Information and terms of Electrical for Construction Projects every Engineer should aware of

Information and terms of Electrical for Construction Projects every Engineer should aware of

What is a Grounding Transformer?
It is a special three-phase autotransformer for establishing a neutral on a 3-wire delta secondary. Also referred to as a 'Zigzag' transformer.

Describe Grounds or Grounding?
Connecting one side of a circuit to the earth through low resistance or low impedance paths.

What is a Harmonic?
A Harmonic is a sinusoidal component of a periodic wave having a frequency that is a multiple of the fundamental frequency. For example, a component whose frequency is twice the fundamental frequency is referred to as the second harmonic, (120 Hz is the 2nd harmonic of 60 Hz).

What does the term Hertz (Hz) mean?
It is a term for AC frequency in cycles per second.

What are High Voltage and Low Voltage windings?
These terms are used to distinguish the winding having the greater voltage rating from that having the lesser in two winding transformers.

Describe Hi Pot?
It is a high potential dielectric test impressed on the windings to check insulation materials and clearances.

What is Impedance?
It is the apparent resistance in a circuit to the flow of an alternating current analogous to the actual resistance to a direct current.

What is an Impulse Test?
It is a dielectric test that determines the BIL capability by applying high frequency, steep wave-front voltage between windings and ground.

What is an Induced Potential Test?
It is a standard dielectric test that verifies the integrity of insulating materials and electrical clearances between turns and layers of a transformer winding.

What is Inductance?
It is a property that opposes a change in current flow.

What is Inrush Current?
It is an abnormally high transient current, caused by residual flux in the core, which maybe drawn when a transformer is energized.

What are Insulating Materials?
Those materials used to electrically insulate the transformer's windings, turn-to-turn or layer-to-layer, and other assemblies in the transformer such as the core and busswork.

What is an Isolation Transformer?
It is a transformer that insulates the primary circuit from the secondary circuit. Also referred to as a two-winding or insulating transformer.

What is the abbreviation KVA stand for?
"Kilovolt Ampere Rating" designates the output that a transformer can deliver for a specified time at rated secondary voltage and rated frequency without exceeding the specified temperature rise. (1 kVA = 1000 VA, or 1000 volt amperes)

What are Knockouts and what are they used for?
They are easily removable circle of metal in an enclosure that eliminates the need for punching holes for conduit.

What is a Lamination?
Thin sheets of special steel used to make the core of a transformer.

What is a Line Reactor?
It is an electrical device whose primary purpose is to introduce a specific amount of inductive reactance into a circuit, usually to reduce or control current.

What is the term Load?
The load of a transformer is the power in kVA or volt-amperes supplied by the transformer.

What are Load Losses?
They are losses in a transformer, which are incident to load carrying. Load loses include I2R loss in the windings due to load current, stray loss due to stray fluxes in the windings, core clamps, etc., and to circulating currents (if any), in parallel windings.

What is a Mid-tap?
It is a reduced capacity tap midway in a winding. Also referred to as a 'Center tap'. Usually it is in the secondary winding.

Describe Moisture Resistance?
Materials or equipment constructed or treated so that it will not be harmed readily by exposure to a moist atmosphere.

What does the abbreviation NEC?
National Electric Code

What does the abbreviation NEMA?
National Electrical Manufacturers Association.

What are No-Load Losses (Excitation Losses)?
It is the loss in a transformer that is excited at rated voltage and frequency, but without a load connected to the secondary. No-load losses include core loss, dielectric loss, and copper loss in the winding due to exciting current.

What is Overload?
When a transformer is overloaded, excessive heat develops and the insulation system begins to breakdown. Life expectancy of the transformer is decreased due to heat exceeding the rating of the insulation system.

What is Parallel Operation?
Single and three phase transformers may be operated in parallel by connecting similarly marked terminals, provided their ratios, voltages, resistances, reactance and ground connections are designed to permit parallel operation. Current and voltage angular displacements are also required to be the same in the case of three phase transformers.

Explain the term Phase?
It is a type of AC electrical circuit; usually single phase 2-wire or 3-wire, or three-phase, 3 or 4 wire.

What is Polarity?
It designates the instantaneous direction of voltages in the primary compared to the secondary.

What is a Potential (Voltage) Transformer?
A transformer generally used in instrumentation circuits for measuring or controlling voltage.

What is Power Factor?
It is the relation of watts to volt amps in a circuit.

What are Primary Taps?
Taps added to the primary winding. (See Taps)

What is Primary Voltage Rating?
Designates the input circuit voltage for which the primary winding is designed.

What is a Primary Winding?
The primary winding is the winding on the energy input (supply) side.

Describe the term Rating?
It is the design characteristics such as primary and secondary voltage, kVA capacity, temperature rise, frequency, etc.

What is Ratio in terms of Voltage?
It is a reference to either the primary to secondary winding turns ratio or to the voltage ratio of the transformer.

What is a Ratio Test?
It is a standard test of transformers to determine the ratio of the primary to secondary voltage.

What is Reactance?
It is the impedance component due to inductance and/or capacitance.

What is a Reactor?
A single winding device with an air or iron core which, produces a specific amount of inductive reactance into a circuit, usually to reduce or control current.

