ence takes on a minor role relat ive t o inter-variable dependence. A still further exten­sion to the control -system concept can be made: namely , the class of control sy s t ems in which both t ime dependence and inter-variable dependence are of primary impor­tance. An example of this is the fol lowing:

.τ = density of vehicles on road X }' = density of vehicles on road Y (for con­

trolling traffic on t w o parallel roads leading t o a c o m m o n dest inat ion, such as a bridge or tunnel )

Thus, three classes of control sy s t ems are now apparent: (1 ) sys tems in which the time dependence of one or more variables is of primary importance, and in which inter-variable dependence is of secondary or no importance; (2 ) sy s t ems in which the de­pendence between t w o or more variables is important, t i m e dependence unimportant ; (3) systems in which t i m e dependence and intervariable dependence are equal ly im­portant. It is suggested that these three classes of sys tems be called ' 'wave control systems," "path control sy s t ems ," and "trace control sy s t ems ," respect ively , where wave, path, and trace denote in general multidimensional curves for which t i m e dependence and intervariable dependence have appropriate a m o u n t s of importance.

A technical correction is suggested as follows:

From equat ion 8 it is clear tha t the authors intend to extend the concept of the phase plane to a n y t w o variables, rather than just d is tance and t ime. In the con­vent ional phase plane the co-ordinates are posit ion and ve loc i ty ; hence, in the general­ized phase p lane the co-ordinates should be y and dy/dx. However , the authors plot curves of y versus x, and call t h e m "phase-plane trajectories." It seems t o m e tha t t h e y would be more properly denoted as "trajectories in the x3'-plane."

Philip Sarachik and J . R. Ragazzini: W e wish to thank Mr. K a l m a n and Dr. Sklansky for their interest ing discussion of this paper.

Mr. Ka lman's method of obtaining the s y s t e m behavior for a n y specified single-va lued functional relation f{xc) is quite novel . H e shows tha t the behavior is equivalent t o that of a s y s t e m with a single "t ime cons tant" responding t o an i n p u t / ( / ) . It is important t o emphasize , however, that the approximat ion m a d e in obtaining the s imple result g iven in equation 30 is per­missible on ly in the very restrict ive condi­t ion g iven in equat ion 3 1 . Actua l ly the s y s t e m will perform well within specifica­t ions even if this condit ion is not satisfied and so mos t sy s t ems of this t y p e will not be designed t o satisfy the condit ion. Unfortu­nate ly , therefore, in most sy s t ems w e would still have t o resort t o an analog computer t o

see how the s y s t e m performs with arbitrary funct ions f{xc)^ T h e single-t ime-constant analogy , however , is a good one and enables one t o understand more clearly how the important s y s t e m parameters affect the be­havior of the sys tem.

W e cannot agree wi th Dr . Sklansky's objection t o the use of the phrase "phase p lane" in connect ion with the sys tem dis­cussed in our paper. There seems t o be some confusion as to just what a phase plane, or, more generally, a phase space or s ta te space, is. I t is admit ted that it has become c o m m o n practice to use position and veloc i ty {y, y) as the variables in the phase plane. This does not mean, however, that these are the only permissible variables. T h e p h a ^ plane m a y be defined b y any two variables which uniquely specify the state of t h e sys t em and in some cases different vari­ables m a y be preferable or even necessary. T h e specific justification for using "phase p lane" in referring t o the x-y plane of the sys tem can be found b y referring to reference 1. Here the authors in discussing sys tems described b y t w o equat ions of the first order lx==P(x,y); y = Q(x,y)] s tate , "In m a n y cases the x-y p lane is a phase plane and so we shall cont inue t o call it that ."

R E F E R E N C E

1. THEORY OF OSCILLATIONS (book), A. A. An-dronow, C. E. Chiaken. Princeton University Press, Princeton, N. J., 1949, p. 182.

Single-Phase Versus 3-Phase Service

for Residential A i r Conditioning

A. S. ANDERSON F E L L O W A I E E

RE S I D E N T I A L air conditioning has made a significant contr ibut ion to

the growth of loads in the warmer pa r t s of the United States . Central ly located units for summer and year-round air conditioning appear on the horizon as potential loads of unprecedented magni­tude to nearly all pa r t s of the country . All phases of uti l i ty operat ions will be affected b u t of immediate concern is the determination of the characterist ics of the distribution system. T h e first question to be answered is : "Shall single-phase or 3-phase service be provided?" T h e cus­tomer, as well as the company, is vital ly interested in the answer.

The most prevalent sizes of motors will be 2, 3, and 5 h p (horsepower). I n t he past, motors of these sizes were seldom used in residences and the choice between single phase and 3-phase was not of great economic importance. Therefore, t he practice varies between companies and

CHASE HUTCHINSON F E L L O W A I E E

sometimes in different areas of the same company. Now however, utilities realize t h a t a s tudy of the problem on a long-range basis is necessary to set a basis for present-day policy. T h e company, cus­tomer, and manufacturer are equally concerned with over-all economics of this impor tan t problem.

Purpose

T h e purpose of this paper is to present the results of a s tudy made in 1954 to determine the difference in cost of a single-phase system as compared to a 3-phase

Paper 57-6, recommended by the AIEE Domestic and Commercial Applications Committee and approved by the AIEE Technical Operations Department for presentation at the AIEE Winter General Meeting, New York. N. Y., January 21-25, 1957. Manuscript submitted August 23, 1956; made available for printing October 22, 1956. A. S. ANDERSON and CHASE HUTCHINSON are with Ebasco Services, Inc., New York, N. Y.

system for serving 3-hp and 5-hp air-conditioning uni ts and heat pumps. Customer costs as well as uti l i ty costs are considered.

T h e secondary systems t h a t are com­pared are as follows:

1. Single-phase 120/240-voIt 3-wire sys ­tem.

2. Three-phase 120 /240-vo l t 4-wire delta sy s t em.

N o t e that the 3-phase 120 /208-vo l t s y s t e m is not economical for general overhead residential secondaries and, while considered in the s tudy, data concerning it will not be presented. Higher secondary v o k a g e s are now being considered b y the industry gener­al ly as a possibil i ty in the future with greater load densities for residential areas. T h e cost of single-phase service as compared to 3-phase service will be more favorable to a single-phase service at any proposed higher secondary vol tages . For this reason higher vo l tage secondary cos ts were not studied, since costs are in favor of the single-phase service a t 120 /240 vo l t s .

T h e following si tuations and demands for other electrical loads in addit ion to the load of air conditioners or hea t pumps are covered b y this s t udy :

1. Exist ing secondary sys tem with 1.25-k v a diversified demand per customer and saturation of air-conditioning or heat-p u m p units in 4 % steps up to 5 0 % satura­tion.

2 . N e w secondary sys tem in new residen-

MAY 1 9 5 7 Andersonf Hutchinson—Service for Residential Air Conditioning 6 1

tial development with 1,25-kva diversified demand per customer and saturation of air-conditioning or heat-pump units of 25, 50, and 100%. 3. New secondary system in new residen­tial development with 7.5-kva maximum demand per customer and saturation of air-conditioning or heat-pump units of 100%.

The following individual customer demands for the air-conditioning or heat-pmnp loads were assumed.

