Yoltage Standards for Electrical DistributionH. B. GEAR'

Fellow, A. L E. E.

Synopsis.-This paper discusses the necessity for standardizing form at all voltages. It also proposes that there should be a recog-voltages and advocates the utilization voltage as the most logical nized itandard for transformers in which the direction of energyreference base. It suggests that the ratios adopted should be uni- flow is subject to change.

T HE necessity of standardization of utilization together,andwhich, insomecases, addsanothervoltagevoltages has been recognized and accepted since level to those already in service.the days when electric lighting systems com- Each additional transformation, with its accompany-

petitive with different lamp voltages and operating ing line, has added to the drop in voltage and necessi-frequencies constituted such an obstacle to progress tated provision of taps or other means of compensatingthat standard voltages and frequency became a com- for the added drop.mercial necessity. The result has been that apparatus is being operatedSystems operating at 55 volts for lighting were dis- at voltages above that for which it was designed, special

carded for 110 volts, and a 220-volt rating was chosen windings have been specified, generators are being over-for use where energy was taken chiefly for power excited at certain hours, and the manufacturers havepurposes. felt it necessary to call a halt for the discussion of

In later years, processes of lamp manufacture were so remedial measures.improved as to permit the concentration of lamp out- As an illustration of what is taking place in someput into three voltages-110, 115, and 120 volts. systems, they present a diagram of voltage drops in theA steady increase in the 115-volt output, and a decrease various parts of a system having five transformationsin the relative outputs of 110- and 120-volt lamps has between the generator and the consumer, with a total ofbeen in progress since that time. about 50 per cent voltage drop between generator and

Utilization voltage standards are now so well recog- consumer.nized that a multitude of household and motor-driven The drops chosen for illustration are average valuesappliances have been produced in quantities and at and do not represent cases which could be found inprices which would have been totally impossible with- practise involving greater drops.out standardization. It is obvious that the maintenance of voltage regula-

Utilities in many states are required by regulatory tion under such conditions is a difficult problem withbodies to adopt a utilization voltage standard and to the best of equipment, and when there is imposed themaintain regulation within prescribed limits above or limitation that the apparatus must not be subjected tobelow such standard.-.. . .over-voltage, the limitation will quite surely in many

This to a considerable extent, fixes the voltages in cases be exceeded.other parts of the system and makes the utilizationvoltage the natural base of reference. PROPOSED CHANGES IN PRACTISEThe proposal to establish ratings which are integral The manufacturers have presented a scheme for

multiples of 115 is a recognition of the fact that the accomplishing this by increasing secondary voltageutilization voltage is the most logical base of reference in ratings to multiples of 115 instead of 110, as at presentan electricity supply system. rated.2The utilization voltage is one which must be kept as This provides a no-load pressure about 5 per cent

nearly constant as possible through all ranges of load, above that given by the present standard and a full-and this is the only part of the system of which this is load pressure, which offsets the drop in the transformertrue. and delivers at full load the same pressure which is

Electricity supply systems have developed during the derived from transformers of the present standard atpast quarter of a century from simple groups of distribu- no load.tion feeders, with one voltage level above the utilization Taps are to be provided in the primary coils, as atpressure, to extended systems serving large areas with present, to care for situations where the drop in con-two or three voltage levels above the utilization necting lines requires more compensation.pressure. It is proposed that generator regulation be heldWe are now in the process of constructing a super- within a range, from plus 5 to minus 5 per cent of

power network through which these areas are being tied standard rating.1. Commonwealth Edison Co. 2. Voltage Standardization of A-C. Systemsfrom the ViewpoitrwPresented] at the Winter Convention of the A. I. E. E., New of the Electrical Manufacturer, by F. C. Hanker and H. R.

York, N. V., February 7-11, 192?7. -Summerhayes, A. I. E. E. Winter Convention, February, 1927.185

186 GEAR: VOLTAGE STANDARDS FOR ELECTRICAL DISTRIBUTION Transactions A. 1. E. E.

SOME LIMITATIONS OF THE PROPOSAL much of the existing 132-kv. equipment is so relatedThe example presented shows the application of the to the system of which it is a part that inevitably it

new plan under full-load conditions, where a single must be subjected to pressures up to 138 kv. or higher,series of circuits is involved under the normal conditions of daily operation.The complete picture of an average system would The proposed plan of adding 5 per cent to the sec-

reveal other circuits taken off at the generating station ondary as a part of the fixed ratio of a transformerdelivering energy at the generator voltage level. It obviously can not be followed on lines where the direc-would also include additional lines taken off at the tion of flow of energy is changed from time to time, as is132/66/13.2-kv. levels, having various percentages of often,the case in tie-lines between power stations.line drop, which must be taken into account in fixing In such lines the transformers must meet the voltagethe setting of transformer taps. requirements of both step-up and step-down trans-

