Siemens 7SR157 Argus, Manual

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Chapter 7 - 7SR157 Applications Guide
© 2016 Siemens Protection Devices Limited Chapter 7 - Page 3 of 14
Section 1: Introduction
The 7SR157 is a combined check and system synchronising relay which can automatically select check or system
synchronise, as appropriate, from measurements of the relative phase angles between the line and bus voltages.
The relay will prevent closure of the circuit breaker if the phase angle, slip frequency or the voltage magnitudes of
the incoming and running voltages fall outside prescribed limits.
If these calculated quantities are within the relays’ setting limits the relay will issue an output which can be used to
close the circuit breaker directly or in conjunction with an autoreclose scheme. Both the check and system
synchronise functions have independent settings and blocking features. The relay also includes split system
detection with a variable time delay, which can be used for blocking purposes within delayed autoreclose (DAR)
schemes.
Synchronising bypass logic is provided to connect a dead line or bus to a live line or bus. For manual
synchronising the relay includes a circuit breaker close guard feature which is used to alarm if the control switch is
being held closed during a synchronising operation. This feature is implemented using internal logic and removes
the need for an external guard relay.