5.1 : ELECTRICAL DISTRIBUTION CHAPTER 5 5.1 : ELECTRICAL DISTRIBUTION

Important terminology Coulomb (C): The basic unit used to measure electric charge. Joule (J): A joule is the work done by a constant 1-N force applied through a 1-m distance. Ampere (A): One ampere or amp is the current that flows when 1 Coulomb of charge passes each second (1 A = 1 C/s) Volt (V): If a charge of 1 Coulomb may be moved between two points in space with expenditure of 1 Joule of work, 1 Volt is said to be a potential difference existing between these points (1 V = 1 J/C) Watt (W): The rate at which work is done or energy expended. The watt is defined as 1 Joule per second (1 J/s).

Quantities and SI Units Six Basic SI unit used in electrical engineering field: Table 1: SI unit Quantity Basic unit Symbol length meter m mass kilogram kg time second s Electric current ampere A Thermodynamic temperature Kelvin/ Celsius K / C Luminous intensity Candela cd

Quantities and SI Units SI UNITS used in electricity: VOLTS (V): unit of potential difference, emf, or voltage OHM (Ω): unit of resistance AMPS (AMPERES) (A): unit of current COULOMBS (C): unit of charge (= the charge moved when one amp of current runs for one second). WATTS (W): unit of power (power energy per unit time). In electrical circuits, one watt is produced when a current of one amp flows down a potential difference of one volt. JOULE (J): unit of energy.

Electrical Simple Rules. One watt is one joule per second. One amp is one coulomb per second. If you double the voltage the current will double. If you halve the voltage the current will halve. If you double the resistance the current will halve. If you halve the resistance the current will double.

Charge Electricity is any effect resulting from the presence and/or movement of electrical charges. Electrical charge is property of the atomic particles, measured in Coulomb (C) Battery (source of electromotive force, emf) + + + Motion of charge Conducting wire (atoms within)

Electric Current An electric current is the flow of electric charges. Conventionally this is the flow of positive charge. In a simple circuit such as that illustrated, the current in the wire is composed of electrons that flow from the negative pole of the battery (the cathode at the bottom of the battery) and return to the positive pole (the anode at the top of the battery, marked by a +).

Electric Current Electric current is the time rate of change of charge, measured in amperes (A). Mathematically, the relationship between current i, charge q, and time t, is Where current is measured in amperes (A), and 1 ampere = 1 coulomb/second

Electric Current Two common types of current are; Direct Current (dc) Alternating Current (ac), A direct current (dc) is a current that remains constant with time. The symbol I is used to represent such a constant current. An alternating current (ac) is a current that varies sinusoidally with time. A time-varying current is represented by the symbol i.

Voltage Some work or energy transfer is required to move the electron in a conductor in a particular direction. This work is performed by an external electromotive force (emf), typically represented by the battery. The emf is also known as voltage or potential difference. Electric potential is the energy required to move a unit of electric charge to a particular place in a static electric field. Voltage can be measured by a voltmeter. The unit of measurement is the volt.

Energy and Power Energy is the fundamental ability to do work and produce action. Energy exists in many forms, such as mechanical, sound, light, electrical, nuclear and chemical. Energy cannot be created or destroyed. It can be converted from one form to another. Energy is measured in joules, but in many fields other units, such as kilowatt-hours and kilocalories, are customary. Electrical energy is the most convenient form of energy that is readily to be convert to other forms. For examples; to mechanical energy through a motor, to lighting energy through a lamp, and to heating energy through a resistance heater. Power is a measure of how fast energy is being used. (power is the rate of consuming energy)

Energy and Power Power is a certain amount of energy used in a certain length of time P = energy/time = W/t Power is the time rate of expending or absorbing energy, measured in watts (W). In direct current resistive circuits, electrical power is calculated using Joule's law: where P is the electric power, V the potential difference, and I the electric current. In the case of resistive (Ohmic, or linear) loads, Joule's law can be combined with Ohm's law (I = V/R) to produce alternative expressions for the dissipated power.

