User Manual
3UG4625 residual current monitoring relay with 3UL23 transformer
9.3 Functions
3UG4 / 3RR2 monitoring relays
Manual, 02/2013, NEB927043002000/RS-AA/002
191
Limits of fault current measurement
In the event of increasing primary currents, transformer production tolerances, imbalances in
the cable routing and current loads in individual cables increasingly cause what appear to be
fault currents that are detected by the evaluation units.
An increased false tripping may occur if excessively low monitoring limit values have been
set at high primary currents. Such tolerances also mean that the measuring accuracy no
longer corresponds to the range of between -7.5 %/+7.5 %.
To avoid these types of measuring errors and false tripping, we recommend to set the limit
values to the minimum values listed in the following graphic, depending on the applicable
primary current.
0LQLPXPDGMXVWDEOHSDUDPHWHUV,
Ⴃ
IRUDOOWUDQVIRUPHUVL]HVDW+]
5DWHGFXUUHQW>$@
0LQLPXPDGMXVWDEOHOLPLW,
Ⴃ
>P$@
If monitoring is required within limit values that are lower than those recommended, we
recommend the use of delay times, particularly if false tripping occurs exclusively during
motor start-up.
If delay times do not lead to the desired result, the use of shield sleeves may considerably
lower the minimum possible monitoring limit.
For more information see Chapters "Installation specifications (Page 323)" and "Potential for
optimizatio
n (Page 327)".