What is a Rectifier Transformer?
A transformer designed to supply AC input to a rectifier to obtain the desired DC output and have the ability to withstand the heating effects caused by rectifier commutation or ripple.

What is RCBN - Reduced Capacity Below Normal?
It is taps that carry full-rated winding current only, thus reducing available power because of lower output voltage.

Define Regulation?
Usually expressed as the percent change output voltage when the load goes from full load to no load at a given power factor.

What is a SCR?
It is a silicon-controlled rectifier.

Describe Saturation?
Saturation is a natural condition in which an increase in current results in a decrease in inductance.

What is a Scott Connection?
It is a connection for polyphase using two special single-phase transformers. Usually used to change from two-phase to three-phase or three-phase to two-phase.

What is Secondary Voltage Rating?
Designates the no-load circuit voltage for which the secondary winding (winding on the output side) is designed.

What is a Secondary Winding?
The transformer winding connected to the load or output side.

Define Series/Multiple?
A winding consisting of two or more sections which can be connected for series operation or multiple (parallel) operation. Also referred to as dual voltage or series-parallel.

What is a Short Circuit?
A short circuit condition occurs when an abnormal connection or relatively low impedance, whether made accidentally or intentionally, occurs between to points of different potential in a circuit.

What is a Solid State Device?
It is a device that contains components that do not depend on electronic conduction in a vacuum or gas. Semiconductors or the use of otherwise completely static components such as resistors or capacitors performs the electrical function of a solid-state device.

What is a Step-Down Transformer?
It is a transformer where the high voltage winding (primary) is connected to the input or power source and the low voltage winding (secondary) to the output or load.

What is a Step-Up Transformer?
A transformer in which the low voltage winding (secondary) is connected to the input or power source and the high voltage winding (primary) is connected to the output or load.

What is a Tap?
A tap is a connection brought out of a winding at some point between its extremities, usually to permit changing the voltage or current ratio.

What is a T-Connection?
A Scott connected three-phase transformer utilizing two primary and two secondary coils called the main and the teaser.

What is Temperature Class?
It is the maximum temperature that the insulation can continuously withstand. The classes of insulation systems in a transformer are rated as follows:
Class 105 Degree C
Class 150 Degree C
Class 180 Degree C
Class 220 Degree C

What is Temperature Rise?
It is the increase over ambient temperature of the winding due to energizing and loading the transformer.

How do you calculate the Total Losses in a transformer?
It is the transformer electrical losses, which include no-load losses (core losses) and load losses (winding losses).

What is a Transformer?
It is a static electrical device, which, by electromagnetic induction transforms energy at one voltage and current to another voltage and current at the same frequency.

Describe Transient?
It is a temporary or brief change in a given parameter. This is typically associated with input voltage or output load parameters.

What are some of the Tests performed on transformers?
Normal, routine production tests include:
  • core loss;
  • load loss - winding or copper loss;
  • Impedance;
  • hi-pot - high voltage between windings and ground;
  • induced - double induced two times voltage.
Optional special tests include:
  • heat run - temperature testing;
  • Noise tests - sound level measurement;
  • impulse tests - BIL tests:
  • partial discharge.
What is Transverse Mode?
It is electrical noise or voltage disturbance that occurs between phase and neutral (between lines), or from spurious signals across the metallic hot line and the neutral conductor.

What is the abbreviation UL?
Underwriters Laboratories

Define VPI Impregnation?
A vacuum and pressure impregnation process using a resin which, 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 Hammond transformer products.

What is Voltage Regulation?
The change in secondary voltage that occurs when the load is reduced from rated value to zero, with the value of all other quantities remaining unchanged. Regulation may be expressed in percent (per unit) on the basis of rated secondary voltage at full load.

What is Volt-Amperes (VA)?
It is the current flowing in a circuit multiplied by the voltage of the circuit. It is an expression of the output rating of a transformer.

What is a Wye Connection?
A standard 3-wire transformer connection with similar ends of the single-phase coils connected. This common point forms the electrical neutral point and may be grounded.

What is a Zig Zag Connection?
It is a special transformer connection commonly used in grounded transformers. See also grounding transformers.

What is a Control Transformer?
A control transformer is an isolation transformer designed to provide a high degree of secondary voltage stability (regulation) during a brief period of overload condition (also referred to as "inrush current"). Control transformers are also known as Machine Tool Transformers, Industrial Control Transformers or Control Power Transformers.

When you calculate the VA requirement of a Transformer, do you use the Primary or the Secondary Voltage?
When selecting the VA requirement, you use the Secondary Voltage.

Can you use a Control Transformer connected in reverse?
Yes, a control transformer can be connected in reverse. However, keep in mind the output voltage will be less than it's rating, due to the compensation factor of the windings.

Can a Control Transformer regulate the output voltage?
A control transformer will not regulate the voltage. Output voltage is a function of the coil's turn ratio only, times the input voltage.

What is the benefit of "Vacuum Impregnation" on a Transformer?
All Hammond Control Transformers are vacuum impregnated with "VT Polyester Resin" and oven cured which seals the surface and eliminates moisture. Impregnating the entire unit provides a strong mechanical bond and offers protection from environmental conditions.

