7SR210 & 7SR220 Description of Operation
Unrestricted ©2018 Siemens Protection Devices Limited
Page 35 of 94
3.4
Current Protection: Measured Earth Fault (67G, 51G, 50G)
The earth current is measured directly via a dedicated current analogue input.
All phase overcurrent elements can be set to measure either fundamental frequency RMS or True RMS current
i.e.
True RMS current: -
50 Measurement
= RMS
51 Measurement
= RMS
Fundamental Frequency RMS current: -
50 Measurement
= Fundamental
51 Measurement
= Fundamental
3.4.1
Directional Control of Measured Earth Fault Protection (67G) – 7SR22
The directional element produces forward and reverse outputs for use with measured earth fault elements. These
outputs can be mapped as controls to each shaped and instantaneous element.
If a protection element is set as non-directional then it will operate independently of the output of the directional
detector. However, if a protection element is programmed for forward directional mode then operation will occur
only for a fault lying within the forward operate zone. Conversely, if a protection element is programmed for
reverse directional mode then operation will occur only for a fault lying within the reverse operate zone. Typically
the forward direction is defined as being ‘away’ from the busbar or towards the protected zone.
The Characteristic angle is the phase angle by which the polarising voltage must be adjusted such that the
directional detector gives maximum sensitivity in the forward operate zone when the current is in phase with it.
The reverse operate zone is the mirror image of the forward zone.
The measured directional earth fault elements use zero phase sequence (ZPS) polarising.
Voltage polarisation is achieved for the earth-fault elements by comparison of the appropriate current with its
equivalent voltage: -
I
0
~ V
0
The characteristic angle can be user programmed to any angle between -95
°
and +95
°
using the
67G Char
Angle
setting. The voltage is the reference phasor (V
ref
) and the
67G Char Angle
setting is added to this to adjust
the forward and reverse zones.
The centre of the forward zone is set by (V
ref
Angle +
67G Char Angle
) and should be set to correspond with I
fault
Angle for maximum sensitivity e.g.
For fault current of -15
°
(I lagging V by 15
°
) a
67G Char Angle
of
-15
°
is required for maximum
sensitivity, OR
For fault current of -45
°
(I lagging V by 45
°
) a
67G Char Angle
of
-45
°
is required for maximum
sensitivity.
Minimum Polarising Voltage
The
67G Minimum Voltage
setting defines the minimum polarising voltage level. Where the measured polarising
voltage is below this level no directional output is given and. Operation of protection elements set as directional
will be inhibited. This prevents mal-operation under fuse failure/MCB tripped conditions where noise voltages can
be present.
Figure 3.4.1-1
Logic Diagram: Measured Directional Earth Fault Protection
Summary of Contents for Argus 7SR21
Page 1: ...Energy Management 7SR21 7SR22 Argus Overcurrent Relay Reyrolle Protection Devices ...
Page 2: ......
Page 4: ...Contents 7SR11 and 7SR12 Page 2 of 2 2018 Siemens Protection Devices Limited ...
Page 185: ...7SR210 Settings Guide Unrestricted 2018 Siemens Protection Devices Limited Page 61 of 61 ...
Page 277: ...7SR220 Settings Guide Unrestricted Page 72 of 107 2013 Siemens Protection Devices Limited ...
Page 382: ...7SR220 Technical Manual Chapter 4 Page 2 of 96 2017 Siemens Protection Devices Limited ...
Page 386: ...7SR220 Technical Manual Chapter 4 Page 6 of 96 2017 Siemens Protection Devices Limited ...
Page 398: ...7SR220 Technical Manual Chapter 4 Page 18 of 96 2017 Siemens Protection Devices Limited ...
Page 414: ...7SR220 Technical Manual Chapter 4 Page 34 of 96 2017 Siemens Protection Devices Limited ...
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