CAPSTONE ch. 10
A transformer has a 240 V primary and a 120 V secondary. With a 30 ohm load connected, what is the primary volt-amps?
480
The efficiency of a transformer with an input power of 60 W from a 115 volt line and an output of 125 mA at 240 volt is
50%
What's the primary line current for a fully loaded 45 kVA, 480V to 120/240V, three-phase transformer?
54 Amps
The correct input of an 89 % efficient trhansformer with a power output of 50 volt-amps is
56 volt-amps
What's the maximum primary overcurrent device rating for a 0.50 kVA, single-phase, 240V transformer?
6 amps
The efficiency of a transformer with an input power of 30 W from a 115 volt line and an output of 90 mA at 240 volt is
72%
The correct input of an 93 % efficient transformer with a power output of 70 volt-amps is
75 volt-amps
What's the maximum primary overcurrent device rating for a 25 kVA continuously loaded, three-phase, 240V transformer?
80 amps
In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.
H, X
Which of the following identifies the un-grounded terminal on the secondary side of the transformer?
X1
The lower voltage windings of a control transformer can be identified by symbols
X1 X2
The transformer that converts a high voltage from the power company down to 240/120 V for homes and businesses is called a(n) _____ transformer.
distribution
Most transformer cores are not made from a solid piece of metal. Instead, they are assembled from many thin sheets of metal. This type of construction is called _____.
laminated
A transformer supplying a house with 240/120 V has a secondary which is center tapped. The conductor connected to the center is called the _____ conductor.
neutral
The transformer winding, which is the power input winding, is called the _____ winding.
primary
The transformer winding to which the load is usually connected is called _______ winding.
secondary
The transformer winding, which is the output winding, is called the _____ winding.
secondary
The rating of a transformer whose maximum safe output is 480 volts at 4.16 amps is
2 KVA
A transformer has a 240 V primary and a 60 V secondary. With a 5 ohm load connected, what is the primary current?
3 amps
A control transformer with a unity power factor and a turns ratio of 5:1 is rated for 240 volts AC at 5 amps for the primary and is rated at _______ in the secondary.
1200 volts-amps
Overcurrent protection for the secondary of a transformer rated 600V or less having a secondary current rating of 9A or more must be set at not more than _____ percent of the secondary current rating.
125
A 45 kVA, 480V primary to 120/208V secondary, three-phase transformer with a 175A secondary overcurrent protection device will require at least _____ secondary conductors (the secondary conductors are 10 ft long).
2/0 awg
The size of the grounding electrode conductor for a single separately derived system must not be smaller than that identified in _____, based on the area of the largest derived ungrounded supply conductor.
250.66
In a certian loaded transformer, the secondary voltage is one-third the primary voltage. The secondary current is _______ the primary current.
3 times
A 45 kVA, 480V primary to 120/208V secondary, three-phase transformer with a 70A primary overcurrent protection device will require at least _____ primary conductors, terminals rated 75°C.
4 awg
The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) _____ transformer.
control
Power transformers are rated in
volt-amps or kVA