Electrical Energy and Power

Electrical energy is the power of charged particles of atoms to cause action or moving objects. The movement of electrons from one atom to another atom is the cause of generating electrical energy.







Electrical energy is the power of charged particles of atoms to cause action or moving objects. The movement of electrons from one atom to another atom is the cause of generating electrical energy. Every time you plug a toaster or mobile phone charger into a wall outlet, the electrical energy will power these devices.

  • N – QV

Recall that Q = lt

: . W = lvt

  • Recall also that V = Lr

: . W = QV = IVt = 1 x IR x t

= 12Rt

W = 12Rt




Electricity is the rate at which electrical energy is transmitted through the circuit per unit time. The SI unit of power is watts, one JOULE per second. Electricity is usually generated by a generator, but it can also be provided by sources such as batteries. It is usually provided by the power industry to enterprises and households through the grid(as the domestic main power supply).


* Active equipment(power supply): If the charge is moved by an “external force” through the device in the direction from a lower potential to a higher potential (and therefore the positive charge moves from the negative end to the positive end), the charge will do the job, and the energy is moving from some other type of potential to the positive end.



* Passive devices(load): When the charge moves from a higher voltage to a lower voltage through the potential difference, that is, when the conventional current(positive charge)moves from the positive (+) terminal to the negative (−) terminal, the work is done by the charge on the device.


* Passive symbol convention: Since power can flow into or out of the assembly, a convention is required where the direction represents a positive power flow. The power flowing out from the circuit to the component is arbitrarily defined as having a positive sign, and the power flowing into the circuit from the component is defined as having a negative sign.


* Resistance circuit: In the case of resistive (ohmic or linear) loads, Joule’s law can be combined with Ohm’s law (V=I•R) to produce an alternative expression of the amount of dissipated power.


* No harmonics in alternating current: In AC circuits, energy storage elements such as inductors and capacitors may lead to periodic inversions in the direction of energy flow. The part of the energy flow (power) that is averaged over a full cycle of the AC waveform, resulting in a net transfer of energy in one direction, is called the actual power (also known as active power).


* Electromagnetic field: Electrical energy flows where electric and magnetic fields co-exist, and fluctuates in the same place. The simplest example is the circuit, as shown in the previous section.



P = work done where w = IVt

Time taken

P = IVt = IV = V2 = 12R

t               R




A circuit breaker is a device that prevents the flow of power around a circuit by turning itself off when there is any problem. A circuit breaker is an automatically operated electrical switch designed to protect the circuit from excessive current damage caused by overload or short circuit. Its basic function is to interrupt the current flow after a fault is detected. Unlike the fuse is operated once and then must be replaced, the circuit breaker can be reset (manual or automatic) to resume normal operation. Circuit breakers vary in size, from small devices that protect low-current circuits or individual household appliances to large switchgear designed to protect high-voltage circuits that power the entire city. Universal function of circuit breaker or fuse, as an automatic means of removing power from the failed system

Circuit Breaker


All circuit breaker systems have common characteristics in their operation, but the details vary greatly according to the voltage level, rated current and type of circuit breaker. The circuit breaker must first detect the fault condition. Once a fault is detected, the circuit breaker contacts must be opened to interrupt the circuit; this is usually done using the mechanical storage energy contained within the circuit breaker. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc generated when interrupting the (opening) circuit. When a high current or voltage is interrupted, an arc is generated. The length of the arc is usually proportional to the voltage, while the strength (or heat) is proportional to the current. This arc must be contained, cooled and extinguished in a controlled manner so that the gap between the contacts can withstand the voltage in the circuit again.

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