For decades, the 15-25kV pad mounted air insulated distribution switchgear has been the prominent switchgear technology used by utilities. The design is widely accepted because of its initial low cost and small environmental impact as compared to oil and gas insulated switchgear. However, the industry is evolving, and power distribution planning strategies are looking beyond “low-cost” solutions and focusing more attention on reliability, safety, operation and maintenance costs, and automation capabilities.
Up Front Analysis Pays Dividends
Life cycle cost (LCC) analyses are becoming a more common tool for utility stakeholders and procurement managers when acquiring a new asset or retrofitting/refurbishing existing assets. LCC assumes that multiple solutions can meet project requirements and achieve acceptable performance, and that these solutions have differing costs, maintenance and operation requirements, and useful life cycles. Using an LCC analysis not only considers initial cost of an asset (acquisition and installation cost), but also factors in long-term costs tied to maintenance, renewal cost, re-tooling, repair, and failure.
Evaluating LCC of distribution switchgear will allow a deeper analysis that may discard solutions with low upfront costs, but high operation and renewal costs related to maintenance, repairs, and a higher failure rate due to adverse conditions.
Cost of Acquisition – Read the Fine Print
When considering the cost of acquisition, remember the total cost will include the purchase price as well as installation, training and re-tooling costs. In the case of solid dielectric switchgear as a replacement for existing air insulated switchgear, it’s critical to ensure design flexibility that minimizes any re-work or added installation costs that may cause the switchgear solution under consideration to be discarded. Certain switchgear configurations available are designed with this in mind. Multi-way configurations provide a high degree of design flexibility and they are ideal for drop-in replacement of legacy air, SF6, and oil insulated switchgear designs.
Do Your Homework on the Cost of Operation
The cost of operation input requires the gathering of data from in-service operation and maintenance practices, sensitivity to service interruptions, and the penalties and/or losses incurred for service interruptions. Well-thought-out maintenance plans can be compromised due to economic factors, natural disasters, and attrition of the workforce.
For example, a “run-to-fail” maintenance strategy can be a viable option, only if direct replacement units are on-hand and/or redundancy is present in the system, limiting the number of customers affected by equipment failure. But, when required and suggested maintenance practices are not adhered to, the probability of failure increases over the life of the switchgear asset.
From a scheduled maintenance perspective, dead-front solid dielectric switchgear offers many advantages over traditional air insulated switchgear such as the use of environmentally-friendly epoxy encapsulation that is maintenance free over its lifetime. In addition, live-front air insulated switchgear is susceptible to failures by flooding, animal ingress, moisture build-up, and debris.
Automation packages are commercially available for air insulated switchgear. However, options such as auto-transfer, voltage/current monitoring, bus fault detection, and fault targeting are not available. It is hardly ideal to automate switchgear when you cannot monitor the condition of your dielectric. Without confirmation that the switchgear enclosure is free of debris or moisture, an air insulated switchgear automating remote operation can lead to catastrophic failure. In fact, there is no solution available that can automate the outdated power fuses used for overcurrent protection.
For reduced maintenance and operation cost, it’s best to install equipment that offers automation and remote monitoring solutions. Doing so helps to reduce penalties incurred for extended outages. There are certain solid dielectric switchgear products designed with automated solutions in mind. Options such as motors, magnetic actuators, auxiliary contacts, and flexibility with many different automation relays allow the end user to deploy switchgear on a network for manual switching and control with the option to easily retrofit automation capabilities in the future. These automation capabilities will help to lower costs by limiting the need to deploy crews for manual switching and reconfiguration.
Investigate Renewal Costs
In the event of a fault, a fuse may only interrupt current on a single-phase and the entire switchgear assembly will typically need to be taken out of service to safely replace an opened or blown fuse. The costs associated with locating and replacing fuses, taking equipment out of service, and keeping fuses in stock will drive up the renewal cost.
Some solid dielectric switchgear available on the market uses resettable vacuum interrupters to protect switchgear cables and other system components in the event of a fault. Once a fault has been cleared, resetting of the fault interrupter is easily accomplished manually with standard tools, or electronically through use of motors, or magnetic actuators. This design eliminates the burden and safety hazard of changing fuses while switchgear is energized. To eliminate renewal costs and further improve overall operator safety, look for switchgear that can allow operators to reset a fault interrupter or reconfigure a circuit without ever leaving their SCADA terminal.
Price Compare, Leverage Public Resources and Employ and LCC
The information in the below table was found by reviewing public utility and municipality budgeting and construction plans that publish costs related to purchase, installation, and repair of distribution switchgear. The remaining information is the result of a sampling of large and small Investor Owned Utilities.
Ultimately, utilities are leaning toward installing emerging technology such as dead-front, automation ready solid dielectric switchgear, which is environmentally friendly and well suited to meet the future needs of their customers.
By using an LCC analysis, utilities can evaluate total cost of ownership of air and solid dielectric switchgear. Many different algorithms and data aggregation methods are utilized to aid in creating a reliable LCC analysis that will identify the most cost-effective solution available. Once the LCC model is developed, informed decisions can be made regarding deploying new assets, exploring new switchgear technologies, or refurbishing existing equipment.
