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Can a transformer be back-fed or used in reverse?

In general, distribution transformers can be reverse connected without de-rating the nameplates KVA capacity. However, this is rarely considered in modern applications due to NEC code changes. Several precautions need to be taken for reverse connection of some smaller transformers. These would include:
Dealing with higher current inrush which can cause nuisance tripping.

HPS transformers under 6kVA three-phase and 3kVA single-phase, there is a “turns ratio compensation” on the low voltage winding. When backfed the turns compensation actually reduces the output voltage.
When a three-phase transformer is reverse connected thus resulting in a Wye-Delta configuration, the neutral terminal must be isolated. This modification may violate the warranty and agency listings such as U.L.

Back-fed transformers increase the installer’s liability since a future user may not realize what is the primary while de-energizing the transformer.

In general HPS suggest that a proper step up transformer which is designed with the low voltage terminals as the primary terminal be used.

  • When can you Reverse Connect a transformer?

      In general, distribution transformers can be reverse connected without de-rating the nameplates KVA capacity. However, this is rarely considered in modern applications due to NEC code changes. Several precautions need to be taken for reverse connection of some smaller transformers. These would include:
      Dealing with higher current inrush which can cause nuisance tripping.

      HPS transformers under 6kVA three-phase and 3kVA single-phase, there is a “turns ratio compensation” on the low voltage winding. When backfed the turns compensation actually reduces the output voltage. When a three-phase transformer is reverse connected thus resulting in a Wye-Delta configuration, the neutral terminal must be isolated. This modification may violate the warranty and agency listings such as U.L.

      Back-fed transformers increase the installer’s liability since a future user may not realize what is the primary while de-energizing the transformer.

      In general HPS suggest that a proper step up transformer which is designed with the low voltage terminals as the primary terminal be used.

  • What is a Buck Boost transformer?
  • What is the energy efficiency regulation compliance in the U.S. and Canada?

      In the past several years, there has been an accelerated rate of change in updating energy efficiency standards for transformers in North America.

      Governments in US and Canada are encouraging users to use higher energy efficiency dry-type transformers, to help reduce carbon dioxide emissions. There is also a long term cost savings in operating higher efficiency transformers translated in lower energy usage, lower cooling cost, etc.

      In U.S.A. the Department of Energy (DOE) has mandated new higher efficiency levels effective Jan. 1st 2016.

      In Canada Natural Resources Canada (NRCan) published SOR/2016-311 which amends the Energy Efficiency Act to align the via amendment 14 the minimum energy efficiency levels for dry type transformers to the ones implemented by DOE in Jan 2016.

      The new NRCan 2019 regulation is going to be enforced across Canada on May 1st, 2019. The Ontario government already adopted these new efficiency levels by publishing the ON Reg.404-12 which in schedule 6 defines the new energy efficiency levels that dry type transformers sold in ON must comply with starting Jan.1st 2018 (Ontario Energy Efficiency Compliance).

      The rest of Canada (including Quebec) is still following the current energy efficiency levels prescribed by CSA C802.2, until the new NRCan regulations come in effect on May 1st 2019.

      To help our valued customers in estimating the cost savings resulting from upgrading their old dry type transformer to the new DOE2016/NRCan2019 efficiency levels, HPS has developed an Energy Savings Calculator available on its website. To find out how HPS can help reduce your energy consumption, click here.

      To visit the Canadian Gazette for more information about the Canadian energy efficiency standards, click here.

      For the Ontario Energy efficiency regulation please click here.

      To view an electronic copy of the U.S. DOE energy efficient standards, click here.

  • What is a Dielectric System in a transformer?
  • What is a Low Voltage General Purpose Transformer?

      HPS’s low voltage general-purpose transformers provide a safe, long lasting, highly reliable power source. They are designed for general lighting and other low voltage applications. They are UL listed and CSA certified.

  • What are the new Energy Efficiency levels coming for Transformers sold in the U.S.?

      Transformers have been and remain an essential part of our electrical infrastructure.  Everywhere we look there is a transformer supplying power to industrial, commercial or residential applications.