Single P h a s e , 3 P h a s e ,

Unit K v a K v a

3-hp air condit ioning. . . , . . . . 4 . 6 5 5 . 0 5 5-hp air condit ioning. . . . . . . 8 . 3 1 8 . 7 4 3-hp heat p u m p , . . . . 9 . 8 8 1 0 . 1 0 5-hp heat p u m p , . . . . 1 6 . 8 0 1 7 . 1 0

T h e 3-hp heat p u m p includes 6 kw of auxil iary resistance heating units and the 5-hp heat p u m p includes 10 kw.

Table III. Investment Savings of Single Phase Over 3 Phase per Installation for Utility System to Serve 3.Hp Air-Conditioning Unite Added to Existing 7,200 to 120/240-Volt Single-Phase

System*

Saturation Sav ings P e r Unit Averaged For Saturation S h o w n f

No. Transformers Primary Secondary M e t e r s Totalt 6 4

12 8 18 12 24 17 30 21 36 25 4 2 29 48 33 54 37 60 4 2 66 46 72 50

. $ 1 8 3 .

. 157.

. 100.

. 121 .

. 8 8 .

. 8 1 .

. 77 .

. 5 9 .

. 5 0 .

. 4 8 .

. 4 6 .

. 4 8 .

. $ 1 1 7 .

. 57 .

. 38 .

. 25 .

. 20 .

. 14.

. 12.

. 11 . 8.

. 7 . 6. 5 .

. $ 1 0 . .

. 7 . .

. 6. .

. 5 . .

. 5 . .

3 . ' .

. $ 3 5 .

. 35 .

. 3 5 .

. 35 .

. 35 .

. 3 5 .

. 35 .

. 35 .

. . 35

. 35

. 35

. $ 3 4 3

. 257

. 180

. 187

. 149

. 135

. 129

. 110

. 98

. 95

. 9 2

. 92

Conclusions

* Exist ing sys t em consists of 25-kva transformer wi th six spans per transformer. Secondary wire s ize , American Wire Gauge no . ( A W G ) 4 copper. Load per customer, 1.25 kva . four customers per pole . Air-condit ioning unit installed n o t more t h a n one span from transformer t o l imit flicker. M i n i m u m size transformer for " l ight ing" load is 15 kva . M a x i m u m load per transformer, 120%. Open Υ t o open-delta banks used for 3-phase service. Load for single-phase unit including fans equals 4.6 kva . Load for 3 -phase units including fans equals 5.0 kva .

t For each saturation shown the average costs are those which will mos t likely have resulted by doing those things required for each lesser saturation progressively up t o the saturation shown.

I Includes excess cost of 3-phase service drop over single-phase service drop of $1 .

1. The sum of utility investment and customer investment is less with the single-phase 120/240-volt system than with the 3-phase 240-volt system for 3- and 5-hp motor-driven compressor units. From data developed, indications are that savings would also be realized for single-phase motor units of larger capacity. 2. The utility investment in a single-phase system including primary, trans­formers, secondary, meters, and services,

Table I. Average Utility Investment Savings Per Unit for Single-Phase 120/240.Volt System as Compared to 3-Phase 120/240·

Volt Delta System

Exist ing Res ident ia l

S y s t e m 1.25.Kva

D e m a n d for o t h e r Load, Saturation

N e w l y Constructed Res ident ia l S y s t e m 1.25-Kva D e m a n d

for o t h e r Load, Saturation

Unit 4% 50% 25% 50% 100%

3-hp air condi­tioner $ 3 4 3 . . $ 9 2 . . $ 1 7 4 . . $ 1 0 5 . . . $ 6 9

5-hp air condi­tioner 3 7 7 . . 1 3 3 . . 1 6 7 . . 1 1 1 . . . 73

3-hp heat p u m p . . 3 0 7 . . 8 1 . . 1 2 3 . . 7 1 . . . 65 5-hp heat p u m p . . 3 9 6 . . 1 2 1 . . 1 0 9 . . 7 9 . . . 74

Table 11. Approximate Utility Investment Savings Per Unit for Slngle-Phase 120/240-Volt System as Compared to 3-Phase 120/ 240-Volt Delta System With 100% Saturation of Air-Conditioner Units in a New Residential

Development

Unit T r a n s ­

formers M e t e r s Otiier Tota

3-hp air condi­t ioner . . . $ 4 2 . . . . . . $ 3 5 . . . . . 1 5 . . . . $ 82

5-hp air condi­tioner . . . 7 7 . . . . . . 3 5 . . . . . — 1 . . . . I l l . . I l l

Table IV. Investment Savings of Single-Phase Over 3 Phase per Installation for Utility System to Serve 5-Hp Alr-Condltloning Units Added to Existing 7,200 to 120/240-VoU Single-Phase

System*

Saturation Sav ings P e r Unit Averaged For Saturation S h o w n f

N o . Transformers Primary Secondary M e t e r s Tota l t

6 4 12 8 18 12 24 17 30 21 36 25 42 29 48 33 54 37 60 42 66 46 72 50

$222 . 249 . 153 . 123 . 112 . 115. 112. 100.

96 . 97 . 9 2 . 8 9 .

. $ 1 1 2 .

. 59 .

. 37.

. 25 .

. 17.

. 13.

. 11 . 9. 7. 6. 5.

: 5 .

. $ 7 .

. 7 .

. 6.

. 5.

. 5 .

. 4 .

. 4 .

. 4 .

. 4 .

. 4 .

. 4 .

. 3 .

. $ 3 5 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

. 35 .

.$377

. 351

. 232

. 189

. 170

. 168

. 163

. 149

. 143

. 143

. 137

. 133

* Exis t ing sys tem consists of 25-kva transformer wi th six spans per transformer. Secondary wire'size, A W G 4 copper. Load per customer, 1.25 kva. Foiu: customers per pole . Air-conditioning unit installed not more t h a n one span from transformer t o l imit flicker. M i n i m u m size transformer is 15 k v a for "light­ing" load for 3-phase secondary and 25 k v a for single-phase secondary. M a x i m u m load per transformer, 120%. Open-Y t o open-delta banks used for 3-phase service. Load for single-phase unit including fans equals 8.3 kva . Load for 3-phase units including fans equals 8.7 kva .

t i See corresponding footnotes . Table I I I .

Table V . Investment Savings of Single Phase Over 3 Phase per Installation for Utility System to Serve 3-Hp Heat Pumps Added to Existing 7,200 to 120/240-Volt System*

Saturation Savings P e r Unit Averaged For Saturation S h o w n f

N o . Transformers Primary Secondary M e t e r s Totalt 6

12 18 24 30 .

. 4

. 8

. 1 2

. 1 7

. 2 1 36 25 42 29 48 33 54 37 60 4 2 66 46 72 50

. $ 1 4 4 .

. 129.

. 8 0 .

. 8 3 .

. 86 .

. 6 5 .

. 68 .

. 47 .

. 3 8 .

. 3 2 .

. 3 6 .

. 37 .

. $117

. 57

. 26

. 22

. 15

. 12

. 10

. 7 7 5

3 .

. . . $ 1 0 .

. . . 10 .

. . . 9 .

. . . 8 .

. . . 7 .

. . . 6.

. . . 6.

. . . 6.

. . . 6.

. . . 6 .

. . · . 5 .

. . . 5 .