Explain the "VA" or "Volt Ampere Output" Rating?
The VA or volt-ampere output rating designates the output that a transformer can deliver for a specified time at its rated secondary voltage and rated frequency, without exceeding its specified temperature rise.

Insulating Materials, what are they made of and what is their purpose?
Hammond Power Solutions utilizes Mylar, Nomex and other high quality insulating materials. Insulation is used to electrically insulate turn-to-turn windings, layer-to-layer windings, primary to secondary windings and ground.

What is the effect of "Overload"?
When a transformer is continually overloaded, excessive heat develops and the insulation system will begin to breakdown. As a result, the life expectancy of the transformer is shortened due to the heat exceeding the rating of the insulation system.

What is a buck-boost transformer?
Buck-boost transformers are small single-phase transformers designed to lower (buck) or raise (boost) line voltage from 5-20%. The most common applications for buck-boost transformers Include boosting 208 volts to 230 or 240 volts for air conditioning systems, boosting 110 to 120 volts and 240 to 277 volts for lighting applications, heating systems and induction motors of all types. Many applications exist where supply voltages are frequently above or below nominal.
Buck-boost transformers are conventional low voltage, single-phase distribution transformer, with standard primary voltages of 120, 240 or 480 volts, and secondary voltages of 12, 16, 24, 32 or 48 volts. They are available in sizes ranging from 50 VA to 10,000 VA. The primary and secondary are wired together to form a single-winding autotransformer. Utilizing the additive and subtractive polarity, small amounts of voltage are either added or subtracted from a distribution circuit.

How does a buck-boost transformer differ from an isolating transformer?
A Buck-Boost transformer is manufactured as an isolating transformer, with separable primary and secondary, and is shipped from the factory in that configuration. When the end user at site connects it, the primary is connected to the secondary changing the transformer's electrical characteristics to those of an autotransformer. This provides the smaller voltage correction that is typical of Buck-Boost. The primary and secondary windings are no longer isolated as they are connected together.

What is the difference between a buck-boost transformer and an autotransformer?
As noted above, when the primary and secondary are connected together to buck or boost voltage, the transformer becomes an autotransformer. If the connection between the primary and secondary winding is not made, then the unit remains as an isolation transformer.

Why are they used?
A Buck-Boost transformer is a simple and effective way of correcting off-standard voltages. Electrical and electronic equipment is designed to operate within a standard tolerance of nominal supply voltages. When the supply voltage is consistently too high or low - typically more than 10%, the equipment will operate below peak efficiency.

Can Buck-Boost transformers be used to power low voltage circuits?
Installed as two-winding, isolation transformers, these units can be used to power low voltage circuits including control, lighting circuits, or other low voltage applications that require 12, 16, 24, 32 or 48 volts output, consistent with the secondary of these designs. The unit is connected as an isolating transformer and the nameplate kVA rating is the transformer's capacity.

Why do Buck-Boost transformers have 4 windings?
A four winding buck-boost transformer with 2 primary and 2 secondary windings can be connected eight different ways to provide a multitude of voltages and kVA's. This provides the flexibility necessary for the broad variety of applications. A two-winding transformer can only be connected in two different ways.

Will a Buck-Boost transformer stabilize voltage?
Autotransformers will not stabilize supply line voltage. The output voltage of an autotransformer is a function of the input voltage. If the input voltage varies, then the output voltage will also vary by the same percentage.

Are there any restrictions on the type of load that can be operated from a Buck-Boost transformer?
There are no restrictions as to application for Buck-Boost, including single or three-phase motor loads.

As an Autotransformer, how can a Buck-Boost transformer supply kVA power?
This is a function of adding voltage - a small amount of voltage is added and a small amount of corresponding power capacity is added as well. For example, if the transformer is connected in such a way that 22 volts is added to a 208 volt primary, a 230-volt output will result.
Using this example, the calculation for autotransformer kVA is as follows:
KVA = (Output Volts x Secondary Amps)/1000
KVA = (230V x 41.67 Amps)/1000 = 9.58 KVA

How are single phase and three phase load amps and load kVA calculated?
Single phase Amps = (kVA x 1000)/Volts
  1. Three phase Amps = (kVA x 1000)/Volts x 1.73
  2. Single phase KVA = (Volts x Amps)/1000
  3. Three phase KVA = (Volts x Amps x 1.73)/1000
Can Buck-Boost transformers be used on 3 phase systems?
Interconnecting two or three single-phase units will readily accommodate three phase systems - refer to the corresponding three-phase section in this catalog. The number of units to be used in a 3-phase installation depends on the number of wires in the supply line. If the 3-phase supply is 4-wire Wye, then three Buck-Boost transformers are required. If the 3-phase supply is 3-wire Wye (neutral not available), two Buck-Boost transformers are needed.

Should Buck-Boost transformers be used to develop 3-phase 4 wire Wye circuits from 3-phase 3 wire Delta circuits?
No - a three-phase "Wye" buck-boost transformer connection should be used only on a 4-wire source of supply. A delta to Wye connection does not provide adequate current capacity to accommodate unbalanced currents fl owing in the neutral wire of the 4-wire circuit.

