transformer 3 phase voltages Flashcards
A poly-phase electrical system having a 90° phase separation is the ? type.
4 phase
A 3-phase motor will deliver ? power to a machine as a single-phase motor of the same size.
1 1/2 greater
The earliest poly-phase systems adopted by the electrical industry in the United States is the ? system.
3 wire delta
Single-phase motors produce vibrations caused by a pulsing torque pattern.
true
The secondary windings of three substation transformers are banked in a delta. The potential across the windings is 2,400 volts. The output voltage from ? is ?
line to line / 2400 v
On wye systems, unlike transformer bushings are joined with jumpers, and lines are connected at points where the bushing leads are connected.
false
Converting a distribution system from delta to wye increases the capacity of the system by ?
73%
When current through the secondary windings of a wye connected transformer bank is 300 amperes, the current through the load lines will be ? .
300 a
The individual sine waves of a 3-phase system are ? out of step with each other
120
A 3-phase line requires ? of the conductive material that is required by a single-phase line to transmit the same power over a fixed distance at a given voltage.
75%
Transformers with single primary bushings may be installed on wye systems.
true
Two lines that have the same rotation will always phase together.
false
Doubling the voltage on a line reduces the current required to supply an equal amount of power by 50%.
true
A single-phase tap take off from a 12.47-kilovolt, 3-phase wye line has a line-to-neutral voltage of ?
7.2 kv
In a 3-phase system, the three voltages are of different magnitudes.
false
If B phase is lagging A phase by 120°, C phase will lag A phase by ?
240
By doubling the voltage of a line, ?
the same load can be supplied at four times the distance
At higher distribution circuit voltages, the risk to line crews increases.
true
The most commonly used distribution system in the country is the ?
12.5 kv wye
Higher voltage distribution circuits with longer reach have greater reliability.
false