. $ 3 5

. 35

. 35

. 35

. 35

. 35

. 35

. 35

. 35

. 35

. 35

. 35

$307 232 151 149 144 119 120

96 87 79 80 81

* Exis t ing s y s t e m consists of 25-kva transformer wi th six spans per transformer. Secondary wire size. A W G 2 copper. Load per customer, 1.25 kva . Four customers per pole. H e a t p u m p installed not more t h a n one span from transformer t o l imit flicker. M i n i m u m size transformer is 15 k v a for "l ight ing" load. M a x i m u m load per transformer, 150%. Open-Y t o open-de'ta banks used for 3-phase service. Load per unit , including fans and 6-kw supplemental heating, equals 9.9 kva for single phase and 10.1 k v a for 3 phase.

f t See corresponding footnotes . Table I I I .

6 2 Anderson, Hutchinson—Service for Residential Air Conditioning M A Y 1 9 5 7

Table VI . Investment Savings of Single Phase Over 3 Phase per Installation ior Utility System to Serve 5-Hp Heat Pumps Added to Existing 7,200 to 120/240.Volt System*

Saturation Sav ings P e r unit Averaged For Saturation S h o w n f

No. Transformers Primary Secondait M e t e r s T o t a l t

e 12

4 8

$228 168

$111 44

18 12 120 19, 24 17 105 15 30 21 88 10 36 25 78 6, 42 29 6 4 . . . 4 48 33 75 . . . . . . 3 64 37 76 2 60 42 72 1, 66 46 64 1, 72 50 68 1

. $ 1 0 . . .

. 1 0 . . . $ 3 5 . . .

3 5 . . . 35 35 35 35 35 35 35 35 35 35

. . $ 3 9 6

. . 269 195 175 152 137 121 131 131 126 117 121

• Existing system consists of 25-kva transformer wi th six spans per transformer. Secondary wire size, AWG 2 copper. Load per customer, 1.25 kva . Four customers per pole. H e a t p u m p installed not more than one span from transformer t o l imit flicker. M i n i m u m size transformer for "l ight ing" load is 25 kva . Maximum load per transformer, 150%. Open-Y to open-delta banks used for 3-phase service. Load per unit, including fans and 10-kw supplemental heating, equals 16.8 k v a for single phase aud 17.1 k v a for 3 phase.

t See corresponding footnote , Table I I I .

t Includes excess cost of 3-phase service drop over single-phase service drop of $12.

Table VII. Investment Savings of Single Phase Over 3 Phase per Installation for Utility System to Serve 3-Hp Air-Conditioning Units in New Areas*

Saturation, % Transformer Primary Secondary M e t e r s Tota l t

25 $115 $18 $5 $35 $174 105 50 61 6 2 3 5 . . . . . . .

$174 105

100 .̂ 0 9. 1

• Three-phase s y s t e m is served b y open-Y to open-delta transformer banks. Light and appliance load assumed to be 1.25 k v a per customer at transformer. Air-conditioning load, including fans, equals 4.6 k v a for single phase and 5.0 k v a for 3 phase.

t Includes $1 for extra cost of 3-phase over single-phase service.

Table VIII. Investment Savings of Single Phase Over 3 Phase per Installation for Utility System to Serve 5-Hp Air-Conditioning Units in New Areas*

Saturation, % Transformer Primary Secondary M e t e r s Tota l f

25 $113 $13 $5 2

$35 $167 50 69 4

$5 2 35 I l l

100 35 1 35 73

• Three-phase sys tem is served b y open-Y to open-delta transformer banks. Light and appliance load assumed to be 1.25 k v a per customer at transformer. Air-conditioning load, including fans, equals 8.3 k v a for single phase and 8.7 k v a for 3 phase.

t See corresponding footnote, Table V I I .

Table IX. Investment Savings of Single Phase Over 3 Phase per Installation for Utility System to Serve 3-Hp Heat Pumps in New Areas*

Saturation, % Transformer Primary Secondary M e t e r s Total f

2 5 . . . $68 . . . $ 1 3 $6 $35 $123 5 0 . . . 28 . . . 4 3

> · · · qpwtr · · · · · • · · · · » · %l XA^V 35 71

100 _ _ __ 26 . . 1 2 .̂ .ς β.ζ

• Three-phase sys tem is served b y open-Y to open-delta transformer banks. Light and appliance load assumed to be 1.25 k v a a t t h e transformer. H e a t - p u m p load, including fans and 6.0-kw supplemental heating, equals 9.9 k v a for single phase and 10.1 k v a for 3 phase.

t See corresponding footnote, Tab le V I I .

Table X. Investment Savings of Single Phase Over 3 Phase per Installation for Utility System to Serve 5-Hp Heat Pumps in New Areas*

Saturation, % Transformer Primary Secondary M e t e r s Tota l f

2 5 . . . $63 . . . $ 9 $7 $35 $109 5 0 . . , 44 . . . 1 4 35 79

1 0 0 . . . 41 . . . 1 '. 2 . . . . ' . . . . ' . . 35.'.'.'.'.'.'.'.'.'.'.'. 74

• Three-phase sys t em is served b y open-Y t o open-delta transformer banks. Light and appl iance load assumed to be 1.25 k v a a t the transformer. H e a t - p u m p load, including fans and 10-kw supplemental heating, equals 16.8 k v a for singlfc phase and 17.1 k v a for 3 phase, t Includes $5 for extra cost of single-phase over 3-phase service.

is lower than the investment in a 3-phase system as shown in Tables III to X and further summarized in Table I.

Tables XI and XII show the possible sav­ings in utility investment for a new resi­dential area where the saturation of units is 100% and the demand of the load other than air conditioning is 7.5 kva. It may be seen that most of these savings are in transformer costs and meters and may be summarized as shown in Table II. 3. The extra cost to the customer of single-phase units over 3-phase units of 3-hp and 5-hp ratings should eventually approach about $50 and $80 respectively. At pres­ent the differentials are somewhat greater for units of some manufacturers. This greyer differential cost is believed due to differences in assembly techniques, pricing, and methods, and relative production.

The extra cost of single phase is caused by need for starting and rmining capacitors and starting relays. If the running power factor of 3-phase motors were made equal to running power factor of single-phase motors, the cost of the 3-phase unit would increase. 4. Estimates of the cost of residential wiring for single-phase and 3-phase air-conditioning units of 3-hp and 5-hp ratings were received from ten operating utility

Table XI. Savings in Investment and Capital­ized Loss of Single Phase Over 3 Phase per Installation in Utility System to Serve a 100% Saturation of 3-Hp Air-Conditioning Unit in a New Area With 7.5-Kva Demand per

Customer for Other Load*

Customers per Transformer

12 16

. . . . $ 4 4

. . . . 1

. . . . 35

. . . . $ 8 0

. . . . 7

. . . . $ 8 7

Transformers $24 $42 Secondary 1 2 S e r v i c e . . . . - 1 1 Meters 35 35

Subtota l $61 $80 Capital ized Losses 13 2

Tota l $74 $82

* Three-phase sys tem is 4-wire delta.

