September 25, 2012
More than a few pitfalls await consulting specifying engineers who are selecting a vendor and system for protection and control automation systems for industrial clients, but a few guidelines may help them avoid those pitfalls and make the best choice for their clients.
One of the first elements that the engineer will need to decide is what integrating system to choose. Often, it will come down to one of two choices: a system fit for purpose, possibly one provided by the protection or substation equipment vendor; or a generic system, perhaps similar to the process automation system used by the industrial client.
Generic systems, such as those employed by programmable logic control (PLCs) systems are attractive in that the client may already be familiar with the system and have trained personnel to maintain the system. Components can be cheaper than those for a utility-grade automation system. In addition, some of the PLC-based integration technologies are extremely mature, closely controlled and in some cases proprietary and licensed. This tends to produce a high degree of interoperability. This also gives the engineer a greater flexibility in mixing and matching intelligent electronic devices (IEDs) from different vendors.
The engineer needs to exercise care in choosing this approach, particularly when determining if the functionality required is supported by the PLC system. In some PLC-based systems, there is no mechanism to transmit time information or file transfer from one IED to another.
Fit for purpose, utility-grade automation systems--provided by the substation equipment vendor, protection system vendor or a third-party system vendor--are usually designed specifically to interface with protection and control system IEDs. The functionality will be more closely in line with the functionality of the IEDs, and the supervisory control and data acquisition (SCADA) interface to the electric utility is typically easier to accomplish. The drawback is that unless a third-party system is employed, the customer may be tied into the original system vendor for the foreseeable future. Also, vendor proprietary systems change over time based on changing market needs or standards revisions. If a station modification is needed sometime in the future, it's possible the vendor may no longer support the earlier version of its own system.
Even when choosing a utility grade vendor-supplied system, there are options that the engineer must consider. It is not uncommon for single protection/substation equipment vendor to offer multiple automation/integration options, including a PLC protocol-based option, IEEE Standard 1815, IEC 61850, and even a proprietary option.
So how does a responsible engineer choose the right option for his/her client? Here are a couple of suggestions.
Consider using the same system that the interconnection utility uses. Chances are that the utility has gone through a good deal of evaluation, and has come up with a very workable solution. Also, the utility may be willing to serve as a resource for the industrial client in automation issues that arise in the future, and any SCADA interface between the industrial client and the utility will likely be simplified.
Another topic to consider is whether or not the substation is expected to be modified or added to in the future. If the owner plans to add new bays or another transformer in 10 to 15 years, it's important that the selected system will be available in the future. Consider very mature standards which are widely used today to improve the likelihood of availability in the future. On the other hand, if there is no chance of station modification in the future, the consulting engineer might choose a more efficient, economical solution available today.
One other consideration: the lifecycle cost of the system. Many approaches may be less costly on initial design and installation, but require the client/owner to incur higher costs for training, spares, and maintenance. Considering the total cost of ownership over the life of the system is a sound engineering practice, and the options should be discussed with the owner's engineer or management to bring these issues to light.
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.