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What are the most common power problems?

Research conducted by both IBM and Bell indicates that most line disturbances to sensitive equipment are line noise and voltage fluctuations.

  • 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 Output Problems Can Occur with Variable Frequency Drives (VFD or VSD) and How Can You Mitigate These Issues?

      A voltage-sourced Variable Frequency Drive (VFD) uses Insulated-Gate Bipolar Transistors (IGBTs) to rapidly switch voltage on and off to form a Pulse Width Modulated (PWM) voltage source for the motor. The PWM simulates a sine wave voltage source to the motor and it operates as if it was being powered by a sine wave.  The PWM wave allows the VFD to change the fundamental frequency of the PWM waveform and simulate sine waves.  Since the speed of a motor is directly related to the fundamental frequency of the sine wave, a VFD can control speeds from a fraction of a hertz to hundreds of hertz.

      Output reactors, dV/dT filters or drive isolation transformers can be used to help mitigate some issues caused by the PWM output.  PWM outputs cause rapid switching transitions which can cause over-voltages due to parasitic capacitance and inductance in the motor’s leads. The parasitic currents and voltages can be determined by the equation of V = L × (Δi/Δt).  VFD’s switching frequencies (the amount of pulses used to simulate the sine wave) generally range from 1,000-20,000 pulses per second.  IGBT’s produce an almost perfect square wave which produces a very high Δv/Δt.   High Δv/Δt can cause higher surge currents in the leads. This then causes high voltage pulses across the parasitic inductances.  Therefore the faster the pulses switch, the greater the impact of cable capacitance and inductance. These voltage pulses stress the motor’s windings causing higher audible noise, heat and possibly premature failure of the insulation. There is also capacitance in the motor’s bearings.  The combination of lubrication and air gaps prevent direct and continuous contact of the bearings to the metal traces that contain them.  Parasitic currents [I = C × (Δv/Δt)] causes current to flow through the bearings.  The amount of current will increase as the VFD output switching speed increases. These currents can cause micro pits to form in the bearings and eventually will lead to premature bearing failure.

  • 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?
  • How are HPS transformers designed to shield against voltage transients?

      Electrostatically shielded transformers may help minimize or limit the effects of voltage transients. Common Mode noise is measured from line to ground and is usually the most troublesome. Transverse Mode noise is measured from line to line. Attenuation is the difference of an incoming transient on the primary of the transformer to the secondary side.

      An electrostatic or Faraday shield is simply a thin piece of grounded non ferrous metal (generally copper foil) placed between the primary and secondary windings of a transformer. The shield extends from the top to the bottom of the windings. Some manufactures use shields that don’t extend the full length of the coil face. While less expensive, they will not offer as much protection as a full shield.

      There is no national standard that gives test methods for measuring CMNA and TMNA. Hence, in the industry, various companies have different claims that they have succeeded in getting into customer or consultant specifications. A lot of the confusion for shielded transformers results from differing claims made by various manufacturers and experts. Some recent reports indicate that and electrostatic shield may have little to no benefit where the secondary is grounded which is in most applications. The difference in the claims results from many variables:

      1. Standard single shielded distribution and drive isolation transformers may theoretically provide typical values of CMNA =60 dB and TMNA = 10 dB.
      2. A single shielded transformer with a low capacitive coupling of less than 30 pF may theoretically provide typical values of CMNA = 100 dB and TMNA = 40 dB.

      A manufacturer should be willing to share their testing procedures and test circuit to verify their
      claims.

      Note attenuation ratings vary by frequency. As the frequency increases, dB ratings go down. The ratings given above may be best case for a wide range of frequencies from 100Hz to 1MHz. Actual attenuation might be significantly higher at the lower frequencies. Some manufactures may claim higher dB’s attenuation by using much lower frequency ranges.

      There may be a large difference between calculated dB and actual dB due to real-life inconsistencies in material and manufacturing. Manufacturers should have actual test data to back up their attenuation claims.

  • 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.

  • how Line Reactor eliminate Nuisance Tripping

      Transients due to switching on the utility line and harmonics from the drive system can cause intermittent tripping of circuit breakers. Furthermore, modern switchgear, equipped with solid-state trip sensing devices, is designed to react to peak current rather than RMS current. As switching transients can peak over 1000 volts on a 600 volt system, the resulting over-voltage will cause undesirable interruptions.

      A reactor added to your circuit restricts the surge current by utilizing its inductive characteristics and mitigates nuisance tripping. The impedance of a transformer will have similar effects.

      Learn about HPS Centurion R Reactors

  • Capacitor switching reactor – definition
  • What is ANSI C57.12.91?
  • What is ANSI C57.12.51?

      IEEE Standard for Ventilated Dry- Type Power Transformers, 501 kVA and Larger, Three-Phase, with High- Voltage 34.5 kV to 601 V and Low- Voltage 208Y/120 V to 4160 V covering General Requirements. The current standard was updated in 2008.

