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“PROPOSED PHILIPPINE NATIONAL STANDARDS FOR RENEWABLE ENERGY TECHNOLOGIES” SOLAR PV SYSTEM COMPONENTS INVERTERS FOR STAND-ALONE PHOTOVOLTAIC APPLICATIONS GENERAL SAFETY AND PERFORMANCE REQUIREMENTS DESIGN QUALIFICATION AND TYPE APPROVAL JUNE 2006 INTRODUCTION This proposed standard covers general, safety and requirements for non-utility interactive sinewave inverters used in photovoltaic systems. Performance requirements for these inverters are also included. Note: Safety requirements ensure that electrical equipment constructed in accordance with these standards does not endanger the safety of person or property when properly installed, maintained, and used in applications for which it was intended. SECTION ONE - GENERAL REQUIREMENTS 1. SCOPE This standard specifies general and safety requirements for non-utility interactive sinewave inverter for small photovoltaic systems particularly for those with rated input voltages of 12 Vdc and 24 Vdc. 2. DEFINITIONS 2.1. Rated voltage range: Range of dc voltage over which the inverter is intended to be operated. 2.2. Design voltage: Voltage declared by the manufacturer to which all the inverter characteristics are related. 2.3. Live part: Conductive part which may cause an electric shock in normal use. The neutral conductor shall, however, be regarded as a live part. 2.4. Type test: Test or series of tests made on a type-test sample for checking compliance of the design of a given product with the requirements of the relevant specifications. 2.5. Type test sample: Sample which consists of one or more similar units submitted by the manufacturer or responsible vendor for the purpose of a type test. 3. GENERAL REQUIREMENTS Inverters should be designed and constructed such that in normal use they do not cause danger to the users and surroundings. In general, compliance for inverters is checked by carrying out all the tests specified and described in Section 3 (Standard Test Methods) of the Inverters for Stand-alone Photovoltaic Applications – Design Qualification and Type Approval. 4. GENERAL NOTES ON TESTS 4.1. Tests according to this standard are type tests. -1- Note: The requirement and tolerances permitted by this standard are related to the testing of a type-test sample submitted for that purpose. Compliance of the type test sample does not ensure compliance of the whole production of a manufacturer with this safety standard. 4.2. Unless otherwise specified, the tests are carried out at room temperature between 20°C and 40°C. 4.3. It is permissible to substitute a battery by a dc power source provided that the source impedance is equivalent to that of a battery. 4.4. Three samples are required for testing. In such cases, if more than one inverter fails, the type sample is rejected. 4.5. If one inverter fails, the test is repeated using the other two inverters and both should comply with the test requirements. 5. MARKINGS 5.1. Inverters should be clearly marked with the following mandatory markings: 5.2. Mark of origin (trade mark, manufacturer's name or name of the responsible supplier), Model number or type reference of the manufacturer, Rated input battery voltage, Rated output ac voltage, Rated output frequency, Rated power output, Peak power rating, Continuous power rating, Intermittent power rating, Rated voltage output wave form, Note or mark indicating whether the inverter is proof against supply voltage polarity reversals. Markings shall be durable and legible. Compliance is checked by inspection and by trying to remove the markings by rubbing lightly for 15 seconds with two pieces of cloth: one soaked in water and the other in petroleum spirit. Note: The petroleum spirit should consist of a solvent hexane with a maximum of 0.1 volume percentage aromatics content, a kauri-butanol value of 29, an initial boiling-point of approximately 65°C, a dry-point of approximately 69°C and a density of approximately 0.68 g/cm3. 5.3. Inverter enclosure Inverter enclosure should be able to sufficiently protect the inverter from the ingress of water spray, dust and small insects. -2- 5.4. Inverter packaging Light emitting diodes (LED) or liquid crystal display (LCD) should be present in the front panel of the inverter to indicate voltage conditions of the battery. Optionally, voltmeters and current meters may be added in the front panel. Furthermore, audio or visual alarms may be incorporated in the inverter to warn users of nearing load disconnection. SECTION TWO - SAFETY REQUIREMENTS 6. TERMINALS 6.1. Terminals should permit the connection of conductors from each component. 6.2. Terminals should be prominently marked for polarities for each component in the PV system. 7. CONSTRUCTIONAL REQUIREMENTS 7.1. Inverters should be mechanically robust and should be designed such that they minimize the effects of moisture and temperature during use as well as prevent the ingress of insects, dust and water spray. 7.2. Adequately robust means of fixing should be provided. 7.3. Inverters must be easily serviceable. 8. PROTECTION AGAINST ACCIDENTAL CONTACT WITH LIVE PARTS 8.1. Inverters should, when installed in normal use, be sufficiently protected against accidental contact with live parts as. Lacquer and enamel are not deemed to be adequate protection or insulation for the purpose of this requirement. 8.2. Parts providing protection against accidental contact should have adequate mechanical strength and should not loosen in normal use. It must not be possible to remove them without the aid of a tool. Compliance is checked by inspection. 