ABB Relion 620 Series - Page 262

Table 246: Reset time characteristics supported by different stages
Reset curve type PH3LPTOC PH3HPTOC Note
(1) Immediate x x Available for all operating time
curves
(2) Def time re-
set
x x Available for all operating time
curves
(3) Inverse reset x x Available only for ANSI and user
programmable curves
The Type of reset curve setting does not apply to PH3IPTOC or when the
DT operation is selected. The reset is purely defined by the Reset delay
time setting.
4.1.2.6 Application
PH3xPTOC is used in several applications in the power system. The applications
include different protections, for example.
• Selective overcurrent and short-circuit protection of feeders in distribution and
subtransmission systems
• Backup overcurrent and short-circuit protection of power transformers and
generators
• Overcurrent and short-circuit protection of various devices connected to the
power system, for example shunt capacitor banks, shunt reactors and motors
• General backup protection
PH3xPTOC is used for single-phase, two-phase and three-phase non-directional
overcurrent and short circuit protection. Typically, overcurrent protection is used
for clearing two-phase and three-phase short circuits. Therefore, it can be chosen
how many phases, at minimum, must have currents above the start level for the
function to operate.
Many applications require several steps using different current start levels and time
delays. PH3xPTOC consists of three protection stages:
• Low PH3LPTOC
• High PH3HPTOC
• Instantaneous PH3IPTOC
PH3LPTOC is used for overcurrent protection. The function contains several types
of time delay characteristics. PH3HPTOC and PH3IPTOC are used for the fast
clearing of very high overcurrent situations.
Transformer overcurrent protection
The purpose of the transformer overcurrent protection is to operate as the main
protection when differential protection is not used. It can also be used as a
coarse backup protection for differential protection in the faults inside the zone
of protection, that is, faults occurring in incoming or outgoing feeders, in the region
of transformer terminals and in the tank cover. This means that the magnitude
range of the fault current can be very wide. The range varies from 6xIn to several
hundred times In, depending on the impedance of the transformer and the source
impedance of the feeding network. From this point of view, it is clear that the
Protection functions
1MRS757644 H
262 620 series
Technical Manual