Integrated Topology Processing: Full-Topology Model

See Also

 

Real-time applications require modeling the power network at a level of detail that includes all the switching devices such as circuit breakers and disconnects and other very low-impedance branch devices. For instance, an operator must have information about specific breaker statuses to coordinate device maintenance procedures.

These detailed models are referred to as “node-breaker” or “full-topology” models. This type of model cannot be solved directly in conventional planning applications because of the large number of very low-impedance branches resulting from the switching devices. The power flow would be forced to use an Ill-Conditioned Jacobian matrix if these low-impedances were directly modeled. In order to solve the power flow on a full-topology model, Simulator dynamically obtains a Consolidated Representation of the power network by dynamically moving the device connection pointers.

 

Simulator models all type of branch objects as transmission line records. To aid in the consolidation, additional input parameters are necessary to properly identify the type of branch object that is being modeled and determine whether or not that branch can be eliminated during consolidation. These fields are accessible from the Topology group in the Available Fields for the Line and Transformer Display in the Model Explorer. Two relevant input fields needed for Topology Processing are:

Branch Device Type

Type of branch specified can be specified as in the table below

	Transformer	A 2-winding transformer (user can not change)
	TransformerWinding	Part of a 3-winding transformer (user can not change)
	SeriesCap	Either a series capacitor or a series reactor
	Line	Transmission line
	ZBR	Zero-impedance branch. Represents a branch with negligible impedance that is not a switching device. Examples include (1) Wires that connect bus segments in different parts of the same substation, (2) Wires that connect 2 substations across the street from one another, possible owned by different companies, (3) A short transmission segment connecting a hydro generation substation another substation at the top of the hill
	Breaker	Circuit breaker is a switching device that can be opened during a fault condition with very high current. (these are used in special algorithms in Simulator)
	Load Break Disconnect	A special disconnect that can be opened under load, but not during a fault. They are very common for switching in and out capacitor or reactor banks (these are used in special algorithms in Simulator)
	Disconnect	Disconnect can be opened but not while current is flowing. They are often placed around Breakers. After a breaker is opened, these are opened to completely isolate the breaker so maintenance can safely be done. (these are used in special algorithms in Simulator)
	Fuse	Added to support the IEEE CIM definition. Have not seen it used much
	Ground Disconnect	Some EMS models include Disconnects that connect to radial buses with nothing attached and these radial buses represent ground. These disconnects are then normally open. They are used in an EMS environment to show visualizations of ground disconnects. This is not important for numerical simulations, but very important for the safety of those operating the system.

Allow Consolidation of Branch

This is a YES or NO field, which tells Simulator to eliminate closed switching devices and other very low-impedance branches from the network model during consolidation. Only branches that have a Branch Device Type equal to Breaker, Load Break Disconnect, Disconnect, ZBR, Fuse, or Ground Disconnect can be consolidated. If an element is of this type and is set not to be consolidated, it will be preserved in the model and its default impedance value will be used in the power flow equations. In the context of consolidation, the term breakeror switching device can be used to include any of the device types that can be consolidated.

There are other instances in which a branch that is marked as allowed to be consolidated will not be consolidated:

• Branches that are area tie lines
• Branches that are connected to a multi-terminal dc line converter
• Branches that are part of a Model Condition
• Branches that are part of a Model Expression
• Branches that are part of a Post Power Flow Solution action
• Branches that are part of Transient Stability event
• Branches that are part of a contingency action if not using Incremental Topology Processing
• Branches that are part of an interface unless the branch is in series with a device that cannot be consolidated, e.g. transformer, line, load, generator, etc. The interface will be automatically modified to monitor the series device instead of the branch so that the branch can be consolidated.

 

Simulator models all of the system connection points: Busbars, Junctions, Terminals, etc. as buses.

Topology Bus Type

Type of connection point. Valid entries include BusbarSection, Junction, Internal_3WND, Ground.

 

Topology Processing provides an optional input field for buses to aid in the consolidation:

Node Priority

Priority level of the bus to become a primary bus. This overrides the default Primary Bus Priority Scheme level for this bus.

 

Topology Processing determines two bus fields as part of the consolidation:

Primary Node

Bus to which all the device connection pointers in a Superbus will point to during Consolidation.

Node Neighbor List

If this is a Primary Bus, this contains a list of all buses that belong to the superbus in which this bus is contained. This entry is blank for buses that are not primary buses.

These four bus fields are available under the Topology group in the Available Fields for the Bus Display found on the Model Explorer.