For someone new to SCADA, which stands for supervisory control and data acquisition, the concept can be confusing. This is because SCADA is a general term that can be used in a wide variety of applications across industries as well as within energy controls systems. Understanding the different types of SCADA systems used in power plants can better position you to understand the control processes as well as aid in specifying requirements when designing and building a plant. Nor-Cal Controls is a key provider of integrated SCADA and control solutions for utility-scale power plant projects.
SCADA systems serve two primary purposes. The first is as a data acquisition system that will aggregate and historize data points from other equipment. The second is to provide control with preprogrammed logic either locally or through remote access. A SCADA system can be used in any application where both functions are needed, but for the purposes of this article, we will focus on power plant SCADA systems, particularly photovoltaic (PV) power plants and battery energy storage system (BESS) sites.
SCADA systems can be used to control the plant using automated processes, but they also allow for remote access which can interface witha human-machine interface (HMI) platform to allow operators to monitor site status and make manual adjustments as required. This means that it isn’t generally necessary to have a person on-site except to perform hands-on maintenance. Since solar plants are most often in remote areas, this provides both convenience and cost savings. Data acquisition makes it possible to track trends and plan maintenance to make for a more efficiently run and maintained plant.
When writing a scope of work (SOW) or a division of responsibilities (DOR), it is important to understand the roles, responsibilities, and definitions between different SCADA systems at a plant to clearly define what the contractors and subcontractors are expected to supply. This will make the process of getting quotations much smoother and create a clear division of labor throughout the duration of the project.
SCADA System Owners
Site owners may have a single SCADA interface at their operating center to manage multiple sites. Commonly referred to as an “Enterprise” SCADA, this overlay can provide the owner with a consolidated hub to help them monitor all their power plants and keep operations in compliance with utility requirements. To communicate with this Enterprise system, the owner may need to provide owner transmission (OT) and IT equipment such as firewalls and remote terminal units (RTUs) in a rack at each site. If the owner cannot supply a rack for their equipment, then Nor-Cal can plan for space in their rack(s) or provide additional network racks including backup UPS systems as requested. Nor-Cal may also be able to supply specialty equipment requested by site owners. The key is communication and planning prior to project execution to ensure that requirements are properly anticipated and accounted for.
Master Plant SCADA
At a local level, it is possible to have co-located or combined plants that each have a separate SCADA or controller, necessitating a master controller to make certain that the logic sets used in the different controllers don’t “fight” each other at the point of interconnection (POI). This master plant controller (MPC) can generally be included at one of the site’s SCADA racks, but if it is added after the plant is built, it may be installed in its own SCADA rack. Nor-Cal can accommodate either option.
BOP SCADA
Nor-Cal’s specialty is with what are often referred to as balance of plant (BOP) SCADA systems to provide power plant control, most often for photovoltaic (PV) solar plants or solar BESS sites. This can also be referred to as the PV SCADA or BESS SCADA, depending on the type of plant. The BOP SCADA is an on-site SCADA system that handles plant devices such as trackers, modules, inverters, and meteorological stations (METs) to ensure that the plant is providing the required power output at the POI. A BOP SCADA will typically require SCADA and historian servers, a power plant controller (PPC), network and root switches, network-attached storage (NAS), a GPS clock, a KVM (keyboard, video, and mouse), high-availability (HA) redundant firewalls, and data concentrators. Software will often be included for the HMI, historian, servers, and applicable hardware selections as well as subscriptions for the firewall and data plan (for short-term or backup internet connectivity). It will also include a data concentrator to work with the substation SCADA to centralize information to a single communication point. There may be some variations depending on the site’s conditions and needs, but those are the basics in the BOP SCADA contractor’s SOW.
Substation SCADA
The substation is the point where power is transmitted to customers or back into the plant to provide power to the facilities and devices used to run it. The substation SCADA is used to monitor the substation equipment and the output demands. The substation SCADA mayhave similar hardware and software to the BOP SCADA. This can lead to some confusion, as it may give the impression that some functionality is duplicated, though this is not the case. Examples include servers, switches, and KVMs. The substation SCADA will also need its own data concentrator to communicate with the BOP data concentrator.
However, there are instances in which equipment being present in one system means it can be eliminated in another. A common example is the GPS clock. This device is used to provide time synchronization across all devices. While it is technically okay to have one included at each rack, if there is a GPS clock in the substation rack that can link with the owner and BOP racks, the device from the other SOWs can be eliminated.
What’s most important is to clearly define the division of labor. It may seem obvious when writing the scope of work that the GPS clock in the substation can be used by the BOP SCADA, but the contractors involved may not realize that unless there is a clear specification written instructing the use of a central device. Alternatively, the substation contractor may not realize that they need to supply a clock that can support additional equipment, and the BOP contractor should not assume that the clock will have sufficient ports for their use.
Another example is cybersecurity. Since security is of such importance at utility-scale plants, it is common to require firewalls in both the BOP and substation SCADA racks with owner-supplied firewalls for overall site traffic, but this isn’t always the case. Some owner racks contain all IT equipment, including firewalls. If this is made clear at the outset, the SCADA racks can include single firewalls for testing purposes that will be replaced later.
When the division of responsibility is not clearly communicated, it can add to the overall cost and cause the site to have unnecessary equipment. It can also lead to frustration as the site is being built, requiring contractors to work out who is responsible for what. Understanding and defining responsibilities makes for a successful project and a smooth-running plant.
Don’t let unclear SOWs lead to unnecessary costs. Contact Nor-Cal today to ensure your plant design is efficient, compliant, and cost-effective.