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５． Auxiliary System : 5-1. Inverter Jun HAGIHARA Tokyo Electric Power Company – e8 Member

５． Auxiliary System : 5-1. Inverter Jun HAGIHARA Tokyo Electric Power Company – e8 Member. Solar PV Design Implementation O&M March 31- April 11, 2008 Marshall Islands. 5-1. Inverter. Contents. 5-1. Inverter. 5-1-1. Outline 5-1-2. Theory 5-1-3. Circuit 5-1-4. Equipped function

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５． Auxiliary System : 5-1. Inverter Jun HAGIHARA Tokyo Electric Power Company – e8 Member

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  1. ５．Auxiliary System:5-1. InverterJun HAGIHARATokyo Electric Power Company – e8 Member Solar PV Design Implementation O&M March 31- April 11, 2008 Marshall Islands

  2. 5-1. Inverter • Contents 5-1. Inverter 5-1-1. Outline 5-1-2. Theory 5-1-3. Circuit 5-1-4. Equipped function 5-1-5. Islanding operation 5-1-6. Grid Connection 5-1-7. Specification 5-1-8. How to select 5-1-9. Inspection 5-1-10. Some examples

  3. 5-1. Auxiliary System: Inverter

  4. 5-1-1. Inverter (Power conditioner): Outline Convert DC power from PV panel into AC Supply AC power to load and produce reverse flow to the grid (if connected and surplus power) Control to produce max power from PV Comply with required guideline on grid connection

  5. 5-1-2. Inverter (Power conditioner): Theory Switch S3 Switch S1 Lamp DC voltage source Switch S2 Switch S4 • Current wave form at lump • Switch S1 and S4 are ON: direction A • Switch S2 and S3 are ON: direction B • Repeat this action at constant frequency

  6. 5-1-2. Inverter (Power conditioner): Theory Carrier Signal at high voltage [a] Signal at low voltage Ed S1,S2 : ON [b] 0 S3,S4 : ON Ed S1,S2 : ON [c] 0 S3,S4 : ON • To change voltage, use PWM (pulse width modulation) control • Current wave form at lump • Switch S1 and S4 are ON: voltage E • Switch S1 and S2 are ON: voltage 0 • Switch S2 and S3 are ON: voltage –E • Switch S4 and S3 are ON: voltage 0 • By changing ON-time of A) and C), we can change pulse width of output voltage • Repeat this action with suitable frequency, average output voltage can be AC.

  7. 5-1-3. Inverter (Power conditioner): Circuit

  8. 5-1-4. Inverter (Power conditioner): Equipped function • Automatic stop • Start at sun rise and stop at sun set automatically by monitoring PV output • Maximum Power Point Tracking (MPPT) control • To correspond to PV output fluctuation • Prevention of stand-alone operation • On power outage, detect it and stop automatically for the safety of maintenance staff • Automatic voltage control • On reverse flow into grid, keep output voltage within specified range • Detection of DC current • DC reverse flow is not allowed. Non-transformer type inverter doesn’t have isolation, so there is a possibility of small DC flow from inverter. • Detection of DC earth fault • On earth fault of PV module, fault current may have superimposed DC and earth leakage breaker may not be able to break. • Anti islanding operation

  9. 5-1-5. Inverter (Power conditioner): Islanding operation • Islanding operation: Operation without grid-connection • Grid-connection: Current control • Islanding: Voltage control • With battery system in some case • Need multiple CBs as specified guideline of grid connection

  10. 5-1-6. Inverter (Power conditioner): Grid connection

  11. 5-1-7. Inverter (Power conditioner): Specification • Inverter type • Switching method • Insulation method • For non-transformer type, take care about AC leakage current on DC side • Filter type • Voltage control method • Auxiliary control function • Operation control: automatic start-up • Protection system for grid connection • Anti islanding operation • Active • Passive • General • Manufacturer • Model number • Indoor/outdoor • Dimension • Inverter capacity • Conversion efficiency • Allowable overload • Environmental temperature • AC side • Phase and wire: 1P2W, 1P3W, 3P3W, 3P4W • Voltage and frequency • Fluctuation range of voltage and frequency • Acceptable output harmonics • Acceptable unity displacement power factor • DC side  determine serial/parallel of PV modules • Rated voltage • Residential use: 100-250V • Commercial/industrial use: 200-400V • Operational voltage range