Table XII. Savings in Investment and Capital­ized Loss of Single Phase Over 3 Phase per Installation in Utility System to Serve a 100% Saturation of 5-Hp Heat Pumps in a New Area With 7.5-Kva Demand per Customer for

Other Load*

Customers per Transformer

12

Transformer $ 91 $ 60 $ 77 Secondary 0 0 Service (5) (5) (5) Meters 35 35 35

Subtota l $121 $ 90 $107 Capital ized Losses 15 15 4

Tota l $136 . . $ 1 0 5 . . $111

( ) D e n o t e s less cost for 3 phase. • Three-phase sys t em is 4-wire delta.

MAY 1 9 5 7 Anderson, Hutchinson—Service for Residential Air Conditioning 63

-companies. Generally, the difference in cost between wiring for single-phase units or 3-phase units does not depend upon whether additional wiring for an existing residence or entirely new wiring for a new residence is being considered. Sixteen sets of estimates indicate that wiring costs for single-phase units are lower by a range of from $6 to $77 or an average of $48. Five sets of estimates show that wiring for 3-phase units are lower by a range of from $3 to $38 or an average of $16. The difference in cost was not affected appreciably by whether the motor is 3-hp or 5-hp rating.

Three sets of estimates for 5-hp heat pumps with 10-kw auxiliary heating were received. Two sets show the wiring cost for single phase units to cost less by an average of $23. The other set shows 3-phase wiring to cost less by $7. The difference in wiring cost for single-phase and 3-phase units generally favors the use of single-phase units. The average of aU differences is $30 in favor of single phase.

5. Capacitor-start, capacitor-run single-phase motors compare very favorably in operating characteristics with 3-phase induc­

tion motors in 3-hp and 5-hp sizes. Some of comparative characteristics of one make of 5-hp motor are:

Sing le P h a s e

R a t e d voltage Running power factor, % . . . Start ing power factor, % . . . Locked rotor amperes EflSciency, % Locked rotor torque, foot­

pounds

3 P h a s e

230 220 93 83 87 69

100 90 80 84

36 28

Di iscussion

Robert F. Lawrence (Westinghouse Electric Corporation, East Pittsburgh, Pa.): We are in general agreement with the authors' results of the very extensive study which they conducted. I would like to discuss the basis of our agreement and also would like to offer an alternate method of presen­tation of data. There is, too, one exception to their general conclusions; namely, that while 3 phase is more costly than single phase at today's conventional secondary voltages, it is not necessarily true at a higher secondary voltage.

In our studies of higher secondary volt­age distribution systems for residential areas,i'2 the cost of a 3-phase 120/208-volt 4-wire system was determined and compared to the cost of a single-phase 120/240-volt system. The primary phase-to-phase volt­age for both systems was 34.5 kv. The pri­mary of the 3-phase system utilized three conductors.

Because our studies applied to new areas our comments are confined to the residts contained in Tables VII, VIII, IX, and X.

For purposes of orientation, let us com­pare the 34.5-kv single-nhase and 3-phase systems that we studied. Later I will make an allowance for costs of a 12.5-kv primary voltage.

In the 120/208-volt 3-phase Y secondary system and the open-Y 3-phase 120/240-volt 4-wire delta system, the number of primary conductors is the same. The size of primary conductors for a given primary voltage would also be the same. The dis­tribution transformers would be 3-phase or three single-phase units in the Y system and two units, open-Y, open delta, in the delta system. All of these factors affect costs and I would expect the costs to be slightly lower had we studied the 120/240-volt 3-phase 4-wire delta system.

The total dollar investment savings, exclusive of meters, of the single-phase sys­tem over the 3-phase system is practicaUy constant at about $110 per house over a range of load densities of 1.6, 2.5, and 5.0 kva per house. The kilovolt-amperage per house is the average diversified peak demand per house as viewed for 1,000 houses. The total savings at 10 kva per house is approximately $200. This sav­ings might be expected to increase at the higher density although we believe that this instance is attributable to the costs used for the larger 19.9-kv transformers to supply the higher density load.

All of our studies were based on a simul­taneous economic analysis of the primary, distribution transformer, and the second­ary, to obtain optimized system costs. It is a lengthy and tedious process and would be very time-consuming to repeat for a primary voltage other than 34.5 kv. How­ever, we have been able to make some quick but reliable approximations of costs of a primary voltage of 12.47 kv to compare our results more directly with the authors* studies. From these, we find that the total investment savings per customer of a single-phase system over a 3-phase system is ap­proximately $55 over a range of load densi­ties of 1.5, 2.5, 5.0, and 10.0 kva. The sav­ings include investment on primaries, distri­bution tmnsformers, and secondaries, but not meters. The savings of $35 per meter as used by the authors could be added to the foregoing figure to give a total invest­ment savings of $90 per house.

In Tables VII-X, the investment savings are given per installation, which we presume to mean per air-conditioning or per heat-pump installation. Thus, in the case of 25% saturation, only one house in fotu has an air conditioner and to determine the savings per customer the values given for the savings of the transformer, primary, and secondary should be divided by 4. Simi­larly for 50% saturation, these costs should be divided by 2. We have for Table VII:

% Saturation Sav ings per Customer

25 $ 6 9 . 5 5 50 6 9 . 5 0

100 6 9 . 0 0

Repeating the foregoing for Tables VIII» IX, and X gives similar results, namely, that the doUar savings is practicaUy con­stant. The value of $90 arrived at is in remarkably close agreement considering the inevitable variations in studies by different groups. We believe that this is the way these data should be presented.

It is our thought, however, that if the investment savings is to be given on some basis other than per customer, the following evaluation is more correct than the per-installation basis shown.

We have selected Table VII to illustrate the point. It is assumed that 12 customers are served per distribution transformer. The savings will be apportioned on the basis of the customer kilovolt-amperage demand.

Let dollar savings per kilovolt-am­perage of demand

1.25-kva demand for non-air-conditioning customer

6.25-kva demand for ah-conditioning customer then, for 25% saturation:

(1.25 X 9)X+ (Q.25XS)X^

=$13.8 savings per kilovolt-amperage

$13.8XI.25=$17.25 savings per non-air-conditioning customer

13.8 X 6.25=$86.25 savings per ah-condi-tioning customer

$86.25 -1-35.00 meter savings

$121.25 total savings per air-conditioning customer

—17.25 savings of 1.25-kva load that is not air conditioning

$104.00 incremental savings per air-condi­tioning customer

For 50% saturation, we have

$ 9.20 savings per kilovolt-amperage 11.4 Savings per non-air-conditioning

customer $57.0 savings per air-conditioning cus­

tomer -f35.0 meter savings

$92.0 total savings per air-conditioning customer

— 11.4 savings of 0.125-kva load that is not air conditioning

$80.6 incremental savings per air-condi­tioning customer

The foregoing method appears to give exhorbitant values of savings and costs to serve the high-demand customer. Since the total costs of the single-phase and 3-phase systems are not given in the paper, we can­not properly evaluate their costs.

I mentioned earlier the costs of the single-phase and 3-phase secondary systems at the higher secondary voltage. Our studies showed them to be about a standoff, exclu­sive of metering. Three-phase metermg is more costly, but with single-phase service to each home, this would no longer be a problem. We stiU conclude that single- or 3-phase higher secondary voltage distribu­tion are about equal in cost, and we are inclined to favor the 3-phase system.

