Unit 17: Electrical Circuits and their Applications
Name: Hani Oladeinde
Student I.D: OLA17005525
Differences between AC and DC voltages
The AC voltage causes an alternating current whereas the DC voltage causes a direct current. The frequency of AC voltage is 50 or 60 Hz depending on the country however the frequency of DC voltage becomes 0 Hz. AC voltage power factor lies between 0 to 1 and DC voltage power factor always remains at 1. A generator generates AC voltage whereas a cell or a battery gives DC voltage. The efficiency of AC voltage is higher than the DC voltage. AC voltage has amplitude whereas DC voltage doesn’t have amplitude. The impedance is the passive parameter of AC voltage and for DC it is resistance.
The peak voltage is the maximum amplitude of the voltage. This is nearly 330V in the UK. It is a waveform which is calculated from the horizontal axis to the top of the waveform. Peak voltage also signifies the amplitude of a waveform. It presents how big the magnitude of a waveform gets from the 0 on the horizontal axis line to the peak of the waveform. Peak-to-peak voltage is a waveform that is calculated from the top of the waveform which is called the crest and to the bottom of the waveform which is called the trough. It is the difference between the maximum positive and the maximum negative amplitudes of a waveform. The root mean square value is the square root of the mean value of the squared function of the values. The root mean square voltage in the UK is 230V.
Rectification is the process of changing AC into DC with the use of diodes. A rectifier is a circuit that converts AC into DC. One diode can create a half-wave rectification. A half of the AC wave is detached because it can’t move across the diode as this converts AC into DC. The diode lets current to run across to the exit when the Alternating Current voltage is positively charged on the cathode area on the diode on the other hand the Alternating Current switches path and goes negatively charged on the cathode area on the diode so the diode breaks the current therefore causing no voltage to appear at the exit.
A bridge rectifier functions by utilising four diodes. The diodes are organised in a diamond arrangement so that on every half phase of the AC sine wave two of the diodes distributes the current to the positively and negatively charged parts of the output and the last 2 diodes deter current. A bridge rectifier doesn’t need a centre-tapped transformer.
AC can step up and down in voltage by transformers whereas DC can’t be stepped up. AC tends to lose less resistance when distributing over long distances however you would lose a lot of resistance when distributing DC over long distances. For AC, you can use leaner wires which are inexpensive to make. It’s much easier to generate AC than DC due to the way the generators work. For AC, transformers can be used simply and effectively step up the voltage at an end and down at the other but DC needs additional dense circuits or ineffective generators to change the voltage.
When an electrical current enters the body the nervous system feels an electric shock. The power of the shock varies on the intensity of the current and the route taken by the current within the body and the length of interaction. In life-threatening events, the shock triggers the stoppage of the heart and lungs leading to unconsciousness or fatality.
When a person gets an electric shock and feels a slight exciting sensation, for men a minimum of 1mA DC and for women a minimum of 0.6mA DC is needed to achieve the effect. For 60Hz AC, a minimum of 0.4mA for men and a minimum of 0.3mA for women is needed to experience the same effect. When a person gets an electric shock and feels pain but the person is able of letting go of the conductor by using the muscles influenced by the current, for men a minimum of 62mA DC and for women a minimum of 41mA DC is needed to achieve this effect. For 60Hz AC, a minimum of 9mA for men and a minimum of 6mA for women is needed to undergo the effect. When a person gets an electric shock and feels pain but the person loses the capability to operate the muscles so they won’t be able to let go of the conductor and this causes physical damage to the body but the heart and lungs continue to work properly; for men a minimum of 76mA DC and for women a minimum of 51mA DC is needed to achieve this effect. For 60Hz AC, a minimum of 16mA for men and a minimum of 10.5mA for women is needed to undergo this effect. When a person gets an electric shock and feels severe pain and experiences difficulty in breathing, for men a minimum of 90mA DC and for women a minimum of 60mA DC is needed to experience this effect. For 60Hz AC, a minimum of 23mA for men and a minimum of 15mA for women is needed to achieve the effect. When a person gets an electric shock and feels deadly pain and possible ventricular fibrillation may occur where the heart stops pumping and the pulse disappears. When the heart stops pumping blood to the brain it begins to stop working. For men a minimum of 500mA DC and for women, a minimum of 500mA DC is needed to achieve this effect. For 60Hz AC, a minimum of 100mA for men and a minimum of 100mA for women is need to experience the effect.
