Creating Resilient Neighborhood Substations

Neighborhood substations are ideal targets for motivated threat actors. Most components are visible from outside the fence, transformers are full of flammable oil and equipped with easily punctured coolers, and physical security consists of a chain link fence topped with razor wire. Most of the 70,000 neighborhood substations in the continental United States are custom designed using transformers that are built to each electric utility’s specifications. Because of this, the initial focus when creating resilient neighborhood substations should be on transformers.

Step 1: Resilient Transformers

Specifications for neighborhood substation transformers need to be enhanced to include physical security concerns.  At the present time, transformers are custom designed, meaning they are very expensive and take weeks to replace. For this article, twelve standard neighborhood substation transformers are presented with 69 KV, 115 KV or 138 KV primary windings and either 13.8 KV or 12.47 KV secondary windings. 

What Can Be Changed?

Interchangeability, ratings, visibility, robustness, operability, and ease of installation are items that need to be explored. Consider a next generation neighborhood substation transformer with the top and section views shown in the following images.

At first glance, it’s easy to see that bushings have been replaced with plug/jack connectors and an oil expansion tank has been placed on top of the transformer tank.  Plus, motor operated valves (ISO MOV) have been placed in the pipes that carry oil from the main tank to the coolers.

While these changes by themselves will go a long way to reducing the vulnerability of neighborhood substation transformers to damage by motivated threat actors, there is so much more to consider. By following the example of other industries, the cost of neighborhood substation transformers can be reduced by at least 25% and delivery times can be as short as six weeks after receipt of order.

Standardized NEMA Ratings

Implementing standardized ratings, like those in the automobile industry, will reduce transformer delivery time. Neighborhood substation transformer ratings should be based on the voltage and current ratings of the secondary winding. Tank sizes can be based on either actual primary voltage, for example, twelve tanks would be needed to accommodate the three primary voltages in this article; or on voltage class, for example, four tanks would be needed to accommodate the three primary voltages in this class.

National Electrical Manufacturers Association (NEMA) could develop standard designations for neighborhood substation transformers, such as

Sample designations for standardized neighborhood transformers, with 138 KV high voltage windings, are listed in Table 1.

With standardized next generation neighborhood substation transformers, manufacturers should be able to optimize procurement of the parts they need and develop just-in-time schedules that can deliver transformers within six weeks of receipt of order.

Electric utilities could continue to order custom transformers, with the understanding that delivery times could be 52 weeks after receipt of order. Emergency repair/replacement of custom transformers would continue to be a challenge as it is today.

Reduced Visibility

Next generation neighborhood substation transformers should look like shipping containers. Everything should be hidden from view; nothing would project above the tank. This will eliminate targets visible to someone outside the fence. Gauges, dials, valves, ground straps, etc. would be shielded from view. The goal is to make next generation neighborhood substation transformers indistinguishable from storage containers.

Improved Robustness

Improving substation robustness will be a challenge institutionally, not technically, as one hundred years of transformer institutional knowledge will need to change.

The first change is to equip each transformer with plug/jack connectors rather than with bushings. This reduces transformer height and visibility.

The next change is to equip each cooler oil flow path with a motor operated valve that closes on low oil level. The goal is to keep transformer windings immersed in oil if coolers are damaged by small arms fire.

The next change is to require that every transformer can carry its lowest MVA rating for one hour, with no more than one year loss of life, when motor operated isolation valves are closed. This requires the insights of material scientists (who use Arrhenius equation concepts), mechanical engineers (who optimize fluid flow paths), and transformer designers (who identify transformer winding stress points) to develop enhanced tank, cooler, and core and coil designs.  This change will challenge the status quo.

Ease of Installation

Next generation neighborhood substation transformers should be designed so that transformers can be completely assembled at the factory, tested, and shipped full of oil. Coolers, cabinets, and plug/jack enclosures should be designed so that they can be removed for shipping and installed within 24 hours.  Final acceptance tests, at a substation, should be completed in less than 8 hours. A new transformer should be ready for energization within 48 hours of delivery.

Interchangeability

Neighborhood substation transformers should be as interchangeable as low voltage circuit breakers. During emergencies, any electric utility should be able to install a substation transformer that has been provided by a neighboring utility in less than 48 hours.

Accepting NEMA’s approach, which has successfully played a critical role in the design, production, installation, and operation of motors destined for both national and international commerce, is essential.

Cost Reductions

Standardized neighborhood substation transformer designs that can be used repeatedly will reduce design costs and minimize inventory. Tank and core and coil designs that enable inspections by fiber optic inspection probes can reduce tank sizes which further reduces costs. Standardizing voltage ratings of windings will further reduce costs. Shipping pre-filled transformers will also reduce costs and installation delays.

Step 2: Resilient Fault Detection and Isolation

As we continue exploring resilient neighborhood substations, our next article will focus on protective relaying applications and lessons learned in other industries.