Siemens SIPROTEC 4 User Manual page 277

NOTE
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Warning!
If the 3-phase voltage connection is established at a motor or generator feeder and the Ux input is operated
at the busbar or at another voltage measuring point other than the feeder, you must select "True RMS" as
the measurement procedure. Otherwise, there is a risk of overfunction or underfunction in a situation
where the feeder voltage and the Ux voltage exhibit significantly different frequencies.
NOTE
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With single-phase voltage protection, the configured voltage threshold is always interpreted as voltage at
the terminal. The parameterization in 213 VT Connect. 3ph (see Power System Data 1) is ignored here.
The forward direction of power (P forward, Q reverse) is the direction of the line. Parameter (1108 P,Q sign)
for sign inversion of the power display in the operating measured values is ignored by the flexible functions.
Via parameter PICKUP WITH it is determined whether the function must be triggered on exceeding or under-
shooting of the set threshold value.
Settings
The pickup thresholds, time delays and dropout ratios of the flexible protection function are set in the
"Settings" dialog box in DIGSI.
The pickup threshold of the function is configured via parameter P.U. THRESHOLD. The OFF-command time
delay is set via parameter T TRIP DELAY. Both setting values must be selected according to the required
application.
The pickup can be delayed via parameter T PICKUP DELAY. This parameter is usually set to zero (default
setting) in protection applications, because a protection function should pick up as quickly as possible. A
setting deviating from zero may be appropriate if a trip log is not desired to be started upon each short-term
exceeding of the pickup threshold, for example, with power protection or when a function is not used as a
protection, but as a monitoring function.
When setting the power threshold values, it is important to take into consideration that a minimum current of
0.03 Ι is required for power calculation. The power calculation is blocked for lower currents.
N
The dropout of pickup can be delayed via parameter T DROPOUT DELAY. This setting is also set to zero by
default (standard setting) A setting deviating from zero may be required if the device is utilized together with
electro-magnetic devices with considerably longer dropout ratios than the digital protection device (see
Section 2.2 for more information). When utilizing the dropout time delay, it is recommended to set it to a
shorter time than the OFF-command time delay in order to avoid both times to "race".
The dropout ratio of the function can be selected in parameter DROPOUT RATIO. The standard dropout ratio
of protection functions is 0.95 (default setting). If the function is used as power protection, a dropout ratio of
at least 0.9 should be set. The same applies to the utilization of the symmetrical components of current and
voltage. If the dropout ratio is decreased, it would be sensible to test the pickup of the function regarding
possible "chatter".
The dropout difference of the frequency elements is set under parameter DO differential. Usually, the
default setting of 0.02 Hz can be retained. A higher dropout difference should be set in weak systems with
larger, short-term frequency fluctuations to avoid chattering of the message.
A fixed dropout difference of 0.1 Hz/s is used for the frequency change (df/dt) measurand. The same applies to
the voltage change (dU/dt) measurand. The permanent dropout difference here is 3 V/s.
Parameter BLK.by Vol.Loss determines whether a function whose measured variable is based on a voltage
measurement (measured quantities voltage, P forward, P reverse, Q forward, Q reverse and power factor),
should be blocked in case of a measured voltage failure (set to YES) or not (set to NO).
Renaming Messages, Checking Configurations
After parameterization of a flexible function, the following steps should be noted:
SIPROTEC 4, 7SJ62/64, Manual
C53000-G1140-C207-8, Edition 08.2016
Functions
2.19 Flexible Protection Functions
277