Why isn't a 'closed Delta' Buck-Boost connection recommended?
This connection requires more kVA power than a "Wye" or open delta connection, and phase shifting occurs on the output. The closed delta connection is more expensive and electrically inferior to other three-phase connections.

How do you know how to connect a Buck-Boost transformer?
A connection chart is provided with each unit that shows how to make the corresponding connections. These same charts are also shown in this section.

Can 60-Hertz Buck-Boost transformers be operated on 50-Hertz?
Due to 'saturation' of the core, 60-Hertz Buck-Boost transformers should only be operated at 60 Hertz, and not 50 Hertz. Units manufactured as 50-Hertz units will however, operate at 60 Hertz.

Why are Buck-Boost transformers shipped from the factory connected as isolating transformers, and not pre-connected autotransformers?
The same 4-winding Buck-Boost transformer can be connected eight different ways to provide a multitude of voltage combinations. The user when assessing the supply voltage at site can best determine the correct connection.

Why is the isolation transformer kVA rating shown on the nameplate instead of the autotransformer kVA rating?
Shipped as an isolating transformer, the nameplate is required to show the performance characteristics accordingly. Additionally, as an autotransformer, the eight different combinations of voltages and kava's would be impractical to list on the nameplate. A connection chart, listing the various connections, is included with each unit.

Do Buck-Boost transformers present a safety hazard compared to conventional autotransformers?
Buck-Boost transformers only change voltage by a small amount, such as 208 to 240 volts. This small increase does not represent a safety hazard. Conventional autotransformers, manufactured as single winding transformers, change much higher magnitudes of voltage, e.g. 480 to 240 volts. In a system where the line is grounded, it is possible to have 480 volts to ground when the expectations are that 240 volts is at the output. For this reason, qualified personnel only should maintain conventional autotransformers.

How does the sound level differ between Buck-Boost and isolation transformers?
Buck-Boost transformers, connected as autotransformers, will be quieter than an equivalent isolation transformer capable of handling the same load. The isolation transformer would have to be physically larger than the buck-boost transformer, and smaller transformers are quieter than larger ones. For example, a 10kVA is 35dB and a 75kVA is 50dB.

How do the costs compare between a Buck-Boost transformer and an Isolation transformer handling the same load?
For most Buck-Boost applications, the savings are about 75% compared to the use of an isolation transformer for the same application.

What is the life expectancy of a Buck-Boost transformer?
Buck-Boost transformers have exactly the same life expectancy as other dry type transformers.

Buck-Boost transformers are almost always installed as autotransformers. Does the National Electrical Code (NEC) permit the use of autotransformers?
Autotransformers are very common and recognized by all the safety and standard authorities. You can refer to N.E.C. Article 450-4, "Autotransformers 600 Volts, Nominal, or Less", as a reference publication. Item (a) details over-current protection for an autotransformer, and Item (b) covers an isolation transformer being field connected as an autotransformer for a Buck-Boost application.

When a Buck-Boost transformer is connected as an autotransformer, what is the procedure for determining the current rating of the over-current protective device, such as the fuse or circuit breaker?
The NEC Article 450-4 outlines over-current protection for autotransformers. It is reproduced as follows: "NEC 450-4 - Autotransformers 600 Volts, Nominal, or Less
Over-current Protection.
Each autotransformer 600 volts nominal, or less shall be protected by an individual over-current device installed in series with each ungrounded input conductor. Such over-current device shall be rated or set at not more than 125 percent of the rated full load input current of the autotransformer. An over-current device shall not be installed in series with the shunt winding.
Exception: Where the rated input current of an auto transformer is 9 amperes or more and 125 percent of this current does not correspond to a standard rating of a fuse or non-adjustable circuit breaker; the next higher standard rating described in our section shall be permitted. When the rated input current is less than 9 amperes, an over-current device rated or set at not more than 167 percent of the input current shall be permitted.

Transformer Field-Connected as an Autotransformer.
A transformer field-connected as autotransformers shall be identified for use at elevated voltage."
Example: A 1kVA transformer, Catalog No. BKN4EA, is rated 120 x 240 to 12 x 24 volts. It is to be connected as an autotransformer to raise 208 to 230 volts single-phase. When connected as an autotransformer in this application, the kVA rating is increased to 9.58 kVA, or 9,580 VA. This is the rating to be used for determining the full load input amps and the corresponding size of the over-current protection device, either a fuse or breaker.

Full load input amps = 9,580 Volt Amps = 46 Amp, 208 Volts.
When the full load current is greater than 9 amps, the over-current protection device - usually a fuse or nonadjustable breaker, the current rating can be up to 125 percent of the full load rating of the autotransformer input current.
Max. current rating of the over-current device = 46 amps x 125% = 57.5 amps.
The National Electrical Code, Article 450-4 (a) Exception, permits the use of the next higher standard ampere rating of the over-current device. This is shown in Article 240-6 of the N.E.C.
Max. size of the fuse or circuit breaker = 60 amps.

