I can see why you would be confused on this one...

EnergyPlus::PlantEquipmentOperationSchemes has nothing to do with OpenStudio::Model::PlantEquipmentOperationScheme

• EnergyPlus::PlantEquipmentOperationSchemes is an object where you list different Plant Equipment Scheme and schedules such as PlantEquipmentOperation:HeatingLoad and so on
• OpenStudio::Model::PlantEquipmentOperationScheme is a base class for all objects that map to Plant Equipment Scheme . If you take OpenStudio::Model::PlantEquipmentOperationCoolingLoad, its base class is OpenStudio::Model::PlantEquipmentOperationRangeBasedScheme which itself has a base class of OpenStudio::Model::PlantEquipmentOperationScheme.

EnergyPlus::PlantEquipmentOperationSchemes has not been implemented in OpenStudio as far as I can tell, meaning you currently cannot add several scheduled Plant Operation Schemes to the same plant loop.

In the above I refer to Plant Equipment Scheme as any object in this list:

PlantEquipmentOperation:ComponentSetpoint
PlantEquipmentOperation:CoolingLoad
PlantEquipmentOperation:HeatingLoad
PlantEquipmentOperation:OutdoorDewpoint
PlantEquipmentOperation:OutdoorDewpointDifference
PlantEquipmentOperation:OutdoorDryBulb
PlantEquipmentOperation:OutdoorDryBulbDifference
PlantEquipmentOperation:OutdoorRelativeHumidity
PlantEquipmentOperation:OutdoorWetBulb
PlantEquipmentOperation:OutdoorWetBulbDifference
PlantEquipmentOperation:ThermalEnergyStorage
PlantEquipmentOperation:Uncontrolled
PlantEquipmentOperation:UserDefined