potential tests were made. A card was

prepared giving the number and location of the test point and cross-referenced with the corresponding records. On the reverse side of this card was shown a diagram of the test point and the location of structures to which connections were made. This was done in order tha t any test could be repeated with identical connections at any time. Those portions of the data capable of graphical presentation were plotted on maps, the areas indicated by the positive potential ordinates being colored red and tha t of the negative potential ordinates, blue.

When sufficient data were obtained in any section from which definite conclusions could be reached, the electrolysis committee, which met weekly, recommended mitigative measures in order tha t these might be applied as the survey progressed.

No quantitative results are given, but the success of the methods outlined in improving the general elec­trolysis conditions in the city has resulted in the continued active existence of the committee which functions as a central clearing house for the investi­gation of all matters relating to electrolysis in Louisville.

• • •

Fog-Type Insulators Eliminate Transmission Line Flashovers

ACCORDING to A. C. Nielsen Company, engineers, Chicago, and J. E. Woods and Ε. T. Ankele,

respectively chief engineer and operating engineer for the Central Power & Light Company, San Antonio, Texas, Lapp standard fog-type insulators have been instrumental in solving a troublesome transmission line problem on the power company's 17-mi., 66-kv. trans­mission line between Sinton and Robstown, Texas. The line in question is subject alternately to dust and salt fogs, and for some time prior to its reinsulation there occurred an average of some ten insulator failures and consequent service interruption. Analysis of maintenance costs showed an average expenditure of of $152.50 annually to cover necessary replacements, and this together with troubles arising from interrup­tions to important service brought about a reinsulation which was completed about two and one-half years ago. At tha t time the 66-kv. pin-type units previously in service were replaced each by three No. 5805 fog-type units. I t is stated that insulator failures due to arcover have been eliminated entirely.

The line in question is carried on Η-frame structures for the most part, using 22-ft. wooden crossarms giving a 10-ft. 6-in. spacing between conductors. Supporting I-bolts of the insulator strings are grounded to a copper strip running along the top of each crossarm and grounded by wires extending down the pole and wrapped around the base of the pole before erection. The line is rated a t 15,000 kv-a., 66 kv.

February 1931 101