A b r i d g m e n t o f

Centralized Control of System Operation BY JAMES T. LAWSON*

M e m b e r , Α . I . Ε . E .

Synopsis.—This paper considers the application of centralized control of system operation of the Public Service Electric and Gas Company in New Jersey. A brief history of events leading to the installation of supervisory system operation is given, with a detailed

description of the apparatus and the methods used to carry out the indications, together with a statement as to what is being accom­plished in improving the service.

IN the early days of the generation of electrical energy, there was little need of load dispatchers or system operators. Then each power station supplied its

own local territory, usually a t 250 or 500 volts, direct current or 1000 or 2400 volts, alternating current. The operating man in charge of the power station or distri­bution system could direct the handling of apparatus and feeders without any trouble. Power stations were not run in multiple and each one could be operated in a manner best suited to it.

Gradually, as consolidation was effected and terri­tories enlarged, several plants were tied together, and in time, voltages were raised. The method of allowing superintendents or chief engineers to operate the dis­tribution systems and the stations according to their own individual ideas led to confusing, inefficient opera­tion, and had to be discontinued.

This forced in a group of men, who would be avail­able at all hours to guard the operation of the system as a whole.

Such a scheme was first started in our system in 1900, to handle d-c. railway feeders. At this time, the operator did the work as a side line to other duties and his entire equipment consisted of a small plug board, somewhat like a cribbage board, with the names of the stations and substations lettered on the left-hand side and the feeder numbers across the top. A series of holes was drilled across the board to match. By placing pegs in the proper holes, it was possible to keep track of the railway feeder operation.

In 1906 parallel operation of the stations became necessary and centralized control of system operation imperative and the first load dispatching office was then started in our Marion Station, Jersey City.

The operating board consisted of a wooden drawing board, an elaboration on the original plug board about 6 ft. by 12 ft., painted white and marked with single-wire diagrams of the transmission lines and station and substation busses, and showing symbolically the main apparatus in each station and substation. The dia­grams of transmission lines, apparatus, and busses were

•Assistant to General Superintendent of Generation, Public Service Electric and Gas Company, Newark, New Jersey.

Presented at the Summer Convention of the Α. I. Ε. E., Toronto, Ont., Canada, June 23-27, 1930. Complete copy upon request.

placed on the board by using gummed paper cut in narrow strips, and gummed letters and numbers.

Wooden plugs, colored red and white, were used, placed in holes drilled in the board. But few private telephone lines were in use.

In 1909 and 1914, load dispatching systems were established in the Central and Southern Divisions. At this time the three divisions were not electrically connected and we thus had four load dispatching offices. The work increased rapidly, and as the system expanded

FIG. 1—MANUALLY CONTROLLED LOAD DISPATCHER'S PILOT BOARD

and the divisions were tied together, the future seemed to point to the need of one central load dispatching office to control the operation of the entire system as a unit, not only within itself but in its relation to connec­tions which might be effected with other companies.

Accordingly, plans were made to consolidate three of the offices and move them into a centralized office at Newark; this was accomplished in 1926.

A load dispatcher must be familiar with every operat­ing detail, and an accurate and up-to-the-minute dia­gram of the bus layout of each station and substation is necessary. The load dispatcher's diagram of busses, and substation and generating station apparatus, is known as a "pilot board." Our first pilot boards were made of wood, using gummed paper for the diagrams and small wooden plugs inserted by hand in holes drilled

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426 L A W S O N : C E N T R A L I Z E D C O N T R O L O F S Y S T E M O P E R A T I O N Journal Α . Ι. Ε . E .

in the board to show the switch and apparatus positions. These were changed to a type of board using instead of plugs, a scheme of small colored lights manually con­trolled by the load dispatcher from his desk'. (See Fig. 1.)

These types of pilot boards are accurate only in so far as the plugs or lights are changed in response to tele­phone messages, or orders given or received. There­fore they are not always an accurate visual record of the system. Time is lost in waiting for each station or substation operator to report switch positions and switch movements, especially in times of stress and trouble.

A board which automatically shows the position and movement of the switches not only serves as a dia­grammatic record but also enables the load dispatcher to follow the switch operations as he directs them, and, more important in times of trouble, gives him an instantaneous indication of system conditions.

From these indications, without waiting for reports from generating station and substation operators, he is in a position to act immediately toward restoring service and maintaining normal system conditions.

Accordingly, when it was decided to centralize the load dispatchers' office, an automatic pilot board was considered; but the cost for the entire territory was so great that it was decided to have only automatic indication from the stations and substations in the vicinity of Newark, the remainder to be manually controlled.

