Siemens SIPROTEC 7SJ62 Manual page 86

Functions
2.2 Overcurrent Protection 50, 51, 50N, 51N
The corresponding time multiplier for an IEC characteristic is set at address 1208 51 TIME DIAL and in
address 1209 51 TIME DIAL for an ANSI characteristic. It must be coordinated with the grading coordination
chart of the system.
The time multiplier can also be set to ∞. In this case, the element will not trip after pickup. However, pickup, will
be signaled. If the 51 element is not required at all, address 112 Charac. Phase should be set to Definite
Time during protective function configuration (see Section 2.1.1.2).
If highly sensitive settings close to the load current are required in weak power systems or transformers, the
element can be stabilized via the undervoltage as an additional criterion for the power system fault. The oper-
ating modes can be set in address 1223 VOLT. INFLUENCE. In a voltage-controlled operation, the voltage
threshold is defined via parameter 1224 51V V< below which the current element is released.
51N Element (ground) with IEC or ANSI Characteristics
Having set address 113 Charac. Ground = TOC IEC when configuring the protection functions (Section
2.1.1), the parameters for the inverse characteristics will also be available. Specify in address 1311 51N IEC
CURVE the desired IEC characteristic (Normal Inverse, Very Inverse, Extremely Inv. or Long
Inverse). If address 113 Charac. Ground was set to TOC ANSI, you can select the desired ANSI
characteristic (Very Inverse, Inverse, Short Inverse, Long Inverse, Moderately Inv.,
Extremely Inv. or Definite Inv.) at address 1312 51N ANSI CURVE.
If the inverse time trip characteristic is selected, it must be noted that a safety factor of about 1.1 has already
been included between the pickup value and the setting value. This means that a pickup will only occur if a
current of about 1.1 times the setting value is present. If Disk Emulation was selected at address 1310 51
Drop-out, reset will occur in accordance with the reset curve as described before.
The current value is set in address 1307 51N PICKUP. The setting is mainly determined by the minimum an-
ticipated ground fault current.
The corresponding time multiplier for an IEC characteristic is set at address 1308 51N TIME DIAL and in
address 1309 51N TIME DIAL for an ANSI characteristic. This has to be coordinated with the grading coor-
dination chart of the network. For ground currents with grounded network, you can often set up a separate
grading coordination chart with shorter delay times.
The time multiplier can also be set to ∞. In this case, the element will not trip after pickup. However, pickup, will
be signaled. If the 51N-TOC element is not required at all, address 113 Charac. Ground should be set to
Definite Time during configuration of the protection functions (see Section 2.1.1).
User-defined Characteristics (phases and ground)
Having set address 112 Charac. Phase or 113 = Charac. Ground = User Defined PU or User def.
Reset when configuring the protective functions (Section 2.1.1.2), the user-defined curves will also be avail-
able. A maximum of 20 value pairs (current and time) may be entered at address 1230 51/51N or 1330
50N/51N in this case. This option allows point-by-point entry of any desired curve. When setting address 112
= User def. Reset or 113 = User def. Reset additional value pairs (current and reset time) may be
entered in address 1231 MofPU Res
Since current values are rounded in a specific pattern before they are processed in the device (see Table 2-4),
we recommend to use exactly the same preferred current values you can find in this table.
The current and time value pairs are entered as multiples of addresses 1207 51 PICKUP and 1208 51 TIME
DIAL for the phase currents and 1307 and 1308 for the ground system. Therefore, it is recommended that
these addresses are initially set to 1.00 for simplicity. Once the curve is entered, the values at addresses 1207
or1307 or/and 1208 or 1308 can be modified later to allow moving the curve in a different direction.
The default setting of current values is ∞. They are, therefore, disabled and no pickup or tripping of these pro-
tection functions will occur.
86
T/Tp or 1331 MofPU Res T/TEp to represent the dropout curve.
C53000-G1140-C207-2, Release date 01.2008
SIPROTEC, 7SJ62/64, Manual