  12. 5-1-8. Inverter (Power conditioner): How to select Check point • General • AC voltage and phase • Certification • Easy installation • Necessity of islanding operation • Reliability and lifetime • Easy setting and test of protection • Easy reading of kW output • Maintenance network • For effective use of solar power • High conversion efficiency • MPPT • Less stand-by power at night • Less loss at low load • Power quality and others • Low noise • Less harmonics • Stable start/stop

  13. 5-1-9. Inverter (Power conditioner): Inspection at mechanical completion

  14. 5-1-9. Inverter (Power conditioner): Routine inspection check (monthly)

  15. 5-1-9. Inverter (Power conditioner): Periodical inspection

  16. 5-1-10. Inverter (Power conditioner): Some examples Source: Nissin Electric

  17. 5. Auxiliary System5-2.WiringHerb WadeConsultant Solar PV Design Implementation O& M March 31- April 11, 2008 Marshall Islands

  18. 5-2. Wiring • Contents 5-2. Wiring 5-2-1. Wiring 5-2-2. Wiring Large Photovoltaic Arrays 5-2-3. Lightning Protection and Grounding

  19. 5-2-1. Wiring

  20. Characteristics of wiring • Number of copper conductors per cable (1 or 2 needed – never use aluminum wire) • Stranded or solid wire • Type of insulation (indoor only, outdoor, direct burial) • Size of conductor (mm2 or AWG) • Length of wire

  21. Choose the correct insulation • If indoor type wire is used to connect to the panels, the insulation will crack and fall off after a few years because of ultra-violet degradation of the plastic by sunlight. If you must use indoor wire, put it inside a plastic or metal pipe (solid plastic or metal conduit or flexible water pipe) to protect it from the sun. • If you bury the wire, always use wire with insulation certified for burial since earth fungus and moisture will gradually cause other types of insulation to fail. If non-burial wire must be used, it has to be placed inside a plastic or metal pipe before burial and the open ends of the pipe sealed with silicone rubber to prevent water and insect entry. Burial type wire will be damaged if exposed to sunlight. Where it comes out of the ground it should be enclosed in plastic pipe

  22. Sizing wire • Voltage drop needs to be kept to the minimum that is affordable. Typically 4%-5%. For a 12V system, 0.5V is reasonable • Voltage drop depends on: • Cross sectional area of the wire in mm2 • Length of the wire • Amperes of current flow through the wire • To correctly size wiring for solar you must know all three things. When sizing wire for regular 110V or 220V wiring all you need to know is the amperes through the wire. That is to be sure the wires do not overheat, not to keep the voltage drop within limits. For solar the voltage drop is the key issue. With the low voltage drop that is allowed, the ampreres cannot get high enough to cause measurable heating.

  23. Voltage loss in wires • All wires have some resistance. The smaller the wire, the greater the resistance. The longer the wire the greater the resistance. Some voltage is always lost in wires. The voltage that is lost is determined by Ohm’s Law. • Ohm’s Law says:Volts = Amperes X Ohms so Voltage loss in wire = Amperes flow X wire resistance For the same Watt load, a 12V circuit carries 10 times the Amperes of a 120V circuit. So 12V wiring has to be 10 times larger in area than 120V wiring for the same voltage drop.

  24. Computing Voltage Drop Voltage drop = Amps X foot X ohms per foot 1 mm2 wire has a resistance of about 0.0061 ohms per foot. So a 100 foot length of 1 mm2 has a resistance of 0.0061 X 100 = 0.61 Ohms If 5 A flows through the wire, it will have a voltage loss of 5 X 0.61 = 3.05 Volts Unfortunately AWG is not a measure of cross sectional area of wires and to calculate voltage drop we have to figure it on the basis of the wire cross section. So mm2 (which is a measure of cross sectional area) needs to be used in the calculations then we can convert with a table to find the correct AWG size. Non-American wire already is in mm2 so no conversion is necessary

  25. Calculating Ohms/meter • 1 mm2 wire has a resistance of .0061 ohms/foot. Since mm2 is a measure of cross sectional area and resistance goes down as area goes up, we can calculate the specific resistance (Ohms/meter) for any wire using the formula: .0061/Wire mm2 So a 4 mm2 wire will have a specific resistance of .0061/4 = .0015 Ohms/foot

