Liquid transformers--the right stuff

In this installment, Guentert gives more reasons for the differences in reliability between liquid transformers and dry-types.

05/23/2012


 

Elbow-Type MOV’s Connected Directly to Primary Windings

We left off last week discussing some of the possible reasons for differences in reliability of liquid transformers versus dry-types, when primary windings are switched by vacuum circuit breakers (all my personal opinions, again). Here are more reasons:

 

1. On all data center projects I’m involved with, we very carefully watch the installation details of the “system,” not just the transformer itself. Using the “loadcenter” concepts discussed earlier, moving the transformations into very close proximity to the loads has the effect of not only reducing high costs of the large secondary feeders, but generally has the added benefit of LENGTHENING the primary feeders, creating “Nature’s Own Snubber” by adding shunt capacitance to the shielded MV cables.

 

2. Then, we always connect a very good set of MOV surge arrestors DIRECTLY to the primary winding terminals. The capacitance of the cables flattens out the extremes of (dv/dt) rate-of-rise, to allow the arrestors to do their job in clamping the surge voltage as the transient develops across the windings. (Many consulting engineers still place arresters on the load runback connections of upstream vacuum breakers – at the source ends of the cables - where they are ineffective. Maximum effectiveness is when the arresters are connected directly to the transformer primary windings.  Remember, this is not a transient voltage entering the windings from upstream at the vacuum breaker.  Instead, the transient is developed within and across the winding itself, and this event occurs with such extreme speed that the winding insulation is damaged before the voltage wave can travel all the way back upstream through the cables to the arresters at the breaker.)

 

3. And, also importantly, we use only vacuum breakers from manufacturers who have performed their due diligence through R&D to ensure that the metallurgy of the power contacts inside their vacuum bottles has the “right stuff” to minimize current chopping and re-ignition phenomena during switching operations.

 

Typical Fan-Cooled, Ventilated Dry-Type Transformer4. Almost all modern VPI dry-type transformers are ventilated and air-cooled, usually by simple convection, sometimes with supplemental forced air from cooling fans. Either way, air is drawn into the lower vents, then either convects or is blown by fans directly over the transformer windings. The problem is, as that happens, microscopic particles of airborne contaminants are deposited on the primary windings, reducing the overall dielectric strength of the insulation system over time, and encouraging partial discharges during large transient events. If a ventilated transformer begins its life with a primary BIL of 110  kV, the BIL can degrade significantly within a few years, unless there is very frequent cleaning and maintenance. (It’s my experience that the majority of the failures I investigated occurred between one and three years after the failed unit had been initially placed into service. When I asked the question, I learned that practically none of them had been ever been maintained and cleaned.)

 

Liquid transformers, on the other hand, have their windings immersed in clean fluid within a sealed tank, so external airborne contaminants and moisture can’t get to the windings. (Use of an epoxy cast resin transformer also eliminates much of this problem.)



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.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
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.
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Controller programming; Safety networks; Enclosure design; Power quality; Safety integrity levels; Increasing process efficiency
Additive manufacturing benefits; HMI and sensor tips; System integrator advice; Innovations from the industry
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

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

Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
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.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
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.
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Controller programming; Safety networks; Enclosure design; Power quality; Safety integrity levels; Increasing process efficiency
Additive manufacturing benefits; HMI and sensor tips; System integrator advice; Innovations from the industry
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

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

Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
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.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
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.
Robotic integration and cloud connections; SCADA and cybersecurity; Motor efficiency standards; Open- and closed-loop control; Augmented reality
Controller programming; Safety networks; Enclosure design; Power quality; Safety integrity levels; Increasing process efficiency
Additive manufacturing benefits; HMI and sensor tips; System integrator advice; Innovations from the industry
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

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

Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me