Accommodating bi-directional power flow in substation design

Address aspects of your client’s substation design to accommodate the bi-directional flow of power.

11/06/2012


A consulting specifying engineer with a large commercial/industrial client that is planning to inject power into the grid must address aspects of that client’s substation design to accommodate the bi-directional flow of power.

The power source could be traditional such as thermally generated power or it could be renewable sources such as wind turbines and/or solar photovoltaics–the same issues apply. These distinct design considerations don’t exist for the simpler paradigm of a uni-directional power flow from the utility to the end-user.

The over-riding objective is to satisfy the utility’s need for situational awareness, a degree of visibility it needs to understand and manage how that bi-directional flow will affect its grid.

First, the consulting engineer needs to design for a greater degree of instrumentation in a substation that will handle a bi-directional flow of power. The design also will be influenced by the scale of power flowing onto the grid. If the bi-directional flow never exceeds 1 to 2 MW, situational awareness is achieved one way; if that flow is on the scale of, say, 100 to 200 MW, a different set of design considerations come into play.

The consulting specifying engineer’s first task, then, is to grasp the local utility’s requirements for situational awareness. Early in the substation design process, the consulting engineer needs to sit down with the local utility and understand what data points the latter requires. That could include bus voltages, power injection on the low side of the transformers–any number of data points might be required that, if not included in the initial design, unanticipated costs are likely later in the process.

The utility may even require a degree of control over the operation of the client’s substation in order to curtail power flowing onto the grid, or call for it, or even request volt/var support.

Both the sensors and the controls in this instance have implications for the substation’s communication network as well.

Further, the consulting engineer must not only understand the utility’s needs and requirements and communicate those to his/her client, but he/she may well serve as a mediator between the two parties. It’s best to stay ahead of the curve in order to properly perform design work and communicate and resolve issues affecting both parties.

Utility requirements may include specifying the equipment going into the substation, down to the level of vendor and device. For the situational awareness that a utility needs, it may require specific remote terminal units, or RTUs, and specific protocols to integrate with its SCADA and energy management system (EMS). At higher, transmission-level voltages, the utility may require specific protective relay equipment, again, down to the specific vendor make and model.

Of course, the utility also has safety concerns for its field crews when bi-directional power flows are integrated with the grid. Line crews may have to access the consulting engineer client’s substation to confirm that no power will flow while they’re working on a problem. Thus, utility-side needs will influence the physical design of the consulting engineer client’s substation, even the access controls.

So if you’re engaged by a client planning for or even just contemplating the future use of bi-directional power flows, be aware that a different set of rules apply. Engage with the affected utility at the earliest possible stage. The consulting engineer may find that the utility already has a set of design strategies, rules, and specifications in hand for just such an occasion. If the consulting engineer’s client is considering adding the capability for bi-directional power flow at some point in the future, certain design considerations might be made up-front at a prudent cost rather than incurring greater expense for a later retrofit.

If areas of uncertainty remain, where existing standards don’t apply to the situation, having a face-to-face meeting with the utility’s engineering staff is a must so that the areas in question can be worked out in a manner satisfactory for both sides.

The key is to understand the utility’s requirements and the client’s needs and future plans and ensure that both parties are well-informed and communicating in the early design stages for a successful project, while eliminating uncertainties.


Sam Sciacca is an active senior member in the IEEE and the International Electrotechnical Commission (IEC) in the area of utility automation. He has more than 25 years of experience in the domestic and international electrical utility industries. Sciacca serves as the chair of two IEEE working groups that focus on cyber security for electric utilities: the Substations Working Group C1 (P1686) and the Power System Relay Committee Working Group H13 (PC37.240). Sciacca also is president of SCS Consulting.



No comments
Consulting-Specifying Engineer's Product of the Year (POY) contest is the premier award for new products in the HVAC, fire, electrical, and...
Consulting-Specifying Engineer magazine is dedicated to encouraging and recognizing the most talented young individuals...
The MEP Giants program lists the top mechanical, electrical, plumbing, and fire protection engineering firms in the United States.
2014 Product of the Year finalists: Vote now; Boiler systems; Indirect cooling; Integrating lighting, HVAC
High-performance buildings; Building envelope and integration; Electrical, HVAC system integration; Smoke control systems; Using BAS for M&V
Pressure piping systems: Designing with ASME; Lab ventilation; Lighting controls; Reduce energy use with VFDs
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Consulting-Specifying Engineer case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Protecting standby generators for mission critical facilities; Selecting energy-efficient transformers; Integrating power monitoring systems; Mitigating harmonics in electrical systems
Commissioning electrical systems in mission critical facilities; Anticipating the Smart Grid; Mitigating arc flash hazards in medium-voltage switchgear; Comparing generator sizing software
Integrating BAS, electrical systems; Electrical system flexibility; Hospital electrical distribution; Electrical system grounding
As brand protection manager for Eaton’s Electrical Sector, Tom Grace oversees counterfeit awareness...
Amara Rozgus is chief editor and content manager of Consulting-Specifier Engineer magazine.
IEEE power industry experts bring their combined experience in the electrical power industry...
Michael Heinsdorf, P.E., LEED AP, CDT is an Engineering Specification Writer at ARCOM MasterSpec.