3.2 Current Distribution Planning and Operational Procedures

3.2.6 Distribution Automation (DA), Outage Reductions, and Voltage Management

Distribution automation (DA) involves providing more local automated equipment on distribution systems as well as including more centralized monitoring and control from distribution SCADA systems. DA capabilities can also include applications that can help analyze the data and suggest (or even carry out) control commands.

The primary purpose of DA is to improve power quality, including reducing the number and length of outages, maintaining appropriate voltage levels, improving efficiency, and minimizing harmonics.

Outage Management

Of these issues, probably the most important to most customers is the reduction of outages. Since most customers are connected to radial feeders (see 3.2.1) (except those on secondary networks, see 3.2.2), if any point of the circuits between the substation and the customer experiences a short circuit or other fault, that customer will experience an outage. Utilities have designed most of these radial feeders with a “normally open” tie switch to another feeder so there can be a second source of power. However, that tie switch cannot be closed unless the faulted segment of the feeder is isolated. Without distribution automation, that process of locating the faulted segment, isolating it, and then restoring power to the unfaulted segments has required field crews to “walk the line” and manually take the appropriate actions.

Fault Location, Isolation and Service Restoration (FLISR) is the automated function that can perform some or all of these manual actions. FLISR autosectionlizers and autoreclosers can be installed on each feeder segment that communicates with each other and/or with a centralized site. This FLISR equipment can detect faults, locate them to the affected segment, and then initiate pre-established switching schemes to isolate the faulted segment and to restore power to the unfaulted segments from nearby substations or feeders from the same substation – thereby isolating power outages keeping more customers with power to their homes and businesses.  Switching , that used to require 20 minutes to an hour for a crew to be dispatched to reconfigure a feeder, can be done in seconds by these intelligent line switching systems and SCADA control operations.  The interaction of these systems with DER adds to the complexity of distribution planning for the next decade and beyond.

Voltage and Var Management

Voltage and var management is managed by voltage regulators and capacitor banks respectively. To compensate for the decrease in voltage along a feeder, the voltage regulators are set at fixed levels to boost the voltage along the feeder.

Reactive power, often generated by motors and other types of equipment, causes decreased efficiency of feeders. To counteract excess reactive power, capacitor banks are strategically placed along a feeder. Typically, these capacitor banks are switched on and off based on timers, which do not always correspond to when they were actually needed. More recently, these capacitor banks are switched based on current, rather than time. With distribution automation, capacitor banks can include communications so that they can be activated from a central site as needed. 

Static var compensators (SVC), which are electrical devices for providing fast-acting reactive power, are also used to manage reactive power more effectively, in particular to solve voltage fluctuation problems. Fast and repetitive voltage fluctuations are usually caused by motor-starting or other pulsating or irregular loads such as welders. Voltage regulators or capacitor banks are not effective in controlling such fast and repetitive voltage fluctuations.

Conservation Voltage Reduction (CVR)

In some jurisdictions, conservation voltage reduction (CVR) is mandated or recommended. CVR is basically just reducing the voltage to customers (without violating the voltage limits) so that their energy usage is lower. This can benefit utilities when they want to shave peaks, and certainly benefits customers by lowering their bills, but of course does lower utility revenues if it is implemented at all times, not just during emergency peaks.