Power system protection
Lecturer: SEAN Piseth
Students:
VORN Rithy e20120795
YA Phalkun e20140873
YAV Leakhena e20140874
YORN Thort e20120815
2015~2016
Institute of Technology of Cambodia
Department Electrical and Energy Engineering
1
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Power system protection
Lecturer: SEAN Piseth
Students:
VORN Rithy e
YA Phalkun e
YAV Leakhena e
YORN Thort e
2015~
Institute of Technology of Cambodia
Department Electrical and Energy Engineering
1
- (^) Introduction
- (^) Generator protection
- (^) Transformer protection
Bus protection
Transmission line
Conclusion
Content
Introduction
Objective
The important protection systems are:
Protection for Generators
Protection for transformers
Protection for transmission line
Protection for bus
Stator protection
Stator earth fault protection: using inverse time relay
The time of operation depends
upon the magnitude of actuating
quantity. If the magnitude of
actuating quantity is very high,
the relay operation is very fast.
8
Stator protection
Differential protection: using 6 CT’s
The secondaries of all CT’s
are connected in star and
other winding of each CT’s
set are connected through
cable called pilot cable. Three
coil are connected in pilot
cable. They are connected in
an equipotential point of pilot
cable.
Stator protection
Biased circulating current protection (percentage differential relay protection)
11
Negative sequence relay:
Negative phase sequence
relays can identify negative
phase sequence condition and
trip the machine.
Overcurrent relay: the fact
that in the event of fault the
current would increase to a
value several times greater
than maximum load current.
Stator protection
Unbalanced stator loading protection: using negative sequence relay with
overcurrent relay
Sensitive relay: The relay
is free from over travel,
thus permitting close
coordination with other
protective devices.
Rotor earth fault protection
Potentiometer method: using sensitive relay
Rotor earth fault
protection
AC injection method
This scheme has an
advantage over the
potentiometer method in that
there is no blind spot in the
supervision of the field
system.
Differential relay:
Protection against such faults
can be afforded by a relay
which compare the magnitudes
of two currents in each phase
and closed its contacted
whenever the ratio of the larger
to the smaller exceeds some
predetermined value.
Abnormal condition protection
Restricted or balanced earth fault protection: using differential relay
Abnormal condition protection
Over voltage protection: using over voltage relay
Over voltage may be caused due to-
Transient over voltage in the transmission line due to
lightening.
- (^) Defective operation of the voltage regulator.
- (^) Sudden loss of load due to line tripping.
Abnormal condition protection
Under/over frequency protection:
Over frequency protection: it can easily be corrected by reduction in the
power outputs with the help of the governor or manual control.
Under frequency protection: using frequency relay