9. MOISTURE RESISTANCE AND INSULATION 9.1. The inverter should be moisture resistant. It should not show any appreciable damage after being subjected to the following test: The inverter is conditioned for 48 hours in an enclosure with relative humidity maintained between 91% and 95%. The temperature of the air at all places where samples are located is maintained within 1oC of about 40°C. -3- 9.2. Insulation should be adequate between the input terminals bonded together and all exposed metal parts. Before the insulation test, remove visible drops of water, if any, with a blotting paper. The insulation resistance should not be less than 2 Mohm. SECTION THREE - PERFORMANCE REQUIREMENTS 10. ELECTRICAL CHARACTERISTICS Electrical characteristics of the inverter should be faithful to the manufacturer's data and should be tested according to the procedures described in Inverters for Stand-alone Photovoltaic Applications – Design Qualification and Type Approval. The inverter must be tested for the following: a. b. c. d. e. f. g. h. i. j. Stand-by power loss Operating voltage range Conversion efficiency DC ripple Power factor Voltage and frequency variation Total Harmonic Distortion Electromagnetic noise Acoustic noise Ground path continuity 11. INVERTER PROTECTION The provisions on Inverters for Stand-alone Photovoltaic Applications – Design Qualification and Type Approval – Section One – Item 4 (Markings) apply together with the following mandatory marking requirement: 11.1. Indication of type and current rating of the fuse or disconnecting means, if applicable. 11.2. Resettable circuit breakers are acceptable as over current devices provided they are rated for their intended use. 11.3. Polarity reversal To check if the inverter is proof against supply voltage polarity reversals, operate it with reverse voltage for about 5 minutes at its maximum voltage range. At the end of this period, the supply should be re-connected correctly and the inverter should operate normally. 11.4. Over-voltage/under-voltage. The inverter should be protected from lightning flashes and inductive over-voltage as well as input under-voltage conditions if applicable. -4- 11.5. In circuits where no transients are anticipated, fast acting fuses can be used. 11.6. The inverter should be subjected to environmental and electrical cycling tests described in the Inverters for Stand-alone Photovoltaic Applications – Design Qualification and Type Approval – Section Two – Item 20 (Temperature Cycling and Endurance Test) to determine potential failures. At the end of these tests, the inverter should operate normally. -5- INVERTERS FOR STAND-ALONE PHOTOVOLTAIC APPLICATIONS DESIGN QUALIFICATION AND TYPE APPROVAL INTRODUCTION This standard covers the requirements for the design qualification and type approval of stand-alone sinewave inverters used in photovoltaic systems. SECTION ONE - GENERAL REQUIREMENTS 1. SCOPE This standard lays down the requirements for the design qualification and type approval of stand-alone sinewave inverters used in photovoltaic systems suitable for long-term operations. 2. PURPOSE To determine the electrical and thermal characteristics of inverters. The actual life expectancy of inverters, so qualified, will depend on their design, their environment and the conditions under which they are operated. 3. SAMPLING Three inverters for qualification testing (plus spares as desired) will be taken at random from a production batch or batches. The inverters should have been subjected to the manufacturer's normal inspection, quality control and production acceptance procedures. The inverters should be complete in every detail and must be accompanied by the manufacturer's handling, mounting and connection instructions, including the maximum permissible voltage. When the inverters are prototypes of a new design and not from production, the fact should be noted in the test report. 4. MARKING Each inverter should carry the following clear indelible markings: Name, monogram or symbol of manufacturer Type or model number Serial number Polarity of terminals Output voltage Nominal system voltage Rated power Peak power rating Continuous power rating Intermittent power rating -6- Voltage/current wave form The date and place of manufacture should be marked on the inverter traceable from the serial number. 5. TESTING The inverter should be subjected to the test sequences detailed in Section 2 of the Inverters for Stand-alone Photovoltaic Applications – Design Qualification and Type Approval. In carrying out the tests the manufacturers’ handling, mounting and connection instructions must be strictly observed. 6. PASS CRITERIA An inverter will be considered to have passed the qualification tests, if each test sample meets the following criteria: 6.1. No apparent damage appears on the inverter after the tests, conditions and functions normally. 6.2. No sample exhibited any short-circuit or open, circuit conditions during the tests. 6.3. There is no visual evidence of a major defect, as defined in Section One - Item 7 (Major Visual Defects). 6.4. The insulation test requirements are met after the tests. Should the first sample fail any test, the other two inverters must be subjected to all relevant tests, following the same sequence. If one or both of the inverters fail, the design will be considered as not meeting the qualification standard. If, however, both inverters pass the test sequence, the design will be considered as successfully meeting the qualification requirements. 