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Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
Measurement Methods
The comparison values to be used for the respective element can be set in the setting sheets for the elements.
• Measurement of the fundamental harmonic (standard method):
This measurement method processes the sampled values of the current and filters in numerical order the
fundamental harmonic so that the higher harmonics or transient peak currents remain largely unconsidered.
• Measurement of the true RMS value
The current amplitude is derived from the sampled values in accordance with the definition equation of the
true RMS value. This measurement method should be selected when higher harmonics are to be considered
by the function (e.g. in capacitor banks).
• Measurement with instantaneous values
This procedure compares the instantaneous values to the set threshold. The element picks up at 2 · √2 ·
setting value (rms). It does not perform a mean-value calculation and is thus sensitive with regard to distur-
bances. This measurement method should only be selected if an especially short pickup time of the element
is required. In this measurement procedure, the operating time of the element is reduced compared to the
measurement of effective values or fundamental harmonics (see „Technical Data").
The type of the comparison values can be set under the following addresses:
50-3 Element
50-2 Element
50-1 Element
51 Element
50N-3 Element
50N-2 Element
50N-1 Element
51N Element
High current elements 50-2, 50-3 (phases)
The pickup current of the high-set element 50-2 PICKUP or 50-3 PICKUP can be set at address 1202 or
1217. The corresponding delay time 50-2 DELAY or 50-3 DELAY can be configured under address 1203 or
1218. It is usually used for purposes of current grading intended for large impedances that are prevalent in
transformers or generators. It is specified in such manner that it picks up faults up to this impedance.
Example of the high-set current element 50-2 PICKUP: Transformer used for busbar supply with the following
data:
Rated apparent power
Transformer impedance
Primary nominal voltage
Secondary nominal voltage
Vector groups
Neutral point
Fault power on 110 kV-side
Based on the data above, the following fault currents are calculated:
Three-Phase High Voltage Side Fault Current
Three-Phase Low Voltage Side Fault Current
On the High Voltage Side Flowing
78
Address 1219 50-3 measurem.
Address 1220 50-2 measurem.
Address 1221 50-1 measurem.
Address 1222 51 measurem.
Address 1319 50N-3 measurem.
Address 1320 50N-2 measurem.
Address 1321 50N-1 measurem.
Address 1322 51N measurem.
S
= 16 MVA
NomT
ZT = 10 %
V
= 110 kV
Nom1
V
= 20 kV
Nom2
Dy 5
Grounded
1 GVA
at 110 kV = 5250 A
at 20 kV = 3928 A
at 110 kV = 714 A
E50417-G1140-C344-A5, Release date 11.2012
SIPROTEC, 7SK80, Manual
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