Transformer Principles Flashcards
Additive Polarity
Polarity where the H1 marking is opposite the X2 marking and the H2 marking is opposite the X1 marking.
Delta Connection
The connection of a transformer to form a “Δ” configuration. Delta connections can be made by connecting odd to even terminals.
Eddy Currents
Currents formed when the magnetic field induces currents in the iron core. This is reduced by the use of laminated cores to construct the transformer.
Efficiency
Efficiency is always the ratio of output to input. It is the ratio of true (output power) to apparent (input power).
Flux Leakage
Each transformer produces line of flux. Each time the transformer is energized there is some flux lost because of coupling.
Hysteresis Losses
The result of the energy wasted in reversing the magnetization of the core every time the current reverses and magnetizes the core in a different direction.
Kilovolt (KVA) Rating
The rating of a transformer in kilovolt-amps.
Mutual Inductance
The effects of inductance are mutual between the primary and secondary. The current in the primary induces a voltage in the secondary.
Open Delta
The connection of two transformers only. One side of the Delta is removed and the transformer is considered open.
Polarity Markings
(+) = Positive and (-) = Negative.
Primary Winding
The primary winding is the winding that is connected to the source voltage. It does not necessarily have to be the high voltage winding.
Secondary Winding
The secondary winding is the winding that is connected to the load. It does not necessarily have to be the low voltage winding.
Significance of 1.73
The multiplier from line to neutral in a 3-phase transformer. Example: A 3-phase “Y” to neutral—208 volts divided by 1.73 equals 120 volts.
Subtractive Polarity
Polarity where the H1 terminal is opposite the X1 terminal and the H2 terminal is opposite the X2 terminal.
Transformer Polarity
A system of (ANSI) markings of the transformer leads. The high voltage leads are “H” leads and the low voltage leads are “X” leads.
Turns Ratio
The ratio of the turns in the primary to the turns in the secondary.
Wye Connection
The connection of transformer to form a “Y” configuration. “Y” connections can be made by connecting either the even terminals or the odd terminals together.
Core Type Transformer
The iron core is used to concentrate the lines of force and produce a better magnetic coupling between the two coils.
Shell Type Transformer
Made up of silicon steel laminations covered with varnish and pressed together. The windings are wound in layers and fit over the center section of the core. The laminated core helps reduce the power losses due to eddy currents and hysteresis, and also reduces flux leakage.
Step-up Transformer
Contains more conductors to be cut by the magnetic field, thus a greater amount of voltage will be induced into the secondary than was applied to the primary. It will increase the voltage.
Step-down Transformer
Contains less conductor to be cut by the magnetic field, thus a smaller amount of voltage will be induced into the secondary than was applied to the primary. It will decrease the voltage
Isolation Transformers
A transformer of the multiple-winding type, with the primary and secondary windings physically separated, which inductively couples its secondary winding to the grounded feeder systems that energize its primary winding.
Subtractive Transformer
The H1 and X1 leads are directly across from each other.
Additive Transformer
The H1 and X1 leads of a transformer with additive polarity are diagonally across from each other.
When paralleling two single-phase transformers, the conditions that must be met are:
Have the same voltage ratings.
Polarities must be correct.
Same percent of impedance.
Polarity Testing
A procedure that verifies that electrical conductors are connected to the correct terminals and are not reversed.
Primary Winding
The winding that receives the power from the source.
Secondary Winding
The winding into which transformed voltage is induced.
Single winding transformers have high voltage winding leads marked ___ and ___.
H1, H2
Single winding transformers have low voltage winding leads marked ___ and ___.
X1, X2
Dual winding transformers have the high voltage winding leads marked…
H1, H2, H3, and H4
Dual winding transformers have the low voltage winding leads marked…
X1, X2, X3, and X4
Subtractive Transformer
If the X1 terminal is directly across from the H1 terminal so it has subtractive polarity.
Additive Transformer
If the X1 terminal sits diagonally across from the H1 terminal so it has additive polarity.
When paralleling two single-phase transformers, they must have…
same voltage, same percentage of impedance, and correct polarities.
Impedance (Z)
Represented by the symbol Z, is a measure of the opposition to electrical flow.
Percent Impedance (%Z)
The percent of the rated load impedance possessed by a transformer.
Transformers may have more than one winding on the high voltage and/or low voltage side. True or false?
True
Autotransformer
A single-winding transformer with a single winding mounted on an iron core with the primary and secondary currents flowing in parts of the same winding.
Control Transformer
A small transformer similar in construction to power or distribution transformer and are used to transform a higher voltage to a safer lower voltage, for electrical control devices.
Current Transformer (CT)
Used to step down a relatively high current to some low value for the operation of instruments and some control devices.
Tap
A device that attaches a branch circuit to a main circuit, a threading tool, or a conductor that combines multiple sized conductors.
There is a possibility for backfeed in which case voltage would feed back through the line making what was the secondary now the primary winding. True or false?
True
