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The protection relay's outputs can be controlled either through the 0X coil objects or 4X holding register control structures. See the Modbus control objects' memory map for the available control objects.

The control objects in this protection relay are either single-point or double-point control objects.

Single point control object output types

Single point control objects can be either pulse outputs or persistent outputs.

The Modbus client should only write "1" to the pulse outputs. This write operation activates the control operation and there is no need for the Modbus client to write "0" to the object. However, writing "0" is not forbidden. The result is that nothing happens to the control object.

The Modbus client can write both "1" and "0" to the persistent outputs. Therefore, the persistent outputs have two defined levels: "0" and "1".

Most of the outputs in this protection relay are pulse outputs.

Double point control operation modes on IEC 61850 level

This protection relay supports two control models: direct-operate and select-before-operate. The IEC 61850 single point control objects in this protection relay are of direct-operate type. The IEC 61850 double point control objects can be configured either into the direct-operate or select-before-operate mode.

Note: An IEC 61850 double point output cannot support both direct-operate and select-before-operate modes at the same time.

Double point control operations on Modbus level

The double-point select-before-operate mode is usually used for the circuit breaker operations. Modbus incorporates a 30-second fixed select time-out on protocol level. Four controllable objects exist on the Modbus level.

Select open
Select close
Cancel selection
Operate (=execute) selection

Direct operate of a double-point object consists of two controllable objects.

Direct open (writing the value "1" opens the circuit breaker)
Direct close (writing the value "1" closes the circuit breaker)

Note: Direct operate of a double point object is always possible over Modbus. In addition, select-before-operate control is possible if the controllable object's control model is set to "sbo-with-enhanced-security."