Siemens SIPROTEC 4 7SJ61 Manual page 60

Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
only the settings for the definite time elements are available. The selection of TOC IEC or TOC ANSI makes
available additional inverse time characteristics. The superimposed high-set elements 50-2, 50-3 or 50N-2,
50N-3 are available in all these cases.
Parameter 250 50/51 2-ph prot can also be set to activate two-phase overcurrent protection.
Under address 1201 FCT 50/51, overcurrent protection for phases and under address 1301 FCT 50N/51N,
the ground overcurrent protection can be switched ON or OFF.
Pickup values, time delays, and characteristics for ground protection are set separately from the pickup values,
time delays and characteristic curves associated with phase protection. Because of this, relay coordination for
ground faults is independent of relay coordination for phase faults, and more sensitive settings can often be
applied to directional ground protection.
Depending on the setting of parameter 251 CT Connect., the device can also be used in specific system
configuration with regard to current connections. Further information can be found under Section
2.1.3.2 Setting
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 unconsid-
ered.
•
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
disturbances. 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
50-2element
50-1 element
51 element
50N-3 element
50N-2 element
50N-1 element
51Nelement
High-set Current Elements 50-2, 50-3 (phases)
The pickup current of the high-set element 50-2 PICKUP or50-3 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
60
Notes, "Current Connections".
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
C53000-G1140-C210-6, Edition 05.2016
SIPROTEC 4, 7SJ61, Manual