Siemens SIPROTEC 7SD610 Manual page 36

Functions
2.1 General
Rated frequency
The rated frequency of the power system is set under address 230 Rated Frequency. The factory presetting
according to the ordering code (MLFB) only needs to be changed if the device is applied in a region different
from the one indicated when ordering. You can set 50 Hz or 60 Hz.
System Starpoint
The manner in which the system starpoint is earthed must be considered for the correct processing of earth
faults and double earth faults. Accordingly, set for address 207 SystemStarpoint = Solid Earthed,
Peterson-Coil or Isolated. For low-resistant earthed systems set Solid Earthed.
Distance Unit
Address 236 Distance Unit allows to define the distance unit (km or Miles). If the compounding function
of the voltage protection is used, the overall line capacitance is calculated from the line length and the capaci-
tance per unit length. If compounding is not used, this parameter is of no consequence. Changing the length
unit will not result in an automatic conversion of the setting values which depend on this length unit. They have
to be re-entered into their corresponding valid addresses.
Trip command duration
In address 240 the minimum trip command duration TMin TRIP CMD is set. It applies to all protection and
control functions which may issue a trip command. It also determines the duration of the trip pulse when a circuit
breaker test is initiated via the device. This parameter can only be altered using DIGSI under Additional Set-
tings.
In address 241 the maximum close command duration TMax CLOSE CMD is set. It applies to all close com-
mands issued by the device. It also determines the length of the close command pulse when a circuit breaker
test cycle is issued via the device. It must be long enough to ensure that the circuit breaker has securely closed.
There is no risk in setting this time too long, as the close command will in any event be terminated following a
new trip command from a protection function. This parameter can only be altered using DIGSI under Addition-
al Settings.
Circuit breaker test
The 7SD610 allows a circuit breaker test during operation by means of a tripping and a closing command
entered on the front panel or using DIGSI. The duration of the trip command is set as explained above. Address
242 T-CBtest-dead determines the duration from the end of the trip command until the start of the close
command for this test. It should not be less than 0.1 s.
Current transformer characteristic
The basic principle of the differential protection assumes that all currents flowing into a healthy protected
section add up to zero. If the current transformer sets at the line ends have different transformation errors in
the overcurrent range, the total of the secondary currents can reach considerable peaks when a short-circuit
current flows through the line. These peaks may feign an internal fault. The measures to prevent errors in case
of current transformer saturation included in 7SD610 work completely satisfying if the protection knows the
transmission behaviour of the current transformers.
For this, the characteristic data of the current transformers and of their secondary circuits are set (see also
Figure 2-17 in Section 2.3). The default setting is adequate in most cases; it considers the data of the worst-
case protective current transformers.
The rated accuracy limit factor n of the current transformers and the rated power P
rating plate of the current transformers. The information refers to nominal conditions (nominal current, nominal
burden). For example (according to VDE 0414 / Part 1 or IEC 60044)
36
are usually stated on the
N
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011