linkage”) through the secondary coil by an iron core
4.The changing flux through the secondary coil, induces a potential difference across the secondary coil
Step-Up Transformer Flux. AC Input Primary Coil Secondary Coil Core AC Input Flux. AC Output ( increased! ) Primary Coil Secondary Coil Core # turns on secondary > # of turn on primary n s > n p
Amount of flux produced in the core depends on a property of the core material - “ permeability ” , , – a constant for different types of material.
Materials that cause lines of flux to move further apart ie. decrease flux density are called “diamagnetic” ; those that concentrate flux by 1 – 10 times are called are called “paramagnetic” ; and those that concentrate flux by >10 times are called “ferromagnetic” .
Certain ferromagnetic materials, especially powdered or laminated iron, steel, or nickel alloys, have µ that can range up to about 1,000,000.
Eddy currents are induced currents that result when there is a B field acting on part of a metal object and there is relative movement between the object and the field, such that the conductor cuts across magnetic flux lines.
Eddy currents are
They are an
Lenz’s Law .
Eddy current motion X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X
Commercial power stations use AC generators to produce their electrical energy.
AC generators are preferred because:
(i) Easy to step up AC emfs to higher voltages for transmission.
(ii) AC electricity transmitted with low energy losses.
Step-up Transformers at Power Generation Plants
Electricity generated at a power station is usually produced at a voltage ranging from a few hundred volts to tens of kilovolts. (Eraring power station at Lake Macquarie has four 660 MW generators with an output of 23 kV).
It is transformed to 330 kV or 500 kV for transmission over the distribution grid .
The transmission grid consists of high voltage overhead lines and underground cable made of either copper or aluminium.
Copper is much heavier than aluminium so it is used primarily in insulated wires and cables.
Aluminium is suitable for transmission and distribution and allows the use of much lighter and more economical support structures. The tensile strength of pure aluminium is not high enough for most applications so aluminium alloys or steel reinforced aluminium alloys are used.
Electrical Transmission Lines – Insulation of Wires In dry air, electrical sparks can jump the following distances for the given potential differences: 10 000 V --------- 1 cm 20 000 V --------- 2 cm 100 000 V ------- 10 cm 330 kV -------- 33 cm *Distances smaller in very humid air
Superconducting transmission cable is a technology intended to increase transmission capability. High temperature superconductivity (HTS) cable has no resistance.
HTS has the potential to deliver twice the power capacity with the same power loss and smaller diameter as conventional cable.
One potential design which is well-suited for retrofitting in networks has an HTS conductor enclosed in a cryogenic environment which is covered by conventional room-temperature dielectric. Prototype cable systems have been developed in the US and actual systems are expected there over the next few years.
If not AC, otherwise would have to be provided by batteries = high cost . TV’s need high voltages to function .
Transformers & Electrical Appliances in the Home Electronically operated domestic appliances require both a step-down transformer to change 240 volts to about 5 - 20 volts & a rectifier to change the low voltage AC to DC. TV, stereo, computer, CD player, clock radio, fluorescent lights, home security systems, microwave oven, answering machines, air conditioner, fax machines, washing machines, microwave oven kettle, hot water heater, toaster, older room heaters, hair dryers, incandescent lights, old model refrigerators, some clothes dryers Appliances with a transformer Appliances without a transformer
Energy Transfers in the Home (2) Copy and complete the table below. Washing machine VCR Hair dryer Electric drill Air conditioner Blender Radio Television Energy Transformation Household Appliance
Transformers were a key to establishing electrical
energy as the driving force behind technological and
industrial development in the 20th century.
Electrical energy rapidly became the means of
lighting homes and cities, with its distribution
facilitated by the use of transformers .
Electrically operated machines thus replaced less efficient machines, resulting in the rapid growth of industry and commerce.
Communication networks grew rapidly as a result of electrical energy and its intimate association with radio, then television and ultimately the computer revolution of the late 20th century.
Every home has dozens of appliances that make use of transformers, permitting a host of electronic devices to be operated from the mains.
Effect of High Voltage Power Lines on Humans Alternating E field induces an alternating current to flow in body Sign changes 100 times/ s. + - - - - - - - - - + + + + + + - - + + + + + + + + - - - - - -- +
At least one study has shown that exposure to strong electric and magnetic fields increases likelihood of developing cancers and leukemia.
Phasing and em Radiation Exposure Levels Phasing assists to reduce the E fields when multiple power lines are present. “ Code” related health effects refer to wiring codes where the conductors are far apart. The closer the supply and return wires are together, the lower the fields due to phase cancellation - - - - - - - - - + + + + - + + + + + + + + - +
Phasing and em Radiation Exposure Levels (cont)
Phasing assists to reduce the B fields when multiple power lines are present as with E-field.
Dynamic magnetic field causes currents to flow in a circular fashion within the body.
They will reverse 100 times / second
Current direction B Magnetic field arising from current Induced current in body