Introduction; General Information; Relay External Connections; Voltage Blocking Element - Siemens 7SG11 Technical Manual

1 Introduction

There are numerous applications for the Argus 8 series of relays, which have been developed suitable for
generation, industrial, distribution and transmission systems. This application guide will illustrate some typical
examples, though actual setting guidelines or recommendations will be limited, as these are very much
.
system dependent

2 General Information

2.1 Relay External Connections

The Argus 8 relay can be configured in many different ways, which usually involve different external
connections to the relay. For phase-neutral and phase-phase connections the relay assumes nominal
63.5V and 110V systems respectively. This does not mean that the relay cannot be applied to nominal
57.7V and 100V systems. For these systems the normal operation of the relay is identical to that of the
63.5 / 110V systems.
Note, however, that if the relay is used in 57.7 / 100V systems and the communications interface is
accessing the relay's measurand data, any Class 2 measurands will be normalised to 63.5 / 110V
nominal secondary voltages.
Figures 2 through to 7 are typical application diagrams, which show ways of connecting and using the
relays in different configurations.

2.2 Voltage Blocking Element

The voltage blocking element acts as a block to the Voltage, Frequency and NPS elements in the
relay. If all phase voltages fall below the threshold level then the blocking operation will operate. This
block does not apply to the NVD elements.
The voltage blocking element performs a number of functions :
1. If the relay has been set up with undervoltage elements enabled and is switched on with no volts
applied to its inputs then, an undervoltage starter would pickup and the relay may issue a trip. The
relay would then stay locked in this trip condition until volts are applied and the element is reset.
To prevent this from happening the voltage blocking threshold has to see volts above its set level
otherwise the relay is fully blocked and no starter or trip operation will follow.
2. In auto-reclose schemes the voltage blocking threshold can be used to prevent unnecessary
operations of the undervoltage elements during the time when the line is de-energised. For this
type of blocking operation the threshold is typically set to 20% of rated volts, though it should
always be set to a value above the expected level of induced voltages on the line.
3. Where the Relay is used in Under / Over Voltage schemes the relay can discriminate between the
condition of a true system Undervoltage which exists for some time i.e. a progressive reduction in
system voltage, caused by increase in loading or due to switching or as a result of problems with
tap changers, and for which a Trip output must be given; or, the condition of an Undervoltage due
to loss of system voltage due to an upstream circuit breaker being opened which results in a rapid
voltage collapse to a much lower voltage, this voltage value being determined by coupling from
parallel lines or grading capacitors across series break contacts in Circuit Breakers, and for which
it may not be desirable for a Trip to be issued, note that resultant differential coupling voltages may
also cause the NPS Element threshold to be exceeded and the NPS element to operate. Setting
the Voltage Blocking Threshold to a setting above the expected induced dead-line voltage causes
the Undervoltage block to be raised to inhibit U/V & NPS elements to prevent unwanted Trips /
alarms from being generated.
The Voltage Blocking Threshold setting should be set either to the minimum setting of 1 volt or to a
value graded above the expected dead-line voltage.
In schemes where detection and Alarm /Trip outputs for absolute zero volts is also required the
UnderVoltage Block output ' V Block Alarm ' should be mapped to the relevant output relay(s). If a
Time delay is needed then the output relay should be connected to a Status input to make use of its
Pick-up and Drop-off time delays.
©2011 Siemens Protection Devices Limited
7SG11 Argus 8 Applications Guide
Chapter 5 Page 2 of 16