This FAQ has been written for NEAL (North East Africa and Levant) region. If you are looking for information for another region, please select the correct country from the top-left dropdown in the page and 'Navigate to Browse FAQs' in the Support menu.
The Cold Load Pick-Up I0 or CLPU 50N/51N function avoids nuisance tripping of the earth fault protection (ANSI 50N/51N) during energization after a long outage.
Depending on the installation characteristics, such operations can actually generate transient inrush currents.
If the residual current measurement is based on the sum of the 3 phase CTs, the aperiodic component of these transient currents can result in
saturation of the phase CTs. This can lead to measurement of an incorrect residual current likely to exceed the protection set points.
These transient currents are essentially due to:
However, if these settings result in inadequate sensitivity levels or delays that are too long, the CLPU 50N/51N function is used to increase or
inhibit set points temporarily after energization.
If the residual current is measured by a correctly installed CT, there is less risk of measuring an incorrect residual current. In this case, there is no need to use the
CLPU 50N/51N function.
Depending on the installation characteristics, such operations can actually generate transient inrush currents.
If the residual current measurement is based on the sum of the 3 phase CTs, the aperiodic component of these transient currents can result in
saturation of the phase CTs. This can lead to measurement of an incorrect residual current likely to exceed the protection set points.
These transient currents are essentially due to:
- the power transformer magnetizing currents,
- the motor starting currents.
However, if these settings result in inadequate sensitivity levels or delays that are too long, the CLPU 50N/51N function is used to increase or
inhibit set points temporarily after energization.
If the residual current is measured by a correctly installed CT, there is less risk of measuring an incorrect residual current. In this case, there is no need to use the
CLPU 50N/51N function.
Released for:Schneider Electric Egypt and North East Africa
