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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.

The Primary voltage is the input voltage.

A transformer overload condition occurs when voltage or current higher than the transformer rating is applied to the unit.

• In certain circumstances, the input voltage is either higher or lower than the Primary Voltage listed on the transformer’s nameplate. To fix this problem, Acutran can include taps. Standard tap increments are ± 2.5%, but a unit can be designed with multiple tap settings.
• Transformers may be designed with full capacity taps ABOVE or BELOW nominal (FCAN and FCBN, respectively). Full capacity taps allow for the input primary voltage to be increased or decreased from its nominal voltage while retaining its ability to deliver its rated kVA output without exceeding its specified temperature rise.

Inductance is the property of a conductor by which when exposed to alternating current flow, the change in current flow induces a voltage across the conductor.

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

An autotransformer is a transformer where the primary and secondary circuits have a common winding. These transformers adjust the input voltage when isolation is not required. They can be used to either step-up or step-down the secondary voltage as required. Typically, autotransformers are used in motor starter applications to reduce quick current overloads or to reduce voltage to the starter motor. A voltage reduction will delay the time it takes for a motor to reach full speed, thus reducing the overall current to the motor during startup.

Temperatures that exceed the rated ambient temperatures for which the insulation system is designed can cause insulation damage and premature failure. This can often occur in hotter environments or in rooms that have inadequate ventilation. Care should be taken in installing stacked transformers because the top transformer may use air that has been heated by the lower unit. Damage from high ambient temperatures often does not cause an immediate failure but can cause damage that results in a failure week, months or years later. High ambient temperatures can be mitigated in several ways:

• Order a transformer designed with a lower temperature rise.
• Use fan cooling, this is typically an economical solution when a unit exceeds 500-1500kVA.
• Place the transformer in a temperature-controlled location.
• Properly ventilate the location that the transformer is located in.
• Never try to use cooling fans directly on a transformer or blow across a transformer’s windings.
• Manufacturers use special fans, specific locations, and cooling patterns to cool transformers. Improper placement of airflow could cause disruption of the convection airflow and cause the transformer to overheat.

A Zig-Zag transformer is a three-phase transformer that provides an artificial grounding path. A specific zero-sequence impedance and ground-fault current ratings are needed to properly design the transformer. Zig-Zag transformers can be paired with neutral grounding resistors or air core reactors form additional current-limiting impedance. Zig-Zag transformers are often used by a Utility company and are attached to their renewable load generators (solar, wind, etc). Zig-Zag systems will usually include a ground fault monitoring relay, a protection relay current transformers and applicable fuses or disconnect switches.

• Transformer maximum temperature is dependent on the insulation used in the construction of the unit. Standard temperature classes are 105°C, 150°C, 180°C, and 220°C.
• 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 busbars. Nomex, polyester, epoxy, rubber, Glastic and plastic are commonly used as insulating materials in the electrical industry.

A Neutral Grounding transformer is a single-phase transformer that provides an artificial grounding path. Neutral Grounding Transformers are often paired with a neutral grounding resistor to dial in the particular impedance required.

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.

• System Voltage and System BIL
• Continuous Amperage
• Fault Current and Duration
• Impedance
• Enclosure Type
• Accessories: Disconnect switches, fuses, ground monitoring relays, current transformers

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.

A Line Reactor is an electrical device that is used to limit the current of a system. Because of the Line Reactor’s impedance, they are used to oppose the rapid change in current. They help protect your equipment with spikes in current.

A test that is used to ensure the correct number of turns on the primary and secondary windings. When the resulting ratio of turns between the primary and secondary windings is applied to the secondary winding phase voltage, you should arrive back at the primary phase voltage.

Practically all transformers (with the exception of Autotransformers) are, in fact, Isolation Transformer. This is due to the fact that their primary and secondary windings are PHYSICALLY isolated from each other (they are not physically connected to each other). The transformation in voltage and current between primary and secondary windings occurs as a result of the shared magnetic field in the core (Mutual Inductance).

• It is a dielectric test that determines the BIL (Basic Impulse Level) capability by applying high frequency, steep wave-front voltage between windings and ground. This test is commonly used to simulate the impact of a lightning strike on power equipment.
• Basic impulse level is a means to express the ability of the insulation system to withstand high voltage surges.

It is a high potential dielectric test applied to the windings to check insulation materials and clearances. It is normally testing the transformers at a higher voltage limit (125-150%) than operating voltage for a 1-minute cycle.

Galvanic corrosion is a process that occurs by electron transfer between two dissimilar metals in a corrosive environment. In this situation, the natural oxidation characteristics of each metal are enhanced such that the metal that is more easily oxidized experiences a higher corrosion rate than it would were it not in contact with the other metal. The metal that is less prone to oxidation experiences a lower corrosion rate than normal. A galvanic shield helps to eliminate the transfer due to the direct connection to the ground.

It is the increase over the ambient temperature of the winding due to energizing and loading.

An air core reactor that limits the short circuit fault current to a manageable value.

• It is the transformer electrical losses, which include no-load losses (core losses) and load losses (winding losses). There is not a specific formula to calculate total losses since they vary by size and manufacturer. Manufacturers will often provide charts that show losses at one or more load points.
• Total losses help determine a transformer’s efficiency. Efficiency is the ratio between the percentage of power transferred from the primary coil to the secondary coil in Watts.

An air core reactor that gets connected to the neutral of a transformer for protection and control circuitries.

• The UL Listed Mark on a product is the manufacturer’s representation that samples of that complete product have been tested by UL to nationally recognized safety standards and are found to be free from a reasonably foreseeable risk of fire, electric shock, and related hazards.
• UL’s Component Recognition Service covers the testing and evaluation of component products that are incomplete or restricted in performance capabilities. These components will later be used in complete end products or systems Listed by UL.

• 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.
• 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.

• Single phase Amps = (kVA x 1000)/Volts
• Single phase KVA = (Volts x Amps)/1000
• Three phase Amps = (kVA x 1000)/Volts x 1.73
• Three phase KVA = (Volts x Amps x 1.73)/1000

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.

Noise is a very broad term that can be applied to a number of AC power line disturbances. Lightning surges or any other sudden changes in load, such as switching motor loads or power factor correcting capacitors can produce voltage spikes and ringing. Phase controlled rectifier loads and arcing devices produce continuous noise unless adequately filtered. Noise sources are either common mode, which appears between both sides of a power line and ground or of transverse mode, which appears from line to line.

A Ground is the reference point in an electrical circuit that all the voltage circuits are measured. Grounding is used to protect equipment or people, by providing a path of least resistance to a protection circuit like a fuse or a circuit breaker. A ground is also used to limit the build-up of static electricity when handling flammable gases or products or a Ground can be used to shunt electrical noise.

• Electrostatically shielded (Faraday Shield) transformers provide a copper electrostatic shield between the primary and secondary windings. The shield is grounded and thus shunts some noise and transients to the ground path rather than passing them through to the secondary. Transformers having a K-Rating are required to have an electrostatic shield.
• Electrostatically shielded transformers often preferred for electrical installations where electronic circuitry operating at low voltage DC is present and is very sensitive to ‘noise’. Recent testing of electrostatically shielded transformers has questioned their perceived effectiveness where the transformer’s secondary is grounded which would cover most applications.

A delta connection in only on a three-phase transformer. It is normally the standard connection where each phase is connected in series to form a closed loop with each phase 120° from each other.

The Secondary voltage is the output voltage to the customer’s electrical load.