      In the past decades the greenhouse gas emissions and the effects on our planet have become the focus of many governments, agencies and individuals. Energy generation is a major contributor to the greenhouse gas emissions. In addition to widespread efforts to make energy generation more environmentally friendly, there is also a goal to lower energy consumption within most industrial, commercial and residential areas. Achieving increased energy efficiency levels for equipment and consumer products has become a priority for many manufacturers.

      Improving the energy efficiency of new transformers is a primary goal of the US Department of Energy (DOE), and they have the legal authority to define efficiency levels and enforce compliance.  Environmentally conscious consumers also recognize that buying a higher energy efficiency transformer will have a societal payback over many years.

      The Department of Energy has established new and more stringent Energy Efficiency levels for Transformers in the U.S. effective January 1st 2016.  The new efficiency levels for Medium Voltage Liquid-Filled, Medium Voltage and Low Voltage Dry-Type Distribution Transformers are defined in DOE’s CFR (Code of Federal Regulations) title 10 part 431.  Widely known as DOE 10 CFR p431, it was published in the Federal Register Vol. 78, No. 75 on Thursday April 18, 2013.  According to the DOE, the new efficiency levels are expected to reduce energy losses by an average of 18% in low-voltage dry-type distribution transformers and 13% for medium-voltage dry-type transformers, over the current TP-1 efficiency levels.

      To put the benefits of this change in perspective, the DOE projects savings up to $12.9 billion in total costs to consumers and 3.63 quadrillion Btu of energy over a 30 year period. In addition, about 265 million metric tons of carbon dioxide emissions will be avoided, equivalent to the annual greenhouse gas emissions of about 52 million automobiles.

      The subject of energy efficiency for transformers raises two main considerations:

      1. Under normal operation a transformer is always on (typically at 35% average loading), making any energy efficiency improvements more significant over an extended period of time.  This means that customers will be rewarded in two manners:  they are reducing greenhouse gas emissions and there is an economic payback through reduced energy costs.  Considering the life expectancy of a transformer and the fact that the transformer will be on 24 hours a day, 7 days a week for the next 25-30 years, even small energy efficiency improvements will pay dividends for decades.  A secondary benefit is that more efficient transformers generate less heat, and in many cases this translates into lower costs to cool the environment in which they are utilized.
      2. The currently mandated energy efficiency levels are already hovering around the 98-99% mark, depending on the type of transformer and ratings.  This means that any further efficiency improvements become more challenging to achieve, typically requiring more and/or better core and conductor materials.  This will directly impact the cost of the transformer in most cases.  However, as noted in point 1 above, there is an economic benefit to offset the higher initial transformer costs.  The new DOE 2016 compliant transformers that will come on the market will also be somewhat heavier than the current TP-1 efficiency level transformers.

      Hammond Power Solutions (HPS) has an online Energy Savings Calculator to help to our customers determine the savings they can achieve by installing a higher efficiency transformer.  It includes a comparison of transformers with older efficiencies to those of higher efficiency (TP1, NEMA Premium and DOE 2016 in the future) as well as specifics of the application and the customer’s cost of energy.

      Currently, for applications that require higher energy efficiency than the DOE regulated TP-1 levels, industry is using Premium Efficiency transformers defined by the NEMA Premium Efficiency Guidelines that stipulate approximately 30% lower loses than the TP-1 levels.  In terms of the environmental benefits of using a NEMA Premium transformer over a TP-1 rated let’s look at an example:

      The Electricity savings resulting from upgrading one three phase 75 kVA transformer can be translated into one of the following:

      • 1.19 Metric Tons of CO2
      • 121 Gallons of Gasoline
      • About 1/6th of the energy used by an average household annually
      • Planting 28 Trees
      • 0.9 Acres of Forest
      • Recycling 0.34 Metric Tons of Waste
      • Savings of $166 per year at $0.12 per kW-Hr

      Forest image 

      At some kVA ratings NEMA Premium energy efficiency levels meet or slightly exceed the DOE 2016 levels, some are slightly below the new requirements.  However, the NEMA Premium products are optional within the market today, and many consumers do not take advantage of the benefits they afford.  Hence, the DOE will require that all transformers manufactured after January 1st, 2016 will meet the new efficiency levels.