      This standard is intended to set forth characteristics relating to performance, limited electrical and mechanical interchangeability, and safety of the equipment described, and to assist in the proper selection of such equipment. Specific rating combinations are described in the range from 750/1000 to 7500/10 000 kVA inclusive, with high-voltage 601 to 34 500 volts inclusive and low-voltage 208Y/120 to 4160 volts inclusive. Part I of this standard describes certain electrical and mechanical requirements and takes into consideration certain safety features of 60-Hz, two-winding, three-phase, ventilated dry-type transformers with self-cooled ratings 501 kVA and larger, generally used for step-down purposes. Part Il describes other requirements or alternatives which may be specified for some applications and lists forced-air-cooled ratings for certain sizes.

  • What is an air terminal chamber (ATC) or line terminal compartment?

      This is an air filled terminal compartment, typically 12″-24″ wide that is bolted to one or both sides of a substation transformer. This typically contains either the primary or secondary connections with a steel barrier separating it from the larger chamber containing the actual transformer core and coil. The ATC may also contain additional connections for loop feeds and/or lightning arresters.

  • Air core motor starting reactor – definition
  • What are dust filters?

      Dust filters are placed over ventilation openings to mitigate dust accumulation within the transformer’s enclosure. Filters are typically made to be removable and washable. Care must be taken for regular maintenance since accumulating dust will limit airflow and reduce air cooling. For this reason, dust filters are typically avoided through using non-ventilated designs or moving the transformer’s location. Because of reduced airflow, transformers cannot be retrofitted with dust filters without derating or using fan forced venting.

  • 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.

  • Line reactor – definition
  • Iron core filter reactor – definition
  • What is an incoming line interrupter switch (electrical disconnect)?

      This is typically a two position, three phase switch designed to disconnect a transformer on the line side. The switch may or may not also have fuses. The switch assembly is typically attached directly to the transformer enclosure and electrically connected through close coupled bussing.

  • What is a solar grounding bank?
  • Air core filter reactor – definition
  • What is a pad mounted transformer?

      A pad mounted transformer typically refers to a specific style of enclosure for larger transformers that is capable of being installed in areas accessible to the general public. The transformer will typically have features including tamper resistant construction, tamper proof bolts and screws, lockable compartments with hinged doors, bottom entry of primary and secondary cabling and baffled ventilation openings if applicable. These should not be confused with the general statement that electrical transformers are often installed on a concrete pad.

  • What is NEMA ST 20?
  • What are Medium Voltage Transformers and where are they used?

      Medium voltage transformers that have one or more windings above 1.2 k-volts. Ventilated medium voltage transformers up to 2500 kVA are covered by DOE 2016 efficiency regulation in the U.S.A. and up to 5000 kVA by NRCan 2019 efficiency regulations in Canada.

      They are primarily for use in stepping down medium voltage power to a lower operating voltage for commercial, institutional or industrial applications. However, medium voltage transformers may also be used to step-up voltage.

  • What does is a reconnectable transformer?

      A reconnectable transformer typically refers to a transformer with two primary connections. These may be used for mobile equipment, test transformers or to accommodate future voltage changes and upgrades in a facility without having to change the transformer. Depending on the difference in voltages and application reconnectable transformers may be exempt from current efficiency regulations.

  • dV/dt reactor – definition
  • What does LV stand for?
  • What is a Unit Substation Style Transformer (USST)?
  • What is U.L. 1562?

      U.L. 1562 covers medium voltage dry-type transformers:

      1.1 These requirements cover single-phase or three-phase, dry-type, distribution transformers, including solid cast and resin encapsulated transformers. The transformers are provided with either ventilated or non-ventilated enclosures and are rated for a primary or secondary voltage from 601 to 35000 V.

      1.2 These transformers are intended for installation in accordance with the National Electrical Code, ANSI/NFPA 70.

      1.3 These requirements do not cover the following transformers:

      1. Instrument transformers
      2. Step-voltage and induction voltage regulators
      3. Current regulators
      4. Arc furnace transformers
      5. Rectifier transformers
      6. Specialty transformers (such as rectifier, ignition, gas tube sign transformers, and the like)
      7. Mining transformers
      8. Motor-starting reactors and transformers

      1.4 These requirements do not cover transformers under the exclusive control of electrical utilities utilized for communication, metering, generation, control, transformation, transmission, and distribution of electric energy regardless of whether such transformers are located indoors, in buildings and rooms used exclusively by utilities for such purposes; or outdoors on property owned, leased, established rights on private property or on public rights of way (highways, streets, roads, and the like).

  • 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 is rodent screening?

      Rodent screens are added over ventilation openings of transformers to prevent rodents from entering the compartment. Large transformers installed directly on concrete pads may also need a steel bottom added. Rodent screens will not prevent the entry of dust or insects.

  • RC filter reactor – definition
  • What are High Voltage and Low Voltage windings?
  • What are the most common power problems?
  • 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.

  • What are Static VAR Compensators (SVCs)?
  • What are Static Synchronous Compensators (STATCOMs)?
  • 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%.

  • Are Harmonic Mitigating Transformers (HMT’s) available in medium voltage configurations?
  • 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.