“Snubber” Networks - Are they effective?

Installing RC snubbers connected directly to the transformer primary windings is a common recommendation, but can snubbers really produce the desired result?

07/12/2012


Figure 1: A typical RC snubber network mounted inside a VPI dry-type enclosure. Courtesy: J. GuentertOver the last 10 or so years, the entire data center industry has become much more aware of the problems with switching medium-voltage (MV) distribution transformers with vacuum breakers, especially after some very high-profile failures of dry-type transformers in data centers around Manhattan and New Jersey, although there have been dozens of other similar failures around the country.

A number of Institute of Electrical and Electronics Engineers (IEEE) committees have performed some solid research, papers have been published, and new IEEE guidelines proposed and issued in IEEE C57.142. There is finally a good understanding of the full nature of the problems, and the steps then can be taken to mitigate. There have been some excellent papers by David Shipp of Eaton Corporation and a number of presentations made by him to various IEEE conferences, as well as some excellent papers and presentations by Phil Hopkinson, owner of HVOLT.

I’ve closely followed David’s and Phil’s works (and IEEE’s work) on this topic since their very beginning, because of my 30+ years of keen interest in this problem. The recommended solution always seems to be the installation of RC snubbers connected directly to, or very close by, the transformer primary windings.

Can snubbers be effective, and produce the desired result? Emphatically, “yes.”

But I think this is the wrong question to be asking, and it begs the more fundamental question: “Why install a data center substation transformer in the first place that requires a snubber in order to survive for a normal lifetime?”

Even the most ardent proponents of use of snubbers generally add a post-script of advice, saying something like “RC snubbers - while useful and often necessary - will likely become points of failure at some time, when the capacitors eventually fail. A systems study should be performed to determine whether a snubber is actually required at any particular transformer. If a snubber is not required, then don’t install one - what’s not there can’t fail.”

I’ve read a number of such system studies performed by study engineers for various projects. They generally end with a conclusion and recommendation that goes something like this:  

Transformers T15 and T16 do not require use of snubbers. Transformers T1 and T2 do require snubbers, because of the very short lengths of the primary feeder cables. Transformers T3 through T14 are ‘borderline’. Prudence suggests that it might be wise to install snubbers on these twelve transformers.

After reading a recommendation like this one from the study engineer, most data center owners and their consulting engineers wouldn’t be able to sleep at night until after they had made a decision like “Why don’t we just install snubbers on every transformer?” (And, who could argue with the logic of that conclusion?)



No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Mobile HMI; PID tuning tips; Mechatronics; Intelligent project management; Cybersecurity in Russia; Engineering education; Road to IANA
Save energy with automation; Process control system upgrades; Dispelling controll myths; Time-sensitive networking; Control system integration; Road to IANA
Additive manufacturing advancements; Machine vision enhances robotics; Fieldbus evolution; Process safety; Advice from System Integrators of the Year; Road to IANA
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Flexible offshore fire protection; Big Data's impact on operations; Bridging the skills gap; Identifying security risks
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial

(copy 5)

click me