What is Nuisance Tripping and how can a Line Reactor eliminate it?
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, the resulting over-voltage will cause undesirable interruptions. A reactor added to your circuit restricts the surge current by utilizing its inductive characteristics, and therefore eliminates nuisance tripping.

How does a Line Reactor extend the life of switching components?
Due to the attenuation of line disturbances, the life of your solid state devices are extended when protected by the use of a Hammond line reactor.

Will a Hammond Line Reactor saturate?
Due to the care in the selection of the core material with its optimum flux density, Hammond line reactors will not saturate under the most adverse line conditions. Since the inductance is linear over a broader current range, equipment is protected even in extreme over-current circumstances.

Will a Hammond Line Reactor extend the life of your motor?
Line reactors, when selected for the output of your drive, will enhance the waveform and virtually eliminate failures due to output circuit faults. Subsequently, motor operating temperatures are reduced by 10 to 20 degrees and motor noise is reduced due to the removal of some of the high frequency harmonic currents.

How do Hammond Line Reactors handle Heat Dissipation?
Particular attention has been focused on the design and field-testing of this product line. The results are reactors with ideal operating features including low temperature rises and reduced losses. Hammond reactors will operate efficiently and heat dissipation in your equipment will be of minimal concern.

How does a Line Reactor minimize harmonic Distortion?
Nonlinear current waveforms contain harmonic distortion. By using a Hammond line reactor you can limit the inrush current to the rectifier in your drive. The peak current is reduced, the waveform is rounded and harmonic distortion is minimized. Current distortion typically is reduced to 30%. Severe Harmonic current distortion can also cause the system voltage to distort. Often, high peak harmonic current drawn by the drive, causes "fl at-topping" of the voltage waveform. Adding a reactor controls the current component, and voltage harmonic distortion is therefore reduced.

What level of Short Circuit Capability do Hammond Line Reactors have?
Hammond line reactors can withstand current under short circuit conditions, reducing the potential of severe damage to electronic equipment. In a short circuit, the inductance of the coil is necessary to limit over-current after the core has saturated. Hammond has extensive experience in designing and testing dry-type transformers to withstand short circuits for the most demanding applications, and this experience has been applied to line reactor design.

How does a Hammond Line Reactor reduce Line Notching?
Whenever a rectifier converts AC power to DC, using a nonlinear device, such as an SCR, the process of commutation occurs. The result is a notch in the voltage waveform. The number of notches is a function of both the number of pulses and the number of SCR's in the rectifier.
Line Reactors are used to provide the inductive reactance needed to reduce notching, which can adversely effect equipment operation.

What are DV/DT Filter Reactors?
The advent of pulse width modulated (PWM) inverters with IGBT high-speed transistors, has resulted in smaller more cost effective drives and increased switching speeds. A waveform with increased harmonics at higher frequencies is the result of these much faster switching devices, usually at frequencies of 10,000 to 20,000 Hertz.
Drives and motors often need to be separated by significant distances. For deep wells or mines, the motors are usually controlled on the surface. As a result, the distance between the drive and the motor creates long motor lead lengths. In some plant applications, the motors can withstand the harsh environment but the sensitive variable frequency drive cannot. This again results in long lead lengths to the motor.
Most manufactures of variable frequency drives will publish a recommended maximum distance between their equipment and the motor. Sometimes these recommendations create application difficulties, thus increased motor lead lengths are inevitable.
DV/DT is explained as the steep-front voltage pulses that travel down these long leads in the circuit to the motor and subsequently reverted back in a "reflective wave". When the conductors are long enough, usually 20 feet or more, the time for reflection matches the time for transmission resulting in a high amplitude 'standing wave' on the circuit. Voltage spikes of up to 2100 volts are frequently experienced for 600-volt systems, and motor winding failures are the result.
A Filter Reactor, installed in front of the motor, combines the current limiting ability of an AC line reactor plus a resistive capacitance circuit that forms a damped, low pass filter. It provides protection for the motor by slowing the rate of voltage increase and minimizing the peak voltage that occurs at the motor terminals.
The cost of a DV/DT Filter Reactor is little more than the cost of the reactor and can be mounted next to the motor, or inside the PWM enclosure.

What are some DV/DT applications?
The Hammond RC series DV/DT filter reactors are specifically designed for drive/motor applications with long lead lengths (usually where the motor cable length is 20 feet and greater). They are always installed between the IGBT variable frequency drive and the motor. Typical installation applications include production process lines, conveyor systems and deep wells.

What is the typical "RC" DV/DT Filter Reactor performance?
The RC series DV/DT filter reactors combine appropriate values of inductance, capacitance and resistance to form a filter, which reduces DV/DT and peak voltages from the PWM voltage waveform. This combined with a 3% impedance reactor that will reduce motor heating harmonics, will significantly increase the life of the motor.
Long lead length motor drive applications can experience motor terminal peak voltage spikes twice the DC bus voltage, and higher. Therefore motor terminal voltage peaks of 1200 volts for 480V drives and 1600 volts for 600V drives are not uncommon. The highest peak voltages will typically occur in lower HP applications.

What are Industrial Control Transformers?
A control transformer is an isolation transformer designed to provide a high degree of secondary voltage stability (regulation) during a brief period of overload condition (also referred to as "Inrush Current"). Control transformers are usually rated for 600 volts or less.

