ABB Relion 650 Series Technical Manual page 609

1MRK 506 326-UUS B
In the case protection B1 shall operate without any intentional delay (instantaneous). When the
fault occurs the protections pickup to detect the fault current. After the time t
send a trip signal to the circuit breaker. The protection A1 starts its delay timer at the same time,
with some deviation in time due to differences between the two protections. There is a possibility
that A1 will start before the trip is sent to the B1 circuit breaker.
At the time t
interrupted. The breaker time (t2 - t1) can differ between different faults. The maximum opening
time can be given from manuals and test protocols. Still at t
At time t
In most applications it is required that the delay times shall reset as fast as possible when the
current fed to the protection drops below the set current level, the reset time shall be minimized.
In some applications it is however beneficial to have some type of delayed reset time of the
overcurrent function. This can be the case in the following applications:
• If there is a risk of intermittent faults. If the current relay, close to the faults, picks up and
resets there is a risk of unselective trip from other protections in the system.
• Delayed resetting could give accelerated fault clearance in case of automatic reclosing to a
permanent fault.
• Overcurrent protection functions are sometimes used as release criterion for other protection
functions. It can often be valuable to have a reset delay to assure the release function.
21.2 Operation principle
21.2.1 Mode of operation
The function can operate in a definite time-lag mode or in a current definite inverse time mode.
For the inverse time characteristic both ANSI and IEC based standard curves are available.
If current in any phase exceeds the set pickup current value , a timer, according to the selected
operating mode, is started. The component always uses the maximum of the three phase current
values as the current level used in timing calculations.
In case of definite time-lag mode the timer will run constantly until the time is reached or until the
current drops below the reset value (pickup value minus the hysteresis) and the reset time has
elapsed.
The general expression for inverse time curves is according to equation 97.
Line distance protection REL650
Technical manual
the circuit breaker B1 has opened its primary contacts and thus the fault current is
2
the protection A1 is reset, i.e. the timer is stopped.
3
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Time inverse characteristics
the protection B1
1
the timer of protection A1 is active.
2
Section 21
IP15777-1 v2
M16687-3 v5
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