Table 219: Reset time characteristics supported by different stages
Reset curve type
PHLPTOC
PHHPTOC
Note
(1) Immediate
x
x
Available for all operate time curves
(2) Def time re-
set
x
x
Available for all operate 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 PHIPTOC or when the
DT operation is selected. The reset is purely defined by the
Reset delay
time setting.
4.1.1.7
Application
PHxPTOC is used in several applications in the power system. The applications
include but are not limited to:
• 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
PHxPTOC 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 and three-phase short circuits. Therefore, the user can choose how
many phases, at minimum, must have currents above the start level for the function
to operate. When the number of start-phase settings is set to "1 out of 3", the
operation of PHxPTOC is enabled with the presence of high current in one-phase.
When the setting is "2 out of 3" or "3 out of 3", single-phase faults are not
detected. The setting "3 out of 3" requires the fault to be present in all
three phases.
Many applications require several steps using different current start levels and time
delays. PHxPTOC consists of three protection stages.
• Low PHLPTOC
• High PHHPTOC
• Instantaneous PHIPTOC
PHLPTOC is used for overcurrent protection. The function contains several types of
time-delay characteristics. PHHPTOC and PHIPTOC are used for fast clearance of
very high overcurrent situations.
Transformer overcurrent protection
The purpose of transformer overcurrent protection is to operate as main
protection, when differential protection is not used. It can also be used as
coarse back-up protection for differential protection in faults inside the zone of
protection, that is, faults occurring in incoming or outgoing feeders, in the region of
transformer terminals and tank cover. This means that the magnitude range of the
fault current can be very wide. The range varies from 6xI
n
to several hundred times I
Protection functions
1MRS757644 H
244
620 series
Technical Manual
