Table Of Content

Digital Differential Protection G. Ziegler Differential Protection Symposium Belo Horizonte, 7 to 9 Nov. 2005 No.: 1 Differential Protection: Discussion Subjects (cid:216) Mode of operation (cid:216) Measuring technique (cid:216) Current transformers (cid:216) Communications (cid:216) Generator and motor differential protection (cid:216) Transformer differential protection (cid:216) Line differential protection (cid:216) Busbardifferential protection Differential Protection Symposium Belo Horizonte, 7 to 9 Nov. 2005 No.: 2 Digital Differential Protection Principles and Application Gerhard Ziegler Differential Protection Symposium BeloHorizonteNovember 2005 G. Ziegler, 10/2005 page1 Contents Pages Mode of operation3 -27 Measuring technique28 -45 Current transformers 46 -86 Communications87 -115 Generator and motor differential protection116 -122 Transformer differential protection123 -178 Line differential protection179 -216 Busbardifferential protection217 -247 7UT6 product features248 -264 Differential Protection Symposium BeloHorizonteNovember 2005 G. Ziegler, 10/2005 page2 Digital Differential Protection Mode of operation Gerhard Ziegler Differential Protection Symposium Belo HorizonteNovember 2005 G. Ziegler, 10/2005 page 3 Comparison protection -Principles Absolute selectivity by using communications I I A B •Directional comparison A B Exchange of YES / NO signals protection range (fault forward / reverse) reverse forward forward reverse • Current comparison | DI | Relay communication Relay Sampled values Phasors I t A I Binary decisions B •comparison of momentary values or phasors D B •| I | = | I - I | > limiting value A B A Differential Protection Symposium Belo HorizonteNovember 2005 G. Ziegler, 10/2005 page 4 Protection Criterion “current difference“ (differential protection) n Kirchhoff‘s law: II + I + I + ... I I= I = 0; 1 2 3 n diff Current difference indicates fault n Security by through-current dependent restraint |I1|+|I2|+ ... |In| = I Res protection n Characteristic: object I diff Trip I res n Absolute zone selectivity (limits: CT locations) No “back-up“for external faults n Differential protection: for generators, motors, transformers, lines and busbars Differential Protection Symposium Belo HorizonteNovember 2005 G. Ziegler, 10/2005 page 5 Current differential protection: Basic principle I I I I 1 2 1 2 Protection Protection object object i i 1 i 1 i 2 2 i D I> DI=I + I 1 D I> DI=I + I 1 2 1 2 =0 i 2 external fault or load internal fault Differential Protection Symposium Belo HorizonteNovember 2005 G. Ziegler, 10/2005 page 6 Generator and transformer differential protection Y d 5 L1 L1 L2 L2 L3 L3 DI DI DI Matching DI DI DI transformer Differential Protection Symposium Belo HorizonteNovember 2005 G. Ziegler, 10/2005 page 8