Functions
2.19 Impedance Protection (ANSI 21)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
163
If safety factor 4 is chosen, dZ/dt should never be set higher than 500 Ω/s (or 100 Ω/s for 5 A transformers).
The default setting for dZ/dt is 300 Ω/s, which should be adequate for most applications. This is also the basis
for the minimum distance P/SPOL - TPOL, assuming that for detection of a power swing there must be one
impedance value between P/SPOL and TPOL.
PPOL - APOL > dZ/dt · Δt = 300 Ω/s · 0.02 s = 6 Ω (setting selected: 8 Ω)
All other settable parameters are advanced parameters which need not normally be modified.
Whether a power swing can cause an overfunctioning of the impedance protection depends mainly on the time
the impedance vector remains inside the trip polygon. This time can only be reliably determined by transient
calculations.
If the rate of change in the proximity of 180° is known, it can be the basis for a rough estimation of the time.
T = 2 · Z
characteristic
/dZ/dt (180°)
The above data yield the following value:
Z
characteristic
= Z1 = 4 Ω
dZ/dt (180°) = 20 Ω/s
T = 2 · 4 Ω/20 Ω/s = 0.4 s
This means that for delay times of more than 0.4 s no power swing blocking is needed.
2.19.4 Settings
Addresses which have an appended "A" can only be changed with DIGSI, under Additional Settings.
The table indicates region-specific presettings. Column C (configuration) indicates the corresponding second-
ary nominal current of the current transformer.
Address Parameters Comments
3316 BLOCKING OF The setting is , as there is little or no delay for this stage. The delay
time of Z2 is determined by the power system protection, and is
longer. (see also the guidelines below)
3317 T-ACTION P/S The default setting is 3.00 sec. This time depends on the minimum
possible power swing frequency.
Addr. Parameter C Setting Options Default Setting Comments
3301 IMPEDANCE PROT. OFF
ON
Block relay
OFF Impedance Protection
3302 IMP I> 5A 0.50 .. 100.00 A 6.75 A Fault Detection I> Pickup
1A 0.10 .. 20.00 A 1.35 A
3303 U< SEAL-IN ON
OFF
OFF State of Undervoltage
Seal-in
3304 U< 10.0 .. 125.0 V 80.0 V Undervoltage Seal-in
Pickup
3305 T-SEAL-IN 0.10 .. 60.00 sec 4.00 sec Duration of Undervoltage
Seal-in
3306 ZONE Z1 5A 0.01 .. 26.00 Ω 0.58 Ω Impedance Zone Z1
1A 0.05 .. 130.00 Ω 2.90 Ω
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