Most refrigerators,air conditioners,pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power(the digital devices you plug into the mains typically have an internal or external power adapter to convert from AC to DC power).AC power has the advantage of being easy to transform between voltages and is able to be generated and utilized by brushless machinery.DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages. The ability to easily transform the voltage of AC power is important for two reasons.Firstly. power can be transmitted over long distances with less loss at higher voltages.So in power systems where generation is distant from the load,it is desirable to step-up(increase)the voltage of power at the generation point and then step-down(decrease)the voltage near the load.Secondly,it is often more economical to install turbines that produce higher voltages than would be used by most appliances,so the ability to easily transform voltages means this mismatch between voltages can be easily managed. A steam turbine used to provide electric power 1 Making sure that the voltage,frequency and amount of power supplied to the loads are in line with expectations is one of the great challenges of power system engineering.However,it is not the only challenge.In addition to the power used by a load to do useful work(termed real power),many AC devices also use an additional amount of power because they cause the alternating voltage and alternating current to become slightly out-of-sync(termed reactive power).The reactive power like the real power must balance(the reactive power produced on a system must equal the reactive power consumed)and can be supplied from the generators,however it is often more economical to supply such power from capacitors. Unit 3 A Glimpse of Electric Power Systems 47s Most refrigerators , air conditioners , pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power (the digital devices you plug into the mains typically have an internal or external power adapter to convert from AC to DC power). AC power has the advantage of being easy to transform between voltages and is able to be generated and utilized by brushless machinery. DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages 9 The ability to easily transform the voltage of AC power is important for two reasons. Firstly, , power can be transmitted over long distances with less loss at highet voltages . So in power systems where generation is distant from the load, it is desirable to step-up (increase) the voltage of power at the generation point and then step-down (decrease) the voltage near the load. Secondly, it is often more economical to install turbines that produce higher voltages than would be used by most appliances , so the ability to easily transform voltages means this mismatch between voltages can be easily managed. A steam tu rbine used to provide electric power 10 Making sure that the voltage , frequency and amount of power supplied to the loads are in line with expectations is one of the great challenges of power system engineering. However , it is not the only challenge. In ad tion to the power used by a load to do useful work (termed real power), many AC devices also use an additional amount of power because they cause the alternating voltage and alternating current to become slightly out-of-sync (termed reactive power) . The reactive power like the real power must balance (the reactive power produced on a system must equal the reactive power consumed) and can be supplied from the generators , however it is often more economical to supply such power from capacitors. Unit 3 A Glimpse of Electric Powe Systems 47