Calculations
In addition to creating analog and digital inputs, it is also possible to create a calculated input. The calculated input does not exist in the real world and is not downloaded to the FEP, rather it obtains its value from child inputs that do exist in the real world.
When creating inputs via the IED inputs Create Inputs... menu option it is possible to select between creating digital, analog or calculated inputs.
Calculation Child View
Once a calculated input has been created it is viewed in the IED's input table and has its type set to 'CALCULATED'. In addition the '+' column indicates how many child inputs are associated with the calculation. Selecting the '+' column changes the IED Input table into Child View and displays only the child inputs associated with the calculation. Note, that the child inputs are not displayed in the normal IED Input table view.
In child view a new column 'Bit' is displayed indicating which bit of the calculations value the child input is responsible for.
A child input cannot be deleted or enabled / disabled while it is associated with a calculation. In order to do this the child must first be removed from the calculation. See Calculation Dialog below.
Adding child inputs to a calculation
Child inputs can be added to a calculation by multi-selecting the calculation and the points to be added, with the following restrictions
• the inputs to be added must be digitals
• the inputs to be added cannot be linked to a device in NMS
• the inputs to be added and the calculation cannot be in the commissioned state
Adding the inputs invokes the Calculation dialog box with the new points added with default bit positions.
Modifying a Calculation
A calculation can be modified by selecting the calculation and selecting the Modify Calculation menu option. This invokes the Calculation dialog.
Calculation Dialog Box
The Calculation dialog is invoked when a calculation is modified or new points are added to the calculation. The dialog box comprises of the following sections:
• Details: The details section contains the following fields:
• Point Name: The calculation inputs point name
• Interpretation: The interpretation table associated with the input.
The fields in the details section can be modified regardless of the commissioning state of the calculated input.
• Digital Inputs: The digital inputs section contains:
• A list of child digital inputs with the following columns:
• Bit: The bit position of the calculated input value that this child will be responsible for reporting.
• Control: Whether the input is enabled or disabled.
• Commissioned: The commissioning state of the input.
• Point Name: The point name of the input.
• Protocol Specific fields: These will vary depending on the protocol of the IED.
- An Up arrow
- A Down arrow
Right clicking on an input or inputs invokes a menu option to Remove the selected inputs from the calculation. Selecting this option removes the child inputs from the calculation and automatically adjusts the bit position of all remaining inputs so that the bit position is contiguous starting from bit position 0.
Selecting the Up or Down arrows allows for the selected child inputs bit positions to be adjusted up or down.
The Remove, Up and Down options are only available if the calculated input is not commissioned.
Buttons
The Calculation dialog box contains the following buttons:
• OK: Save all changes and close the dialog box.
• Cancel: Cancel all changes and close the dialog box.
• Help...: Invoke online help for the calculation dialog box.
Enabling / Disabling a Calculation
If a calculation is enabled or disabled in the IED input table then all child inputs are also enabled or disabled.
Linking Calculations to NMS Devices
Only the calculated input can be linked to an NMS device. Child inputs shall not appear in the IED's device links view.
Commissioning a Calculation
Individual child inputs can have their commissioning state modified in the Commissioning tool but cannot be set to the Commissioned state. Only the calculated input can be set to the commissioned state by an operator.
Commissioning a calculated input automatically commissions all child inputs. Likewise decommissioning a calculation decommissions all child inputs.
The Calculated Value
The calculation derives its value from each of its child inputs. Each child supplies the value of one bit in the calculations value.
If any of the child inputs are bad quality then the calculation is also deemed to be bad quality. Likewise if one of the child inputs is jittering then the calculation is also deemed to be jittering.