What is the difference between an Air Core Reactor and an Iron Core Reactor?
Air Core:
They are used primarily as current or voltage limiting devices, particularly where large currents can enter a system that uses small amounts of power. An example is the telephone system, which uses very small voltages where the current in a fault condition needs to be kept to a minimum.
Iron Core:
An iron core reactor provides the same current or voltage control on a system as its air core counterpart. Iron core units tend to be used on smaller applications where the variables need greater or more sensitive control.

What are General Purpose Distribution Transformers and where are they used?
General Purpose distribution transformers are rated for 600 volts and below. They are generally used for supplying appliance, lighting, motorized machine and power loads from electrical distribution systems. They are either ventilated or totally enclosed, and are available in standard ratings from 250VA up to 750kVA.

What are Shielded Distribution Transformers and where are they used?
Hammond shielded distribution transformers provide a copper electrostatic shield between the primary and secondary windings. The shield is grounded and thus shunts most noise and transients to the ground path rather than passing them through to the secondary. Applications for shielded transformers are similar to those above, and they are ideal for commercial or electrical installations where electronic circuitry operating at low voltage DC is present and is very sensitive to 'noise'.

What are K-Factor Transformers and where are they used?
K-factor transformers are used as a general-purpose transformer but are designed to withstand the variety of harmonics created in today's office and industrial environments. The expanding use of devices with switch-mode power supplies and rectifier circuits with the subsequent wave distortion requires transformers to withstand the higher harmonics in the neutral conductor in the distribution system.

Define K-Factor?
K-Factor is defined as a ratio between the additional losses created by the harmonics and the eddy losses at the rated 60 Hz. This factor is used to specify the size of the transformer to meet the magnitude of the harmonic load in the circuit. A standard general-purpose transformer does not have the shielding, conductor sizes, core cross-section, or the capacity in the neutral to provide the same service.

What is a Low Voltage General Purpose Transformer?
Hammond'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 Buck-Boost Transformers and where are they used?
Buck-Boost transformers are control transformers with low voltage secondary windings. By field connecting the primary and secondary windings in an autotransformer configuration, they offer an economical solution to the adjustment of line voltages that are slightly above or below normal.
Buck-Boost transformers can be used to adjust stable voltages only. Fluctuating line voltages should be regulated with a Hammond Voltage Conditioner.

What are Autotransformers?
Autotransformers are similar to Buck-Boost transformers in that they are also an economical means of adjusting an output voltage. Autotransformers are designed to adjust the supply voltage when isolation from the line is not necessary and where local electrical codes permit. Units are designed in either a step-up or step-down application and to meet motor inrush currents.

What are Motor Starting Autotransformers?
Motors have a large inrush current component that requires a special design. Motor starting transformers are designed to withstand an inrush of upward of 25 times normal current. They typically are tapped on larger sizes to soft-start the motor until it is up to full RPM.

What are Energy Efficient (TP1) Transformers?
There is a growing movement in the electrical industry towards energy efficient products in all sectors including dry type transformers. In addition to the benefits to the environment, energy efficient transformers also can realize substantial savings in operating costs thereby having a direct impact on the initial investment evaluated over a period of time.

The specifications covering energy efficiency in transformers, is the NEMA Standards Publication, TP-1-1996, "Guide for Determining Energy Efficiency for Distribution Transformers". This specification has carefully considered the total owning cost unique for industrial or commercial installations where the load factor is an integral part of the efficiency rating.

What are Low Temperature Rise Transformers?

All transformers have operating losses, and heat is the product of these losses. Hammond low temperature rise transformers are designed with reduced 115 Degree C or Degree C full load operating temperature rises. These units decrease total operating losses by 20% and 35% respectively, compared with the standard 150 Degree C rise operating system. Hammond low temperature rise transformers provide greater efficiency under normal operating conditions, and overload capability without harm to their service life or reliability.

What are Encapsulated Transformers and where are they used?
These units are encapsulated and completely enclosed. The encapsulated design is especially suited for installations in harsh environments where dust, lint, moisture and corrosive contaminants are present. Typical applications include: pulp and paper plants; steel mills; food processing plants; breweries; mines; marine and shipboard installations.

What are Medium Voltage Transformers and where are they used?
Hammond medium voltage transformers are really 5kV class dry type distribution transformers. They are designed primarily for use in stepping down medium voltage power to a lower operating voltage for commercial, institutional or industrial applications.

What are Drive Isolation Transformers and where are they used?
Drive isolation transformers are designed to supply power to AC and DC variable speed drives. The harmonics created by SCR type drives requires careful designing to match the rated hp of each drive system. The duty cycle included is approximately one start every 2 hours. The windings are designed for an over-current of 150% for 60 seconds, or 200% for 30 seconds.

What are Clean Power Products?
Computer regulators and hard-wired line voltage conditioners protect equipment from both noise and voltage fluctuations while super isolation transformers are all designed to provide protection against frequency variation or noise related disturbances.