7. MAJOR VISUAL DEFECTS For the purposes of design qualification and type approval, the following are considered to be major visual defects: shorted terminals shorted routes in the printed circuit board shorted electronic parts in the printed circuit board 8. REPORT A certified test report of the qualification tests, with the measured performance characteristics and details of any failures and re-tests should be prepared by the test agency. A copy of this report must be provided to the manufacturers and be kept for reference purposes. -7- 9. MODIFICATIONS Any change in the design, materials, components or processing of the inverter may require a repetition of some or all the qualification tests to maintain type approval. SECTION TWO - STANDARD TEST METHODS 10. GENERAL REQUIREMENTS Tests are type test. One inverter will be subjected to all tests. 10.1. Ambient temperatures Tests should be made in a draught free room and at an ambient temperature of about 20 to 40°C. 10.2. Supply voltage Unless otherwise specified the inverter to be tested must be operated at its design voltage. 10.3. Inverter stability a. An inverter should be brought to a condition of stable operation before carrying out measurements. b. The characteristics of an inverter should be checked immediately before and immediately after each series of tests. 10.4. Instrument characteristics 10.4.1. Potential circuit Potential circuits of instruments connected across the inverter must not pass more than 3% of the nominal running current. 10.4.2. Current circuit Instruments connected in series with the inverter should have sufficiently low impedance such that the voltage drop will not exceed 2% of the inverter voltage. 10.4.3. R.M.S. measurements Instruments should be essentially free from errors due to wave form distortion and should be suitable for the operating frequencies. 10.4.4. Inverter power source It is permissible to substitute a battery by a D.C. power source, provided that the source impedance is equivalent to that of a battery. -8- 11. MEASUREMENT OF STAND-BY POWER Figure 1 gives a typical testing circuit. If this circuit is used, no correction is necessary for the current drawn by the voltmeter, provided that the resistance of the voltmeter complies with the requirements of item 10.4.1. Stand-by power should not exceed 1% of rated power. 12. DETERMINATION OF OPERATING VOLTAGE Figure 2 gives a typical circuit for the determination of operating voltage. 13. MEASUREMENT OF CONVERSION EFFICIENCY The inverter efficiency must not be less than 90% at full load. Figure 3 gives a typical circuit for the determination of inverter efficiency. 14. MEASUREMENT OF D.C. RIPPLE There should be no ripple on the D.C. supply side of the inverter Figure 4 gives the circuit for measurement of D.C. ripple. 15. VOLTAGE AND FREQUENCY VARIATION The voltage regulation of the inverter should be less than or equal to 5% of the rated output voltage while the frequency variation of the inverter should be less than or equal to 1% of the rated output frequency. 16. TOTAL HARMONIC DISTORTION The total harmonic distortion (THD) of the inverter should be less than or equal to 5% with linear loads. 17. ELECTROMAGNETIC COMPATIBILITY Electromagnetic compatibility must be lower than 40 dB at a distance of 10m. 18. ACOUSTIC NOISE When operating over the rated voltage range and with load connected the inverter must comply with the following requirements: at and above an operating frequency of 18 kHz: no requirements; below an operating frequency of 18 kHz: requirements under consideration. -9- 19. ELECTRIC SHOCK CONDUCTIVITY TEST In order to determine whether a conductive part is a live part which may cause an electric shock, the inverter is operated at rated voltage and the following tests are conducted: 19.1. The current flowing between the parts connected and earth is measured, the measuring instrument having a non-inductive resistance of 2000 ± 50 ohms. The part concerned is a live part if a current of more than 0.7 mA (peak) or 2 mAdc is measured. 19.2. The voltage between the part concerned and any accessible part is measured, the measuring instrument having a non-inductive resistance of 50,000 ohms. The part concerned is a live part if a voltage or more than 34V (peak) is measured. For the above test, one pole of the test supply should be at earth potential. 20. TEMPERATURE CYCLING AND ENDURANCE TEST Compliance is checked using the following tests: The inverter should be mounted in accordance with the manufacturer's instructions, operated in association with full load conditions at the maximum voltage of the rated load and subjected to a temperature cycling test and an endurance test, as follows: 20.1. The temperature cycling test will be carried out first at the lower limit of the ambient temperature range for 1 hour. The temperature will be raised to the upper limit of the ambient temperature range for 1 hour. Five such temperature cycles are carried out. 20.2. The endurance test should be carried out at the ambient temperature for the following test period: 20.3. for continual operation inverters: 200 h; for intermittent operation inverters: 50 h. At the end of this time, and after cooling to room temperature, the inverter should operate the load at the rated voltage. - 10 - APPENDIX A - TEST CIRCUITS INVERTER A + D C S U P P L Y V - Figure 1. Circuit for Measurement of standby power loss AC OUTPUT V 220 V INVERTER A + VARIABLE DC SUPPLY V Figure 2. Circuit for measurement of inverter operating voltage - 11 - LOAD A V INVERTER A + DC SUPPLY V - Figure 3. Circuit for measurement of conversion efficiency + A INVERTER D.C. SUPPLY - SHUNT WAVE ANALYZER/ OSCILLOSCOPE Figure 4. Circuit for measurement of D.C. ripple - 12 -