Energy and Power Power can be delivered or absorbed as defined by the polarity of the voltage and the direction of the current. Two polarity of the voltage and the direction of the current

Energy and Power Ohm’s Law defines the relationship between the three fundamental electrical quantities: current, voltage, and resistance . When a voltage is applied to a circuit containing only resistive elements, current flows according to Ohm's Law, which is shown below; Ohm's law states that the electrical current (I) flowing in a circuit is proportional to the voltage (V) and inversely proportional to the resistance (R). If the voltage is increased, the current will increase provided the resistance of the circuit does not change. Increasing the resistance of the circuit will lower the current flow if the voltage is not changed. In Ohm’s law, the constant of proportionality R is called the resistance. The unit is called Ohms. The formula; I = V/R

Energy and Power Ohm’s Law The formula can be reorganized so that the relationship can easily be seen for all of the three variables. V = I R or I = V/R or R = V/I Where: I = Electrical Current (Amperes) V = Voltage (Volt) R = Resistance (Ohms) To apply the law v = iR, the current and voltage must conform to the passive sign convention. This implies that the current flows from a higher potential to a lower potential (v = iR). If current flows from a lower to high potential, then v = -iR.

Energy and Power Resistor A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage (V) is applied across the terminals of a resistor, a current (I) will flow through the resistor in direct proportion to that voltage. It is usually made from metallic alloys and carbon compounds. Resistance factor depend on cross-sectional area (A), length (l) and resistivity (ρ) of the material used as shown in the figure. Mathematically:

Energy and Power A material with low resistivity is a good conductor; examples are gold, copper and aluminum. An insulator like mica and paper has a very high resistivity. Table 2: Resistivity of common materials at 20o C

Energy and Power Example; Calculate the electrical resistance per meter length at 20o C of a cooper conductor of 2.5mm2 cross section area.

Energy and Power Conductance Reciprocal of resistance is conductance and denoted by G It measures of how well an element will conduct electric current. The unit for conductance is Siemens (S), and previously called mho (Ʊ) - ohm spelled back-ward.

Circuit Design (series) A series circuit is a circuit which provides only one path for current to flow between two points in a circuit so that the current is the same through each series component. The total resistance of a series circuit is equal to the sum of the resistances of each individual resistor.

Circuit Design (parallel) and Current Division Resistors in a parallel configuration are each subject to the same potential difference (voltage), however the currents through them add. The conductance of the resistors then add to determine the conductance of the network.

Circuit (parallel) and Current Division The equivalent resistance (Req) of the network can be computed: Current:

Exercise Calculate: Solutions: Total resistance RT Total current , I V1, V2 and V3 Solutions: 150V R 1 = 5  R 2 = 10  R 3 = 15 

Circuit Design (combination) A resistor network that is a combination of parallel and series connections can be broken up into smaller parts that are either one or the other,

Exercise Determine the total resistance of the following circuit between points A and B 10  4  7  5  12  A B Answer: RT= 20 Ω

Exercise One 100W lamp and one 200W lamp are plugged into a 120V circuit. For either DC or AC. The two lamps are connected in parallel. Calculate the current flow through each lamp, the total resistance of the circuit, the total energy consumed in a year, and the cost of electrical energy for the year (based on $0.10/kWh).

Calculate the following current flow through each lamp, the total resistance of the circuit, the total energy consumed in a year, the cost of electrical energy for the year

answer current flow through each lamp, (2.5A) the total resistance of the circuit, (47.6Ω) the total energy consumed in a year, (600kWh) the cost of electrical energy for the year ($60)

Measurement Equipment multimeter ammeter ohmmeter megger Watt-hour meter voltmeter wattmeter

QUIZ One 18 watt lamp and two 60-watt light bulb are plugged into a 120V circuit. For either DC or AC, the two bulbs are connected each other in parallel and in series with the lamp in the same circuit. Calculate; i. the current flow through each light ii. the total resistance of the circuit, iii. the total energy consumed in a year, iv. the cost of electrical energy for the year (assume 365 days per year) if the lights have been used for 8 hour per day (based on $0.286/kWh).

QUIZ_answer i. the current flow through each light (0.15A,05A,0.5A) ii. the total resistance of the circuit, (RT=920Ω) iii. the total energy consumed in a year, (402.96kW) iv. the cost of electrical energy for the year (assume 365 days per year) if the lights have been used for 8 hour per day (based on $0.286/kWh). ($115.25)