See Also
Switched Shunt Time Step Options are found on the Time Step Options subtab of the Control Options tab of the Switched Shunt Information dialog in either Edit mode or Run mode. These options can be modified if the switched shunt is on either discrete or continuous automatic control. The options are only used as part of the Time Step Simulation tool.
These options allow the specification of time delays between the time when a switched shunt is considered in violation of its regulation range and the time when the switched shunt nominal Mvar is changed by stepping through Mvar blocks in an attempt to bring the switched shunt back within its regulation range. Because time delays are involved, it is only possible in Simulator to use this type of control during a Time Step Simulation when there is an accounting of system changes over time.
The options described below dictate how an individual switched shunt using time delays will be evaluated during a time step simulation. For a description of the overall process of how switching time delays and time delay actions are applied during a time step simulation run, see the Time Step Simulation: Application of Controller Time Delays topic.
The following options are available for specifying switched shunt time delays:
Model Switching Delay in Time Step Simulation
Check this box to use the time delay during a time step simulation AND indicate that this switched shunt should be on control during the time step simulation. Simulator only allows one switched shunt at a given bus to be on automatic control. During the time step simulation, multiple shunts are allowed to be on control, but some special handling must be done for this to happen. For a switched shunt to be on control during the time step simulation, at least one switched shunt at its bus must have its Control Mode set to Discrete or Continuousand that switched shunt must also have its Model Switching Delay in Time Step Simulation option checked. All of the other switched shunts must have their Control Mode set to Fixed. Fixed switched shunts that also have their Model Switching Delay in Time Step Simulation option checked will be on control during the time step simulation. The control mode for the switched shunt that is not fixed will dictate the control mode for all of the fixed switched shunts during the time step simulation. If a switched shunt is allowed to be on control during the time step simulation and a time step simulation is processing, the switched shunt nominal Mvar setting will only be allowed to change (step through Mvar blocks) if the switched shunt is violating its regulation range for the specified period of time. During a power flow solution outside of the time step simulation, the switched shunt will operate in the usual manner based on all relevant control settings without implementing any time delay in the switching.
When this box is not checked, the switched shunt will operate in the usual manner based on all relevant control settings without implementing any time delay in the switching during the time step simulation and any power flow solutions outside of the time step simulation.
During the time step simulation, switched shunt switching delays will only be implemented if doing a complete time step simulation run. A complete run is one that is started using the Do Run button on the Time Step Simulation dialog and is allowed to run to completion without running any time steps out of order or repeating time steps.
The Regulation Low Value and High Value specified on the Parameters tab of the Switched Shunt Information dialog are used to define the primary regulation range when modeling a switching delay.
At each time step, the regulated value of the switched shunt will be checked to determine if it falls outside of the regulation range. If so, a timer will be started to determine how long the value is outside of the regulation range. If the timer has already been started and the regulated value is still outside and on the same side of the regulation range, the appropriate time delay, as described below, will be used to determine if the switched shunt has been outside its regulation range for the specified amount of time and is now allowed to start stepping through Mvar blocks to bring the regulated value back in range. Once the switched shunt is allowed to start switching, the timer will be reset and the appropriate time delay will be used to determine when the next move can occur if the regulated value continues to remain outside the regulation range and on the same side of the range. Once the regulated value falls inside the regulation range or the regulated value switches sides of the regulation range, the timer will be reset.
Maximum Steps to Move
Once a switched shunt has been outside of its regulation range for the specified period of time and is actually allowed to switch, this is the maximum amount of steps that it is allowed to move at the current time step even if additional steps would be required to bring the switched shunt back within its regulation range.
First Move Delay (Below and Above) (secs.)
These two options specify the amount of time to wait in seconds before the switched shunt is allowed to switch if its regulated value falls outside of the regulation range. These values must be specified in whole seconds with the minimum delay being 1. These delays are used when the regulated value first falls outside its regulation range and the switched shunt has not started to switch. Once the switched shunt has started to switch, but the regulated value still remains outside its regulation range on the same side of the range and needs to continue stepping through Mvar blocks, the Next Move Delays will be used. Once the regulated value falls inside the regulation range or the regulated value switches sides of the range (i.e. it was below the range and is now above), the First Move Delays will be used if the regulated value again falls outside the regulation range.
The Below entry specifies the delay to use when the regulated value is below the regulation range. The Above entry specifies the delay to use when the regulated value is above the regulation range.
Next Move Delay (Below and Above) (secs.)
These two options specify the amount of time to wait in seconds before the switched shunt is allowed to switch if its regulated value falls outside of the regulation range. These values must be specified in whole seconds with the minimum delay being 1. These delays are used once the switched shunt has started to switch but the regulated value remains outside of the regulation range on the same side of the range and needs to continue stepping through Mvar blocks. The Next Move Delay will continue to be used for subsequent delays as long as the regulated value remains outside of and on the same side of the regulation range. Once the regulated value falls inside the regulation range or the regulated value switches sides of the range, the First Move Delays will be used if the regulated value again falls outside of the regulation range.
