DPM Change Request1

1.Change Summary

Following the September 8, 2011 Southwest outage, TSS formed the Modeling SPS and Relay Ad-Hoc Task Force. The task force made recommendations to begin transitioning the planning model from bus-branch to node-breaker representation. One characteristic of the node-breaker representation is the ability to characterize modeling objects connecting two nodes as breakers, switches, zero impedance branches, etc. This DPM change request is intended to provide flexibility to data submitters with the ability to properly characterize branches between nodes.

2.Schedule

Incorporate language into DPM: May 2017 for inclusion in 2018 DPM

Adherence to revised DPM language: Same as 2018 DPM

3.Detailed Description

The existing language in the DPM does not provide a method for representing objects connecting two buses other than transformers and transmission lines. Adding the language to define how breakers, switches and similar devices can be represented will aid in ability to more accurately represent some bus configurations and help the transition to node-breaker representation. The proposed change is intended to have objects classified as breakers, switches, and other negligible impedance devices included in the model. Depending on the software used, these objects could be defined in a specific table or an additional field within an existing table can identify the object type.

The typical study methodologies used by transmission planners relies on the simplification of substation topologies to single buses or multiple single buses connected by transmission lines with small impedances. PSLF, PSSE and PowerWorld are at various stages in their capability to explicitly represent breakers and similar devices. SRWG should consider defining a process to create interconnection-wide models with hybrid node-breaker representation and consolidating the model to bus-branch. Both a consolidated and non-consolidated version of each case could be posted.

Benefits

The following benefits are intended by completing the proposed DPM change request:

  • Objects in the interconnection wide model can be properly classified as the type of elements they are representing.
  • Data submitters begin the understanding and ability to represent their system in a node-breaker representation.
  • The efforts of the MSRATF can be put to use.
  • Transitioning to a node-breaker representation will allow for easier identification of appropriate contingency actions during bus and breaker related contingencies.

Cost

The following “costs” may be incurred by completing the proposed DPM change request:

  • None identified.

Alternatives

Maintaining the existing language in the DPM will provide no progress to improving the interconnection-wide model.

4.Proposed Edits

The following modifications to the presently approved DPM are proposed to implement the change being requested. Existing language is identified in teal and changed language in red:

AC Transmission Lines

  1. When bus ties are necessaryexplicitly represented in the model, they shall be modeled as Branches with the Branch Type field set to Breaker. the impedance should be R = 0.0 pu and X = 0.00029 pu, or less. No value of charging (G or B) is allowed on lines having less than the jumper threshold impedance. Do not make a closed loop (ring-bus representation) with ties that are less than the threshold impedance. In addition, do not use bus ties to connect different areas.
  2. AC transmission lines modeled with impedance below X = 0.00029 pu (the default threshold impedance in PSLF) shall not be used to represent a closed loop (ring bus representation.)

Branches

  1. For the purpose of this DPM, branches should be considered as objects other than transmission lines and transformers connecting two buses.

Table X: Data Requirements (Branches)

Field / Description / Requirements / Measure
FROM Bus Number / Number of the bus to which the FROM end of the branch is attached.
  • See “Data Requirements (Buses)”

TO Bus Number / Number of the bus to which the TO end of the branch is attached.
  • See “Data Requirements (Buses)”

ID / Branch identifier
  • Two-character branch identifier

Status / Branch status
  • 0 = out-of-service
  • 1 = in-service
  • 2 = bypass
/ B1. Branch shall have the anticipated status of the line in the case.
Branch Type / Branch device type
  • Breaker
  • Load break disconnect
  • Disconnect
  • ZBR
  • Fuse
  • Ground disconnect
  • Series capacitor
  • Series reactor

Allow Consolidation / Flag for allowing topology processing to consolidate the branch within a “superbus”
  • YES
  • NO

6.Examples

In the below screen shot a transmission line with low impedance is used to represent a tie breaker between two buses in the same station. The proposed DPM change should allow for changing the device type of the object to be a Breaker as highlighted below.

Below is example of implementing the proposed DPM change request in PSLF using the Breaker table.

Western Electricity Coordinating Council