weighing 165 pounds was able to stand upon a 6′′ square piece cut from one of the blocks, and his weight caused no apparent compression. The high insulating efficiency of 85 per cent magnesia is a matter of common knowledge. It is well to know that this high value does not have to be saccrificed by the substitution of some less efficient insulation as a protective medium to be first applied around the pipe. CHAIRMAN MOULTROP: I very much regret that it was necessary to bring the discussion of this very interesting report to a close, but we promised to release you at six o'clock. This is the closing session of the Technical Section of this Convention. It finishes two years of my services as your Chairman in this organization. When I undertook the work I did not realize what was ahead of me. I appreciate most heartily the co-operation and support which I have received from the Executive Committee, the members of the various national geographic committees and the members of the Section generally. It is natural that the one who is in the limelight gets most of the credit for the things achieved, and he also has the opportunity to blame some other fellow for the things that don't go well. Without your loyal and hearty support we could not have had the successful work that has been done in the last two years. In closing, I want to thank you all most heartily for the support you have given to myself, to the Executive Committee and to the Association, and I bespeak the same support for the incoming Chairman, Mr. Carle. Gentlemen, this session is now adjourned. (The meeting then adjourned.) Third Technical National Section Session Mr. F. E. Ricketts, Chairman of the Committee on Underground Systems, acted as Chairman of the meeting. A. H. LAWTON (Vice-Chairman of Section): Gentlemen, in the absence of Mr. Moultrop and Mr. Carle, it devolves upon the speaker to open this meeting. As is customary, the Chairman of the Committee will take charge of the meeting during the discussions. Report of Underground Systems Committee D C and A C Distribution Systems Distribution systems in general, as operated in America, while having many features in common, still exhibit a wide diversity in details of equip ment and methods employed in supplying light and power service. While local conditions may be responsible for the adoption of special methods, in some cases it would still appear that a considerable amount of standardization might be accomplished in the arrangement of circuits and protective devices as well as in transformer connections. In view of the present tendency toward standardization of all the equipment normally required in Central Station Systems it is believed that a careful. study of present day practice will develop certain possibilities which may be of material benefit in effecting more uniform methods of distribution. Further, the present efforts toward the standardization of lamp voltages may be very favorably af fected by any efforts in the direction previously suggested. The principal features of the numerous systems sketches, Figures 786 to 791 showing diagrammatiin general use are illustrated in a number of cally the several arrangements of connections known to be employed in American practice. Direct Current Systems Fig. 786-Illustrates two D. C. systems which are typical of existing systems now in operation. These systems differ as to the use of sub-feeders paralleling service mains between junction boxes, certain systems dispensing with these sub-feeders as unnecessary while others consider their use as desirable for successful operation. In the use of various types of conductors, the practice is quite uniform since most systems use any or all the types enumerated in sizes best suited to the local loading conditions. The prevailing practice in the use of protective devices on D. C. systems shows a wide divergence in opinion as to operating requirements in some respects; for example, certain companies operate D. C. feeders without fuses at either end while others employ fuses at the station or in the junction boxes or at both locations. In one case circuit breakers are to be installed at the station and in junction boxes on all D. C. feeders. The practice of fusing mains in all junction boxes is quite uniform, as is the practice of fusing all service connections on consumer's premises. Station equipment in all modern stations is usually protected by circuit breakers although fuses are employed to some extent on equipment of small capacity and in a few instances reliance is placed upon manual operation of switching devices as affording the required protection. Alternating Current Systems Single, two and three phase systems in general use are illustrated in Figs. 787 to 790. In single phase systems the usual transformer connections for two and three wire services are shown with grounding connections as ordinarily employed. There is also shown a single phase circuit using a ground return for one side of the primary circuit, a form of distribution employed to some extent where cost of construction is a controlling factor. Two phase systems are used to a limited extent with the usual arrangement of transformers con nected to four wire and three wire primary circuits. Secondary connections from these systems conform to regular practice in the use of single phase transformers operating independently or in interconnected banks. Three wire, three phase systems are operated under two general arrangements of primary conductors: (b) (a) With load on two phases, the remaining conductor serving as a common return. With a balanced load on all three phases, the load being made up of single phase transformers connected for single phase supply. Three phase transformers are also used for the delivery of three phase supply. Connections of transformers for three phase supply are noted to be arranged in a variety of ways. Delta-Y, Y-Y, Delta-Delta, and in some cases open Delta operation is adopted. The regulation of this type of circuits is effected by the use of one, two or three single phase regulators or one three phase regulator as desired. Four wire, three phase systems exhibit the widest variety of operating arrangements of any of the other systems in general use. Transformers connected to primary circuits include single phase units connected between the neutral conductor and phase wires for single phase service and either single or three phase units connected to phase wires for three phase supply. In some systems when Y connected