There are 42 distributors in all, located in 21 substa­tions and in Marion, Kearny, and Essex generating stations. Some of the smaller substations do not have distributors, the positions of the oil circuit breakers being indicated over direct-wire connections.

Each distributor will automatically indicate from 50 to 100 switches, depending on whether or not super­visory control of the switches is desired in conjunction with automatic indication. Therefore, one distributor will usually take care of a substation while two or more are needed for the generating stations.

The positions of the oil circuit breakers in substations not equipped with automatic indicating apparatus are shown by means of small control switches, manually operated, that light red and green lamps, the informa­tion for keeping these indications correct being obtained by the load dispatcher by telephone from the substation operators.

The load dispatcher's office consists of two rooms. The office proper contains the remote metering panels, telephone switchboards, pilot board, etc.; the second room contains the apparatus, batteries, motor generator sets, etc., for obtaining automatic indication of the switches in the substations and power stations.

Red and green lights indicate the closed and open positions of oil circuit breakers, and white lights with a horizontal or vertical black line across the lamp, the closed or open positions of disconnecting switches. A

group of three lights is used for an oil circuit breaker, (the red and green referred to above), and in addition, a clear white light, the function of which is to indicate that the oil circuit breaker has changed its position. This white light is extinguished by a small push-pull, single-pole double-throw switch, thus compelling the load dispatcher to acknowledge the operation of the oil circuit breaker and also giving him notice that an oil circuit breaker has operated, since under normal opera­tion the board is operated with all white lights un-lighted. In the arrangement used, the white light is on top, the red and green lights directly below in the Order given. Underneath the green light, the oil circuit breaker designation is painted on the face of the board. So far as practicable, the various oil circuit breakers and disconnecting switches are shown in their correct positions relative to one another. While all oil circuit breakers in the transmission system are indicated, only

FIG. 3 — R E L A Y AND DISTRIBUTOR CABINETS

such disconnecting switches as perform a switching function are shown. Disconnecting switches which serve only to isolate other apparatus from the system are not shown on the load dispatcher's board, since in most cases such isolating disconnecting switches are stick operated, so there is no simple means of obtaining automatic indication. The load dispatcher is supplied with simplified wiring diagrams of each station and substation, which show all such isolating switches as well as other necessary information not feasible to show on the indicating board.

Fig. 3 shows some of the relay and distributor cabi­nets. The cabinet at the left is a 100-relay cabinet, there being 50 relays on the reverse side of the cabinet. The second from the left is a combined distributor and relay cabinet. The third and fourth from the left show cabinets with a capacity of three distributors each, although the two middle distributors have been re­moved.

A general view of the front of the load dispatcher's board is shown in Fig. 6.

June 1930

The Public Service Electric and Gas Company supplies the more populous sections of the State of New Jersey with electric light and power. That portion of the state served from the New York State line on the east to the Delaware River below Camden on the west is outlined on the map of the State of New Jersey, in Fig. 8. The territory is 110 mi. long and covers an area approximately of 1700 sq. mi. as compared with 8224 sq. mi. in the state. This area includes about 88 per cent of the population of the state, which exceeds

FIG. 6—LOAD DISPATCHER'S PILOT BOARD, FRONT VIEW

3,500,000; electric meters, December 31, 1929, num­bered 886,797. The portion of the territory directly supervised and operated from the Newark Terminal load dispatchers' office is shown in the clear area. The stations and substations which have automatic indica­tion on the load dispatchers' board are located within or adjacent to the City of Newark. Indications from the other stations and substations are controlled by manually operated miniature switches manipulated by the load dispatchers from information obtained by telephone.

The entire Public Service territory is supervised from the Newark load dispatching center, although the southern area, or shaded portion of the map, is operated directly from a load dispatching office at Burlington.

In the entire system, there are 131 Public Service and industrial substations, nine switching stations, and five generating stations. Of this number, the Newark load dispatcher has direct supervision over and operates 87 substations, eight switching stations, and four generating stations, leaving 44 substations, one switching station, and one generating station in the Southern Zone.

It is difficult to estimate the value of a load dispatching system or the value of one type of load dispatching equipment over another; these, we believe, are matters of local importance and must be judged by the individual utility which may wish to employ the

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several methods. No doubt load dispatching can be, and is, handled with simple as well as elaborate equipment,—a matter of opinion. Our experience in using the simplest as compared with the elaborate leads us to believe that the automatic indicating equip­ment, backed up with accessory apparatus, gives the best results as regards safety, service, and economical handling of station load.

