FREQUENTLY ASKED QUESTIONS
Acutran is an industry-leading manufacturer of custom transformers. Through our years of experience, we have compiled a list of frequently asked questions. Please read below to learn more about the different types of transformers we offer, the characteristics of these products, and industry-related terminology.
- 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.
- System Voltage and System BIL
- Continuous Amperage
- Fault Current and Duration
- Enclosure Type
- Accessories: disconnect switches, fuses, ground monitoring relays, current transformers
- 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.
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.
- 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.
- 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.
- 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.
- 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
- 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.
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