Electrical Power System Fundamentals for Non-Electrical Engineers

Transcription

1 Electrical Power System Fundamentals for Non-Electrical Engineers by Steve Mackay EIT Micro-Course Series Every two weeks we present a 35 to 45 minute interactive course Practical, useful with Q & A throughout PID loop Tuning / Arc Flash Protection, Functional Safety, Troubleshooting conveyors presented so far Upcoming: Electrical Troubleshooting and much much more.. Go to You get the recording and slides 1

2 Overall Presentation The focus of this session is the building blocks of electrical engineering, the fundamentals of electrical design and integrating electrical engineering know-how into the other disciplines within an organisation. Objectives The basics Design rules Selection, installation and commissioning of electrical systems 2

3 Topics 1. Generation, Transmission & Distribution 2. Transformers 3. Earthing/grounding 4. Power Quality 5. Protection 1.0Electrical Power Generation, Transmission & Distribution 3

4 Energy Conversion Process of transforming one form of energy into another In physics and engineering, energy transformation is often referred to as energy conversion Energy of fossil fuels, solar radiation, or nuclear fuels can be converted into other energy forms Such as electrical, propulsive, or heating that are more useful to us. Electrical Energy Electrical energy is undoubtedly the primary source of energy consumption in any modern household. Most electrical energy is supplied by commercial power plants. The most common sources of power plants are: Fuel energy Hydro-potential energy Nuclear energy 4

5 Turbine Rotary engine that extracts energy from a fluid flow Has a number of blades, like a windmill Blades rotate when a liquid or gas (steam) is forced through it under pressure. The rotating turbine is connected to a generator which produces alternating current electricity Electrical Generator Device that converts kinetic energy to electrical energy, using electromagnetic induction. Reverse conversion of electrical energy into mechanical energy is done by a motor The source of mechanical energy may be A turbine steam engine, Water falling through a turbine or waterwheel, An internal combustion engine, Or any other source of mechanical energy. 5

6 Electrical Generator (contd ) The generators are the key to getting electricity These are very large containing magnets and wires Power lines are connected to the generator to carry electricity. Electrical Generator (contd ) A metal shaft connected to a turbine is being turned by falling water or steam. As the turbine rotates, the shaft coupled to the generator also rotates Therefore the generator components also rotate and produces electricity. 6

7 Coal-Fired Power Plant Combustion Turbine Power Plant 7

8 Hydroelectric Power Plant Hydro-electric power plants convert the kinetic energy contained in falling water into electricity. There are two types: Hydroelectric dam Pump-storage plant Nuclear Power Plant (contd ) 8

9 Modern Power Station Overview Alternative Energy Sources Renewable energy sources are the alternative sources to generate electricity Solar energy Geothermal energy Biomass energy Ocean energy Wind energy 9

10 Transmission of Electric Power Generated electricity at power plant is sent out over a power grid through transmission lines. Transmission Transporting high-voltage electricity using a giant network of cables (the National Grid) Power transmission is between power station and substation. Transmission is carried out by bare overhead conductors strung between tall steel towers. Transmission (contd ) When electricity leaves the power station, it is transformed upwards to 400,000 volts (400kV) Transmission takes place at very high voltages to minimise losses. Super Grid is a giant network of overhead lines and underground cables It transports the electricity to substations and then distributed. 10

11 Transmission Losses Lightning strokes cause huge current flow, therefore produces I 2 R losses. Tree limbs falling across the power lines cause short circuits. Due to the interference of the communication cables losses occur. Accumulation of ice on the conductors in cold countries cause damage to the conductors. Environmental conditions also effect the transmission efficiency. Distribution of Power Taking electricity to homes, industries and schools in towns and cities in different areas. Then supplied to homes at 230V,50Hz or 110V, 60Hz by local distribution Power is transformed down from the ultra high transmission voltages to lower voltages by series of substations When higher voltages (132kV) are used, this area of supply is called 'Sub-Transmission. 11

12 Distribution (contd ) Typical distribution voltages vary from 34,500/19,920 volts to 4,160/2400 volts. The end point of this supply is a "Zone" Sub-station Here the electricity is transformed down to 11kV or 22kV for distribution to the immediate vicinity of customers. Power is carried through overhead wires or through underground cables. Distribution (contd ) For supply to residential consumers -- the voltage has to be transformed down again to 415/240 volts This occurs at local sub-stations which are located close to customers. Padmount Transformers are transformers which supply small voltages at this local sub-station. From here power is carried directly to the customer's premises 12