The Below entry specifies the delay to use when the regulated value is below the regulation range. The Above entry specifies the delay to use when the regulated value is above the regulation range.
Use Secondary Regulation Range
Check this box to specify a secondary regulation range that is different than the primary range specified with the switched shunt. The secondary range can only be used if the primary range is also used (i.e. Model Switching Delay in Time Step Simulation is checked). The expectation is that this range will be larger and the delays would be shorter to model the fact that the controls will act more quickly to a very large deviation.
To properly define the regulation ranges, one of the ranges must be completely contained within the other range. This is necessary to prevent conflicting control actions in which one range would require nominal Mvar changes to increase the regulated value while another range would require nominal Mvar changes to decrease the regulated value.
The secondary regulation range works somewhat independently of the primary regulation range. At each time step, the secondary regulation range is checked first. If the regulated value falls outside of the secondary regulation range, a timer is started for the secondary regulation range. If the timer for the secondary regulation range has already been started, the regulated value is still outside of the secondary regulation range and on the same side of the range, and the appropriate secondary time delay is met such that the switched shunt is allowed to switch, the timers for both the primary and secondary regulation ranges are reset and whether or not the primary regulation range is violated is not checked at that time step. If the secondary regulation range timer has not exceeded the appropriate time delay or the regulated value is within the secondary regulation range, the primary regulation range is checked to see if the regulated value is outside of that range. If the regulated value falls outside of the primary regulation range, a timer is started for the primary regulation range. If the timer for the primary regulation range has already been started, the regulated value is still outside of the primary regulation range and on the same side of the range, and the appropriate primary time delay is met such that the switched shunt is allowed to switch, the timers for both the primary and secondary regulation ranges will be reset. Once the switched shunt has started stepping through Mvar blocks for either of the regulation ranges and continues to remain outside one or both regulation ranges and on the same side of the appropriate range, the Next Move Delay, appropriate for the given range, will be used by both ranges to determine when the next move can occur.
Secondary Minimum and Secondary Maximum
Use these fields to specify the secondary regulation range.
Secondary Max Steps to Move
Once a switched shunt has been outside of its secondary regulation range for the specified period of time and is actually allowed to switch, this is the maximum amount of steps that it is allowed to move at the current time step even if additional steps would be required to bring the switched shunt back within its secondary regulation range.
Sec. First Move Delay (Below and Above) (secs.)
When using the secondary regulation range, define the time delays in the same manner as described above for the primary regulation range in First Move Delay (Below and Above) (secs.).
Sec. Next Move Delay (Below and Above) (secs.)
When using the secondary regulation range, define the time delays in the same manner as described above for the primary regulation range in Next Move Delay (Below and Above) (secs.).
Processing Switched Shunts
At each time step, all switched shunts that are allowed to be on control during the time step simulation are processed to determine if their regulated values are outside of their regulation range. If they are and the time delay has been met such that the switched shunt is allowed to switch in an attempt to bring the regulated value back inside the regulation range, that switched shunt is marked for further processing. The options specified above determine the outcome of this initial check.
Further processing marches through the list of switched shunts that are allowed to switch one-by-one. They are processed in the order of ascending bus number with only one switched shunt at a bus allowed to be on control at a time. If there are multiple switched shunts at a bus that are allowed to be on control during the time step simulation, these are processed one-by-one in iterative steps. For each iteration of this process, the one switched shunt at each bus that is allowed to be on control will be checked to determine if its regulated value is still outside of its regulation range and adjust its Mvar injection if necessary. If any adjustments are made, an estimate is made of any impact on system voltages and the voltages are updated before the next switched shunt in the list is processed. In this way, an estimate is made of the impact that one switched shunt adjustment has on the others. This process is repeated with only one switched shunt at a given bus allowed to be on control at a time until all switched shunts that are allowed to be on control during the time step simulation have been processed.
As an example, assume that at a given time step there are 6 switched shunts with regulated values outside of their regulation ranges and the necessary time delays have passed so that an attempt needs to be made to adjust these switched shunts to bring the regulated values back in range. Shunt A is at bus 1, shunts B and C are at bus 2, and Shunts D, E, and F are at bus 3. All shunts that are not being processed because of their time delay being met are set to be on fixed control. Shunts A, B, and D are set to their specified control mode while shunts C, E, and F are set to fixed. The shunts on control are then processed in the manner described above that determines the shunt adjustments and estimates new voltages. Shunts C, E, and F still have not been processed. Shunts A, B, and D are set to fixed with shunts C and E being set to their specified control modes. These shunts are then processed in the order of ascending bus number as described above. At the next iteration, all of the shunts are fixed except shunt F. This process will continue with only a single shunt at a given bus on control until all shunts that have met their time delay have been processed.