ABB REC 561 User Manual page 387

1MRK 580 151-XEN
Page 6 - 102
2 Application
Interlocking
interpreted as unknown (it may be in an intermediate position, or there
may be a control system error, such as bad contact). If both indications
stay high, then there is something wrong, and the state is again treated as
unknown. In both cases an alarm is given to the operator. In the interlock-
ing logic, the signals are used to avoid dangerous enable or release of
operation conditions. Unknown positions are not allowed to release opera-
tion.
For switches with individual operation gear per phase, the evaluation must
consider possible phase discrepancies. This is done by ANDing all three
phases of open and close state. This leads to an unknown state double
indication in case of phase discrepancies.
Because circuit breaker closing is usually not interlocked take care to
avoid energizing onto earthed parts by CB closing. So the open discon-
nectors rather than open CB are used to release the earthing switch (ES)
closing.
The interlocking function consists of software modules located in each
control terminal. The function is distributed and not dependent on any
central function. Communication between modules in different bays is
performed via the station bus.
The basic method is the use of the reservation function (see the section of
apparatus control). This method ensures that the position of the HV appa-
ratuses are not changed during the time gap, which arises between the
position updatings. This can occur by reserving all of those HV appara-
tuses by means of the communication system, which might influence the
interlocking condition of the intended operation. The reservation is
intended to remain until the operation is performed.
After the selection and reservation of an apparatus, the function has full
information on all positions of the apparatuses in the switchyard that are
affected by the selection. This status cannot be affected by other operators
because the selection is blocked for all apparatuses of which the status is
important for the selected one.
The positions of the HV apparatuses are inputs to software modules dis-
tributed in the control terminals. Each module contains the interlocking
logic for a bay. The interlocking logic in a module is different, depending
on the bay function and the switchyard arrangements, that is, double-
breaker or 1 1/2 breaker bays have different modules. Specific interlock-
ing conditions and connections between standard interlocking modules
are performed by an engineering tool. The signals involved in the bay-
level interlocking can consist of these types:
• Positions of HV apparatuses (sometimes per phase)
• Valid positions (if evaluated in the control module)
• External release (to add special conditions for release)
• Line voltage (to block operation of line earthing switch)
• Output signals to release the HV apparatus
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