Functions
2.19 Impedance Protection (ANSI 21)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
158
Figure 2-64 Logic Diagram for the Power Swing Blocking of the Impedance Protection
Z(Tent) First value inside the power swing polygon (at the moment of Tent)
Z
(Tent-Δt) Last value outside the power swing polygon
P/SPOL Power swing polygon
TPOL Trip polygon
ΔZ/Δt Rate of change of the impedance phasor
2.19.3 Setting Notes
General
Machine impedance protection is only effective and available if enabled during configuration (Section 2.4,
address 133, IMPEDANCE PROT. = Enabled. If the function is not required Disabled is set. Address 3301
IMPEDANCE PROT. serves to switch the function ON or OFF or to block only the trip command (Block relay).
Pickup
The maximum load current during operation is the most important criterion for setting overcurrent pickup. A
pickup by an overload must be excluded! For this reason, the 3302 IMP I> pickup value must be set above
the maximum (over) load current to be expected. Recommended setting: 1.2 to 1.5 times the nominal machine
current. The pickup logic corresponds to the logic of the UMZ I> definite time-overcurrent protection.
If the excitation is derived from the generator terminals with the short circuit current possibly falling below the
pickup value (address 3302) due to the collapsing voltage, the undervoltage seal-in feature of the pickup is
used, i.e. address 3303 U< SEAL-IN is switched to ON.
The undervoltage seal-in setting U< (address 3304) is set to a value just below the lowest phase-to-phase
voltage occurring during operation, e.g. to U< = 75 % to 80 % of the nominal voltage. The seal-in time (address
3305 T-SEAL-IN) must exceed the maximum fault clearance time in a back-up case (recommended setting:
address 3312 T END + 1 s).
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