single phase units are employed for three phase service the neutral point in the transformer bank is also connected to the neutral wire of the circuit. Four wire, three phase systems are operated with and without the neutral grounded. Where grounding is employed the ground connection is usually made at the station. One system operating with the neutral grounded has used the cable sheath as the neutral conductor for a number of years with great success. Regulation of four wire three phase circuits is accomplished by the use of one to three single phase regulators where individual regulation is required, or by three phase regulators where a circuit is operated with load sufficiently well balanced to not require each phase to be regulated separately. Three phase regulators are also used satisfactorily when three phase power service predominates in any particular circuit. Certain systems find it desirable, as a further refinement to improve voltage regulation, to insert a single phase regulator in the neutral conductor at the station to compensate for voltage drop in the neutral conductor. The installation of single phase regulators at points on distribution circuits other than the station is considered good practice for the regulation of remote portions of circuits which cannot be properly regulated from the station. Fig. 790 illustrates various arrangements of distribution circuits showing methods and equipment used for sectionalizing and interconnecting primary circuits. In general two types of circuits. predominate, viz.: (a) The tree type circuit with transformers connected at any convenient point regard less of distance from the station. (b) The type of circuit which includes a distri bution center from which taps radiate to supply the required service. The regulation of the first type of circuit is oùviously inferior to the second type, although there may be many locations where the additional expense involved in the construction for the latter type cannot be justified until a specific volume ci business is acquired. The various switching, disconnecting and protective devices employed in connection with underground transformers are indicated in Fig. 791 Practice in this direction varies with each system some preferring to operate with transformers solidly connected to primary and secondary cir cuits, while others provide oil and air brake switches, fuses, or equivalent devices to disconnect transformers either manually or automatically The more recent practice appears to favor c switches for this work. Transformers connected to underground systems are located in manholes, vaults under sidewalks and in buildings, and in buildings specially constructed for the reception of transformers. Transformers are generally of the oil cooled type although the air cooled type is employed to some extent. The limitations in radiation of heat imposed by the restricted area of manholes and vaults frequently require that special means be provided for the ventilation of such enclosures in order to safeguard transforming equipment. Secondary distribution as used includes the usual forms of two and three wire single phase mains. and three and four wire three phase mains. Five wire secondary systems are used to some extent in connection with two phase distribution. Special methods of distribution have been employed by certain operating companies, among which is the four wire three phase secondary system using a teaser wire as adopted by the Cleveland Co. Attempts have been made to operate extensive networks constructed along lines paralleling D. C. practice without much success since all such systems have been rearranged for other methods of operation. These experimental systems have usually employed single phase primary feeders, each supplying banks of transformers of suitable capacity located underground at each feeding point on the network. Regulation of voltage was effected by automatic feeder regulators in each primary circuit. The grounding of secondary mains and services is usually carried out under, well-recognized rules and may be said to be standardized in a very satisfactory manner. Grounding connections for transformer secondaries are variously made to water mains, ground stakes, buried plates, etc., as may be the established practice in each locality. Underground cables for both primary and secondary circuits are of the single and multiple conductor types, using paper varnished cambric and rubber insulation according to the fancy of the user. Good practice requires that careful attention be given to the proper protection of cables from external injuries in manholes or wherever exposed, as well as to adequate provision for identification and bonding, and grounding of the cable sheaths of all cables. Present day practice in the design and construc A tion of primary and secondary distribution systems has been perfected to such an extent that in general an underground system may reasonably be expected to furnish practically uninterrupted service when compared with an overhead system with its never-ending battle with aerial obstructions and the elements. Manhole and Conduit Construction As a result of the Committee's request for information on this subject, replies were received from the representatives of twenty-eight companies, most of them including information in considerable detail, supplemented by blue prints showing designs and methods of construction. There appears to have been but few improvements made in manhole design during the past year, the more recent tendencies toward greater separation of ducts and better accommodations for training and splicing cables being emphasized in previous reports of the Committee. One company is planning what is thought will be an improvement in duct spacing at the manhole wall which consists of stopping the ducts in two different planes, alternating the plane from duct to duct both vertically and horizontally. With a two inch separation in the case of fibre or concrete ducts the distance between any two adjoining duct faces is increased by at least 100% over the method of stopping all ducts in one plane. The idea is illustrated in Fig. 792. In providing for the future service connections to manholes and conduits your Committee finds no new ideas available for report. In the matter of design of manhole frames and covers and methods of preventing excessive wear of castings and rocking of covers under heavy automobile traffic, several companies report that no troubles have been experienced. |