What are Power Transformers?
Hammond offers a wide range of dry type power transformers, rated from 750kVA up to 25 MVA. They are suitable for commercial, industrial, manufacturing or production process applications. With three phase ratings to 46 kV class and up to 25 MVA, Hammond offers the latest technology and manufacturing processes available today.

Explain the Banking of Transformers?
Two or three, single-phase transformers can be connected to make a three-phase bank. The primary windings of the single-phase transformers can be connected in delta or Wye and the secondary windings can be connected in either a delta or Wye configuration. The equivalent capacity of the bank will be equal to three times the nameplate rating of each single-phase transformer. Usually this type of installation is more expensive than using a single three phase transformer.

What are Primary Voltage Taps?
In some cases, the actual supply voltage to the primary of the transformer is either slightly higher or lower than the nameplate rating. Taps are provided on most transformers on the primary winding to correct this condition and maintain full rated output voltage and capacity. Standard taps are usually in 2 1/2% or 5% increments. Example: The transformer has a 480V primary rating and the incoming voltage is at 504V. The primary connection should be made at the +5% tap in order to maintain the nominal secondary voltage.

Can you operate a 60Hz Transformer at 50 Hz?
Transformers rated at 60Hz should not be used on a 50Hz supply due to higher losses and core saturation, and the resultant higher temperature rise. Transformers rated for 50Hz, however, can be operated on a 60Hz supply.

Explain Balance Loading on Single and Three Phase Transformers?
A single-phase transformer with 120/240V secondary has two separate 120V secondary windings and is usually connected into a 3-wire system. Care must be exercised in distributing the load on the two 120V windings evenly, so each winding is carrying about half of the total load.
Similarly for a three-phase transformer, each phase should be considered as a single-phase transformer. When distributing single-phase loads between the three phases, each of the three windings should be evenly loaded.

When is Sound Level an issue in the design?
Sound needs to be considered when transformers are located in close proximity to occupied areas. All energized transformers emanate sound due to the alternating flux in the core. This normal sound emitted by the transformer can be a source of annoyance unless it is kept below acceptable levels. There are ways of minimizing sound emission as discussed in the Hammond "Field Service Guide". Hammond Transformers are built to meet the latest ANSI, CSA and UL standards. These standards are outlined in the accompanying table.

When can you Reverse Connect a transformer?
In general, distribution transformers can be reverse connected without de-rating the nameplate
KVA capacity. However some precautions need to be taken for reverse connection of some smaller transformers. On Hammond transformers under 6kVA three phase and 3kVA single phase, there is a "turns ratio compensation" on the low voltage winding.
When the input voltage, equal to the nameplate rated voltage, is connected to the low voltage winding, the output voltage will be slightly lower than the nameplate rating.
When a three-phase transformer is reverse connected thus resulting in a Wye-Delta configuration, the neutral terminal must be isolated. Further, the reverse connected transformer may draw a higher inrush current during energization. Hence the sizing of the line fusing or circuit breaker may be affected.

Under what circumstance does need D.C. Resistance Measurement?
Current from a D.C. resistance bridge is applied to the transformers windings to determine the D.C. resistance voltage of the coils. This test is important for the calculation of I2R for use in the winding temperature test, and as base data for future assessment in the field.

What is a Polarity and Phase-Relation test for?
Polarity and phase-relation tests are made to determine angular displacement and relative phase sequence to facilitate connections in a transformer. Determining polarity is also essential when paralleling or banking two or more transformers.

What is an Air Cooled transformer?
It is a transformer that uses "air" as the cooling medium. This term is abbreviated with the ANSI designation AA, indicating open, natural draft ventilated construction.

What is Ambient Noise Level?
The noise level of the surrounding area, measured in decibels (dB).

What is Ambient Temperature?
It is the inherent or existing temperature of the atmosphere surrounding a transformer into which its heat is dissipated.

What is an Ampere?
It is the unit of measurement for electric current flow.

What does ANSI stand for?
The American National Standards Institute Inc. - one of the recognized organizations that specify the standards for transformers.

What is an Autotransformer?
It is a transformer that has only one winding per phase, part of which is common to both the primary and secondary circuits.

What does the term Banked describe?
Two or more single-phase transformers connected together to supply a three-phase load.

What does the term BIL mean?
Basic impulse level is a means to express the ability of the insulation system to withstand high voltage surges.

What is a Buck Boost transformer?
It is a two-winding, single-phase transformer with low voltage secondary windings, which can be connected as an autotransformer. Used to raise or lower single and three phase line voltages by 10 - 20%.

What is a Cast Coil transformer?
A transformer with coils solidly cast in epoxy resin under vacuum in a mold. Also called cast resin or epoxy cast coil transformers.

What is a Center Tap?
It is a reduced capacity tap at the midpoint in a winding.

What makes up a Coil?
Turns of electrical grade wire or strip conductor material wound on a form, referred to as a winding.

What is Coil Hot-Spot Temperature?
It is the absolute maximum temperature present in the transformer. This number is equal to the sum of the ambient temperature, temperature rise and a variable.
T Hot Spot = T ambient + T rise + (10-20) Degree C.

What is Common Mode?
An electrical noise or voltage disturbance, that occurs between all of the line leads and the common ground, or between the ground plane and either line or the neutral.

