ABB Relion 670 series - The Basics of the High Impedance Principle

ANSI05000163-1-en.vsd
3·87
87N
3·87T
G
3·87G
3·87B
3·87T
3·87
3·87
3·87B
ANSI05000163 V2 EN
Figure 48: Different applications of a 1Ph High impedance differential protection
HZPDIF (87) function
7.1.2.1 The basics of the high impedance principle
The high impedance differential protection principle has been used for many years and is
well documented in literature publicly available. Its operating principle provides very
good sensitivity and high speed operation. One main benefit offered by the principle is an
absolute stability (that is, no operation) for external faults even in the presence of heavy
CT saturation. The principle is based on the CT secondary current circulating between
involved current transformers and not through the IED due to high impedance in the
measuring branch. This stabilizing resistance is in the range of hundreds of ohms and
Section 7 1MRK 506 369-UUS -
Differential protection
136 Line distance protection REL670 2.2 ANSI
Application manual