Ramp Down Rate Column
Column Type = Text
The optional Ramp Down Rate column is used to ensure that a unit cannot decrease its output by more than the input ramp down amount. The value is expressed as a percent (%), which is divided by 100 and multiplied by the resource capacity to determine the decrease in resource capability available in the next hour. If the cell contains zero or NULL, then no ramp down rate is applied. A unit will always be allowed to turn off in one hour once it has reached the Minimum Capacity regardless of this value.
Example:
For a plant with a capacity of 50 MW and a Ramp Down Rate of 20%:
(20/100) * 50 = 10 MW allowed decrease in the resource capability available in the next hour.
Typically, the ramp rate logic will be effective when the project file is set to dispatch for all hours of the study. Some hourly sampling is allowed as long as all days are included in the study, in which case the ramp rates will automatically be converted to match the sampling level. For example, when sampling Every Day, Every 2nd Hour a resource with a ramp down rate of 20% per hour would ramp down its generation 40% between dispatch hours. One exception is when running sub-hourly, ramp rates will only be applied when running all hours.
The capability will also look ahead to future outages and derates (via MST, Daily Change table, Forced Outage, Maintenance Outage, and Maint Begin/End) to see if the resource needs to start decreasing its output in order to honor both the outage/derate and the ramp down constraint. For example, if a resource will be on outage on Feb 1st Hr 1, and the ramp down rate is 25%, then the unit will not be able to output at more than 25% on Jan 31st Hr 24, 50% on Jan 31st Hr 23, etc.
If the resource has a Minimum Capacity then as it approaches the min output level the ramp down percent decrease may be ignored in the step getting to the min. In essence, capability will equal the Minimum Capacity for one hour and then go to zero in the next hour.
NOTE: Ramp rates are effective only if the Use ramp rates switch is selected (located in the Resource folder of Simulation Options).
NOTE: When using ramp rates with the nodal capability, the current hour’s constraints (maximum resource capability) will be based on the previous hour’s nodal output for each zonal resource that is mapped to one or more nodal generators.
NOTE: Inputs can be specified for any time period (annual, monthly, weekly, hourly or sub-hourly). For information on how to specify a time series for a variable, see Entering a Time Series.
Ramp Down Rate Column