What is a Compensated Transformer?
It is a transformer with a turn's ratio that provides a higher than rated voltage at no load, and rated voltage at rated load. These transformers CANNOT be used for reverse feed.

What is the term Continuous Rating?
The constant load which a transformer can carry its rated primary voltage and frequency, without exceeding its specified temperature rise.

What is a Control Transformer?
It is a transformer that is designed to supply good voltage regulation characteristics when low power factor or high inrush current is drawn. Usually referred to as an Industrial Control Transformer.

What is the Core of a transformer?
It is the electrical grade steel laminations, which carry the magnetic flux.

What is Core Loss?
Losses in watts caused by magnetization of the core and its resistance to magnetic flux when excited or energized at rated voltage and frequency. Also referred to as excitation loss or no-load loss.

What is a Current Transformer?
It is a transformer generally used in control or instrumentation circuits for measuring current.

What is a Delta connection?
The delta connection is a standard three phase connection with the ends of each phase winding connected in series to form a closed loop with each phase 120 degrees from the other.

What is a Delta-Wye connection?
A Delta Wye is when the primary is connected in delta and the secondary in Wye when pertaining to a three-phase transformer bank or three-phase transformer.

What are "Dielectric Tests"?
These tests consist of the application of a voltage higher than the rated voltage for a specified time, for the purpose of determining the adequacy against breakdowns of insulating materials and spacing under normal conditions.

What is a "Dry Type" transformer?
A dry type transformer is one in which the transformer core and coils are not immersed in a liquid.

What is a "Dual Winding"?
A winding consisting of two separate parts which can be connected in series or parallel. Also referred to as dual voltage or series-multiple winding.

What is the "Efficiency" of a transformer?
The percentage of power transferred from the input of equipment to the output of equipment in Watts. (power out/power in x 100)

What is an "Electrostatic Shield"?
It is Copper or other conducting material placed between the primary and secondary winding and grounded to reduce electrical interference and to provide additional protection.

What is "Exciting Current (No-Load Current)"?
Current which flows in any winding used to excite the transformer when all other windings are open-circuited. It is usually expressed in percent of the rated current of a winding in which it is measured.

What does the term "Encapsulated" describe?
A transformer with its coils either encased or cast in an epoxy resin or other encapsulating materials.

What does the abbreviation FCAN stand for?
"Full Capacity Above Normal." This designates that a transformer will deliver its rated kVA when connected to a voltage source that is higher than the rated voltage.

What does the abbreviation FCBN stand for?
"Full Capacity Below Normal." Same as FCAN except that the taps are below rated voltage.

What is a Fan Cooled transformer?
A transformer cooled mechanically to maintain its rated temperature rise, typically using auxiliary fans to accelerate heat dissipation.

Describe a Flexible Connection?
A non-rigid connection used to reduce transmission of noise and vibration.

Describe Flux Density?
The magnetic field strength in the core, typically measured in Telsa or Gauss.

Explain Frequency?
On AC circuits, designates the number of times the polarity alternates from positive to negative and back again . . . such as 60 cycles per second. Measured in Hertz.

What is a Full Capacity Tap?
A full capacity tap is one through which the transformer can deliver its rated kVA output without exceeding the specified temperature rise.

Explain Voltage Ratio (turns ratio)?
To confirm the voltage ratio of a transformer, the ratio of the number of turns in the high-voltage winding with respect to the number of turns in the low-voltage winding, is measured.

What are No-Load and Excitation Current tests?
No-load losses (excitation losses) are the core losses of a transformer that are "excited" at rated voltage and frequency, but which do not supply load. No-load losses include core loss, dielectric loss, and losses in the windings due to exciting current. The transformer is excited at rated voltage with all other windings open circuited. The exciting current and no load loss is then measured.
(Note: This is a standard test only on units over 500kVA. It will only be carried out on lower kVA units when specifically requested.)

What are Dielectric tests?
The purpose of dielectric tests is to demonstrate that the transformer has been designed and constructed to withstand the voltages associated with specified insulation levels.

What is an Applied Voltage test?
A normal power frequency such as 60hz is applied to each winding for one minute. These tests are in accordance with table (3) in ANSI C57-12-01.

What is an Induced Voltage test?
The induced voltage test is applied for 7200 cycles or 60 seconds whichever is shorter. The voltage applied is twice the operating voltage, and confines the integrity of the insulation

What are Impedance Voltage and Load Loss tests?
The voltage required to circulate the rated current under short-circuit conditions when connected on the rated voltage tap, is the impedance voltage. Rated current is circulated through the windings with the secondary short-circuited. The impedance voltage and load loss is measured. They are corrected to rise +20 Degree C reference temperature. (Note: This is a standard test only on units over 500kVA. It will only be carried out on lower kVA units when specifically requested.)

What are Type Tests?
Type Tests are required either to qualify a new product or to further certify a production product. The following is a list of type tests performed on Hammond Transformers.
  • Temperature Rise Test
  • Sound Level Test
  • Partial Discharge (corona)
  • Basic Impulse Insulation Level (BIL)
  • Short-Circuit Test

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