SBCT Outdoor Mounted Slip-Over Bushing Current Transformer


The Problem:
You have been tasked with upgrading the oldest substation on record so that it can meet the uptime performance standards that your customers have come to expect. It certainly would be much easier if the power transformer weren’t 40+ years old. It sure would be helpful if more CTs had been installed at the time of manufacture. Now to get all of the readings that you need, you need to add CTs in the field. While spec’ing the technical needs of the CT may be a bit of a challenge, the real challenge will be mounting it. There is hardly any available space on the top of the transformer to begin with, let alone any unobstructed space. You’re going to need a customized plan to slip the CT over the bushing and to then seat and secure it, all while making sure there is sufficient creep distance. This is not going to be easy, and no two-power transformer lids/decks seem to be the same. This is really going to require some mounting design help. Where do you go to get this kind of technical support?
“Aging equipment has resulted in an increasing number of intermittent power disruptions, as well as vulnerability to cyber attacks. Significant power outages have risen from 76 in 2007 to 307 in 2011.” (ASCE’s 2013 Report Card for America’s Infrastructure)

“Congestion at key points in the electric transmission grid has been rising over the last five years, which raises concerns with distribution, reliability and cost of service. Preliminary findings of the 2012 National Electric Congestion Study indicate that critical areas of congestion still exist in the Northeast and in southern California. This congestion can lead to system-wide failures and unplanned outages. The public has a low tolerance for these outages, even in extreme weather events. Additionally, these outages put public safety at risk and increase costs to consumers and businesses. The average cost of a one-hour power outage is just over $1,000 for a commercial business. Utilities also often pass on “congestion charges” to consumers when transmission lines are overloaded.”

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(ASCE’s 2013 Report Card for America’s Infrastructure)

The Solution:
Your solution is Meramec’s Outdoor Mounted Slip-Over Bushing Current Transformer.

The toroidal core is continuously tape-wound using cold-rolled, grain-oriented electrical grade silicon steel, which receives a full stress relief anneal after it is wound to its specified dimensions. The secondary winding is then wound of insulated copper magnet wire over the insulated core with the turns equally spaced around the core periphery. When taps are pulled, they are wound in a manner that assures a fully distributed winding between any connections. The coil is then fully encapsulated in an ANSI 70 (sky grey) resin system that has been developed and tested for outdoor use. The potting compound is U.V. stabilized, is flexible to allow for expansions caused by temperature variations from -50°C to +65°C, has good chemical resistance, high dielectric strength, rugged physical properties to endure mechanical shock, and overall excellent weather resistance.

The SBCT is custom-designed to fit over any bushing. It can be supported by mounting clamps with standard 5/8” bolt arm assembly & hardware for vertical adjustment. The placement of the bolts can be configured from either the ID or OD and attached to the apparatus tank top. The number of clamps required is dependent on physical size and weight of the SBCT. Custom mounting that permits attachment of clamping brackets directly to the bushing flange can also be provided – consult the factory for this option. In addition, a custom-fitted ground shield may be installed on the top of the SBCT and secured by the mounting clamps. This is highly recommended to direct any possible flash-over to the ground, thus bypassing the SBCT preventing destruction of the SBCT and connected equipment. Installation instructions are provided. What makes Meramec the right choice is our customization, quality and delivery. Every CT we produce is custom-designed to your specific application. Our engineering design, our technicians’ attention to detail, and our 100% verification all contribute to the achievement of our 5 year 99.978% quality performance rating. Our customer service is paramount as well. If you are in a scheduled maintenance mode, we deliver as needed. If you are in a downtime crisis situation, we pull out all the stops to get you up and running.

Additional Features & Options
  • Dual-core configurations may be possible, same ratings or mixed, with 3kV isolation between coils.
  • Other conduit openings are available – threaded up to 1.5” NPT or non-threaded holes up to 52mm.
  • Designs can be made to match existing CT characteristics.
  • Gapped cores for remanence control and transient response are available.
  • Air core linear couplers are available.

The Meramec Difference:
  • We are available 24/7 to support you.
  • RFQs are quickly turned.
  • Delivery performance
    • In project mode, rest assured it is delivered on time.
    • In crisis mode, we pull out all the stops to get you up and running.
  • Custom CT designs with custom mounting.
  • Known and proven product quality – install and forget.
  • Technical support that allows your engineers to focus on other issues and not the CT’s design.
  • 99.978% Quality Performance.
  • We are the Instrument CT Specialists. Instrument Transformers are what we do.




Meramec’s Rapid Response is available for rush situations. We are available to support your needs. Designs can be made to match the existing current transformer characteristics or to optimize your chosen parameters. Our products are guaranteed and backed by our 99.978% quality performance rating.

When you are in need of Current Transformers to directly replace existing units, to upgrade your system, or to outfit new equipment – Spec Meramec…When it has to be Right!