Loss-Of-Potential (60Lop) Protection; Element Description; Functional Description; Setting Descriptions - Schweitzer Engineering Laboratories SEL-300G Instruction Manual

2-14 Relay Element Settings
L - -P
OSS OF OTENTIAL

Element Description

Functional Description

The SEL-300G Relay provides an easy method to detect loss of relaying potential caused by
blown potential fuses or operation of molded case circuit breakers in the potential circuit
secondary. The relay declares a loss-of-potential if there is a 10% drop in the measured
positive-sequence voltage with no corresponding change in positive-, negative-, or zero-sequence
currents. If the condition persists for 60 cycles, it latches in. 60LOP resets when V1 returns to
greater than 0.43 · VNOM, and V0 and V2 are both less than 5 V secondary.

Setting Descriptions

This function has no settings and is always active.

Relay Word Bits

Relay Word Bit
60LOP
100% S G
TATOR ROUND
Element Description
Functional Description
The SEL-300G Relay provides a two-zone function designed to detect stator winding ground
faults on resistance and high-impedance grounded generators. The Zone 1 element, 64G1, uses a
fundamental-frequency neutral overvoltage element that is sensitive to faults in the middle and
upper portions of the winding. The Zone 2 element, 64G2, uses a third-harmonic voltage
differential function to detect faults in the upper and lower portions of the winding. By using the
two zones together, the relay provides 100% stator ground fault coverage.
Note: Most generators produce enough third-harmonic voltage for proper application
of the 64G2 element; however, some generators (e.g., those with 2/3 and 5/6
pitch windings) may not. In those cases the element based on the third-harmonic
voltage, such as the 64G2, cannot be used for 100% Stator Ground Protection.
When a ground fault occurs high in the winding of a resistance or high-impedance grounded
generator, a voltage appears at the generator neutral. The neutral voltage magnitude during the
fault is proportional to the fault location within the winding. For instance, if a fault occurs 85%
up the winding from the neutral point, the neutral voltage is 85% of the generator rated
line-neutral voltage. The SEL-300G Relay asserts the 64G1 Relay Word bit when neutral
voltage is greater than the 64G1P setting.
Date Code 20020206
(60LOP) P
ROTECTION
Function Description
Loss of Relaying Potential Detected
P E
ROTECTION LEMENTS
Typical Applications
Indication, Control
SEL-300G Instruction Manual