13 Distribution (contd ) Distribution (contd ) 13

14 AC Power AC power flow has the three components: Real power (P) It is in phase with the applied voltage (V) Also known as the active component. Measured in watts (W) Reactive power (Q) It is not in phase with the applied voltage (V) Also known as Idle or wattless power Measured in reactive volt-amperes (VAr) Power Factor It is the ratio of the real power to the apparent power. An ideal power factor is unity or 1. 14

15 Power Factor (Contd ) Fig.1 Fig.2 Fig Transformers 15

16 Transformers A transformer efficiently raises or lowers AC voltages It cannot increase power so that if the voltage is raised, the current is proportionally lowered and vice versa For an Ideal Transformer The voltage ratio is equal to the turns ratio Power In is equal to Power Out Transformers Internal losses reduce the power Out V s V p = N s N p P p = V p I p = V s I s = P s 16

17 Large power transformers Distribution Boards Serve as the point at which electricity is distributed within a building. Usually consists of breakers or fuses. 17

18 3.0 Earthing/Grounding Need for Earthing The primary goal of earthing system is SAFETY. Secondary goals are effective lightning protection, diminishing electromagnetic coupling (EMC), and the protection against electromagnetic pulses (EMP). 18

19 Need for Earthing Earthing reduce the risks of fires and personnel injuries. To provide a low impedance route for high frequency leakage currents. Electric shock (Direct and indirect) An electric shock occurs when electric current passes through human body Two categories of electric shocks are: Direct contact shock Indirect contact shock 19

20 Direct contact shock A direct contact shock occurs when conductors that are meant to be live such as bare wire or terminals are touched. Indirect contact shock Indirect contact shock is touching an exposed conductive part that has become live under fault conditions. 20

21 Effects of electrical shock The effects depend upon the following: The amount of current The path of the current The length of time the body remains in contact with the circuit The frequency of the current Effects of electrical shock Muscular contractions freeze the body when the amount of current flowing through the body reaches a level at which person cannot let go increases length of exposure current flow causes blisters, reduces surface resistance to current flow, increases current flow, causes severe injury or death 21

22 Effects of electrical shock Extensor muscles fling the body Jerk reaction results in falls, cuts, bruises, bone fractures, and even death Touch and Step voltage 22

23 Protection From the Hazards of Ground-Potential Gradients Protection From the Hazards of Ground-Potential Gradients The use of insulated equipment can protect employees handling grounded equipment, and conductors. Restricting employees from areas where hazardous step or touch potentials could arise can protect employees not directly involved in the operation being performed 23

24 Earth conductors and Electrodes There are two main types of earth conductor, "bonding" conductors and earth electrodes. Bonding and Protective Conductors are two types: Circuit Protective Conductor (CPC) Bonding Conductors Earth conductors and Electrodes Bonding Conductors These ensure that exposed conductive parts remain at the same potential during electrical fault conditions. The two forms of bonding conductor are:- Main equipotential bonding conductors Supplementary bonding conductors 24

25 Earth conductors and Electrodes Bonding Conductors The conductor size is capable of dealing with anticipated fault current. If a fault develops, the whole of the fault current may flow through via the earth conductor through to the "in ground" electrode system. Once there, it will normally be split up between the various electrodes. Earth conductors and Electrodes Earth Electrodes Direct contact with the ground provides a means of releasing or collecting any earth leakage currents. Earthed systems requires to carry quite a large fault current for a short period of time and, It has a cross-sectional area large enough to carry fault current safely. 25

26 Earth conductors and Electrodes Electrodes must have adequate mechanical and electrical properties. To meet demand for long period of time. During which actual testing or inspection is difficult. The material should have good electrical conductivity and should not corrode in a wide range of soil conditions. Materials used include copper, galvanized steel, stainless steel and cast iron. Copper is generally the preferred material Aluminium is sometimes used for ground bonding. The corrosive product - an oxide layer - is non-conductive. Corrosive product reduce the effectiveness of the earthing. Earth conductors and Electrodes 26

27 4.0 Power Quality Power Quality It is defined with respect to three primary components Continuity Quality Efficiency 27

28 Causes of Power Quality Problems Voltage fluctuations (flicker) Voltage dips and interruptions Voltage Imbalance (unbalance) Power frequency variations Harmonics Voltage Variations Short duration (sag, swell) Long duration Undervoltage Overvoltage Voltage Imbalance Voltage Fluctuations. 28