Ring main In the ring main, the live, neutral and earth wires form a loop of cable that runs from the meter to the consumer unit around the household to the sockets then back to the consumer unit. The live wire carries current to the house at a high voltage. The neutral wire completes the circuit and carries current away at low voltage. The earth wire carries current safely into the ground if a fault occurs.
Three pin plug A three pin plug contains the live, neutral and earth wires that are made from copper which are coated with plastic. The cable grip grips the cable firmly in place so that the wire doesn’t become free. It contains a fuse which is a ceramic cylinder holding a fine wire that melts if the current gets very high. The plug has outer insulation where all three wires in the cable are packed collectively and there is additional plastic insulation covered around them for safety. The earth wire is coated in striped plastic that offers a way for current to run from the casing of the appliance to the earth if there is an error.
Fuse A fuse contains a very thin wire that heats up and melts if too much current passes through it. The rating of a fuse is the maximum current that can pass through it without melting the wire. Once the fuse has melted the circuit is stopped and no current can flow through the appliance. This means there’s no more risk of electrocution and fires from starting.
Insulation Electrical insulation is various insulating material (e.g. plastic, PVC and etc) used to bind electrical cables and wires. The material is resilient to an electrical current and it shields the wire and cable. It stops current from interacting with other conductors (e.g. humans).
Double Insulation Some appliances don’t have an earth wire because they have plastic casings instead of the metal casing. If there’s a fault in the appliance, the casing can’t give out an electric shock. This is double insulation.
EarthingThe earth wire is linked to the casing of the device and is connected to a metal plate underground. The wire is made of copper so it offers a small resistance pathway to the ground. If a fault happens the live current flowing within the casing will flow to the pathway and to the ground instead of passing through a person.
RCCB A residual current circuit breaker (RCCB) switches off a circuit when there’s a variation between the current in the live wire and the current in the neutral wire of an electrical device. When an electrical device is functioning properly all of the current going into the device from the live wire is restored to the power supply from the neutral wire. If a fault occurs with the device nearly all of the current will flow into the earth wire. There’s a decrease in current flowing into the neutral wire and this causes the dissimilarity between the current in the live and neutral wires. The RCCB switches off the device and makes it safe.
ELCB An earth leakage circuit breaker (ELCB) is a safety device used in electrical circuits with elevated electrical impedance to prevent electrocution. Unlike an RCCB, an ELCB is operated by voltage. It notices tiny lost voltages on metal casings of electrical devices and disrupts the circuit if a hazardous voltage is spotted. So the main purpose of ELCB is to avoid harm to people as a result of electric shock.
Isolating Transformers An isolating transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source usually for safety reasons. Isolating transformers provide galvanic isolation and are used to protect against electric shock. They block transmission of DC component in signals from one circuit to the other but allow AC components and signals to pass.
You should avoid using water when working with electricity. This reduces the risks as water boosts the conductivity of electric current.
Never use electrical equipment with broken insulation or damaged plugs. This reduces the risks as wires can be loose and can cause electrocution.
Always use insulated (rubber) gloves and safety goggles whilst operating on any electrical circuits. This reduces the risks as rubber can’t conduct electrical current.
Always remove metal valuables from your possession when working with electricity. This reduces the risks as metal objects can conduct electrical current.
If a person touches a charged electrical conductor, don’t come into contact with the tools or the person that is electrocuted as the current may pass to you. This reduces the risks as you can switch off the main power supply and disconnect the device using rubber gloves.
Do not pull an electrical cord from the socket. This reduces the risk as yanking the cord can break the plug.
An electrical fire is one of the electrical safety hazards in the Solihull College laboratory. This can occur when improper or hazardous cords and plugs are used. Mainly hazards are electrical components which are placed nearby to liquid.
Devices in the laboratory that contain a fuse will reduce the risks of working with electricity. The fuse protects the device from over-flowing of current. It is made to melt and cut off the circuit when the current surpasses its rating. It is vital to make sure that the right fuse is utilised for the device.