  26. Conversion AWG to mm2

  27. Ohms per foot for AWG wire 4 AWG = .000290 Ohms/foot = .00095 Ohms/meter 6 AWG = .000457 Ohms/foot = .0015 Ohms/meter 8 AWG = .000732 Ohms/foot = .0024 Ohms/meter 10 AWG = .00116 Ohms/foot = .0038 Ohms/meter 12 AWG = .00183 Ohms/foot = .006 Ohms/meter 14 AWG = .00290 Ohms/foot = .0095 Ohms/meter 16 AWG = .00457 Ohms/foot = .015 Ohms/meter

  28. Ohms Per Meter for Metric Wire 16 mm2 = .00038 Ohms per foot = .00125 Ohms per meter 12 mm2 = .000509 Ohms per foot = .00167 Ohms per meter 10 mm2 = .000610 Ohms per foot = .002 Ohms per meter 8 mm2 = .000762 Ohms per foot =.0025 Ohms per meter 6 mm2 = .00102 Ohms per foot = .00333 Ohms per meter 4 mm2 = .00152 Ohms per foot = .005 Ohms per meter 2.5 mm2 = .00244 Ohms per foot = .008 Ohms per meter 1.5 mm2 = .00405 Ohms per foot = .0133 Ohms per meter

  29. Calculating Proper Wire Size • Determine the maximum Amperes to flow in the wire • Determine the distance in meters (along the wire path) between the battery and the load or the panels being connected • For 12V systems, use the formula: mm2 = .0244 X Amperes X Feet

  30. Use of the Wire Tables • The wire tables result in a wire size that causes exactly a 0.5V drop for the listed Amperes and length. • Enter Watts or Amperes on the left side of the table and go across to the meters or feet distance on the table. The distance listed is the measured distance between the two ends of the cable. The number represents the exact wire size in mm2 that will result in a voltage drop of 0.5 V • Choose the next larger standard size of wire either AWG or metric. (For AWG convert from mm2 using the previous conversion table)

  31. Wire sizes from Panels to the Battery • Use the Isc of the array as the Amperes to enter the wire table or to calculate using the formula. This will be a conservative value since the panel will always deliver less than the rated Isc • If the rated Isc is not known, divide the Wp of the panel by 12V to estimate it (or enter the table using the Wp rating in the Watts column). • Since ALL the energy for the PV system passes through the panel wires, the voltage drop should be as low as practical. • The wire to the battery from the controller should be the same size as or larger than the wire from the panel to the controller for best results

  32. Wiring a Refrigerator or Pump • Because an electric motor requires as much as three times the Amperes for starting as for running, wires used to connect an appliance that has a motor, especially refrigerators, freezers and pumps, must be at least twice the mm2 size as the table shows. If that is not done, the voltage drop during starting may be too high to allow the motor to start and it will stall.

  33. 24 V System wire sizes • The wire sizes needed to connect panels and loads in a 24V system need be only ¼ the mm2 of wires used in a 12V system to connect the same size of load or panels. This is because for the same Watts, the Amperes is cut in half if the voltage is doubled. But also an allowable 5% voltage drop at 24V is twice that allowed for 12V. So the wire only has to be 1/4 the size for the same Watts and percent voltage drop. • For any solar installation that requires bigger than 10 AWG wire for connecting loads at 12V, raising the battery voltage to 24 V is suggested.

  34. Using multiple parallel wires • If you run two wires together between the same connection points (wires connected in parallel), the voltage drop will be cut in half because the effect is the same as doubling the conductor area for a single wire. So if larger wires are needed than are available, it is reasonable to connect two or more smaller wires together in parallel in order to have the necessary capacity. So if you calculate you need 25mm2 of wire to connect a large inverter, you can put 6 AWG 10 wires together for a total of 26.4mm2 of conductor.

  35. Connections • Because 12V is very low pressure electricity, the wiring connections must be of very low internal resistance. Otherwise the voltage drop will be excessive. • The connections need to be ones that will not change internal resistance over time due to corrosion or loosening • Only screw type connections or properly soldered connections should be used. Note that most field soldered connections are “cold” solder joints and are not adequate. Solder must be fully melted and flowing onto the wires.

