Synchronising; Check Sync, System Sync; Rated Voltage Setting - V.t. Connection; Bus/Line Undervolts Settings - Siemens 7SR224 Technical Manual

4.2

Synchronising

The 7SR224 includes an optional Synchronising function which can be incorporated into the
autoreclose and manual close sequences. The device provides
synchronising function 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. Both the check and system synchronise functions have independent
settings and blocking features. Synchronising bypass logic is provided to close or block close when the circuit
breaker is dead on the line side, bus side or both.
4.2.1

Check Sync, System Sync

The function can be used as a check and system synchronising relay for applications where two power systems
are to be connected. The following examples show various ways that the relay can be enabled for different
applications.
The device will switch between check sync (CS) and system sync (SS) modes to suit system conditions. If the
requirement is for the relay to be used as a check before closing or reclosing a normal distribution network, then
system sync consideration is not required:
Set MC Split Mode to CS
Set DAR Split Mode to CS
This specifies that when a system split is detected during a MC or DAR operation, the CS mode will be retained
and the split detection ignored.
If the possibility of a system split is applicable but the network should not be reclosed by DAR in these
circumstances then:
Set DAR Split Mode to LO (Lockout)
If the independent System Sync settings are to be used following a Split detection during DAR, then:
Set DAR Split Mode to SS
The reaction to a split detection during a Manual Close operation can be specified separately:
Set MC Split Mode to SS
Similarly, the device can be set to use Close On Zero (COZ) for either or both modes following a split detection.
4.2.2 Rated Voltage Setting – V.T. Connection
The Vx analogue voltage input is used for the synchronising Bus voltage and can be either Van, Vbn, Vcn, Vab,
Vbc or Vca. The voltage is compared to the respective Line voltage connected to the V1-V3 analogue voltage
inputs.
V.T. ratings for secondary connections are normally either 100V or 110V for phase-phase, with the associated
phase-neutral ratings being 57.7V and 63.5V respectively. For phase-neutral connections the Vx Nom Voltage
setting in the CT/VT Config menu should be set to 63.5V. For phase-phase connections the Rated Voltage setting
should be set to 110V etc. Voltage element settings are a percentage of this setting..
4.2.3

Bus/Line Undervolts Settings

The relay undervoltage blocking elements, if enabled, can be used to block the close operation if either the line
(incoming) or bus (running) voltages fall below a certain percentage of rated voltage. Typically, the undervoltage
elements are set between 80% and 90% of rating.
Note : when using the undervoltage elements care should be taken to ensure that the reset of the element occurs
at below the expected minimum normal operating voltage of the system. The undervoltage elements reset at
<103% of the operate level. If the system is expected to run at less than the rated voltage, the undervoltage
element reset level must be set to operate at a value below this plus a discrimination margin.
e.g. - for a phase to neutral connection nominally at 63.5 Vrms but which can run as low as 59 Vrms,
the undervoltage setting should be set no higher than 59 V – 1 V (margin) = 58V / 103% = 56.31V (the actual
setting would have to be 56.5V). This is equivalent to approximately 89% of rated voltage. If the setting is set
higher than this then the element may never reset and will continuously block.
©2010 Siemens Protection Devices Limited
7SR224 Argus Applications
a combined check and system
Chapter 7 Page 32 of 50