
Section 4
1MAC050144-MB C
Protection functions
114
615 series ANSI
Technical Manual
Table 89:
Reset time characteristics supported by different stages
4.1.1.7
Application
51P/50P 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
51P/50P 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 pickup level for the function to trip. When the number of
pickup-phase settings is set to "1 out of 3", the operation of 51P/50P is enabled with the
presence of high current in one-phase.
Many applications require several steps using different current pickup levels and time
delays. 51P/50P consists of three protection stages:
• Low 51P
• High 50P-1/2
• Instantaneous 50P-3.
51P is used for overcurrent protection. The function contains several types of time-delay
characteristics. 50P-1/2 and 50P-3 are used for fast clearance of very high overcurrent
situations.
Reset curve type
Supported by
51P
50P-1/2
Note
(1) Immediate
x
x
Available for all reset
time curves
(2) Def time reset
x
x
Available for all reset
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 50P-3 or when the DT
operation is selected. The reset is purely defined by the
Reset delay time
setting.
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.
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