ABB Relion 670 Series Applications Manual page 323

1MRK 505 370-UUS Rev. K
• To avoid the dangerous or damaging operation of switchgear
• To enforce restrictions on the operation of the substation for other reasons for example, load
configuration. Examples of the latter are to limit the number of parallel transformers to a maximum of
two or to ensure that energizing is always from one side, for example, the high voltage side of a
transformer.
This section only deals with the first point, and only with restrictions caused by switching devices other
than the one to be controlled. This means that switch interlock, because of device alarms, is not included
in this section.
Disconnectors and grounding switches have a limited switching capacity. Disconnectors may therefore
only operate:
• With basically zero current. The circuit is open on one side and has a small extension. The
capacitive current is small (for example, < 5A) and power transformers with inrush current are not
allowed.
• To connect or disconnect a parallel circuit carrying load current. The switching voltage across the
open contacts is thus virtually zero, thanks to the parallel circuit (for example, < 1% of rated voltage).
Paralleling of power transformers is not allowed.
Grounding switches are allowed to connect and disconnect grounding of isolated points. Due to
capacitive or inductive coupling there may be some voltage (for example < 40% of rated voltage) before
grounding and some current (for example < 100A) after grounding of a line.
Circuit breakers are usually not interlocked. Closing is only interlocked against running disconnectors in
the same bay, and the bus-coupler opening is interlocked during a busbar transfer.
The positions of all switching devices in a bay and from some other bays determine the conditions for
operational interlocking. Conditions from other stations are usually not available. Therefore, a line
grounding switch is usually not fully interlocked. The operator must be convinced that the line is not
energized from the other side before closing the grounding switch. As an option, a voltage indication can
be used for interlocking. Take care to avoid a dangerous enable condition at the loss of a VT secondary
voltage, for example, because of a blown fuse.
The switch positions used by the operational interlocking logic are obtained from auxiliary contacts or
position sensors. For each end position (open or closed) a true indication is needed - thus forming a
double indication. The apparatus control function continuously checks its consistency. If neither condition
is high (1 or TRUE), the switch may be in an intermediate position, for example, moving. This dynamic
state may continue for some time, which in the case of disconnectors may be up to 10 seconds. Should
both indications stay low for a longer period, the position indication will be interpreted as unknown. If both
indications stay high, something is wrong, and the state is again treated as unknown.
In both cases an alarm is sent to the operator. Indications from position sensors shall be self-checked
and system faults indicated by a fault signal. In the interlocking logic, the signals are used to avoid
dangerous enable or release conditions. When the switching state of a switching device cannot be
determined operation is not permitted.
For switches with an individual operation gear per phase, the evaluation must consider possible phase
discrepancies. This is done with the aid of an AND-function for all three phases in each apparatus for
both open and close indications. Phase discrepancies will result in an unknown double indication state.
12.4.1 Configuration guidelines
The following sections describe how the interlocking for a certain switchgear configuration can be
realized in the IED by using standard interlocking modules and their interconnections. They also describe
Busbar protection REB670
Application manual
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Section 12
Control
M13529-4 v4
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