Table of Contents
Advertisement
3
3.1
3.2
3.3
112
Time delayed residual overcurrent protection
(TEF)
Time delayed residual overcurrent protection
(TEF)
Application
Use the inverse and definite time delayed residual overcurrent functions in solidly earthed sys-
tems to get a sensitive and fast fault clearance of phase to earth faults.
The directional residual overcurrent protection can be used in a number of applications:
1. Main protection for phase to earth faults on the radial lines in solidly earthed sys-
tems. Selectivity is achieved by using time delayed function according to prac-
tices in the system (definite time delay or some type of inverse time
characteristic).
2. Main protection for phase to earth faults on lines in a meshed solidly earthed sys-
tem. The directional function can be used in an permissive overreach communi-
cation scheme or a blocking scheme. In this application the directional residual
overcurrent function is used together with the communication logic for residual
overcurrent protection.
3. Back-up protection for phase to earth faults for lines in solidly earthed systems.
By using the directional residual protection as back-up function, the back-up fault
clearance time can be kept relatively short together with the maintained selectiv-
ity.
4. Etc.
Functionality
The residual overcurrent protection can be set directional. The residual voltage is used as a po-
larizing quantity. This voltage is either derived as the vectorial sum of inputs U1+U2+U3 or as
the input U4. The fault is defined to be in the forward direction if the residual current component
in the characteristic angle 65° (residual current lagging the reference voltage, -3U0), is larger
than the set operating current in forward direction. The same kind of measurement is performed
also in the reverse direction.
Function block
TEF--
TEF
BLOCK
TRIP
BLKTR
TRSOTF
BC
START
STFW
STRV
xx00000203.vsd
Figure 58:
Function block, directional and nondirectional
Chapter 5
Current
Advertisement
Table of Contents
