Transformer Control: Time Step Options

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Transformer Time Step Options are found on the Time Step Options tab of the Transformer Control Info dialog (this dialog is different based on the automatic control types of Voltage Regulation (AVR), Reactive Power Control, and Phase Shift Control).  These options can be modified if the transformer is on some sort of 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 transformer is considered in violation of its regulation range and the time when the transformer tap settings are actually changed in an attempt to bring the transformer 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 transformer 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 Time Delays topic.

 

The following options are available for specifying transformer time delays:

Model Tap Delay in Time Step Simulation

Check this box to use the time delay during a time step simulation. If this option it checked, the transformer is on automatic control (transformer must allow automatic control at the device, area, and global level), and a time step simulation is processing, the transformer tap (phase angle if a phase shifter) setting will only be allowed to move if the transformer is violating its regulation range for the specified period of time. During a power flow solution outside of the time step simulation, the transformer 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 transformer 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, transformer tap 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 Minimum and Maximum values specified on the Common Options tab of the Transformer Control Info dialog are used to define the primary regulation range when modeling a tap delay.

At each time step, the regulated value of the transformer 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 transformer has been outside its regulation range for the specified amount of time and is now allowed to start moving tap positions to bring the regulated value back in range. Once the transformer is allowed to move tap positions, 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 transformer has been outside of its regulation range for the specified period of time and is actually allowed to change tap positions (phase angle if a phase shifter), 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 transformer 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 transformer is allowed to change tap positions (phase angle if a phase shifter) 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 transformer has not started to change tap positions. Once the transformer has started to change tap positions, but the regulated value still remains outside its regulation range on the same side of the range and needs to continue changing tap positions, 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 transformer is allowed to change tap positions (phase angle if a phase shifter) 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 transformer has started to change tap positions but the regulated value remains outside of the regulation range on the same side of the range and needs to continue changing tap positions. 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 transformer. The secondary range can only be used if the primary range is also used (i.e. Model Tap 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 tap changes to increase the regulated value while another range would require tap 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 transformer is allowed to change tap positions, 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 transformer is allowed to change tap positions, the timers for both the primary and secondary regulation ranges will be reset. Once the transformer has started to move tap positions 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 transformer has been outside of its secondary regulation range for the specified period of time and is actually allowed to change tap positions (phase angle if a phase shifter), 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 transformer 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.).