ABB RET670 Applications Manual

67N
Three phase CT
summated
Single CT
YN/D or YN/Y
transformer
Single phase-
to- ground fault
ANSI05000493_3_en.vsd
0
3I
alt
ANSI05000493 V3 EN
Figure 197: Step 1 fault calculation 1
The fault is located at the borderline between instantaneous and delayed operation of
the line protection, such as Distance protection or line residual overcurrent protection.
This calculation gives the current fed to the protection: 3I
0fault2
The setting of step 1 can be chosen within the interval shown in equation 351.
0fault 2 step1 0fault1
3I lowmar I 3I highmar× < < ×
EQUATION1455 V2 EN
(Equation 351)
Where:
lowmar is a margin to assure selectivity (typical 1.2) and
highmar is a margin to assure fast fault clearance of busbar fault (typical 1.2).
Setting of step 2
The setting of the sensitive step 2 is dependent of the chosen time delay. Often a
relatively long definite time delay or inverse time delay is chosen. The current setting
Section 3 1MRK504116-UUS C
IED application
434
Application manual

ABB RET670 Specifications

General

Rated Frequency	50/60 Hz
Inputs	Analog and binary inputs
Application	Protection of power systems
Communication Protocols	IEC 61850, DNP3, Modbus
Operating Temperature Range	-25°C to +55°C
Mounting	Rack mounted
Number of Binary Inputs	Up to 48
Number of Binary Outputs	32
Protection Functions	Overcurrent Protection
Outputs	Binary outputs
Enclosure	IP 54
Type	Line Differential Protection
Number of Analog Inputs	24