      The environmental impact and savings for our customers resulting from the DOE changes are positive and significant.  HPS fully embraces and supports this change, and the environmental benefits our society will receive as a result.  We proudly offer high quality transformers meeting the most stringent Energy efficiency requirements today and will be in a position to support the migration to the new DOE 2016 higher-efficiency designs for our valued partners and customers, beginning in the latter half of 2015.

  • Can a transformer be back-fed or used in reverse?

      In general, distribution transformers can be reverse connected without de-rating the nameplates KVA capacity. However, this is rarely considered in modern applications due to NEC code changes. Several precautions need to be taken for reverse connection of some smaller transformers. These would include:
      Dealing with higher current inrush which can cause nuisance tripping.

      HPS transformers under 6kVA three-phase and 3kVA single-phase, there is a “turns ratio compensation” on the low voltage winding. When backfed the turns compensation actually reduces the output voltage.
      When a three-phase transformer is reverse connected thus resulting in a Wye-Delta configuration, the neutral terminal must be isolated. This modification may violate the warranty and agency listings such as U.L.

      Back-fed transformers increase the installer’s liability since a future user may not realize what is the primary while de-energizing the transformer.

      In general HPS suggest that a proper step up transformer which is designed with the low voltage terminals as the primary terminal be used.

  • New Energy Efficiency levels US 2016

      Transformers have been and remain an essential part of our electrical infrastructure.  Everywhere we look there is a transformer supplying power to industrial, commercial or residential applications.

      In the past decades the greenhouse gas emissions and the effects on our planet have become the focus of many governments, agencies and individuals. Energy generation is a major contributor to the greenhouse gas emissions. In addition to widespread efforts to make energy generation more environmentally friendly, there is also a goal to lower energy consumption within most industrial, commercial and residential areas. Achieving increased energy efficiency levels for equipment and consumer products has become a priority for many manufacturers.

      Improving the energy efficiency of new transformers is a primary goal of the US Department of Energy (DOE), and they have the legal authority to define efficiency levels and enforce compliance.  Environmentally conscious consumers also recognize that buying a higher energy efficiency transformer will have a societal payback over many years.

      The Department of Energy has established new and more stringent Energy Efficiency levels for Transformers in the U.S. effective January 1st 2016.  The new efficiency levels for Medium Voltage Liquid-Filled, Medium Voltage and Low Voltage Dry-Type Distribution Transformers are defined in DOE’s CFR (Code of Federal Regulations) title 10 part 431.  Widely known as DOE 10 CFR p431, it was published in the Federal Register Vol. 78, No. 75 on Thursday April 18, 2013.  According to the DOE, the new efficiency levels are expected to reduce energy losses by an average of 18% in low-voltage dry-type distribution transformers and 13% for medium-voltage dry-type transformers, over the current TP-1 efficiency levels.

      To put the benefits of this change in perspective, the DOE projects savings up to $12.9 billion in total costs to consumers and 3.63 quadrillion Btu of energy over a 30 year period. In addition, about 265 million metric tons of carbon dioxide emissions will be avoided, equivalent to the annual greenhouse gas emissions of about 52 million automobiles.

      The subject of energy efficiency for transformers raises two main considerations:

      (1) Under normal operation a transformer is always on (typically at 35% average loading), making any energy efficiency improvements more significant over an extended period of time.  This means that customers will be rewarded in two manners:  they are reducing greenhouse gas emissions and there is an economic payback through reduced energy costs.  Considering the life expectancy of a transformer and the fact that the transformer will be on 24 hours a day, 7 days a week for the next 25-30 years, even small energy efficiency improvements will pay dividends for decades.  A secondary benefit is that more efficient transformers generate less heat, and in many cases this translates into lower costs to cool the environment in which they are utilized.

      (2) The currently mandated energy efficiency levels are already hovering around the 98-99% mark, depending on the type of transformer and ratings.  This means that any further efficiency improvements become more challenging to achieve, typically requiring more and/or better core and conductor materials.  This will directly impact the cost of the transformer in most cases.  However, as noted in point 1 above, there is an economic benefit to offset the higher initial transformer costs.  The new DOE 2016 compliant transformers that will come on the market will also be somewhat heavier than the current TP-1 efficiency level transformers.