6 4 Anderson, Hutchinson—Service for Residential Air Conditioning M A Y 1 9 5 7

REFERENCES

1. R E S I D E N T I A L D I S T R I B U T I O N — A N A N A L Y S I S O P SYSTEMS TO S E R V E E X P A N D I N G L O A D S , S . B . Griscom, R . P . Lawrence . AIEE Transactions, vol. 75, pt. I l l , Aug. 1956, pp. 5 3 3 - 4 2 .

2. ECONOMIC C O M P A R I S O N O P S E C O N D A R Y V O L T ­AGES; S I N G L E - A N D T H R E E - P H A S E D I S T R I B U T I O N FOR R E S I D E N T I A L A R E A S , R . A. Z immerman, H . E . Lokay. Ibid., pp. 5 4 3 - 5 2 .

A. E. Diehl (Borg-Warner Corporation, York, Pa.): We would like to commend the authors of this paper on doing a very comprehensive job with respect to single-phase versus 3-phase service for residential air conditioning. We believe that this is an excellent, condensed summary of a complete study conducted by the authors.

This paper concerns the application of 3-and 5-ton air conditioners, both of the con­ventional and the heat-pump type. The authors are to be complimented on selecting the most popular sizes of residential air conditioners as a basis for their study.

The results, as summarized, are quite indicative that definite savings to the utility result by furnishing single-phase power for the various types of distribution systems that are generally being used today.

The authors are aware of the fact that the single-phase air conditioners in 3- and 5-ton sizes are considerably more expensive in that they involve the use of starting relays and starting and running capacitors. The additional electrical components, naturally, result in more field service than is normally experienced on polyphase applications. It is therefore necessary to compare the in­creased unit cost plus the increased possi­bility of field service cost versus increased power factor and possible savings in the electric wiring costs for the customer, before making general conclusions that would apply to all areas of the United States.

We believe that the air-conditioning and refrigeration industry requires fmther time and experience to develop less costly and more reliable single-phase equipment before the use of single phases only should be con­sidered for application to residential air conditioning. Experience to date indicated that the polyphase units are more rugged and will withstand more abuse.

There is an added incentive to consider single-phase power supply more seriously by the air-conditioning and refrigeration manu­facturers in view of a rather increasing difficulty experienced with single-phasing of polyphase circuits by electrical disturbances, power failures, etc. It is difficult to provide necessary motor protection for this condi­tion, which, of course, is eliminated when single-phase supply is used.

May we take this opportunity to con­gratulate the authors on a fine, thorough study of a very pertinent problem with respect to the application of residential air conditioning and its inherent electrical application problems.

H. L. McClure (Delaware Power and Light Company, Wilmington, Dela.): Study of this paper raises a question of prime impor­tance to those companies with 2,400/4.160-volt distribution. The comparisons made in the paper are for 7,200/12,470-volt pri­maries which have relatively high single-phase to neutral load capabilities. Would

the same conclusions hold for 2,400/4,160-volt primaries, where presumably much more of the primary system would have to be multiphase?

We are greatly in favor of single-phase supply because of the cle9.ner appearance of lines and poles, simplified tree trimming, ease of banking secondaries, better power factor of motors, and, of course, lower cost.

Carl C. Ambrosius and Robert H. Sarikas (Illinois Power Company, Decatur, 111.): The results obtained by the authors check fairly close with those we obtained in a similar study prepared in 1955. That study indicated a savings to the utility as high as $331 per 5-hp unit in 12.47-kv subur­ban areas where usually a single customer is served by a transformer. The savings with eight customers served from the same trans­former on the 4.16-kv system were estimated to be $162 per customer. In general, it was found that the minimum increase in utility investment to provide 3-phase service was in the order of 30% of the required single-phase investment. The author's findings have also been substantiated by a number of other investigations.^'2»»

Customer equipment cost differences obtained from suppliers varied from $40 to as much as $125. The range of cost esti­mates for rewiring, received from con­tractors, was considerable. Three-phase wiring averaged about $25 higher than single-phase wiring. In many instances the total cost to the customer, equipment plus wiring, may be less for single-phase than for 3-phase service, especially if the existing single-phase service is adequate.

One argument frequently used by cus­tomers and contractors in favor of 3-phase service is increased reliability and efficiency. The tabulation in paragraph 5 of the author's "Conclusions" shows that the slight difference in efficiency is almost negligible. This tabulation also shows that vrith identical motor terminal voltages the starting current of a 3-phase motor is approximptely equal to that of a single-phase motor. As a consequence, the flicker due to 3-phase motor starting is about equal to that of single-phase motor, and may be greater where the saturation of 3-phase motors permits the use of a smaller distribution transformer for the "lighting" load in an open-Y to open-delta transformer bank.

As regards reliability, a check with a large supplier of heat pumps and central air-conditioning units reveals that the failure rate of 3-phase units is about equal to that of single-phase unit. This is attributed primarily to motor bum-out caused by single-phasing due to an outage of one phase of the primary distribution system from such causes as fuse-blowing or single-phase oil-circuit recloser operation. A case of this type of burn-out, due to failure of the motor phase protection to operate, is described in a paper concerning some of the early heat-pump test installations.* Fur­ther, it would appear that in a residential area, the probability of an outage of either phase of an open-Y system would be con­siderably greater than that of an individual phase, due to the increased expostue in circuit-miles. Since the loss of either phase will result in a 3-phase service interruption, this matter should be of importance to both

utility and customer, especially with regard to heat-pump applications.

REFERENCES

1. P R O B L E M S P O S E D B Y H O M E - M O T O R L O A D S , H . E . Campbell . Electrical World, N e w York, N . Y . , M a y 17, 1954.

2. 1 2 0 / 2 4 0 V C A N S E R V E B I G G E R L O A D S , H . G . B a m e t t , L . W . Manning . Ibid.

3 . S E R V I N G A I R - C O N D I T I O N I N G C H E A P L Y , H . W . Grate . Ibid., Dec . 6, 1954.

4. R E S I D E N T I A L H E A T P U M P E X P E R I M E N T S I N P H I L A D E L P H I A — I N S T A L L A T I O N A N D O P E R A T I N G E X P E R I E N C E , J . H . Harlow, G. E . Klapper. AIEE Transactions, vol . 7 1 , pt. I I , 1952 (Jan. 1953 sec­t ion) , pp . 3 6 6 - 7 5 .

Wayne H. Johnson (American Gas and Electric Service Corporation, New York, N. Y.): The conclusions reached in the paper that 3- and 5-hp motors and heat pumps can be more economically served single phase than 3 phase confirms our con­clusions made over 10 years ago. A review of present costs indicates there is no reason to change our thinking from an eco­nomical cost to serve standpoint.

However, I do wish to comment specifi­cally on the flicker limitation proposed in this paper. At present, the flicker problem in connection with heat pumps does not appear to be serious. Flicker difficulties in connection with automatically controlled heat pumps starting across the line are more likely to occur during equilibrium weather, that is, when the outside weather is close to that required by the inside controUmg thermostats. Starting under these condi­tions may be as frequent as once in 15 to 20 minutes.

A review of the various flicker curves indicates that an average requirement permits about 4% flicker for a frequency of 15 to 20 mmutes. The flicker to be expected at the secondary terminals of a 7,200/120/ 240-volt distribution transformer with sus­tained high side voltage when a 5-ton General Electric Weathertron is starting is 4% on a 25-kva, 2.4% on a 37V2-kva, and 1.67% on a 50-kva load. Adding a 125-foot span of no. 2 copper, or no. 1/0 steel-rein­forced almninum cable secondary on racks, causes these flicker percentages to become 8.13%, 6.59%, and 5.94% respectively. This indicates that other customers con­nected to the same service pole (one span from the transformer) might complain during equilibrium weather conditions.

