Protection Functions
PRS-7367 77
maximum capacity of the transmission line then according to the basic principle joule’s law the
dissipation of heat is greater and greater. In simple words the temperature of transmission lines
conductor is increased and it’s a possible chance of enormous damage in power system.
Therefore, the thermal overload protection (49F) initially completely underneath the protection of
all above mentioned cases. If the thermal level of transmission line is increased due to any reason,
three-phase thermal overload protection (49F) will protect.
3.8.4 49F Settings
Table 3.8-3 49F settings
3.9 Phase discontinuity protection 46D
3.9.1 46D Overview
This relay provides a one-stage phase discontinuity protection with definite time delay
characteristics to detect the unbalance current fault.
The relay incorporates an element which measures the ratio of negative to positive sequence
current (I
2
/I
1
). This will be affected to a lesser extent than the measurement of negative sequence
current alone, since the ratio is approximately constant with variations in load current. Hence, a
more sensitive setting may be achieved.
At the moment when the circuit breaker is closed, because the three poles of the circuit breaker
are discrepant for a very short time, and if the broken conductor protection is enabled, it is easy to
make the broken conductor protection pick up, and it will restore after the load current is stable.
3.9.1.1 Function Block
The function block of the protection is as below.
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