      Hammond Power Solutions (HPS) has an online Energy Savings Calculator to help to our customers determine the savings they can achieve by installing a higher efficiency transformer.  It includes a comparison of transformers with older efficiencies to those of higher efficiency (TP1, NEMA Premium and DOE 2016 in the future) as well as specifics of the application and the customer’s cost of energy.

      Currently, for applications that require higher energy efficiency than the DOE regulated TP-1 levels, industry is using Premium Efficiency transformers defined by the NEMA Premium Efficiency Guidelines that stipulate approximately 30% lower loses than the TP-1 levels.  In terms of the environmental benefits of using a NEMA Premium transformer over a TP-1 rated let’s look at an example:

      The Electricity savings resulting from upgrading one three phase 75 kVA transformer can be translated into one of the following:

      • 1.19 Metric Tons of CO2
      • 121 Gallons of Gasoline
      • About 1/6th of the energy used by an average household annually
      • Planting 28 Trees
      • 0.9 Acres of Forest
      • Recycling 0.34 Metric Tons of Waste
      • Savings of $166 per year at $0.12 per kW-Hr

      Dense Forest

       

      At some kVA ratings NEMA Premium energy efficiency levels meet or slightly exceed the DOE 2016 levels, some are slightly below the new requirements.  However, the NEMA Premium products are optional within the market today, and many consumers do not take advantage of the benefits they afford.  Hence, the DOE will require that all transformers manufactured after January 1st, 2016 will meet the new efficiency levels.

      The environmental impact and savings for our customers resulting from the DOE changes are positive and significant.  HPS fully embraces and supports this change, and the environmental benefits our society will receive as a result.  We proudly offer high quality transformers meeting the most stringent Energy efficiency requirements today and will be in a position to support the migration to the new DOE 2016 higher-efficiency designs for our valued partners and customers, beginning in the latter half of 2015.

  • What is ANSI C57.12.91?
  • What are solar transformers?

      Solar transformers covers a broad selection of transformers which are designed for the unique requirements of a solar power system. These transformers can include solar inverter transformers, grid tie transformers and zig-zag autotransformers or isolation transformers specially designed to be used in grounding banks for utility hook-ups. Transformers used to directly deliver power to utilities must often be capable of bidirectional current flow.

  • What is a solar grounding bank?
  • What is NEMA ST 20?
  • What does LV stand for?
  • What is a Unit Substation Style Transformer (USST)?
  • What is U.L. 1561?

      UL1561 covers 600 Volt Class Transformers:

      1.1 These requirements cover:

      1. General purpose and power transformers of the air-cooled, dry, ventilated, and non-ventilated types to be used in accordance with the National Electrical Code, ANSI/NFPA 70. Construction types include step up, step down, insulating, and autotransformer type transformers as well as air-cooled and dry-type reactors

      OR

      1. General purpose and power transformers of the exposed core, air-cooled, dry, and compound-filled types rated more than 10 kVA to be used in accordance with the National Electrical Code, ANSI/NFPA 70. Constructions include step up, step down, insulating, and autotransformer type transformers as well as air-cooled, dry, and compound-filled type reactors.

      1.2 These requirements do not cover ballasts for high intensity discharge (HID) lamps (metal halide, mercury vapor, and sodium types) or fluorescent lamps, exposed core transformers, compound-filled transformers, liquid-filled transformers, voltage regulators, general use or special types of transformers covered in requirements for other electrical equipment, autotransformers forming part of industrial control equipment, motor-starting autotransformers, variable voltage autotransformers, transformers having a nominal primary or secondary rating of more than 600 volts, or overvoltage taps rated greater than 660 volts.

      1.3 These requirements do not cover transformers provided with waveshaping or rectifying circuitry. Waveshaping or rectifying circuits may include components such as diodes and transistors. Components such as capacitors, transient voltage surge suppressors, and surge arresters are not considered to be waveshaping or rectifying devices.

