Siemens Ohmega 406 7SG16 Bedienungsanleitung
7SG16 Ohmega 406 Loss of Load
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©2010 Siemens Protection Devices Limited
7SG16 Ohmega 406
Distance Protection Relays
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This document is issue 2010/02. The list of revisions up to and including this issue is:
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7SG16 Ohmega 406 Loss of Load
Contents
1Loss of Load Protection ................................................................................................................................3
2Settings...........................................................................................................................................................4
©2010 Siemens Protection Devices Limited Chapter 12 Page 2 of 4
7SG16 Ohmega 406 Loss of Load
1 Loss of Load Protection
The Loss of Load protection scheme in the relay 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 waiting for the operation of the zone 2 elements. The logic diagram for this scheme is
shown below;
Z1D
Z2D
Z3D 1SOLOTRIP
LOLUCA
LOLUCB
LOLUCC 1
&
Z2G
PoleScatterDelay
20 / 0
OperateWindow
40 / 0
AIDTRIP
LOL
LOL
LOL
LOLUCA
LOLUCB
LOLUCC &
&
There must be a loss of load current in at least one phase.
Fault current must continue to flow in at least one other phase for at least 20ms after the
loss of load, to allow time for all the poles of the breaker at the start of the next line to open.
The Zone 2 protection must pickup within 40ms of the loss of load.
For a Loss Of Load trip to occur:
_Latch1
S
RQ
=2k+1
&
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.
©2010 Siemens Protection Devices Limited Chapter 12 Page 3 of 4
7SG16 Ohmega 406 Loss of Load
©2010 Siemens Protection Devices Limited Chapter 12 Page 4 of 4
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.
LOL Level [0.50 xIn]
The current setting can be selected between 10 – 90% of In.
LOL CB Op Delay or LOL Pole Scatter Delay [20 ms]
The pole discrepancy timer setting is between 0 and 50ms.
LOL Time Limit [40 ms]
The alarm function can be mapped to any of the output contacts. The trip function will operate whichever
contact(s), has been set to cause a trip.
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