Loss Of Load (Some Models Only) - Siemens 7SG164 Ohmega 400 Series Manual

1.2 Loss of Load (Some models only).

1.2.1 Scheme Operation
The Loss of Load protection scheme is used to give faster fault clearance time for an end zone fault (i.e between
the Zone 1 boundary and the line end) when there is no signalling channel available. This allows a faster
clearance time than the time-delayed Zone 2 elements.
Consider a fault occurring near to the remote end, i.e outside of the Zone 1 reach, but within the line length. In a
normal time stepped distance scheme, the remote end relay would trip in Zone 1 time, and the local end relay
would trip after the Zone 2 time delay. The Loss of Load scheme monitors the current in the healthy phases and
can remove the Zone 2 time delay, speeding up the local end trip, when the remote end trip occurs.
If the relay detects a drop in current in one or two phases below the Loss of Load Level, with the current on the
remaining phases above this level, it will remove the time delay from zone 2, for a fixed time delay (the LOL Time
Limit) to allow the relay to trip instantaneously. This will allow the relay to trip more quickly for single or double
phase faults, but will not affect operation for three phase faults.
A short time delay (typically 20ms), known as the Loss of Load Pole Scatter Delay or the LOL CB Op Delay is
introduced to prevent the Loss of Load feature picking up during normal breaker operation.
1.2.2 Settings
The Loss Of Load function (LOL) is made active by selecting the scheme in the scheme selection menu. If a
conventional scheme is selected and a communications failure occurs then a group setting change could be
used to switch the scheme on until the communications is restored.
Distance Scheme
LOL Level
LOL CB Op Delay or LOL Pole Scatter Delay
LOL Time Limit
Status Inputs: N/A
Relay Outputs: AIDED TRIP, LOSS OF LOAD
©2010 Siemens Protection Devices Limited
7SG16 Ohmega 402 60 Protection Schemes
LOSS OF LOAD
0.1..0.9 (0.5x In)
0..50 (20ms)
0..60000 (40ms)
Chapter 3 Page 4 of 13