over currents it can lead to situations, where the failure current remains under the
generator rated current. In this case a normal over current monitoring does not trip. The
voltage restraint over current monitoring considers this and decreases the configured
over current limit according to a modification factor, that it comes to a trip.
The considered voltages are either the single phase-phase or phase-neutral voltages.
(Refer to "Generator voltage monitoring"
). The monitor takes always the lowest
considered voltage into account for calculating the modification factor.
Voltage restraint over current monitoring can be activated individually for “Generator
over current (limit 1-3)” and Generator inverse time over current, if the according
parameter 2227 “Voltage restraint monitoring” is switched to “Yes”.
The modification factor depends on the measured voltage in percent of rated voltage. It is
defined by a characteristic which is defined by three parameters (ID 2230, 2231, 2232 cf.
figure). This characteristic is taken into account for all over current monitoring functions,
if enabled.
Fig. 185:
Example for generator voltage restraint overcurrent characteristic
Beginning at a voltage dip of 95% rated voltage (configured by 2231), the modification
factor will be linearly reduced (cf. figure 86). If the voltage reaches 25% or less
(configured by 2230) the modification factor will remain at 25% (configured by 2232).
Now the effective limit is calculated as:
Effective limit [%] = Limit [%] * Modification Factor [%]/ 100[%]
Supposed the configured limit of an over current monitor is 110% and the measured
voltage is 25%:
Effective limit [%] =110% * 25%/100% = 27.5%
439
easYgen-3000XT Series
B37574
4 Configuration
4.5.1.4.3 Generator Voltage Restrained Overcurrent Monitoring - ANSI #51V
Released