  • What is ANSI C57.12.01?
  • What are High Voltage and Low Voltage windings?
  • What is the induction principle of transformers?

      A transformer consists of laminated silicon steel cores on which one or more coils of wire have been wound. The two windings are electrically isolated from each other (with the exception of autotransformers) and usually have widely different numbers of turns.

      If the transformer primary is connected to an A.C. power source of suitable voltage, a small no-load current called the exciting current will flow into the coil and produce a magnetic flux in the iron core. Since the source is A.C., the flux will also be alternating. This alternating magnetic flux links the secondary turns and induces a small voltage in each turn. The induced volts per turn of the secondary windings adds to appear across the secondary terminals. It should be understood that the flux induces a voltage in each primary turn equal to that in each secondary turn. The difference between the total induced primary voltage and the applied voltage is approximately equal to the IR drop. The ratio of turns between the primary and secondary coils determines the output voltage.

  • Should low voltage system be assessed for arc-flash hazards?

      IEEE 1584-2018 provides mathematical models for designers and facility operators to apply in determining the arc-flash hazard distance and the incident energy to which workers could be exposed during their work on or near electrical equipment.

      It generally indicates that systems with an available short circuit current of 2000 Amps or higher should be assessed for arc-flash potential. A rule of thumb would indicate that most systems fed by a 45 kVA or larger transformer will need to be assessed if impedance (%Z) of 45 kVA is less than 6%, 30 kVA if %Z is less than 4% or 15 kVA if %Z is less than 2%.

  • What is considered Low Voltage for distribution transformers?

      The term “Low Voltage” for electrical distribution transformers can refer to different voltages. Generally transformers with primary and secondary voltages at or below 600 volts are considered “Low Voltage”.

      • 690 Volts is sometimes considered low voltage. It is sometimes referred to as a 600/690 volt system.
      • The National Electric Code considers voltages <1000 volts to be low voltage.
      • Some regulatory agencies consider 1.2 kV and below to be low voltage.

      As a result there is some market confusion for voltages between 600 and 1200 volts with some regulations having a definition gap for some of these voltages.

  • Does HPS build secondary unit substation transformers?

      Secondary Unit Substation Transformers feed low voltage switchgear or switchboards. They typically range from 150 kVA to 2,500 kVA three-phase. The Primary voltage ranges from 2400 VAC to 34,500 VAC and the secondary from 600VAC to 480 VAC. Taps are typically manually changed while the unit is de-energized. The primary connections are typically delta connected while the secondaries are usually wye connected.

      The units are typically installed inside a building and are either dry (VPI) or cast coil because of safety and installation concerns. These units are often connected directly close coupled to the switchgear. HPS can provide both VPI and Cast Coil Secondary Unit Substation Transformers.

  • What are Important Specifications for a Marine Duty Transformer?

      Marine Duty is often left to the manufacturer to define.  HPS provides American Bureau of Shipping (ABS) approved transformers which include:

      • Copper or aluminum windings
      • Dry-type convection-cooled
      • Standard NEMA taps
      • 150ºC, 115ºC or 80ºC temperature rise available
      • 220ºC, 200ºC or 180ºC insulation system available
      • VPI Impregnation for salt environments
      • Fungus resistant
      • Braced for marine applications
      • Enclosures:  NEMA 2 or NEMA 3R (per ABS requirements)
      • Stainless steel hardware (on units over 1000kVA)
      • UV protection for outdoor enclosures
      • UL50 frames, channels, etc.
      • CSA, UL and ABS approval (Lloyd’s Register and DNV approval available upon request)

  • Do dry-type, potted or cast resin transformers contain PCB’s?
  • Define Vacuum Pressure Impregnation?

      A vacuum and pressure impregnation process using a resin that is then oven cured to completely seal and protect the surface of a transformer and provides a strong mechanical bond. This process is standard on all HPS transformer products.

  • Define VPI Impregnation?

      A vacuum and pressure impregnation process using a resin that is then oven cured to completely seal and protect the surface of a transformer and provides a strong mechanical bond. This process is standard on all HPS transformer products.