Design, Install &Commission grid connected photovoltaic power systems

1. Design, Install &Commission grid connected photovoltaic power systems Electrical Basics Session 3 DAMON FYSON

2. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Voltage & Potential Difference • Potential refers to the possibility of doing work. • When energy is applied to a material to cause a change in its state of charge (that is, we give it 'potential') it is given the ability to do work as it attempts to return to the neutral state. • One unit of charge, called a Coulomb (C), has a quantum number of 6.27 x 1018 electrons. The difference between two charge states is called the potential difference (or voltage) and is measured in units called Volts. DAMON FYSON

3. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Voltage • The Volt (V) is the unit that measures the work needed to move one unit of charge between two points. • Briefly, when 1 Joule of energy is needed to move 1 Coulomb of charge between two points there is a potential difference between the two points of 1 Volt. Voltage is the potential difference between two points. • Voltage is sometimes referred to as Electromotive Force or EMF and given the symbol (E) but the standard symbol for a potential difference is V, either for a generating source or a voltage drop across a passive component DAMON FYSON

4. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Current • potential difference causes a charge to move between two points, the charge in motion is called an electric current. • The number of electrons that can be forced to move depends on the potential difference between the two points. • The greater the potential difference, • the greater the current flow. • Current flow is measured in Amperes (A). • When 1 Coulomb (6.27 x 1018 electrons) flows past a given point in 1 second it is called 1 Ampere (A) of current. • The symbol for current is I (this stands for 'intensity', as it is a measure of the concentration or intensity of electron flow). • All electrons move with the same speed, only the quantity changes DAMON FYSON

5. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Conventional flow All electrons move with the same speed, only the quantity changes. So if potential difference doubles, the quantity of electrons doubles Electrons flow from a negative terminal to a positive terminal as seen in the figure below. Conventional current flow, is in the direction of the positive charge, i.e. the direction of current is reversed compared to the direction of flow of electrons in a conductor. The flow of electrons from negative to positive (electron flow) is equivalent to a flow of positive charges from positive to negative (conventional flow). Conventional current flow is normally used to explain the operation of electrical and electronic, devices and circuits. Conventional flow is used throughout this course.  DAMON FYSON

6. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Resistance • A conductor carrying electric current will always provide some amount of opposition to that current. • This opposition is called resistance and limits the amount of current that can be made to flow through the conductor. • Good conductors have very little resistance; insulators have large values of resistance. The unit used to measure resistance is the Ohm (Ω). • A resistance that develops one joule of heat energy when one ampere flows through it for one second has one ohm of resistance. • Resistance is abbreviated to R or r and is represented by the Greek letter, Omega (Ω). • A good conductor such as copper wire has a typical resistance of 0.0183Ω / mm2 for a one metre length. Resistance wire such as that used as the heating element in a toaster may have a value of 24Ω. • In circuit diagrams resistance is represented by a rectangle as shown below. DAMON FYSON

7. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Ohm's Law • There is a direct relationship between Current (I), Voltage (V) and Resistance (R). These relationships are expressed in Ohm's Law, as follows; • This can be rewritten as R = V/I I=V/R V= IXR DAMON FYSON

8. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Power • The unit of electric power is the Watt (W). One Watt of power equals the work done in one second by one Volt of potential difference in moving one Coulomb of charge. As one Coulomb per second is an Ampere, it follows that power in Watts is equal to the product of Volts x Amperes. • Power (watts) = Voltage (volts) x Current (amps) • Power (watts) = Voltage² (volts)/ Resistance (ohms) • Power (watts) = Current (amps) ² x Resistance (ohms) Watts as the unit of power is the rate of doing work. For example, the amount of energy used to walk up a set of stairs compared to walking up a ramp to the same level is equal but the rate at which the work is done varies. Kilowatts (kW) or Megawatts (MW) are the terms most commonly used for large amounts of power; i.e. 1000 Watts = 1kW and 1000kW = 1MW. DAMON FYSON

9. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Energy • Energy is defined as the capacity to do work. • Large amounts of electrical work or energy are expressed in kilowatt-hours being simply the amount of power multiplied by the time it is used for. • For example, a 60 Watt light globe running all day will use 60 x 24 Watt-hours = 1440 Wh = 1.44 kWh. • Note: The difference between power and energy is an important concept as energy usage is used as the basis for determining the output of renewable energy systems for a given period DAMON FYSON

10. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Circuits • The path that current (I) flows from one charged point to another is called a circuit. A potential difference (V) is applied to a circuit to cause current to flow. • Current flows through a circuit from an energy source to a load. The current that flows is referred to as load current. • When any part of the current path is broken we have an open circuit and no current can flow. • If a fault should occur and current is flowing in a closed path across the terminals of a source we have a short circuit. • Current in a short circuit condition can be very high and we generally fit a fuse in the circuit to protect against this. • Circuits may be series or parallel, or even a combination of both, and are dealt with in more detail later. DAMON FYSON

11. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics • Fuses and Circuit Breakers • A fuse is a device fitted to protect against excessive current flows that could damage conductors in a circuit, and to reduce the risk of fire due to overheating of conductors. This will commonly consist of a short section of conductor, mounted in an insulating enclosure that is of sufficient size to carry the load current but will open circuit under a fault condition. They may be either rewirable, or a cartridge style. • Another alternative is the circuit breaker, which is a mechanical device that will open the circuit under fault conditions and can be reset when the fault is removed. • Currents in excess of the fuse or circuit breaker rating will cause the device to operate (open). Rewirable type fuses are no longer considered sufficient to protect a wiring system. • (HRC) fuses or appropriately rated (a.c. or d.c.) circuit breakers should be used. DAMON FYSON

12. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Direct current (d.c.) and alternating current (a.c.) • In a d.c. circuit current can only flow in one direction because the polarity of the battery is fixed. To reverse the current flow reverse, the connections to the battery must be reversed. The terminal voltage of the battery is relatively constant and so there is a steady d.c. voltage applied to the circuit. • An alternating current (a.c.) source regularly reverses the polarity of its output. In Australia the grid supply reverses polarity 100 times per second to give us a 50-cycle (50Hz) a.c. supply at 240 Volts. Alternating current has the advantage of being easily converted to a different voltage by the use of a transformer. Electricians generally only deal with a.c. power as the main grid is a.c.  DAMON FYSON

13. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Magnetic Effect & Electromagnetism • Then any current flows in a conductor, a magnetic field is set up around the wire. The magnetic field exists in a plane perpendicular to the direction of the current. This magnetic field is the basis for many electromagnetic applications such as speakers, electromagnets, relays, transformers, motors etc. Electromagnetism The figure above shows that a magnetic field is produced when current flows in a wire. The strength of the field is directly related to the amount of current flowing in the wire. This magnetic field can be concentrated by forming the wire into a coil (primary winding). DAMON FYSON

14. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Basic transformer • By varying the current flow, such as would happen with an a.c. supply the strength of the magnetic field is varied. By placing another conductor (secondary wiring) into the varying magnetic field a current will be induced into it. This is the basis of a transformer. • The voltage and current that will flow in the secondary circuit will be in relationship to the ratio of the turns of wire in the primary and secondary windings. DAMON FYSON

15. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Generator . • By moving a conductor in a stationary magnetic field, again a current will be induced in it. This is the basis of a generator. The output will vary with the strength of the magnetic field and the number of turns of the conductor interacting with the magnetic field. • The output can be taken as varying d.c. (a generator) by using a commutator, or as a.c. (an alternator) by using slip rings. • This theory is important to understand when wiring a PV array, and preventing conducting loops that might attract lightning. This will be discussed in future modules. DAMON FYSON

16. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Characteristics of a.c. •  A.c. voltage, current and power formulae are fundamentally different from the d.c. formulae. In order to express these parameters it is necessary to arrive at some kind of average of the waveform because the instantaneous voltage and current in a.c. are constantly varying. There are two types of averages commonly used in a.c. electric circuits. • The first kind is the RMS or "root mean squared" voltage (VRMS) which allows for the fact that the power consumed by a resistive load is proportional to the square of the instantaneous voltage. • The second "average" voltage is the simple sum of the voltages divided by time. The average voltage is used to determine the magnetising behaviour of transformers and motors. Depending on the wave shape the average voltage may be above or below the "true RMS".   DAMON FYSON

17. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics The expression that relates the RMS and peak voltages for sine waves is; •  It follows that in a.c. sine wave circuits, the current also has RMS and peak values related as follows; • Note: Different waveforms (i.e. square-wave, modified square-wave etc.) will have different relationships between the RMS and peak values. DAMON FYSON

18. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Harmonic Distortion • Harmonic Distortion • Harmonic currents are also present in a.c. They can cause distortions in the waveform. Harmonics are generated by non-linear loads such as switch-mode power supplies, battery chargers and fluorescent lighting. In mains power, these distortions are generally sinusoidal, but at higher frequencies, so that the waveform is distorted. • In an inverter the accuracy of a sine wave is expressed in terms of harmonic distortion; the lower the harmonic distortion, the better. • In grid interactive inverters, the total harmonic distortion shall be less than 5% or they will typically not be accepted by the authorities to be allowed to connect to the distribution grid. DAMON FYSON

19. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Frequency & Harmonics • The frequency of an a.c waveform is defined as the number of cycles per second (Hertz. Hz) Frequency affects the function of some appliances to varying extents. Many appliances with timers depend on the supply frequency and their clocks will drift unless the frequency is accurate. • Major deviations will adversely affect transformers and induction motors. Low frequency often burns out this equipment. The standard grid (sometimes called mains or supply) frequency in Australia is 50 Hz (cycles per second). DAMON FYSON

20. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Power Factor • A further consideration in a.c. circuits is the impedance. Impedance can be thought of as the analogy for resistance based on Ohm's Law applied to a.c. circuits. Impedance is a combination of reactance and resistance in an a.c. circuit. • Reactance is the behaviour of inductance and capacitance to a sine wave a.c. Inductance, L, is a property of inductors (e.g. a coil of conducting wire) and capacitance, C, is a property of capacitors, both of which are common components in a.c. powered circuits and equipment, besides the omni-present resistance, R. • Thus, for an a.c. circuit, it is very common that the circuit is called an RLC circuit. DAMON FYSON

21. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics True/apparent power • Reactance is either capacitive or inductive, but the effect of either type is to cause current flow in the circuit, without doing work. However, resistance uses all of the current flow in the circuit to perform work. Thus, in this sense, for an ideal a.c. circuit, it is best to have the minimum reactance and the maximum resistance. • Power in d.c. circuits is simply the product of volts and amps, i.e. • Power (W) = Voltage (V) x Current (I) A wattmeter averages power over a short period of time and accumulates the results to record energy (watt-hours). In a.c. circuits the reactance of a load will cause a phase shift of the current waveform in relation to the applied voltage. Because of this phase shift the energy supplied to the load is greater than the energy recorded on a Wh meter. The measure of power supplied to an a.c. load is Apparent Power and the units used are Volt-Amps (VA). DAMON FYSON

22. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Power factor • All reactive loads cause a phase shift dependant on their inductance and/or capacitance. The measure of the phase difference between voltage and current is called the Power Factor (PF). This is the cosine of the phase angle between voltage and current and is expressed as: • Purely resistive loads (e.g. heaters, incandescent lamps) will not cause any phase difference and in this case the power used is equal to the apparent power (P (Watts) = Apparent Power (VA)). Because there is no phase difference between voltage and current (ie Φ =0°) the Power Factor is equal to 1 (cos 0° = 1). 0 I V DAMON FYSON

23. Design, Install &Commission grid connected photovoltaic power systems Session 3 Electrical Basics • In a.c. circuits the power consumed by a load, measured in watts, is called the true power (Pt) and is expressed as: •  Generally, inductive (or lagging) power factors are created in electrical systems by electric motors, transformers and ballasts. Capacitors are then installed within the system to compensate for the lagging power factors by providing capacitive (or leading) power factors. • An a.c. motor, in particular, is able to register low true power readings, as measured on a watt meter, but at the same time cause high apparent power to flow in the a.c. distribution equipment such as transformers and cabling, resulting in additional heat losses. DAMON FYSON

24. Design, Install &Commission grid connected photovoltaic power systems Power factor cont… • To calculate power factor for an appliance, the measurement of both the a.c. RMS current and voltage are both taken and the two values are multiplied together. This gives the value of the Apparent Power with the units of Volt - Amps (VA). • A True Power measurement is also taken using an a.c. wattmeter. • The power factor for the appliance is then calculated from the formula: • Pf=TP true power/AP apparent power • The relationship between the three proceeding parameters can be related in a phase diagram DAMON FYSON

25. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Note : The value of the power factor can only be between 0 and 1. Low power factor appliances (PF < 0.7) can be a problem to electricity authorities since the high apparent power causes additional losses in their distribution system. So the industrial consumers are often directed by the supply authorities to "correct" any power factor problems by installing power factor correction capacitors on site. This has the desired effect of bringing the power factor closer to the ideal value of 1.0. . Grid interactive inverters have a power factor of 1; i.e. their kVA rating and kW rating are identical DAMON FYSON

26. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics pf=1 pf =0.75 • Session 3 Electrical Basics DAMON FYSON

27. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Voltage across a resistorThe current flowing through a 60Ώ resistor is 0.5A. What is the voltage across the resistor?. Include the units as well.Answer: V=IXR V=0.5X60 V=30VPower over timeWhich of the following terms is used to define the use of power over a period of time? Watt joules/ Joule seconds/ Watt-hours/Watt –secondsAnswer: Watt hoursEnergy of a light Bulb.How much energy would a 75 watt light bulb consume if left on for 12 minutes?Answer: 15 watt-hours or 0.015kWHsTrue PowerWhat is the true power of a 240VAC Fluorescent light bulb that draws 0.2A and has a power factor of 0.7 lagging.Answer: 33.6 watts Summative questions DAMON FYSON

28. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Licensing requirements • AS3000:2007 define extra low voltage 50VAC or120VDC ripple free. All states and territories require that any work must be preformed by a licensed electrician. • Restricted electrical license is not appropriate for Grid Connect work • There are also a number of now mandatory standards that people must adhere to if they are to design and install grid connected PV systems within Australia see next slide DAMON FYSON

29. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Standards • AS/NZS 3000:2007 Wiring Rules • AS/NZS 3008 Selection of cables • Part 1.1 Cables for alternating voltages up to and including 0.6/kV • Typical Australian installation conditions • AS 4777.1 Grid connect of energy systems via inverters • AS 4777.2 Inverter requirements • AS 4777.3 Grid protection requirements • AS/NZS5033 Installation of Photovoltaic (PV) Arrays • AS 1768 Lightning Protection • AS 1170.2 part 2: Wind Loads • AS2050 Installation of roof tiles • AS/NZS 1562.1 Design and installation of sheet roof and wall cladding. • AS 4509 Stand-alone Power Systems • NSW Local Service Rules Electrical installation DAMON FYSON

30. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Electric Shock • Electric shock occurs upon contact of a (human) body with any source of electricity that causes a sufficient current through the skin, muscles or hair • A 500 volt potential across the body’s resistance of 25000Ωs will produce a current 20mA, which can be fatal Ventricular fibrillation • A domestic power supply voltage (110 or 230 V), 50 or 60 Hz AC current through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60 mA. With DC, 300 to 500 mA is required DAMON FYSON

31. Body impedance Session 3 Electrical Basics • The International Electrotechnical Commission gives the following values for the total body impedance of a hand to hand circuit for dry skin, large contact areas, 50 Hz AC currents (the columns contain the distribution of the impedance in the population percentile; for example at 100 V 50% of the population had an impedance of 1875Ω or less):[10] DAMON FYSON

32. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics first aid • Freeing a victim from electrical contact • Before attempting to free any victim, always assess the danger. Do not • become the next victim — anyone touching a victim still in contact with • an electrical current may also receive a severe electric shock. Remember, • you should always assume that overhead power lines are live. • When freeing a victim from electrical contact: • • isolate the power immediately and before any other action is taken • • call emergency services on 000, or if calling from a mobile phone, 112 • • start resuscitation immediately if required, but only if it is safe to do so. Courtesy :Workplace Standards Tasmania DAMON FYSON

33. Design, Install &Commission grid connected photovoltaic power systems Resuscitation • If breathing or circulation stops and you need to perform resuscitation, • remember the DRABCD action plan: • D Check for danger: to yourself, others and the victim • R Check for response: is the casualty conscious or unconscious • A Check the airway: is the airway clear and open? • B Check breathing: look, listen and feel • If the victim is breathing: place them on their side and monitor • signs of life • If the victim is not breathing: give two initial breaths; check for • signs of life • C Start CPR if no signs of life: if the victim is unconscious, not • breathing, not moving • Start CPR with 30 compressions followed by two breaths • Continue CPR in this way (30:2) at the rate 100 compressions a • minute until help arrives • D Use a defibrillator if available. Follow the voice prompts • Courtesy :Workplace Standards Tasmania DAMON FYSON

34. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Session 3 Take home questions • 1. An atom has 14 protons and 14 electrons. What is the net charge? • 2. If one electron were removed, what would be the net charge. • 3. What are conductors; insulators and semiconductors • 4. The metal is a good conductor. What feature makes it so? • 5. Define the following terms • a) potential difference • b)Volts • c) Current • d) Resistance • e) Power DAMON FYSON

35. Design, Install &Commission grid connected photovoltaic power systems • Session 3 Electrical Basics Session 3 Take home questions continued…… • 6. What is an electromagnet? Give some examples. • 7. Write the formula that relates power, voltage and current. • 8.Write the formula that relates power , voltage and current • 9.Write the formula that relates power , voltage and resistance • 10.Write the formula that relates power , current and resistance • 11.Write the formula that relates power to energy • 12.What is the minimum fatal current for the human body? DAMON FYSON