Differential Protection; Differential Zone A Or B Bzntpdif, Bznspdif - ABB Relion 670 Series Technical Reference Manual

Section 5

Differential protection

5.1.3
5.1.4
100
called protection zones in relay protection literature. On the other hand, the
protection function is quite specific, because typically all CTs in the station are
connected to it. It is, therefore, of outmost importance that individually connected
CT inputs are appropriately routed to the relevant protection zone. Sometimes these
connections need to be dynamically changed in accordance with the actual
connections within the station. Therefore, the busbar differential protection has two
essential parts:
1. Differential Protection, which provide differential protection algorithm for
each busbar section
2. Zone Selection, which provide dynamic linking between input CTs and
individual protection zones as well as routing of zone trip signals to the
individual bay CBs
It is also important to understand that all function blocks described in the next
sections, except the Switch Status function block, are not independent from each
other. Hidden connections are pre-made in the software in order to simplify the
required engineering work in PCM600 for the end user.
Differential protection
This part of busbar protection consists of differential protection algorithm,
sensitive differential protection algorithm, check zone algorithm, open CT
algorithm and two supervision algorithms. It is presented to the end user as three
function blocks:
1. Zone A
2. Zone B (functionality wise completely identical to the Zone A)
3. Check Zone

Differential Zone A or B BZNTPDIF, BZNSPDIF

The numerical, low-impedance differential protection function is designed for fast
and selective protection for faults within protected zone. All connected CT inputs
are provided with a restraint feature. The minimum pick-up value for the
differential current is set to give a suitable sensitivity for all internal faults. For
busbar protection applications typical setting value for the minimum differential
operating current is from 50% to 150% of the biggest CT. This setting is made
directly in primary amperes. The operating slope for the differential operating
characteristic is fixed to 53% in the algorithm. The fast tripping time of the low-
impedance differential protection function is especially advantages for power
system networks with high fault levels or where fast fault clearance is required for
power system stability. The advanced open CT detection algorithm detects
instantly the open CT secondary circuits and prevents differential protection
operation without any need for additional check zone.
1MRK 505 208-UEN B
Technical reference manual