Masters Theses


"The recent developments in harnessing electrical power have opened a new field in the improvement and betterment of the existing types of relays and the development of new types. Thus about 1930 the manufacturers introduced the high speed circuit breaker with operating times of the order of 8 cycles and the engineers awoke to the possibilities of high speed or one-cycle relays.

Many developments took place since that time which gave us the improved forms of Instantaneous Overcurrent Protective schemes, the Distance Relay Protection, the Carrier Current Protection and many others. Later, because of the war time problems of increased loads and shortage of materials, it was often necessary to put heavy loads on existing transmission lines rather than build new ones.

When transmission lines are heavily loaded it becomes very difficult to retain relay selectivity, because the currents and voltages which the relays measure are not sufficiently different to distinguish between faults and power oscillations, it is necessary to include in the system different auxiliary relays which check the rate of change of the impedance. As far as these relays now are concerned they add complexity to the system and furthermore they can not distinguish between power oscillations, during which they must not trip and out-of-step conditions during which their tripping might be desired.

The relay performances under such power swings and out-of-step conditions will be discussed and as a good starting point, the impedance seen by these relays and the loci of the impedances will be taken up first"--Introduction, pages 1-2.


Lovett, I. H.


Electrical and Computer Engineering

Degree Name

M.S. in Electrical Engineering


Missouri School of Mines and Metallurgy

Publication Date



v, 59 pages

Note about bibliography

Includes bibliographical references (pages 57-58).


© 1951 Emil D. Grigoriadis, All rights reserved.

Document Type

Thesis - Open Access

File Type




Subject Headings

Electric relays
Electric power systems

Thesis Number

T 960

Print OCLC #


Electronic OCLC #