We wish to point out, however, that even though our calculations indicate a possible difficulty, our experience does not prove that we have it. The matter of flicker, in connection with single-phase heat pumps, needs to be more completely explored and our flicker curves need to be re-exammed.

WiUiam A. McGrath (Carrier Corporation, Syracuse, N. Y.): I am commenting on this paper as an air-conditioning manufac-ttuer. From the standpoint of our indus­try, I think it is proper to say that the analysis offered represents a real contribu­tion to our understanding of the electrical utility problems as influenced by the air-conditioning load. It is our feeling, how­ever, that this is a subject which is not static and that conclusions that might be proper today cotdd very well be obsolete another day.

M A Y 1 9 5 7 Anderson, Hutchinson—Service for Residential Air Conditioning 6 5

There are a number of questions and observations which arise in the mind of the equipment manufacturer which may be worth offering for discussion.

1. While the title of the paper restricted the scope to residential air conditioning, it is hard to see how one can exclude commercial air conditioning from such a discussion since the equipment that is used for residential and commercial air conditioning is in the majority of cases identical. It would seem, therefore, that a complete answer to the question is not found until the needs of the commercial market are considered. If single-phase equipment is really the better choice for residential service, is this not also true for commercial service? Obviously, if the manufacturer's efforts could be directed to a standardized line of equipment, more progress in cost reduction and improvement would be achieved than if both types have to be furnished.

2. This paper states that the extra cost of single-phase air conditioners over 3 phase should be $50 for the 3-hp and $80 for the 5-hp size. It is unfortunate that the authors did not disclose the source of these estimates because the figures do not agree with our knowledge of the present cost level of this equipment. It is apparent from a review of current selling prices of different manufac­turers in this industry that the actual cost will average $60 to $65 more for a 3-hp unit and $110 to $115 more for a 5-hp unit.

Also, in arriving at projected or ultimate cost differentials, it would be well to esti­mate the inherent excesses of materials and components that occm in the single-phase versus 3-phase equipment. Extra cost is represented in the capacitors required, starting relays, and equipment, and in addi­tion more copper and iron are required in single-phase equipment for the same per­formance. Even beyond this, current sin­gle-phase motors are commonly machine-wound, which tends to reduce the labor cost, but most 3-phase motors of the same size are not machine-wound. On this basis, it could be assumed that if the usage of the 3-phase motors were increased the cost differential might favor the 3-phase equipment by an even greater margin.

3. A saving in utility investment cost was tabulated and indicates that 3-phase transformers and meters are substantially more expensive than single-phase units. It would be interesting to know why, for the same kilowatt capacity, this cost discrepancy should exist.

4. The discussion of the cost of resi­dential wiring as between single-phase and 3-phase equipment does not actually present a very good case for assuming that these costs will favor single phase. The wide discrepancy of estimates received would seem to indicate that some factors other than the basic factor of cost and labor enter into these estimates. It would seem that a more precise comparison could be obtained by directly estimating and tabulating material costs and labor costs independently for the two systems. Also in this connec­tion, it would be interesting to know what the estimated difference in utility wiring cost is between the two systems.

5. A related topic that might be appro­priate for discussion in this connection is the matter of voltage regulations and phase unbalance on air-conditioning loads. It

seems rather certain that air-conditioning equipment is frequently damaged by being exposed to voltages outside of the range of standards recommended in the Edison Electric Institute-National Electrical Manufacturers Association Standard R-6. Even beyond this, we have encountered serious conditions of phase unbalance which are not limited by this standard. In some cases these destructive conditions have been traced to the use of open-transformer arrangements, apparently inspired by the desire to place 3-phase equipment on single phase distribution systems. If a case can be made for better voltage regulation with the single-phase systems, this would be an important consideration to the industry.

6. Another similar question which might be worth exploring is the question of light flicker or television sag as might result from starting impulses. The question here is whether there is any margin of superiority of the 3-phase service versus single phase on this score.

B. M. Gallaher (Texas Electric Service Com­pany, Fort Worth, Tex.): The paper is a well-documented contribution to the prob­lem facing many utilities as to the choice of furnishing single-phase or 3-phase power for residential use. The utility with which I am connected supplies both single-phase and 3-phase service to many residential customers. It is the purpose of this dis­cussion to emphasize and to concur with the authors' conclusions and possibly to view the problem from a slightly different angle. Most people in the electrical business take 3-phase primary distribution for granted but are inclined to overlook the costs of com­ponents necessary to obtain 3 phase at secondary voltage levels. Some of these components are:

1. Although the kilowatt-hours (or energy) in supplying power to home appli­ances is practically the same for either single-phase or 3-phase power, the principal part of the *'cost to serve" is represented in cost of the demand component (fixed costs of plant investment) rather than in the energy (fuel) component, hence any major saving in investment cost is an economical solution.

2. One way to consider the cost of a distribution transformer, including its acces­sories of lightning arresters and cutouts, may be expressed as:

Total installed cost = base cost-f-isTX kva where "base cost" is that component of cost that is approximately constant for several sizes of transformers in the range used for distribution loads, Κ is the incremental cost per kilovolt-ampere of transformer capacity, and "kva" is the kilovolt-amperage name-plate rating of the transformer.

Typical installed costs for a 7,200-volt/ 120/240 transformer is in the order of:

Total installed cost=$2104-$10X kva When two transformers are installed to

serve a 3-phase secondary, the costs become: Total installed cost = $410+$10 X kva Obviously, this additional $200 in the

"base cost" is the minimum additional cost to establish a 3-phase secondary source to serve a single customer. Should two or more 3-phase residences share the same secondary, then this extra cost may be prorated.

3. As brought out in the paper, the in­vestment cost of 3-phase meters is consider­ably greater than the investment cost of single-phase meters. In addition to invest­ment costs, higher operating costs, both in maintenance and testing of 3-phase meters, are appreciable.

4. Additional operating costs to serve a 3-phase customer must include provision for monitoring load on two transformers rather than a single transformer. With our present practice of relating kilowatt-hours to kilovolt-amperage size of transformer for monitoring loads on transformers this mix­ture of 3-phase and single-phase loads adds another factor. Voltage balance on 3-phase motors is quite critical, necessitating more attention being given to balancing distribu­tion loads between each phase on the pri­mary. Also, with capacitors used on the newer single-phase motors, secondary power factor has been increased, thereby lowering the reactive power requirements.

The Southwest has had a phenomenal increase in saturation of home air condi­tioners during the past 10 years. From a negligible saturation at the end of the war, it is estimated that the present saturation is in the order of 25%. The problem of single-phase service versus 3-phase service to homes is, therefore, a real problem, and a studied approach to it, such as the paper under discussion, is greatly appreciated.

H. E. Campbell (General Electric Company, Schenectady, N. Y.): This paper gives a very fair comparison of the over-all econom­ics of serving single-phase versus 3-phase residential air conditioning. The conclu­sions reached in this analysis are very similar to other studies of this subject which we have seen.