29 Short Duration Voltage Variations Voltage Sags (dips): Causes: Decrease between 0.1 and 0.9 p.u. in rms voltage or current at the power frequency for duration from 0.5 cycles to 1 min. Local and remote faults. (contd ) Impacts: Dropouts of sensitive customer equipment such as Computer crashes Bulbs glow dim Fan speed reduces Effect on motor speed Poor video quality of televisions etc. 29

30 Voltage Swells (surges): Increase to between 1.1 and 1.8 p.u in the rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min. Causes: Single-line-to-ground faults. Equipment over voltage. (contd ) Impacts: Electronic equipments such as television, computers will mis-operate Small fuses in electronic equipment will blow off Bulbs of low power rating will blow off Failure of MOVs forced into conduction etc. 30

31 Long Duration Voltage variations Overvoltage: Increase in the rms ac voltage greater than 110 percent at the power frequency for a duration longer than 1 min. Causes: Load switching off Capacitor switching on System voltage regulation. (contd ) Impacts: Electronic devices will burn Refrigerator will blow off Winding of motors of fan mixers and grinders will burn Over heating of equipment Bulbs will blow off Fuses will blow off Causes short circuits which will result sparks in the circuit etc. 31

32 Under Voltage (Brown out) Decrease in the rms ac voltage to less than 90 percent at the power frequency for a duration longer than 1 min. Causes: Load switching on Capacitor switching off System voltage regulation. (contd ) Impacts: Video on the TV will not appear but one can still hear the audio Mixers and grinders may not start Computer crashes Filament bulbs will glow dim but fluorescent bulbs may not glow. Mis-operation of refrigerators etc. 32

33 Variation of frequency The deviation of the power system fundamental frequency from its specified nominal value (e.g. 50 or 60 Hz). (contd ) Causes: Poor speed regulations of local generation Faults on the bulk power system Large block of load being disconnected Disconnecting a large source of generation. 33

34 (contd ) Impacts: Equipment Failure Black outs Transformers will blow off Motor windings will burn due to over heating. Motors in mixers, grinders, fans will burn. Interruptions Momentary Interruption: 1/2-3secs Temporary Interruption: 3-60 secs Long-Term interruption (outage): >1 min 34

35 (contd ) Causes: Temporary faults. Lightning stroke. Tree limbs falling across conductors. Impacts: Operation interruption. Production losses. Revenue losses. Surge An unexpected increase in voltage i.e. a increase of 110% of normal voltage for more than three nanoseconds is considered a surge. 35

36 Surge Protector A device that shields electronic devices from surges in electrical power, or transient voltage, that flow from the power supply. Switching Surges A transient disturbance caused due to switching on/off of reactive load. Load switching Oscillatory switching Capacitor switching Multiple re-strike switching Power system switching Arcing faults Fault clearing Power system recovery. 36

37 Lightning Surges A high voltage transient in an electric circuit due to lightning. (contd ) Lightning surges in electrical systems can in general be classified according to their origin as follows: Direct flashes to overhead lines Induced over voltages on overhead lines Over voltages caused by coupling from other systems. 37

38 Effects of Surges Electronic devices may operate erratically. Equipment could lock up or produced garbled results. Electronic devices may operate at decreased efficiencies. Integrated circuits may fail immediately or fail prematurely. Most of the time, the failure is attributed to "age of the equipment". (contd ) Motors will run at high temperatures resulting in motor vibration, noise, excessive heat, winding insulation is lost. Degrade the contacting surfaces of switches, disconnects, and circuit breakers. Electrical and electronic appliances will blow 38

39 Lightning Arrestors A device that protects from lightning surges. Lightning arrestors 5.0 Protection of Electrical Systems 39

40 Incipient faults A fault that takes a long time to develop into a breakdown of insulation caused by: Partial discharge currents Normally become solid faults in time. Breakdown of Insulation Solid fault Immediate, complete breakdown of insulation causing: High fault currents / energy Danger to personnel High stressing of all network equipment due to heating and electromechanical forces and possibility of combustion Dips on the network voltage affecting other parties Faults spreading to other phases 40

41 Need for protection Protection is also needed to avoid Electric shocks Electrical burns Arc blast injuries Fire THANK YOU FOR ATTENDING If you are interested in further training please visit; IDC Technologies Two-day practical workshops available to the public: On-site customised workshops: Technical Manuals: Conferences: The Engineering Institute of Technologies Practical online Certificate, Advanced Diploma and Graduate Certificate programs: 41

42 If you are interested in further training in the area UK Manchester 3 & 4 November Birmingham 7 & 8 November London 10 & 11 November South Africa Johannesburg 8 & 9 September Canada Toronto 28 & 29 November Calgary 1 & 2 December New Zealand Auckland 5 & 6 December 42