GE Power Management LPS-O Line Protection System 1-
5
1 PRODUCT DESCRIPTION 1.2 INTRODUCTION
1
When phase distance functions are used for a zone of protection, three individual measuring functions are
available. The algorithm that implements the variable-mho measuring functions is derived from designs that
have evolved through several different families of static analog and digital relay systems which have accumu-
lated decades of dependable and secure in-service experience.
An instantaneous overcurrent tripping function (50G) provides direct tripping for severe phase-to-ground faults.
A time-overcurrent tripping function (51G) provides time-delayed backup tripping for phase-to-ground faults.
Either or both of these ground-overcurrent functions can be controlled by the NT negative-sequence directional
trip unit, at the customer’s discretion.
Table 1–2: LPS-O MEASUREMENT FUNCTIONS
Zone or Type Functions
Zone 1 • 3 Variable-Mho phase-distance functions with time delay
Zone 2 (Pilot Zone) • 3 Variable-Mho phase distance functions with time delay
and
Ground directional-overcurrent functions consisting of:
IPT: Ground Trip overcurrent
NT: Negative Sequence Directional Trip
IPB: Ground Block overcurrent
NB: Negative Sequence directional block
Zone 3 • 3 Variable-Mho phase-distance functions with time delay
Zone 4 • 3 Variable-Mho phase-distance functions (reverse looking) with time
delay.
Out of Step Blocking (OSB) 3 Variable-Mho phase-distance functions
Overcurrent Backup 50 — Phase-overcurrent direct trip (directional or nondirectional
50G — Ground-overcurrent direct trip (directional or nondirectional)
51G — Ground time-overcurrent direct trip (directional or nondirectional)
Overcurrent Supervision IT — Trip-supervision overcurrent
IB — Block-supervision overcurrent
Fault Detector FD
Line-Pickup Overcurrent I1
Remote-Open Detectors ROD
Line-Overload Detectors Level 1 Overcurrent
Level 2 Overcurrent
Over/Undervoltage Three adjustable over or under voltage detectors with time delay
Out of Step Tripping (OST) 3 Variable-Mho positive sequence-distance functions
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