ABB Relion 670 series, Technical Manual

Page: 1389 / 1432

In the case protection B1 shall trip without any intentional delay (instantaneous). When the fault
occurs the protections pickup to detect the fault current. After the time t
1
the protection B1 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 pickup before the trip is sent to the B1 circuit breaker. At the time t
2
the circuit breaker B1
has opened its primary contacts and thus the fault current is 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
2
the timer of protection A1 is active. At time t
3
the protection A1 is reset,
that is the timer is stopped.
In most applications it is required that the 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 IED, 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.
26.2 Principle of operation
IP15777-1 v2
26.2.1 Mode of operation
M16687-3 v6
The function can trip 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. Also
programmable curve types are supported via the component inputs: p, A, B, C pr, tr, and cr.
Different characteristics for reset delay can also be chosen.
If current in any phase exceeds the set pickup current value (here internal signal pickupValue), 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.
For definite time delay curve ANSI/IEEE Definite time or IEC Definite time are chosen.
The general expression for inverse time curves is according to equation 228 .
1MRK 502 066-UUS B Section 26
Inverse time characteristics
1383
Technical manual