Functions
2.10 Inverse-Time Overcurrent Protection (ANSI 51V)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
79
2.10.2 Setting Notes
General
The inverse overcurrent time protection is only effective and available if this function was allocated to the input
CTs of either side 1 or side 2 during configuration (see Section 2.4), i.e. if address 114 O/C PROT. Ip was
set to IEC SIDE 1, ANSI SIDE 1, IEC SIDE 2 or ANSI SIDE 2. If the function is not needed it is set to .
Overcurrent Stage Ip
The address 1401 O/C Ip serves to switch the function ON or OFF or to block only the trip command (Block
relay). In this context, it must be considered that, for the inverse O/C time protection, a safety factor of about
1.1 has already been included between the pick-up value and the setting value. This means that a pickup is
only performed if a current of about 1.1 times the setting value is present. The function will reset as soon as the
value falls below 95 % of the pickup value.
The current value is set at address 1402 Ip. The maximum operating current is of primary importance for the
setting. A pickup caused by an overload must be excluded, as the device operates in this mode as fault pro-
tection with correspondingly short tripping times and not as overload protection.
The corresponding time multiplier for configuration of IEC characteristics (address 114 O/C PROT. Ip = IEC
Page n) is accessible under address 1403 T Ip. At address 1405 IEC CURVE, 3 IEC characteristics can be
selected.
The time multiplier for configuring ANSI characteristics (address 114 O/C PROT. Ip= ANSI Page) can be
found at address 1404 TIME DIAL: TD; parameter 1406 ANSI CURVE offers a choice between 5 ANSI char-
acteristics.
The time multipliers must be coordinated with the network grading plan.
The time multipliers can also be set to ∞. If set to infinity, the pickup of this function will be indicated but the
stage will not trip after pickup. If the Ip stage is not required, on configuration of the protection function (Section
2.4) address 114 O/C PROT. Ip is set to Disabled
or this function switched under 1401 O/C Ip = OFF.
The address 1408 serves to predefine the U< pick-up value for the undervoltage trip of the Ip pickup value for
voltage-controlled inverse overcurrent time protection/AMZ (parameter 1407 VOLT. INFLUENCE = Volt.
controll.). The parameter is set to a value just below the lowest phase-to-phase voltage admissible during
operation, e.g. from 75 to 80 V. In this context, the same rules apply as for the undervoltage seal-in of the def-
inite overcurrent time protection (see also Subsection 2.8.2).
If at address 1407 VOLT. INFLUENCE is set to without or Volt. restraint, the parameter 1408 has no
function.
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