As the Company's business expanded these interruptions became more and more serious, involving as they did, an increasing number of large industries taking power from the system. The Company kept in close touch with relay developments and suitable relays were installed, when available, for the proper protection of the expanding system. The following is a brief description of the Company's relay protection for the 60 cycle system. Similar protection for the 25 cycle system with some modifications is also installed.

Figure 7 shows the various types of relays used to automatically segregate a fault occurring in any part of the system from the remainder of the system, thereby preserving continuity of service except in the faulty section. The 11,000 volt buses at the various stations are shown shaded and the 4150 volt buses clear. It will be noted that the protection of the distribution system is shown at Station No. 6 for the various classes of service, i. e., 4150 volt and 11,000 volt lighting and power feeders, street lighting circuits, Edison and Railway feeders. Similar distribution circuits with similar protection emanate from the other stations but, to simplify the drawings, these are not shown.

TIE LINE PROTECTION

It is first of all vital to preserve the integrity of the 11,000 volt tie line system between stations. This is effected by the use of parallel tie lines equipped at each end with Single Phase discriminating balanced Reverse Power relays (c), the function of which is to trip out the circuit breakers on each end of a tie line on which a fault occurs without interfering with the operation of the other parallel line or lines (Fig. 8). For instance if a fault occurs at X as shown in fig. 7 on tie line between Stations 5 and 6 the relays operate to trip out the breakers at each end of this particular line at Stations 5 and 6, thereby

Fig. 9-A Three Phase Reverse Power Relay for Protection of 3 or more Parallel Tie Lines.

sult the generators in the new Station would be overloaded with a possible lowering of voltage and frequency on the system. In the latter case this protection is applied to 3 tie lines between Stations 3 and 34. As Station 34 is fed from Station 3

exclusively the whole district supplied from Station 34 would be down in case all tie lines should trip out due to a fault occurring in any one tie line. As load is taken off the other two tie lines between Stations 3 and 34, balanced relays are not applicable to these lines. It is intended in the near future to cut the two 11,000 volt tie lines between Stations 5 and 6 into Station 34 and eliminate all 4150 volt tie lines between Stations 3 and 34, thus implifying the tie line system and securing better protection.

GENERATOR PROTECTION

The alternating current generators feeding into the system are also a menace to continuity of service in case of a fault occurring in a generator winding as in this case all other generators feed back into the fault with a consequent impairment of service. It is, therefore, necessary to cut a faulty generator loose from the bus and this is taken care of by the use of differential (A) and reverse current (L) relays. Reverse current relays are used on the old 4150 V. generators at Stations 3 and 5 to cut out the oil

Fig. 9-B

POLARITY

Fig. 10. Differential Relay Protection for A. C. Generators and Lowering Transformers.

switch in case of generator fault causing current to flow the from bus into generator. These are not as positive as the newer type but are the best protection possible under the condition for these generators which are seldom operated. The larger 11,000 volt generators were ordered with the six leads brought out of the generator frame to permit installing current transformers in each phase before connecting to the neutral. This permits the use of the improved differential relays, (A) (Fig. 10), which operate between one set of current transformers installed in generator windings and another set installed in the connections of the generator leads to the station bus. Relays do not operate on overload, thereby insuring generators remaining on the system during heavy load periods, but any unbalance in the phases of either the generator or cable between generator and bus, produced by ground or short circuit, causes the relays to operate which trips out the main generator oil switch and the generator field switch. In addition to freeing the system from the faulty generator, this prevents also the destruction of the generator if a fire has been started in the windings due to a short circuit.

TRANSFORMER PROTECTION As the A. C. distribution voltage is 4150 it is necessary to step down the transmission voltage of 11,000 to 4150 at the sub-stations. This is accomplished by means of duplicate lower

ing transformers installed in the substations. To insure continuity of service it is necessary to have transformers so protected that a heavy overload on one feeder circuit will not trip them out thereby interrupting service on all other feeders supplied through the transformers. It is also necessary to separate a transformer from the 11,000 and 4150 V. buses in case of a fault occurring in the transformer itself. This is effected by the use of the same differential type of relay used on generators. Circuit breakers on each side of transformers can not trip on overload but only from an internal fault in which case the defective transformer is cut loose service to carry the load. and the duplicate still remains in

ROTARY PROTECTION

All rotaries on the system are protected on the alternating current side by instantaneous overload relays (F) which immediately separate a faulty rotary from the A. C. system.