  36. Improper connections • Twisting wires together will quickly result in high voltage drops. DO NOT USE • Using “twist lok” connectors that twist the two wires together in a plastic holder will be better than just twisted wires but will gradually increase in voltage drop. DO NOT USE • Crimped lug connections are ok only if the proper tool is used by a person well trained in the proper technique for crimping. Rarely are crimped lug connections made in the field good for more than a year or two. DO NOT USE

  37. Color Coding of Wires • To comply with the US National Electrical Code, a useful working code for installing solar systems, the following colors are to be used: • White designates the conductor that is grounded (if any) or marked with white at each termination • Bare wire, green or green with yellow stripe insulation is to be used for module or appliance frame grounding wires (never use the grounded conductor for grounding array frames or appliance frames). • Other conductors may be any color though normally black is used. If a center tapped array or AC circuit is installed the center tap is grounded and one “hot” wire is black and the other red.

  38. Switches • Switches often greatly increase in voltage drop with age, particularly cheap “slide contact” type switches commonly used for house installations. • For long life, use snap action “toggle” type switches that use a spring to snap the contacts together.

  39. Check Switches Annually • Voltage drops on switches should be checked at least once a year. To do that, turn the switch on and measure the voltage across the switch terminals. It should not be over 0.05V. • If the cheap “slide contact” switches are used, they should be replaced every time the battery is replaced to ensure that the voltage drop does not become excessive.

  40. 5-2-2. Wiring Large Photovoltaic Arrays

  41. Large array wiring • In large arrays there are typically a number of series “strings” that are enough panels in series to reach the desired voltage. Then those strings are usually connected in parallel at junction boxes, often called combiner boxes. From the combiner boxes, large wires with outdoor rated insulation (or run inside of conduit) take the array power to a controller or inverter. • Wire sizing rules are used that limit losses to 4% at the ISC of the strings -- the same as earlier described for SHS wiring -- result in an overall loss that is on the order of 2%. Generally lower losses than that are practical since wire runs are not very long. • Combiner boxes must be accessible for testing of arrays and array wiring must be labeled so problems can be isolated.

  42. HV (over 50V) Array connections • For arrays over 50V that have a grounded terminal, each string should be connected through a fuse to a DC bus, not “daisy chained” in parallel. With the “daisy chain” configuration it is possible to disconnect part of the array from the grounding bus which is a safety hazard.

  43. Array disconnects • For safety reasons as well as for troubleshooting, there needs to be a main array disconnecting switch, circuit breaker or fuse between the array combiner box and the controller (there there is a battery installed) or the inverter (for grid-connected PV). • For very large arrays, sub-array disconnects are also advisable to allow for maintenance and troubleshooting.

  44. 5-2-3. Lightning Protection and Grounding

  45. Grounding of wiring for solar installations • For any installation that has voltages greater than 50V, grounding of one side of the circuitry is needed for safety. • All installations that include inverters for mains voltge AC production should be grounded using the same methods and standards as regular grid power systems • All grounding for a system should come together at one point, not using several grounding rods for the earth connection • Usually the negative side of the DC circuit is grounded though the positive side will work as well as long as it is clearly marked. • Frames of panels should be grounded if circuitry is grounded

  46. Lightning and low voltage solar systems • For most of the Pacific Islands, cloud to ground direct strikes by lightning is much less common than in continental areas. Cloud to cloud strikes remain fairly common. So most damage to PV systems is the result of a cloud to cloud strike inducing a high voltage spike in the wire between a solar panel and the battery which acts like an antenna for the electromagnetic waves that spread from the strike. • Grounding low voltage (below 50V) DC solar systems, such as most SHS, may increase the likelihood of damage due to induced voltage spikes from nearby lightning strikes though it may reduce the likelihood of damage due to direct strikes. Since direct strikes are rare and installing a proper grounding system may cost 10% or more of the total SHS cost, most installations are not grounded.

  47. Lightning and larger PV systems • For larger systems grounding will be done for operating safety reasons. This may reduce the chance of damage to installations due to lightning strokes but in some cases may place the control electronics that are connected between panel and battery at increased risk of voltage surges due to induced voltage spikes from lightning. So the electronics should be protected by spike and surge supressing devices such as varactors. • Lightning rods may be installed on a pole near the solar system to dissipate local charges between clouds and the ground however there is no evidence that this decreases the frequency or damage done by lightning to a Pacific Island solar installation

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