Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
83
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 r.m.s. value
The current amplitude is derived from the sampled values in accordance with the definition equation of the
true r.m.s. value. This measurement method should be selected when higher harmonics are to be consid-
ered by the function (e.g. in capacitor banks).
• Measurement with
instantaneous values
This method compares the instantaneous values to the set threshold. It does not perform a mean-value cal-
culation and is thus sensitive with regard to disturbances. This measurement method should only be select-
ed if an especially short pickup time of the element is required. With this measurement method, the operating
time of the element is reduced compared to the measurement of true r.m.s. values or fundamental harmonics
(see „Technical Data“).
The type of the comparison values can be set under the following addresses:
50-3 element
Address
1219
50-3 measurem.
50-2 element
Address
1220
50-2 measurem.
50-1 element
Address
1221
50-1 measurem.
51 element
Address
1222
51 measurem.
50N-3 element
Address
1319
50N-3 measurem.
50N-2 element
Address
1320
50N-2 measurem.
50N-1 element
Address
1321
50N-1 measurem.
51N element
Address
1322
51N measurem.
High-set Current Elements 50-2, 50-3 (phases)
The pickup currents of the high-set elements
50-2 PICKUP
or
50-3 PICKUP
can be set either 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 prev-
alent 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:
Based on the data above, the following fault currents are calculated:
Rated power of the transformer
S
NomT
= 16 MVA
Transformer impedance
ZTX = 10 %
Primary nominal voltage
V
Nom1
= 110 kV
Secondary nominal voltage
V
Nom2
= 20 kV
Vector groups
Dy 5
Starpoint
Grounded
Fault power on 110 kV–side
1 GVA
3-Phase High Voltage Side Fault Current
I
"
k3, 1, 110
= 5250 A
3-Phase Low Voltage Side Fault Current
I
"
k3, 2, 20
= 3928 A
On the High Voltage Side Flowing
I
"
k3, 2, 110
= 714 A
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