What is exciting current?
Exciting current, when used in connection with transformers, is the current or amperes required for excitation. The exciting current on most lighting and power transformers varies from approximately 10% on small sizes of about 1 KVA and smaller to approximately .5% to 4% on larger sizes of 750 KVA.
The exciting current is made up of two components, one of which is a real component and is in the form of losses or referred to as no load watts; the other is in the form of reactive power and is referred to as KVAR.
What is polarity, when associated with a transformer?
Polarity is the instantaneous voltage obtained from the primary winding in relation to the secondary winding. Transformers 600 volts and below are normally connected in additive polarity — that is, when tested the terminals of the high voltage and low voltage windings on the left hand side are connected together, refer to diagram below:
This leaves one high voltage and one low voltage terminal unconnected. When the transformer is excited, the resultant voltage appearing across a voltmeter will be the sum of the high and low voltage windings.
This is useful when connecting single phase transformers in parallel for three phase operations. Polarity is a term used only with single phase transformers.
What is BIL and how does it apply to Acme transformers?
BIL is an abbreviation for Basic Impulse Level. Impulse tests are dielectric tests that consist of the application of a high frequency steep wave front voltage between windings, and between windings and ground.
The Basic Impulse Level of a transformer is a method of expressing the voltage surge (lightning, switching surges, etc.) that a transformer will tolerate without breakdown.
All transformers manufactured by Acme, 600 volts and below, will withstand the NEMA standard BIL rating, which is 10 KV. This assures the user that he will not experience breakdowns when his system is properly protected with lightning arrestors or similar surge protection devices.
What is meant by "impedance" in transformers?
Impedance is the current limiting characteristic of a transformer and is expressed in percentage.
What is "Class" in insulation?
Insulation class was the original method used to distinguish insulating materials operating at different temperature levels. Letters were used for different designations.
Letter classifications have been replaced by insulation system temperatures in degrees Celsius. The system temperature is the maximum temperature at the hottest spot in the winding (coil).
Graphical representations of six insulation systems recognized by Underwriters’ Laboratories, Inc. (UL) are shown in Figure A (Below). These systems are used by Acme for a large part of the product line.
What is temperature rise in a transformer?
Temperature rise in a transformer is the temperature of the windings and insulation above the existing ambient or surrounding temperature.
What is meant by regulation in a transformer?
Voltage regulation in transformers is the difference between the no load voltage and the full load voltage. This is usuallyexpressed in terms of percentage.
For example: A transformer delivers 100 volts at no load and the voltage drops to 95 volts at full load, the regulation would be 5%.
Acme dry-type distribution transformers generally have regulation from 2% to 4%, depending on the size and the application for which they are used.
What is the difference between "Insulating," "Isolating," and "Shielded Winding" transformers?
Insulating and isolating transformers are identical. These terms are used to describe the isolation of the primary and secondary windings, or insulation between the two.
A shielded transformer is designed with a metallic shield between the primary and secondary windings to attenuate transient noise. This is especially important in critical applications such as computers, process controllers and many other microprocessor controlled devices.
All two, three and four winding transformers are of the insulating or isolating types. Only autotransformers, whose primary and secondary are connected to each other electrically, are not of the insulating or isolating variety.
What are taps and when are they used?
Taps are provided on some transformers on the high voltage winding to correct for high or low voltage conditions, and still deliver full rated output voltages at the secondary terminals.
Standard tap arrangements are at 2.5%and 5% of the rated primary voltage for both high and low voltage conditions.
For example, if the transformer has a 480 volt primary and the available line voltage is running at 504 volts, the primary should be connected to the 5% tap above normal in order that the secondary voltage be maintained at the proper rating.
The standard ASA and NEMA designation for taps are “ANFC” (above normal full capacity) and “BNFC” (below normal full capacity).
What is a transformer and how does it work?
A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. It can be designed to “step up” or “step down” voltages and works on the magnetic induction principle. A transformer has no moving parts and is a completely static solid state device, which insures, under normal operating conditions, a long and trouble-free life.
It consists, in its simplest form, of two or more coils of insulated wire wound on a laminated steel core. When voltage is introduced to one coil, called the primary, it magnetizes the iron core. A voltage is then induced in the other coil, called the secondary or output coil. The change of voltage (or voltage ratio) between the primary and secondary depends on the turns ratio of the two coils.