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40 Cards in this Set
- Front
- Back
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What determines strength of magnetic field when current flows through conducter |
#of turns, current and iron core |
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Name three factors that determine the amount of induced voltage in a coil |
#of turns of wire, strength of magnet, speed of cutting action |
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How many lines of magnetic flux must be cut to induce 1 volt |
1 Weber (100,000,000) |
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What is the effect on induced voltage of adding more turns of wire to a coil |
Induced voltage increases |
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What is a transformer |
A magnetically operated machine that changes values of volts, current and impedance
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What are common efficiencies for transformers |
90-99% |
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What is an iso transformer |
Transformer that have there primary and secondary windings electronically and mechanically separates from each other |
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All values of a transformer are proportional to its |
Turns ratio |
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What is an auto transformers |
Autotransformers have one winding that is both primary and secondary |
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What is a disadvantage of an auto transformer |
No line isolation between primary and secondary (no surge protection) |
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Explain the difference between a step up and step down transformer |
Step up has lower primary voltage then secondary Step down has a higher primary voltage then secondary |
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A transformer has a primary voltage of 240V and a secondary voltage of 48V what is the turns ratio |
5:1 |
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What are three basic split phase motors |
Resistant start induction, capacitor start induction, capacitor start capacitor ran |
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The voltages of a two phase system are how many degrees out of phase with each other |
90• |
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How are the start and run windings of a split phase motor connected in relation to each other |
Start winding is top of core, run winding is bottom, start winding resistance produces a phase angle difference between the current of both |
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How many degrees out of phase in a split phase motor should the two winding be to create the most starting torque |
90• |
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What is the advantage of the capacitor start induction run motor over the resistant start induction run motor |
Uses and ac electronic capacitor to increase phase angle difference between start and run current, increasing starting torque |
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On the average how many degrees out of phase with each other are the start and run winding currents in a resistance start induction run motor |
35-40• |
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What device is used to disconnect the start windings for the circuit in most non hermetically sealed capacitor start induction run motors |
Centrifugal switch |
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Why does a split phase motor continue to operate after the start windings have been disconnected from the circuit |
Changing polarity of windings |
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What is voltage |
Electrical pressure/force and the potential difference between two points. Measured in volts |
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What is a current transformer |
Clamp on ammeter, primary wire is the line side and secondary is load side |
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What is a autotransformer |
Transformers that contain only one winding. The line and load share the same winding . There 99% efficient. Cheaper and have no surge protection |
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What is an isolation transformer c |
They have the ability to reduce voltage spikes on the line There 96-97% efficient and do offer surge protection |
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Voltage chart rules ho |
Voltage is directly proportional to the turns ratio. Current is inversely proportional to the turns ratio. Both windings always do the same amount of work. |
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How many single phase motors are there |
5 |
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Resistance start induction run motor R.S.I.R |
Start winding is thinner, more resistive and less inductive. They have a 35-40 degree phase shift between the start and run current At 75% rated speed the start winding is removed from the circuit |
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Why are split phase motors called split phase motors? |
Because they have a start winding and run winding |
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Capacitor start induction run C.S.I.R |
The capacitor is in series with the start winding, 90 degrees phase angle is peak torque Capacitor stores and discharges electrons God starting torque 75% capacity, start winding kicks out and causes poor running torque 30-40% efficient |
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What are the starting relays |
Centrifugal switch- momentum operated Hot wire relay Current relay Solid state starting relay which contains a thermistor Potential relay |
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Where are the coils in relation to the winding in current and potential relays |
Current relay has coil in series with run winding Potential relay has cool in parallel with the start winding |
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What is current |
The flow of electrons, intensity of flow measured in amps |
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What is resistance |
Opposition to current flow measured in ohms |
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What is power |
Amount of work being done by current measured in watts |
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Definition of flux density |
The more lines of flux there are the stronger the force is |
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Define electromagnetism and what affects it |
Whenever current flows in a conductor a magnetic field is formed around it •# of turns •current •iron core |
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What two cores are there |
Air core- does not affect flux lines Iron core- will affect lines of flux and add them |
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What is Lenz’s law define el |
An induced voltage or current opposes the motion that caused it |
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Define electromagnetic induction and what affects it |
Anytime a conductor passes through lines of flux a voltage and current is inducted into that conductor Strength of magnet Speed of cutting action Number of turns |
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What are the three transformers? |
Current transformer Auto transformer Isolation transformer |
