CIRCUIT ANALYSIS
`
`OF A—C POWER
`
`SYSTEMS
`
`VOLUME II
`
`BY
`
`EDITH CLARKE
`
`PROFESSOR OF ELECTRICAL ENGINEERING
`
`THE UNIVERSITY OF TEXAS
`
`One of a Seriex Written in the Interext Of
`
`the General Elecmic Admmed
`
`Engineering Program
`
`
`iii-“NEW YORK ., JOHN WILEY a; SONS,
`
`
`LONDON . CHAPMAN 8; HALL, LIMIT-ED
`
`'-
`
`INC.
`
`GE 2017
`Vestas v. GE
`|PR201 8-0101 5
`
`GE 2017
`Vestas v. GE
`IPR2018-01015
`
`i
`
`

`

`COPYRIGHT, 1950
`
`BY GENERAL ELECTRIC COMPANY
`
`All Rights Reserved
`
`This book or (my part thereof must not
`be reproduced in (my form without the
`written permission of the publisher.
`
`PRINTED IN THE UNITED STATES OF AMERICA
`
`ii
`
`

`

`{CH. IX]
`
`EQUIVALENT TWOwMACHINE SYSTEM
`
`331
`
`If the system impedance
`conditions, are plotted to the same scale.
`seen by a relay falls within the boundary of the characteristic curve
`of the relay, the relay will operate;
`if it falls outside this boundary,
`the relay will not operate. This method of determining relay per-
`formance is given by J. H. Neherl in a paper on the performance of
`distance relays,
`in Which he plots the characteristic curves of the
`boundary of operation of various types of relays in terms of resistance
`and reactance.
`Figure 1 (parts a, b, c, and d) indicates characteristic curves of the
`limit of operation of four types of directional distance relays. All of
`them are set to protect approximately 90 per cent of the line between
`the relay location at the origin 0 and the terminal of the section of
`line at T. Either the impedance relay, Fig. 1(0), or
`the offset—
`impedance2 relay, Fig. 1(b), will operate when the system impedance
`seen by it falls within its circular characteristic and is above and to
`the right of its directional element. The reactance-type relay, Fig.
`1(6), Will operate for system impedances which fall below its constant
`reactance straight line and within the circumference of its starting
`unit. The mho-type3 relay, Fig. 1(d), will operate for system im-
`pedances which fall within the circumference of its circle which passes
`through the origin 0 with its diameter at an angle with the x-axis.
`All the relays in Fig. 1 are adjustable as the diameters of the circles
`can be varied; adjustment is also possible of the location of the centers
`of the circles in Figs. 1(5), 1 (c), and 1(d).
`
`POWER SWINGS
`
`When a fault occurs, only those relays which control the faulty -
`section should trip. During a fault, and also after a circuit is switched
`out of service,
`the synchronous machines of
`the system undergo
`changes in the relative positions of
`their rotors. With constant
`internal generated voltages, the phase angles between these voltages
`will vary until a new condition of equilibrium is established; or, if the
`disturbance is sufficiently severe, loss of synchronism will result.
`In
`cases where there will be no loss of synchronism, it is important that
`those relays which do not control the faulty section refuse to trip during
`power swings while the fault is on the system and also after it has
`been cleared.
`
`Equivalent Two-Machine System
`
`For determining the performance of distance-type transmission-line
`relays during power swings, many three~phase power systems can be
`
`