Repairing, refurbishing and recycling household appliances

Unit 3Electricity Basics –

a brief roundup of the main elements

PARTS OF THE UNIT1. Principles and laws2. Safety3. Tools and equipment

We assume that, at the start of this course, you already have a grasp on the fundamentals of electricity. This unit serves as a refresher of some important concepts. If they are not fully up to speed, we advice you to sign up for a more extensive course that focusses on the basics of electricity.

Sub-unit 1 - PRINCIPLES AND LAWS

Objectives• To be able to explain basic electricity principles (current, voltage and resistance; Ohm’s law; conductor or

insulator; Pouillet’s law).• To be able to tell the difference between series and parallel circuit.• To be able to indicate the difference between energy and power.• To be familiar with basic components of an electrical installation.• To be able to carry out measurements of electrical components.

Basic valuesRecap:

Voltage ( U, Volt, V ) = the differnce in charge between two poles.

Current ( I, Ampere, A) = a displacement of electrons.

Resistance ( R, Ohm, Ω ) = the difficulty that a current flowing through a conductor experiences.

Ohm’s law

The relationship between R,U and I

R= Resistance (Ohm, Ω)=

U

I

Voltage (Volt, V)

Current (Ampere, A)

Energy & Power

Power

Energy used per time unit, expressed in Watt.

P= E / t where E= energy in Joule

P = U . I P = R . I2 of P = U2 / R

Example:

20 W => 20 Joule per second used.

50 W => 50 Joule per second used (more light than 20 W).

Conductor or insulatorQUESTION: What is the difference between a conductor & insulator?

-> Give examples of each!

Cu core = conductor PVC jacket = insulator

CONDUCTOR = a material that allows electric current to flow easily and has a low resistance. While all metals are conductors, some conduct better than others.INSULATOR = a material that is very difficult for electric current to pass through, if at all, and has a high resistance. E.g.: PVC, glass, porcelain,...

Pouillet’s lawPouillet’s law: calculates the resistance of a conductor in relation to the

specific resistance of the material, the length of the conductor and the

diameter of the conductor.

R = ρ𝒍

𝒔

→ the greater the l, the conductor’s length, the greater the resistance

→ the greater the S, the conductor’s diameter, the smaller the resistance

QUESTION: What is the relationship between Pouillet’s law and Ohm’s law?

Series and parallel circuitU= U1 + U2 + U3I is the same everywhere!!

I= I1 + I2 + I3U is the same everywhere!!

SERIES CIRCUIT PARALLEL CIRCUIT

ElectromagnetismElectromagnetism is a form of energy transformation. Electric energy

becomes magnetic energy. This magnetic energy can bring about

mechanical movement.

Example: the electromotor

Basic components

Resistance ( R, Ohm, Ω, KΩ, MΩ ): Electrical resistance is the electrical property of materials to impede the passage of electric current. The resistance component hinders te flow of electrical current. This casues a voltage drop.

Capacitator (C, Farad, F, μF, ηF, pF): A capacitator is anelectrical component that stores electrical charge. It canalso be used as a filter.

Transformer: A transformer converts AC voltage to lower or higher AC voltage.

Basic components

Coil ( L, Henry, H ): A coil, like a capacitor, can storeenergy. It can also be used as a filter or to convertenergy.

The coil is also widely used as an energy converter: theelectrical energy is converted to magnetic energy andcan then be used to bring about mechanicalmovement.

Relay: Can switch a larger power from a distancethrough a low-power control signal. Electromagnetic.

Basic components

Diode: example of a semi-conductor.

A diode conducts current easily in one direction butnot in the other direction.

Triac: example of a semi-conductor.

A triac has three electrodes and is able to conduct acurrent in either direction when it receives an impulse.

It is a special type of thyristor.

(triode for alternating current)

ADSThe automatic differential switch

= residual current switch

PURPOSE: To de-energise the electrical installation as soon as a loss in current of a certain level is detected.

This prevents us from getting a serious shock in the event of an insulation error.

Measures the outgoing and incoming current. If the difference between both is greater than a certainvalue, it will switch off.

Most known values (and mandatory in residential homes):

300 mA for "dry" rooms.

30 mA for “wet” rooms such as the bathroom.

The circuit breakerThe circuit breaker

PURPOSE: To protect the electrical installation against short circuits and overcurrent.

The circuit breaker contains a magnetic mechanism and a thermal mechanism:

The magnetic mechanism reacts to short-circuiting.

The thermal mechanism reacts to overloading.

Earthing/grounding system

Essential for a safe electrical installation – protects people, appliances and parts of the electrical installation.

By connecting all metal parts => same electrical potential, same voltage. Connection to the earth.

QUESTION: What are the different parts of an earthing system?

Power supply

Single phase (1x230V)Two copper wires (conductors) with 230V alternating current arrive in the building. Possibility of a neutral conductor (when one off the two conductors lies at the transformer on the ground).

Three phase (3x230V)Three copper wires (conductors) with 230V alternating current between each pair arrive in the building. Neutral conductor not common.

Three-phase star connection (3x400V+N)One neutral conductor (lies at the transformer on the ground) and three phase conductors. Between each of the phase conductors and neutral conductor there is 230V alternating current. Between each pair of phase conductors it measures 400V.

Three-phase connection: electric cookers, electric warm water heater.

A neutral conductor carries electric current and is NOT safe to touch!

Short circuit and overloadShort-circuit

Two active conductors make direct contact witheach other.

In order to prevent the current from getting toohigh, a circuit breaker is installed as a safetydevice. In the event of a short circuit, thiscircuit breaker or fuse will trip.

Overload

Too much current through 1 conductor -conductor heats up.

To avoid overloading, the fuse or circuitbreaker trips after a certain period of time.

No fault in the electrical circuit, but too manydevices connected to one circuit.

Residual-current switch:only works in case of leakage of current and NOT in case of overloading or short-circuiting.

The use of a multimeter

Watch the clip by clicking on the following link: https://www.youtube.com/watch?v=TdUK6RPdIrA .

ASSIGNMENT: Get started with the multimeter yourself! Measure voltage, current and resistance.

This project has been funded with support

from the European Commission. This

publication reflects the views only author,

and the Commission cannot be held

responsible for any use which may be made

of the information contained therein.