After an experience of three years with the automatic indication system, we have not changed our opinion.

With the completion of the 132-kv. transmission system and the existing and approaching interconnec­tions with other companies, the advantage of centralized control of system operation to this company has become more apparent.

The 132-kv. transmission system has made it possible to schedule the loading of generating stations so as to obtain operating economy. These load schedules would

FIG. 8—MAP OP NEW JERSEY SHOWING THE TERRITORY OP THE ELECTRIC AND GAS COMPANY. THE UNSHADED PORTION IS OPERATED BY NEWARK LOAD DISPATCHING OFFICE

be almost impossible to follow effectively if the system were not controlled at a central point.

At the end of the current year, 1930, this company will be interconnected with three other companies, and there will be operating agreements with each, governing the interchange of power. This interchange will fall into several classes and each class will be regulated by different conditions and restrictions. I t is evident that centralized control will be required to procure reliable

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428 CHARLTON A N D KETCHUM: D E T E R M I N A T I O N OF GENERATOR S P E E D Journal A. I . E . E.

action, to take advantage of effecting economies, and to avoid penalties which might result from the lack of coordination.

During 1929, the load dispatchers issued a total of 238,986 operating orders in connection with switching changes; and of this total, only one operating mistake

resulting in interruption to service is chargeable to the load dispatcher. This one interruption occurred at a time which caused no inconvenience to the customer; in fact, it was not noticed or reported. We feel justified therefore in having incurred the cost of installing and maintaining the automatic indicating system.

A b r i d g m e n t o f

Determination of Generator Speed and Retardation During Loss Measurements

BY Ο. E. CHARLTON* and W. D. KETCHUM* A s s o c i a t e , Α. I. Ε. E . A s s o c i a t e , Α . I . Ε . E.

Synopsis.—This paper describes an instrument which was The principle of numerical differentiation is discussed and its developed to make graphic records of generator revolutions and time, application to the determination of the slope of the speed—time curve as the generator slows down under the action of its losses during is pointed out. retardation tests. The construction of speed—time curves from the A complete example illustrating the application of this principle records thus obtained is outlined. is included in the unabridged paper.

INTRODUCTION

DURING the past two years, efficiency tests have been made upon generating units in several hydro plants on the Alabama Power Company

system. In determining generator efficiency, the fundamental formula

Efficiency = Output

Output plus losses (1)

was used. The losses were determined by the retardation

method as described by J. Allen Johnson 1 from the equation

dE WR2 I ds dt 9

. 4 π 2 . s (•if) (2)

where dE dt = power.

? Ä 2

9 s

d s HT

= flywheel effect of rotating parts. = acceleration of gravity. = angular velocity of rotating parts.

= angular retardation of rotating parts.

The scope of this paper is limited to a description of the methods used in evaluating the speed (s) and the

retardation y ds \

-^j J for use in Equation (2).

*Southeastern Engg. Co., Birmingham, Ala. 1. For references see Bibliography. Presented at the North Eastern District Meeting of the A.I.E.E.,

Springfield, Mass., May 7-10, 1980. Complete copy upon request.

M E A S U R E M E N T OF GENERATOR S P E E D The precision of the results to be obtained from the

retardation method depends primarily upon the ac­curate determination of the speed—time curve as the generator slows down, and upon the most exact de­termination possible of the slope of this curve at various points. Experience has shown that a tachometer and a stop watch do not provide the necessary degree of precision, particularly when the generator under test has relatively low W R2 and consequently slows down rapidly. An attempt was therefore made to develop an instrument which would record these quantities accurately.

The ideal device for this purpose would be a recording instrument which would measure retardation directly, such as that suggested by V. Karapetoff.2 No such instrument is on the market at the present time, how­ever, and difficulties were encountered which prevented the construction of one for the tests.

As a substitute for this ideal instrument, a chrono­graph was constructed.

Essentially, it consists of a driving motor, an electrically operated tuning fork, and an electrically operated stylus. The record is made upon a strip of waxed paper which is unwound from a supply spool and passed under the stylus and tuning fork, continuing around the two driving rollers to the rewind spool. The tuning fork is electrically driven at 100 vibrations per second, while the stylus is energized through a contact on the generator shaft. Fig. 3 is a general view of this instrument, and Fig. 4 shows a typical record taken by it.

One refinement which has been found to contribute materially to the facility with which the records may be interpreted is the constant linear speed drive for the

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