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Prior to controlling a device, the interlock-check function is used to determine whether the
control of a device is correct or not. If the interlock-check finds that the conditions for device
control have not been satisfied in accordance with the appropriate interlock condition, control
of the device is forbidden. Figure 4.7-1 provides an overview of the interlock-check process.
Formulae for interlock-check are stored in an ILK database; these formulae are used in order
to enable the interlock-check function to output a decision. If the proposed operation of a
particular device is deemed correct then an “OK-decision” is determined by the formulae, and
device control is allowed. However, if the proposed operation of the device is deemed incorrect
then an “NG-decision” is determined by the formulae, and device control is not allowed.
Interlock Control
Function (ILK)
GOOSE receiving information
Figure 4.7-1 Interlock–check process
4.7.1 ILK specification
(i) Maximum number of interlock-checks
Since the maximum number of interlock-checks is 83, ILK can be used to supervise 83 control
devices. An interlock-check can include up to 500 nodes; an interlock operator and input/output
signals are configured for each node; a node can accept up to 64 input signals. (Nodes are
discussed separately. See section 4.7.3)
(ii) GOOSE receiving information
When an interlock-check is required to determine an “OK/NG-decision”, the interlock-check
function collects the device status from all of the other IEDs during the interlock-check process.
In this case, GOOSE subscription information is used to acquire the device status required;
configuration of the interlock-check formula, including quality information corresponding to
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