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20 Cards in this Set
- Front
- Back
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What is the formula to determine a generators output frequency? |
freq= rpm*n/120 |
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What is a device that has no moving parts and that transfers energy from one circuit to another by electromagnetic induction called? |
A transformer |
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The energy in a transformer is always transferred without a change in _______, but usually with changes in _______________ and _________. |
without frequency
with voltage and current |
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Most power-supply transformers for electronic equipment are designed to operate at a frequency of ____________ |
50-60hz |
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What are power supply transformers, used in electronics circuits, characterized by? |
- single-phase, constant-potential transformers with either one or more secondary windings, or a single secondary with several tap connections.
-low volt-ampere capacity
-less efficient than large constant-potential power transformers. |
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What electrical principle do transformers operate off of? |
mutual induction |
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What is the turns ratio of a transformer? |
E1/E2=N1/N2 |
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It is not permissible to operate transformers at _________ |
more than 10 percent below their rated frequency because they will overheat. |
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The ordinary power transformer has an efficiency of _________________ |
97 to 99 percent |
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An open-delta connection results when? |
-any one of the three transformers is removed from the delta-connected transformer bank
-the line current must be reduced so as not to exceed the rated current of the individual transformers if they are not to be overloaded. |
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The line current is equal to ________________ in the open-delta connection. |
the transformer phase current |
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The full load capacity in a delta connection at unity power factor is what? |
3(Current Phase)(Voltage Phase) = √3(Voltage line)(Current line) |
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The power delivered to the primary of a transformer is equal to what? |
The power delivered to the secondary, neglecting losses
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transformer efficiency = |
output/input |
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If the three secondaries of an energized transformer bank are properly connected in delta and are supplying a balanced three-phase load, the line current will be equal to ____________ |
1.73 x phase current |
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In an open-delta connection, the line current is limited to the rated phase current of: |
(Current line)/ √3 |
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The ratio of the load that can be carried by two transformers connected in open delta to the load that can be carried by three transformers in closed delta is: |
• Pv = Eline x Iline / (√3 x Eline x Iline) = 1/√3 = .577 or 57.7 percent of the closed-delta rating. |
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What does a shore tie power station consist of? |
a receptacle and portable cable with plugs on each end |
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What is the shore tie receptacle rated for? |
400 amps |
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What type of cable is used for shore ties? |
three-conductor, flexible, unshielded, 600-volt, type THOF-500 or THOF-400
(rated for 500/400 amps respectively) |
