There is no need for utility network engineers to dread the expenditure in maintaining or augmenting a distribution network as significant costs can be avoided by deploying ACRs in place of traditional substation circuit breakers. Here’s what you need to know.
When budgets are under intense public scrutiny, critical reliability projects such as substation construction and upgrade are often postponed purely to avoid investing in expensive substation grade breakers.
The costs are associated with the scale of the equipment required, but also with the separation of primary (switchgear, circuit breakers, switches and other high voltage equipment) and secondary (control, protection and automation devices) systems within the substation. Both of these classes of capital equipment are mandatory, and both require substantial investment. Considering that on average there is a corresponding secondary system for almost every primary device in the substation, it is easy to note how this price can quickly escalate.
However, there is a class of switchgear already in use, which consolidates the primary and secondary side of equipment into a single integrated solution. This class of switchgear often carries current interruption capabilities far beyond true expectations out on distribution lines. The solution is the distribution network staple: the Automatic Circuit Recloser (ACR).
ACRs are already deployed around the world with protection, control and automation in mind. Oftentimes the only difference between ACRs and substation class circuit breakers is the fault interrupting capacity. Provided that substation fault currents are below 16kA with average load current below 800A, there is no reason a substation could not utilise ACRs as incoming and outgoing circuit breakers in lieu of traditional, expensive substation class equipment.
Since ARCs are an integrated solution, commissioning and testing of new secondary systems is simplified, as a single vendor is chosen for the particular infrastructure. Modern ACR control systems such as NOJA Power’s RC10 controller is preloaded with all the anticipated standard substation protection capabilities, along with advanced capabilities such as
IEC61850, Neutral Voltage Displacement and ANSI25 Synchrocheck. Utilities can stand to save a fortune on secondary systems as all the usual ‘options’ are simply supplied as standard with modern ACRs.
Given the maximum fault ratings of ACRs being around 16kA with constant load currents at 800A, there is a reasonable limit as to where this economic solution can be deployed. However, it is still well within reason that the majority of rural substations can be run using ACRs operating under these limits. This application is commonplace world-wide, where for example the 38kV incomer is fed through a NOJA Power OSM38 Auto-Recloser, into a 38kV/15kV transformer and out through multiple 15kV feeders each protected by a NOJA Power OSM15 Auto-Recloser.
This solution has become so popular that NOJA Power has developed a suite of substation standard functionality and products designed to assist in solving substation challenges with traditional pole top ACRs. NOJA Power’s substation mounting bracket, remote HMI panel, Ground Mount Recloser Kiosk and IEC61850 are just a few of the solutions developed to solve these unique challenges.
The key factor in deploying substation ACRs is the fault break capacity. Provided the design of the substation does not call for fault interruption greater than 16kA, why would a utility use anything else? ESI