XRA-112 Transformers
transformers work on the principle of?
induction, hence requires AC
transformers are not ___ effecient
100%
A typical power loss is ___ occurs as heat
5%
If 2 coil are placed next to each other, by changing the electric current in one of the coils what happens?
A current is induced or produced in the other coil
What is a transformer?
A device that does not convert one form of energy into another form of energy, rather it transforms the energy (current and voltage in an AC circuit) to either higher or lower intensities
What is a step up transformer?
A transformer which increases the voltage in the secondary coil i.e. it reduces current in order to maintain the same power on the secondary side
What is a step down transformer?
Decreases the voltage in the secondary coil but increases the current on the secondary side
What is turn ratio?
Defined as ratio of number of turns in the secondary coil to number of turns in primary coil
what is hysteresis loss in regards to what causes heat production?
Due to constant rearrangement of the atoms in the core
what is copper loss in regards to what causes heat production?
Due to resistance and back EMF in the windings
what is eddy currents in regards to what causes heat production?
Due to swirling random currents in the core
What is the formula for turn ratio?
Formula=Ns/Np Ns=Number of turns in secondary coil Np=Number of turns in primary coil
Step down transformer is ______ than Ip
Greater
A step up transformer has a turn ratio of?
Greater than 1 i.e. secondary to be greater than primary (x-ray machine)
What is the transformer law for current formula?
Ip/Is=Ns/Np Where Is=Current in secondary coil Ip=Current in primary coil Ns=Number of turns in secondary coil Np=Number of turns in primary coil
The turn ratio of a transformer is 0.125. What will be the current in the secondary coil if the current flowing through the primary coil is 0.8 A?
Is/Ip = Np/Ns Is = Ip x Np /Ns = 0.8 x 1/0.125 = 6.4 A
What is the formula for transformer law for voltage and current?
Is/Ip=Vp/Vs where Is=Current in secondary coil Ip=Current in primary coil Vs=Voltage in secondary coil Vp=Voltage in primary coil
What is an autotransformer?
It consists of an iron core with "one coil" which acts as both primary and secondary winding to raise or lower the voltage i.e. acts as step up or step down transformer, it works on the principle of self induction rather than mutual induction
What best describes a shell type transformer?
It is made by combining 2 closed cores, it has 2 coils wound on the same central portion of the core, it works on the principle of mutual induction, it is more efficient than core-type transformer because it confines more magnetic field i.e. x-ra equipment
What best describes a closed core transformer?
It is not a single piece of iron, it is slab made up laminated iron, "2 coils are wounded on the separate arms of the core", it works on the principle of mutual induction, it helps reduce the energy loss caused by heat built up
When is autotransformer used?
Only if small increments of voltage is required i.e. kV selector in x-ray machine
How does lamination of the core help prevent heat production?
Reduces eddy currents
How does use of hardened ferromagnetic material (steel) help to prevent heat production?
Reduces hysteresis
Step up transformer is _______ than Ip
Smaller
What is transformer law for voltage and current?
The change in the current across a transformer is in the opposite direction from the voltage but in the same proportion i.e. if the voltage is doubled, current will be half
What is transformer law for current?
The change in the current between the primary or inducing side and the secondary or induced side is "inversely proportional" to the change in the number of turns from primary to secondary
What is Transformer law for voltage?
The change in the voltage between the primary or inducing side and the secondary or induced side is directly proportional to the change in the number of turns from primary to secondary
What describes a step down transformer? (not the answer saying what it does)
The right side or secondary side has less turns than the left side or primary side (5 times), hence voltage is also decreased 5 times on secondary side since current is inversely related to voltage, therefore, current on the secondary side is 5 times of the primary side
Calculate the turns ratio where Np=100 and Ns is 50
Turns ratio =Ns/Np =50/100 =0.5
There are 125 turns in the primary coil of a transformer which has 90,000 turns in the secondary coil. If 110 volts is supplied to primary coil, what will be the induced voltage in the secondary coil?
Vs/Vp = Ns/Np Vs = Ns/Np x Vp = 90,000/125 x 110 = 720 x 110 = 79, 200 V = 79.2 kV (transformer law for voltage)
What is transformer law for voltage formula?
Vs/Vp=Ns/Np where Vs=Voltage in secondary coil Vp=Voltage in primary coil Ns=Number of turns in secondary coil Np=Number of turns in primary coil
