SUBREL

A Computer Program for SUBstation

RELiability Evaluation


An example of SUBREL program Input/ Output & its relationship with

TRANSREL

GR SUBREL Program

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SUBREL PROGRAM OUTLINE

Input data is provided by entering information for components and network connectivity in a MS ACCESS database file. It includes the following data:

  1. Substation equipment information
  1. Substation topology (connectivity model)
  1. Automatic switching following an equipment failure event

No input is normally required because it is simulated by SUBREL, unless there is a special switching such as a Remedial Action Scheme (RAS).

  1. Manual switching following a failure event (optional)
  1. Substation equipment forced and maintenance outage data. This optional data include component outage rate, outage duration, stuck breaker/fuse probability and switching time. If it is not available to the user, SUBREL provides default values, obtained from published power industry outage statistics.

The substation equipment includes: breaker, switch, fuse, transformer, and bus-section.

  1. Outage data for incoming line (transmission, subtransmission) or distribution circuit
  1. Load data - For each load point:
  • MW
  • Number of Customers (optional)
  • Number of Distribution Circuits (optional)
  1. Load profile (optional, if not provided SUBREL assumes a constant load)

Load profile can be provided in any of the following forms:

  • Load Profile (Load values in chronological order) through the year.
  • Load Duration Curve (LDC)
  • Load values and corresponding Probability Distribution Function (PDF)
  • Load values and corresponding Cumulative Density Function (CDF)
  1. Outage cost or Performance Based Ratemaking (PBR) incentives (optional):
    (Outage cost per kW, kWhr, CMI, or distribution circuit interruptions)


SUBREL models the following outage events, including all required subsequent automatic and manual switching operations:

  1. Up to N-3 forced outages of any substation component:
  • Breaker
  • Transformer
  • Bus Section
  • Switch
  • Fuse
  1. Up to N-3 forced outage of an incoming line
  2. Up to N-3 combinations of a forced outage overlapping a maintenance outage for substation equipment or an incoming line
  3. Stuck breaker/fuse (failure to open when needed to clear the fault)
  4. Time-sequenced switching actions (automatic and manual) including load curtailing or load transfer (or load rolling) required to avoid overload of transformer, or under specified Remedial Action Scheme (RAS)

SUBREL distinguishes “primary” forced outages from “secondary” forced outages.
A primary outage is the initiating outage, for example a fault on a line or a substation component.
A secondary outage occurs as a result of the non-operation or incorrect operation of a fault interrupting device (such as a stuck breaker) or the switching actions that are taken following an outage (for example, opening a switch or a breaker to isolate the faulty section).
It can be seen that even for a small substation configuration the number of outage events considered by SUBREL is very large (several hundreds). It should also be noted that for each event SUBREL determines all required reliability indices by performing calculations based on the Markov theory.

SUBREL can be used to simulate one substation by itself. It can also simulate several substations inter-connected by lines simultaneously by considering only the outage events resulting from loss of continuity in the power flow path.
SUBREL can also be used in conjunction with transmission reliability TRANSREL program to determine the impact of substation equipment outage events on the reliability of a transmission or subtransmission system. Basically, for each substation in the system, SUBREL determines all substation equipment outage events resulting in outages of system components.

SUBREL provides four categories of results:

  1. Contingency summary
  2. Outage frequency and duration of terminating components and/or load points for each outage event
  3. Load points reliability indices
  4. Total substation or system reliability indices

The Contingency summary gives the total number of primary and secondary outages which were examined by SUBREL. It also indicates the contingencies that resulted in a total or partial loss of substation load.
When SUBREL is used in conjunction with TRANSREL the outage frequency and duration of terminating components are is used as an input to define the system outages caused by substation component outages (because the terminating components are part of the lines connecting the substations to the system).

The reliability indices for load points and for the total substation or system are the standard reliability indices as well as the CMI (Customer Minutes of Interruption) and the number of distribution circuits which are used to determine the resulting Performance Based Ratemaking (PBR) benefits or penalties. These indices are as follows:

Load Point Indices
  • Frequency of Interruption (per year)
  • Number of Distribution Circuits Interruptions (per year)
  • Outage Duration (minutes per outage)
  • Annual Total Outage Duration (minutes per year)
  • Customer Minutes of Interruption CMI (per year)
  • Expected unsupplied energy (EUE) (kWh per year)
  • Expected outage cost ($ per year)
Total Substation or System Indices
  • Frequency of Interruption (per year)
  • Number of Distribution Circuits Interruptions (per year)
  • Outage Duration (minutes per outage)
  • Annual Total Outage Duration (minutes per year)
  • Customer Minutes of Interruption CMI ( per year)
  • Expected unsupplied energy (EUE) (kWh per year)
  • Expected outage cost ($ per year)
  • Unavailability / Availability Index

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