Transformers Flashcards
What is an isolation transformer?
The second windings are physically and Electrically isolated from the primary winding
What is an autotransformer?
They only have one winding
What is a current transformer?
They are used for metering alternating current
What is a transformer?
It is a magnetically operated machine that can charge values of E, I without changing frequency
What are the primary windings?
Power Input
What are the secondary windings?
Power Output
What is excitation current?
The amount of current flow in the primary windings of a transformer. It is required to magnetize the core
When does excitation current exist?
It exists when there is no load connected to the secondary
How is the amount of voltage induced in the secondary windings determined?
It is determined by the ratio of the number of turns of wire on the secondary to those in the primary
What are volts per turn ratio?
The ratio of the number of turns of wire on a coil to the voltage
What are all values of transformers proportional to?
Its turn ratio
What will power inout always be equal to?
Power output. The VARS will always be the same
What are advantages of three phase power?
- HP ratings of 3 phase motors and KVA ratings of 3 phase motors or transformers is about 150% greater than those of single phase that are the same size
- Three phase power pulsates just like single phase power but does not pulsate to zero
- Balanced three phase systems require conductors of 75% of the of conductors required to get the same power from a single system
What is Phase Sequence( Phase Rotation)?
The order in which the three voltages of a three phase circuit follow each other
How can the three phase sequence be changed?
- Reversing the direction of rotation of the three phase generator
- interchanging the connections of any two of the three line connections