Inevitably there will be certain of these branches formers. Also, they are often so related to each otherwhich will deliver a pressure above or below normal that, in order to transfer energy in the desired amountduring certain parts of the day. without displacing the general level of system pressure,

In the particular circuit shown, the pressure at they must be equipped with pressure taps adjustablequarter load would be from 10 to 12 per cent above under load.normal at the utilization circuits, assuming that the This requires pressure taps giving a range of 15 to 20generator pressure was reduced from 1.3.8 to 12.8, as per cent in either direction to deliver proper pressureproposed, during the light load period and the feeder at the bus of the receiving station.regulator were run at full choke. In addition to this, OBSERVANCE OF STANDARDSthe transformer and line equipment at the 69-kv. and13.8-kv. levels are also operating at 10 to 12 per cent It iso ust if a stndris to accompisitabove the proposed maximum voltage ratings. apurpose, it mustbe onewhlch will be generally recognized

This, of course, can be avoided by the use of tap practicable of applicatlon and feasible in operation.changing devices operable under load, and it is quite Thefalurofsprevio adoptedsndards tobapparent~ ~ ~tha suc auiir qimn utb generally observed seems to have resulted, in part, fromapparent that such auxiliary equipment must be .includ'ed in the completed picture of the situation. a lack of adaptability of apparatus to working con-

The*necessitofhaving considerabl rangeofco- ditions, and perhaps from a lack of appreciation on theThe~~~~~~~~~~~~~neest.fhvn osdrberneo on

part of some engineers of the wide range of volt'age dropstrol between light-load and full-load conditions suggests... . * . . ~~~~~Which have been introduced in recent years into dis-the desirability of having as wide a range as is economi-cally feasible in the generator voltage. It is proposed to tributing systems.The lack of adaptability has been met as nearly as isget a range of 10 per cent by operating at pressuresbelow normal (down to minus 5 per cent) during light possible by the manufacturer's proposal to increaseload, and at pressures above normal (up to plus a per voltage ratings to a point where they will be similar to

during hours of heavy load, pressures which are normally encountered in practise.cent) during hours of heavy load. cent The discussion of this subject in connection with theThis will prevent over-excitation of generators if

proposed changes has and will further serve to bring atransformer taps are connected to give the necessary

bostn votg tcopnaefrull-loa drop greater number of. engineers face to face with the situa-boosting voltage to compensate for full-load drop.At light load periods, tap changers will be required where tion in a way which will be beneficial.

The adoption of standards which automatically addthe total compensation in transformers is more than voltage for full-load conditions will draw attention tothe combined range of generator and potential regulators. the g

It s popoedhatthevolage abve 9 k. b lethenecessity of providing means of preventing over-It is proposed that the voltages above 69 kv. be left voltage at light loads.as multiples of 110.The stage of development thus far attained may be CONCLUSION

such that it is a difficult matter to make a change how, Voltage standards are a basic necessity for utilizationbut to those of us who have not until recent years been equipment and are the basis of voltage throughout thebrought into pressures above 69 kv., it comes as some- system.thing of a shock to learn that if we subject our 132-kv. The manufacturer's proposal offers a decidedequipment to any pressure above 132 kv., we are ex- improvement over present standards, but should treatceeding the manufacturer's rating and presumably all voltages on a uniform basis.taking a risk in operation which is not shared by the There should be a recognized standard for trans-manufacturer. formers used in interconnections where the direction ofThe manufacturer's explanation that it is not flow is subject to change.

necessary to use the multiples of 11.5 in fixing rated When standards have been fixed which are applicablevoltages at pressures above 69 kv. is lacking in any without radical change in existing equipment, they will,reasons sufficient to warrant a break of so fundamental no doubt, be accepted and adopted by users ofa character in the proposed standards. equipment.

Whether the 132-ky. equipment in service has been Discussiondesigned for a maximum pressure of 132 kv. or not, For discussion of this paper see page 205.