The authors point out that the cost of single-phase service as compared to 3-phase service wiU be more favorable to a single-phase service at any proposed higher secondary voltages. Another Winter Meet­ing paper! analyzes the cost of the higher voltage secondary and it shows that the higher voltage single-phase is considerably less expensive than the higher voltage 3-phase system, even for customer loads ten tunes that of a present day "full-use cus­tomer," This certainly confirms the au­thors' comment.

Despite the fact that economic analyses show single phase to be the most economical from an over-all point of view, there are some utilities who still wish to supply these loads 3 phase. This is usually done so that the utihty's customer can get a lower cost unit and thereby encourage him to add the electrical load. When we first looked at this problem the 3-phase 5-ton unit at the customer's level was about $200 less expen­sive than the single phase. At the time the authors analyzed the problem hermetically sealed motors had been applied to the units and the price difference was about $80 less for the 3-phase unit. I have just learned that there is a differential of only about $35 at the customer's level for our 1957 heat pumps. This just about balances the $30 wiring cost in favor of single phase that the authors found in their analysis. Under these conditions the customer should not care which service he receives.

When single-phase service is used, the utility gets a load with about 10% better

6 6 Anderson, Hutchinson—Service for Residential Air Conditioning M A Y 1 9 5 7

power factor, no difficulty from voltage un­balance, and no single-phasing problem. The economics are also in favor of smgle phase now and indications are that it will be more so in the future. Seldom do we get an answer to an economic analysis as clearcut as this one.

REPBRBNCE

1. ECONOMIC A N A L Y S I S OP R B S I D B N T I A L S E C O N D ­ARY SYSTEMS, H . E . Campbell , H . £ . Sinnott . AIEE Transactions, vol . 7 6 , pt . I l l , 1 9 5 7 (Paper no. 57^169).

Bryce Brady and Bela Mohr (Oklahoma Gas and Electric Company, Oklahoma City, Okla.): The authors have selected a very timely subject. The years 1956 and 1957 will probably show a new record in sales of central air-conditioning units for residential use. The indications are that the trend toward air-to-air central air-conditioning units in residential areas will increase. Certainly the people of the utility industry are studying their distribution design so that this new load will be served in the most economical manner.

We agree with the results as given by the authors. Studies made by our company during the last 3 years also show that single-phase utilization in residential areas is more economical than 3-phase utilization for all conceivable load densities. Our studies show that the 3-phase imits are a little less expensive for the customer but that the additional investment required by the utility is more than enough to offset any possible saving to the customer. The 3-phase distribution system utilizing the open-delta transformer bank design as used by the authors is the most economical for 3-phase distribution. It gives every possible economic benefit to 3-phase utilization.

The economic analysis does not give credit to the single-phase system for the higher power factor of single-phase capac­itor-type motors. The 3-phase system should be penalized by the addition of sufficient capacitors to produce equal power factor.

The extra cost to the customer for single-phase air-conditioning tmits is now less than the 1954 values quoted in the paper for 3-hp and 5-hp sizes. Recent sturveys made in otu territory show that the cost differential has dropped very appreciably during the last 2 years. We smcerely hope that this trend continues.

The authors have shown conclusively that single-phase utilization in residential areas provides investment savings to the utility. Our company is now completing a study of the total economics, i.e., investment and operating costs of the utility plant plus in­vestment and operating costs of the cus­tomers equipment. (The customers even­tually pay for all of these.)

We recognize that the problem of holding the line on expansion of 3-phase utilization in residential areas has many facets, not the least of which is maintenance of good rela­tions with customers, dealers, and housing developers. However the rewards are high, amounting to many millions of dollars, and we recommend that the conclusions of this paper be recognized and accepted; that we examine our company rules pertaining to extension of 3-phase service in residential areas and adjust them if necessary; that we

examine our rules pertaining to maximtun starting current of single-phase motors and adjust them, if necessary, to accommodate 5-ton air-conditioning installations; and that oiu customers and dealers be fully informed of the merits of single-phase service up to and including 5-ton units as well as the merits of multiple single-phase tmits where more than 5 tons are required.

N. H. Erlandson (Carolina Power and Light Company, Raleigh, N. C ) : The authors have presented a very timely paper which deals with a problem confronting many utilities today, with the results indi­cating that the sum of the utility invest­ment and the customer investment is the lowest for single-phase installations.

The indications are now that the future markets for home air conditioning are almost unlimited. At the present time, in the south at least, the single-phase room-type window units of 1 hp or less have taken over the market. This may be due to standardization of this type of imit. but its use is definitely affected by the cost of in­stallation and in rate differentials applied by numerous utilities to cover the additional cost of serving small 3-phase loads.

There are other facts that favor single-phase installations that are difficult to evaluate but should be considered. In areas with no series street-light ckcuits, pole-top pin construction can be used for single-phase laterals. This type of con­struction requires less tree trimming, is subject to fewer outages, and is less notice­able than crossarm construction. Since operating personnel are accustomed to single-phase installation in residential areas, the installation of 3-phase tmits would residt in both single-phase and 3-phase services, meters, and equipment in residen­tial areas which will make installation and operating problems more difficult. Future conversions to higher voltages would also be more costly with 3 phase than single phase.

In makmg a study of this kind, certain assumptions must be made; however, there is one point that is not clear and that is the reason for the secondary conductor sizes for existing systems used in the paper. Tables III and IV for 3- and 5-hp air-conditioning units are based on an existing system con­sisting of 25-kva transformers, six spans of no. 4 copper secondary, four customers per pole, and load per customer of 1.25 kva. Tables V and VI for 3- and 5-hp heat pumps are based on existing system with the same conditions except the secondary size is no. 2 copper. If the existing secondary for the heat pump was no. 4 copper, it may be possible to stay within voltage limits and use the no. 4 copper to serve the 3-phase units while the single-phase units wovdd require changing conductor. Since all other exist­ing conditions were equal, it seems that a more realistic comparison would have been made by using the same size secondary conductor.

The 1.25-kva diversified demand per customer probably is applicable to areas with high saturation of gas appliances, but areas with high satturation of electric ranges and water heaters will have a much higher demand. A recent test on the Carolina Power and Light Company system showed a 3.6-kw peak diversified demand per cus­tomer at the transformer, with a 100%

range and water-heater saturation but no air conditioning. A comparison of Tables VII, X, XI, and XII for 100% saturation mdi-cates that higher lighting and appliance demands would increase the savings of single phase over 3 phase. It seems reason­able to conclude that an increase in the 1.25-kva demand figtue used would increase the smgle-phase advantage m any of the cases studied.

A. H. Kidder (Philadelphia Electric Com­pany, Philadelphia, Pa.): Review of this paper leads me to confirm the authors' conclusion that it is more economical from the power companies' standpoint to provide single-phase supply for residential air-conditioning loads. A spot check of the differential cost for the case of 4% satura­tion in Table III, indicates that the savings would be considerably lower but neverthe­less appreciable on our system. The down­ward trend of savings with increased satiua-tion is, of coiuse to be expected, because the 3-phase cost would be relatively high ini­tially in a single-phase area and would de­crease naturally as the number of 3-phase loads per transformer installation increases.

