ABB Relion 620 Series Protocol Manual page 38

Section 3
Vendor-specific implementation
32
The control objects in this IED 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 IED are pulse outputs.
Double point control operation modes on IEC 61850 level
This IED supports two control models: direct-operate and select-before-operate. The
IEC 61850 single point control objects in this IED 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.
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)
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."
1MRS757645 B
620 series
Communication Protocol Manual