On

Connections for Reverse Current Circuit Breaker.

the direct current side the Edison rotaries are provided with reverse current circuit breakers, (H)-(Fig. 11), which allow rotaries to carry heavy overloads for maintaining service on the Edison System in case of trouble but prevent current feeding back into the rotary from the Edison System in case the A. C. breaker trips out or for other causes. (A rotary connected to the D. C. bus with the field circuit open and A. C. breaker out is in danger of wrecking itself from overspeed). Railway rotaries are equipped with combination overload and reverse current circuit breakers, (K), to protect against heavy short circuits occurring on the Railway System in addition to reverse current protection as above.

FEEDER PROTECTION

All A. C. feeders are equipped with inverse time limit overload relays, (E)-(Fig. 12), set for approximately 200% load and two seconds time. In

oil circuit breakers equipped with inverse time limit overload relays (E) and the transformers are balanced on the three phases. In case of trouble in a transformer of such severity as to trip the main switch feeding the street lighting bus, only one phase is tripped and only the arc transformers fed from this phase are

cut out.

All railway feeders are equipped with overload circuit breakers (G), to protect system against heavy short circuits caused by trolley wires dropping across rails, etc.

The Edison System is protected by means of fuses in the outside network which segregate a faulty section from the remainder of the Edison network.

In general it will be seen from the above description that any part of the system on which trouble occurs, feeder, transformer, rotary, generator, tie line, etc., is automatically cut out of service leaving the remainder of the system in operation. The most perfect relay system, however, will not give the best results unless properly installed and maintained. A thorough study of the characteristics of available relays with reference to the general system is necessary for proper application and after relays are installed a positive test must be made duplicating actual operating conditions to eliminate the possibility of trouble due to error in connection or open circuit. Such tests were made on all relays as soon as same were connected. instance, in the case of the discriminating balanced relays for tie line protection, a large rotary was connected to the line side of current transformers, operating the relays, as at X shown on drawing (Fig. 7), and started

up.

For

This caused current to flow to the rotary through the tie line from both stations and duplicated a short circuit condition on this particular tie line. The relays operated perfectly, tripping out the switches on each end of the line at each station. Similar

positive tests were made on other types of relays. This method is much more conclusive than simply testing the secondary relay wiring as it checks back to the primary current and is positive through the various connections including series transformer polarity, etc.

After initial test, all relays are tested periodically to guard against mechanical or electrical troubles which might render relays inoperative. All wattmeter type relays are operated from the secondary of

The Principle

separate potential transformers connected to the station bus and pilot lamps, connected to the secondary of these transformers, are placed in a conspicuous position on the operating switchboard to burn normally when connections are O. K. Should a transformer fuse blow, light goes out and trouble is immediately repaired.

The present relay equipment has resulted in a great improvement in service and should render impossible a general interruption from any but the most extraordinary case of trouble.

of Insurance

same principle the recognition of the law of average probabilities and its application to protect the individual against misfortune.

Insurance collects from the many to pay the few who are unfortunate enough to meet the inevitable disasters that become average disasters by inexorable laws. It exacts from us, in the form known as "premium," a deposit or advance payment which, when gathered with the deposits of the other ninety-nine thousand nine hundred and ninety-nine, furnish an average experience. Out of these collective deposits or premiums Insurance pays your loss and mine, sets aside a fund called a reserve to give us added security and meet the liability assumed under its contract with us; pays the agent who induced us to protect our own interests; give us suggestions and instructions to prevent accident and prolong life; has our risks inspected, one by one, and points out and has corrected defects that might produce loss; pays its taxes, some just and others unjust; pays its administrative expenses; allows itself a dividend on its capitalized investment, if there is anything left; and passes a balance to (or in years of excessive loss draws from) its accumulated funds that give security

its payment of losses, when losses come, no matter how great the calamity.

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