Reliability Analysis

Reliability Analysis may be used on radial circuits to predict reliability impacts resulting from circuit modifications or from the addition of distributed resource generation.

Application Overview:

• See Reliability Analysis Setup for details on user input options for this application.

• For general details on running an application, selecting and displaying output variables, see Running DEW Applications.  

• The Available Output Variables for the application are described in the last section of this topic.

Reliability Analysis incorporates a simplified restoration process to predict performance of applicable distribution system, considering customer service priorities, switch operation times, equipment overloads, and system operating limits.  

• Reliability involves calculating indices associated with customer downtime and restoration time.

• Reliability analysis requires failure rate inputs.

• The (optionally available) restoration process restores power to the next highest priority interrupted segment in the least possible time.

• The restoration analysis requires knowledge (i.e. historical database) of load priorities and repair times of failed components.

• Network topology data provides switch or protective device status, failed components, and available alternative feeds that are energized.

• If multiple alternative feeds are available, then one that can be switched the quickest (without a constraint violation) will be used.
   

Application Run / Results:

Reliability Analysis evaluates key industry standard indices by circuit and at system level to indicate overall reliability performance.

• SAIDI (System Average Interruption Duration Index) is the average outage duration for each customer, calculated as:

• (sum of all customer interruption durations) / (total number of customers served)
   

• CAIDI (Customer Average Interruption Duration Index) is the average outage duration that any given customer would experience, or the average restoration time, which is calculated as:

• (sum of all customer interruption durations) / (total number of customer interruptions)
   

Reliability also evaluates performance in terms of circuit segments, where a segment is a group of components whose entry component is a switch or a protective device and each segment contains only one such switch or protective device, referred to as the segment device.

• If any component in segment has suffered a power loss, then all segment components have lost power.

• Load priority of segment is set equal to highest priority load in segment.

• Repair time of segment is a weighted average of the repair times of segment's components.

• Segment is considered failed if it contains a failed component.

Segment performance is evaluated by a new characteristic index for reliability, Relative-CAIDI, which summarizes the performance for a defined segment relative to that of the circuit.  

• CAIDI-Rel (Relative Customer Average Interruption Duration Index) is the ratio of average outage duration for a given circuit relative to that of an applicable segment, which is calculated as:

• CAIDIckt / CAIDIj

• Relative CAIDI can be used to quickly assess those segments of circuit where reliability improvements are most needed, as values decrease below one indicate worsening reliability performance. Average segment performance is found at values around one and better performing segments are indicated as values exceed one.  
   

Available Output Variables:

For general details on running an application, selecting and displaying output variables, see Running DEW Applications.  The output variables available for display from the application are described in the following table.

For this application, the Reliability Analysis Report is generally the best way to review output for a system run, as it conveniently displays summary of the key reliability indices at system and circuit levels.  

If the user prefers to review output graphically on the drawing, i.e. for a picked component run or to review characteristic reliability/restoration parameters, the following application variables are available for display: