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4.
If all of the phase voltages fall below 29V. This is independent of the voltage blocking threshold and
is required to ensure that the frequency accuracy claims are within ±10mHz. (Below 29V the
frequency accuracy deteriorates marginally).
Figure 4 shows the basic operation of the frequency elements. The 'event' and 'instrument' labels in the diagram
indicate where this type of information is generated.
F Element
Pickup Value
(VA & VB & VC)
☯
V Block Threshold
Status Input
V Element Inhibit
(VA & VB & VC)
☯
29Vrms
The frequency calculation is performed on data from one input phase only. If all phase voltages are above an
internal threshold of 29V, then the frequency calculation will be derived from the phase A input. If however, phase
A falls below 29V, then the calculation will automatically switch to phase B data. During the switchover process
the last frequency value measured is held until phase B returns a valid frequency answer. This will take
approximately 180ms. The switchover precedence is A-B-C and as each phase recovers its voltage then the
frequency calculation is switched back to this phase. This method ensures that the frequency calculation is
performed on a solid system voltage and not on low levels of input voltage where noise could cause incorrect
calculation.
3.6
Two Systems Connection
Two pole Argus 8 variants have a '2 Systems A/B' connection setting. This setting re-configures the relay to
become a 4 element voltage relay but with the ability to assign the voltage elements to two different systems.
System A has voltage elements VE1 and VE2 assigned to it and System B has VE3 and VE4 assigned to it.
The System A input voltage is applied at the Va / Vab input terminals. System B is applied at the Vo / Vbc input
terminals.
3.7
External Tripping
Any status input can be programmed to receive a trip signal from another device. The status input should firstly be
mapped to the trip output contact in the Output Configuration Menu, so that energisation of the status input results
in a trip signal being issued. If the same trip contact is specified in the 'Fault trigger' setting then the relay will
switch to the fault data mode and indicate that an external trip has occurred.
4
Other Features
4.1 Metering
The Argus metering feature provides real-time data available from the relay fascia in the 'Instruments Mode' or via
the communications interface. The following displays are available :
•
Primary RMS volts for VA, VB, VC and VO (alternatively VAB, VBC, VCA)
•
Secondary RMS volts for Va, Vb, Vc, V1, V2 and Vo (alternatively Vab, Vbc, Vca)
©2011 Siemens Protection Devices Limited
Event
Instrument
Event
(F Element Inhibit)
Block
1
Figure 4 - Frequency Element
7SG11 Argus 8 Description of Operation
Frequency
DTL
&
Element
Starter
Event
Instrument
Trip
Event
Instrument
Chapter 1 Page 10 of 20
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