A. S. Anderson and Chase Hutchinson: The number and length of discussions are such that we will attempt to reply only to the more pertinent issues that have been raised. We appreciate the interest in this subject and are glad to get conformation of views of the tremendous economic impor­tance of making the proper decision as to whether the future air-conditioned home should receive single-phase or 3-phase ser­vice.

Mr. Lawrence's method of determming the unit savings is satisfactory provided there is a good way of allocating the extra cost of 3-phase units to the customers not using air conditioning.

Mr. Diehl states that experience to date indicates .that the polyphase tmit is more rugged than a single-phase unit. Other manufacturers using hermetically sealed units have not made this observation. There is need to collect and analyze data which are available by some central agency. His remarks emphasize the need for protec­tion of all three phases of 3-phase units.

Mr. McClure asks if the same conclusions hold regardless of prhnary distribution voltage. The answer is yes. This may be seen from the tables. Note that the savings in primary decreased to an insignificant amoimt for a comparatively low saturation. With lower primary voltage the decrease would occur at somewhat lower saturation but the net result would remain the same.

The discussion by Mr. Ambrosius and Mr. Sarikas emphasizes the need for complete 3-phase protection which is lacking on all units except of one manufacture. Their viewpoint with regard to probability of more outages with a 3-phase unit is a practical consideration.

Mr. Johnson's plea that the industry needs to study the flicker problem has been voiced by the authors repeatedly before the AIEE and the Edison Electric Institute. We agree most wholeheartedly with Mr. Johnson that modern experience shows the customers will tolerate much more flicker than is presently allowed in published data

M A Y 1 9 5 7 Andersouy Hutchinson—Service for Residential Air Conditioning 6 7

on the subject. Secondary designs based on such data can be very costly.

Mr. McGrath asked some questions which are answered as follows:

1. Offhand, it would appear that the same-size single-phase units for residential service should be applicable to commercial service.

2. Our cost differentials of $50 compared to Mr, McGrath's quotation of $65 for 3-hp units and $80 compared to his $115 do not seem too far apart. We were indicating possible cost differentials if a substantial part of the market were all one phase or all 3 phase. He is quoting today's cost.

3. The extra cost of transformers and meters for 3-phase application is intrinsic.

4. We agree with Mr. McGrath's observation regarding the wiring costs. However, our estimates for a typical in­stallation checked the average. This was coincidental, of course, but indicated the differential either way would not affect the final conclusion.

5. Some manufacturers still have the philosophy that 3-phase voltage should be balanced at the service switch. We are not in accord with this viewpoint and have urged both the AIEE and the Edison Elec­tric Institute by formal papers of this kind to consider an industry study of the prob­lem.

6. Locked rotor currents are about the same and locked rotor torque for single-phase motor is somewhat better. Also for the same investment, larger conductors can be installed for single-phase service. There­fore, the flicker for the single-phase system should be less. Actually, the study is made on an equal flicker basis wherever flicker is limiting.

Mr. Gallaher's company serves central-unit residential air conditioners with either single-phase or 3-phase motors. It is im­portant, therefore, to note that Mr. Gallaher sees considerable operating advantages as well as investment savings in single-phase units.

Mr. Campbell states that the differential

cost between a single-phase and 3-phase heat pump has been reduced to about $35 to the customer. We agree with his pithy conclusion: "Seldom do we get an answer to an economic analysis as clearcut as this one."

Mr. Brady and Mr. Mohr state the sav­ings to the utility and eventually to the customer will run into millions of dollars. We wholeheartedly recommend that utilities take the steps recommended in their dis­cussion.

Mr. Erlandson questions the use of different-size secondary for Tables V and VI than in Tables III and IV. Since some companies have used no. 2 copper as stand­ard size for a great number of years, they would be interested in the case where exist-iiffe copper of no. 2 size was used hence Tables V and VI. There is not enough difference in starting current of single-phase and 3-phase motors of same horsepower rating to make these two sizes of conductor equivalent from a flicker standpoint which is usually limiting.

The Electric System of the Rectifier-Type

Locomotives for the Virginian Railway

J. C. BROWN ASSOCIATE MEMBER AIEE

IN OCTOBER 1956 delivery began on an order of twelve 3,300-hp (horsepower)

rectifier-type locomotives for The Vir­ginian Railway Company. These loco­motives mark the climax of 45 years of development since the first experimental mercury-arc rectifier locomotive was built, and represent the acceptance of this type of motive power for main-line railroad freight service.

While basically similar in characteris­tics and performance to the 4,000-hp locomotives dehvered in 1955 to the New York, New Haven and Hartford Raihoad for passenger service,^ the present units are designed for low speed, heavy freight service on the 134-mile electrified zone of the Virginian Railway between Mullens, W. Va., and Roanoke, Va. In this serv­ice they will supplement the fom 6,800-hp motor-generator locomotives acquired by the railroad in 1948, and will replace the original phase-converter locomotives

Paper 5 7 - 3 2 , recommended by t h e A I E E Land Transportat ion Commit tee and approved b y tl ie A I B E Technical Operations Department for pre­sentation at the A I E E Winter General Meet ing , N e w York, N . Y. , January 2 1 - 2 5 , 1957. M a n u -script submitted October 22, 1956; m a d e available for printing N o v e m b e r 27, 1956.

J. C. B R O W N is with the General Electric Company , Brie. Pa.

that have been operating since the beginning of the electrification in 1926.

General Considerations

The performance of this locomotive in terms of tractive effort and speed is shown in Fig. 1. Selective auxiliary notching is provided on any of the 17 basic controller steps so that a maximum number of tractive-effort increments are obtained for opthnum performance. This minimizes the possibihty of slipping the wheels as the master controUer is ad­vanced, and assures extremely smooth starting of heavy tonnage trains.

The dynamic braking characteristic is shown in Fig. 2. The circuits are designed to give a peak braking effort of 63,000 pounds at 25 mph (miles per hour).

Description

The locomotive, classified as a road-switcher type, is shown in Fig. 3. I t has a total weight of 396,000 pounds, all on drivers, and is 69V2 feet long over cou­plers. Location of the principal pieces of apparatus is shown in Fig. 4. The con­

trol equipment is of the electropneumatic type and is designed for single-end mul­tiple-unit operation. The propulsion equipment consists of six General Electric Company 752 motors geared for a maxi­mum locomotive speed of 65 mph with 40-inch diameter wheels. The total weight of the locomotive is supported on two 3-axle rigid bolster trucks through a centerplate and loading-pad arrange­ment.

One spring-raised air-lowered panto­graph is located over the short-end cab at the front of the locomotive to collect current from the 11,000-volt 25-cycle trolley wire. A high-voltage bus hue is provided for multiple-unit operation. The main transformer is Pyranol*-filled and force-ventilated. The rectifier equip­ment, consisting of 12 ignitron rectifier tubes and their associated firing circuits, is housed in two cubicles. The auxihary rotating equipment includes one motor-generator set for 75-volt control power and battery charging, one motor-driven axial-flow equipment blower, one motor-driven air compressor, a water pump for rectifier coohng, and two axial-flow double-end resistor blowers. All the elec­tric equipment is arranged to give ready access for inspection and maintenance.

Electric Apparatus

The prime objective in the develop­ment of the electric system for this loco­motive is to produce a rehable, low-cost

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6 8 Brown—Rectifier-Type Locomotives jor the Virginian Railway M A Y 1 9 5 7