Keeping tabs on emerging trends, Part II: Interconnections, revised standards and communication networks
In part I of this two-part blog, I discussed the introduction of bidirectional power flows on the distribution network and the utility’s resulting need for situational awareness that may extend into the client’s substation. In this installment, I’d like to discuss interconnections and relevant standards.
In the first installment of this two-part blog, I stated that it’s “important that the consulting-specifying engineer understands how his or her client’s project may impact the affected utility. In fact, that’s often the first step to designing appropriate solutions on the client’s side.”
Specifically, when a commercial or industrial plant presents a single-source, large-scale power injection onto the grid from an intermittent PV source – an increasingly likely event, given myriad drivers – the potential impacts on the affected utility will influence the CSE’s work on design factors on the client’s side.
In Part I of this two-part blog, I discussed the introduction of bidirectional power flows on the distribution network and the utility’s resulting need for situational awareness that may extend into the client’s substation. In this installment, I’d like to discuss interconnections and relevant standards.
Interconnections, governed locally
An interconnection or point of common coupling (PCC) is required for large customer facilities that inject significant levels of bidirectional power into the distribution grid.
The CSE needs to understand that interconnection policies typically are generated by state public utility commissions and siting commissions and their municipal counterparts. A public service commission often establishes the price a regulated utility must pay for distributed energy, while a siting commission may determine the type and location of a distributed energy facility owned by a client.
Both utility representatives and their counterparts on the client side must understand these local rules. The CSE must even take into account factors such as local elections that could produce changes in policy as a project seeks approval. Another challenge is that deregulation in some states has only added to the patchwork policy quilt that characterizes the United States. Familiarity with the resources made available by NARUC, the National Association of Regulatory Utility Commissioners, may be helpful in keeping tabs on developments in this area.
The CSE also should recognize that, given the time projects take to reach fruition, stakeholders can stir grassroots opposition to projects even late in the process. Anticipating possible challenges is one practical step to mitigating them.
Standards revisions and microgrids
Not only do CSEs need to keep tabs on interconnection policies, they need to pay attention to the revision process for applicable standards. The primary interconnection standard is IEEE 1547, "Standard for Interconnecting Distributed Resources with Electric Power Systems."
IEEE 1547 is actually a series of standards and it is being revised on a fast track to address rapidly increasing interest in DG management and microgrid-related capabilities. (Microgrids comprise yet another strategy for managing DG at the distribution level.) Fundamentally, IEEE 1547 defines interface points – points to be monitored and metered – and provides protection and control strategies for substations handling bidirectional power flows. Eight related standards have been approved so far in the revision process.
For instance, IEEE 1547.8 articulates recommended practices for utility integration of DG. San Diego Gas & Electric is in the vanguard in this area, as DG penetration in Southern California – encouraged by high solar activity and policy – is already causing effects that require mitigation.
IEEE P1547a-Amendment 1 is aimed at speeding up changes to IEEE 1547 that address voltage regulation and responses to abnormal voltage and frequency conditions on the grid sometimes caused by high penetration of solar PV.
Because microgrids can assist utilities in managing the intermittent nature of solar PV, Amendment 1547.4 will integrate distribution control systems and microgrids to allow utilities to integrate DG systems as grid-supporting resources, including a role in voltage regulation via real and reactive power supplies.
Amendment 1547.4 also revises anti-islanding provisions of the original standard. Grid-tied DG systems shut down automatically when an outage occurs, which prevents unintentional islanding that could pose safety issues. For microgrid-managed DG designed to operate under both grid-connected and disconnected scenarios, an amended IEEE 1547 will allow intentional islanding. That supports a primary value proposition for microgrid investments.
The foregoing are simply examples of areas that CSEs need to maintain ongoing interest and awareness to remain up-to-date with industry developments that affect their responsibilities to clients. In the case of a likely trend such as solar PV uptake and microgrid implementations that can help manage the impacts of intermittent DG on the distribution system, vigilance will pay dividends.
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