chapter three transformer Flashcards
diff and menthion one used on the following
- step down
- step UP
- To decrease the voltage and increases the intensity of A.C ( this is used to operates some electric devices )
- To increase the voltage and decreases the intensity of A.C ( this used to transfer A.C current through wires without large loss of electric )
what is the construction and properties of Step down OR step up
- primary coil connected to A.C source (copper , thick)
- secondery coil connected to load resistance (copper ., thick)
- siliconic soft iron core ( thin insulated shets )
what is the idea of operation of step down or step up
depends on the mutual induction between two coils
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when A.C currens passes through the primary coil will be associated with variable magnetic flux which is concentrated by the aid of the silicones soft iron core and link the turns of secondary coil so mutual induction takes place
waht is the code when you tell step up or step down
step up Ns > Np , Vs > Vp
step down Np > Ns , Vp > Vs
Pout = ??
Pin = ??
Is X Vs
Ip X Vp
diff efficiency of transforemer and sympol and the rule and ratio
it is the ratio between the electric energy produced from the secondary coil that consumed in the primary coil
OR
itis the ratio between the electric power produced in secondary coil to that given from primary coil
n = Is x Vs / Ip x Vp = Pout /Pin
n x Vp / Vs =Np / Ns = Is / Ip
when you say transformer od effciency 80% that means
80 \ 100 is the ratio between the electric energy produced from the secondary coil that consumed from primary coil OR
80\100 it is the ratio between the out put power to the in put power
efficiency of transformer has NO unit GR
because it is the ratio betwenn two similar physical quantities
effciency of transformer alwys less than 100% GR
because part of electric energy is lost as
- thermal energy in coil dueto their ohmic resistance
- thermal energy in soft iron core due to formation of eddy current
- mechanical energy caused to move the molecules of the metalic core in the magnetic filed
- loss in magnetic flux when it travel from the primary coil to the secondary coil
what is the suggestions to increase the efficiency of the transformer and why
- the coils should be made of copper with large cross sectional area [to decrease its ohmic resistance as copper has low resistavity and R & 1\A SO the electric energy lost in form of heat energy in coils due to its ohmic resistance wil decrease that will increase the efficiency]
- metallic core should be divided into thin insulated sheets [to minimize the loss of energy as thermal energy due to eddy current that will increase the efficiency]
- the metallic core should be made from silliconic soft iron [because it has high resistivity so it will decrease the intensity of the eddy current and minmize the loss of energy as thermal energy ,, its molecules can move easily in the magnetic filed that will minmize the electric energy consumed as mechanical energy to arrange the molecules to increase efficiency of transformer]
- the primary coil should be placed inside the secondary coil [To decrease the loss of the magnetic flux that is will increase the efficiency]
transformer cant be used D.C source GR
because direct current is associated with sable magnetic filed SO no mutal induction tkes palce as there in no vartion in magnetic flux that link the secondery coil except only at the vmoment of switching ON or OF
transaformet doesnt consumed electric energy if the circuit of its secondary coil is opened ( switched off ) GR
because opposing E.M.F is generated by self induction in the primary coil which equels E.M.F of the source oppose it
using step up transformer in generating stations while step down transformers are used in distribution stations GR
- to increase the volage and decrease the current intensity ( Ieff ) so the rate of consuming of electric energy as thermal energy through wires due to their ohmic resistance will decrease will decrease P&I2
- while using step down transformer in distriburion stations to decrease E.M.F to 220 and increase the effective current to suitable value
step up trnasformer increases voltage and decreases current while step on trnasformer decreasesvoltage and increases current GR
from the ratio Np\Ns = Vp\Vs = Is\Ip
step up
Ns > Np
Vs > Vp
Is > Ip
from the ratio Np\Ns = Vp\Vs = Is\Ip
Np > Ns
Vp > Vs
Ip > Is
electric power is transferd from the electric generating power stations to the consumers using high voltage and low current GR
By increasing the voltage and decreasing the effective current intensity the rate of consuming of electric energy as thermal energy through wires due to ohmic resistance will decrease P&I2