Functionality; Operation Principle - ABB 615 series Technical Manual

1MAC059074-MB A
4.3.1.3
4.3.1.4
615 series ANSI
Technical Manual

Functionality

The line differential protection with in-zone power transformer function 87L is used as
feeder differential protection for the distribution network lines and cables. 87L includes
low, stabilized and high, non-stabilized stages. The line differential protection can also be
used when there is an in-zone transformer in the protected feeder section.
The stabilized low stage provides a fast clearance of faults while remaining stable with
high currents passing through the protected zone increasing errors on current measuring.
Second harmonic restraint insures that the low stage does not operate due to energizing of
a tapped or in-zone transformer. The high stage provides a very fast clearance of severe
faults with a high differential current regardless of their harmonics.
The operating time characteristic for the low stage can be selected to be either definite time
(DT) or inverse definite time (IDMT). The direct inter-trip ensures both ends are always
operated, even without local criteria.

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The function can also be set into test mode by setting the Operation setting to "test/
blocked".
The operation of 87L can be described using a module diagram. All the modules in the
diagram are explained in the following sections.
Section 4
Protection functions
461