1、UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULUNDERWRITERS LABORATORIES INC. CERTIFICATION REQUIREMENT DECISIONThis Certification Requirement Decision is prepared and published by Underwriters Laboratories Inc.(UL). It is normative for the a
2、pplicable UL Product Certification Program(s); however, it is currently notpart of the UL Standard(s) referenced below.Product Category (CCN): QIKHStandard Number: UL 1741Edition Date: January 28, 2010Edition Number: 2Section / Paragraph Reference: New Sections 109 to 112Subject: Isolated Inverters
3、Intended for Use with Ungrounded PV ArraysDECISION:The requirements below, (include new definitions and Sections 109 112) are to be used for theevaluation of isolated Electric Power System (EPS)-interactive PV inverters for connection to ungroundedphotovoltaic systems installed in accordance with Se
4、c. 690.35 of the NEC.DefinitionsISOLATION MONITOR INTERRUPTER (IMI) A device that monitors the insulation resistance of a PVarray circuit to ground and prevents energization of the inverter AC output circuit or disconnects anenergized output circuit when the PV array input circuit insulation resista
5、nce drops below a predeterminedvalue. Some IMIs may have monitoring circuitry that verify functionality and take appropriate actions in theevent of circuit failures. The IMI circuit may include or provide signals to control the critical isolationcomponents.GROUND FAULT A loss or electrical isolation
6、 or unintentional current path from ground to a componentor circuit.ISOLATED INVERTER An inverter that provides galvanic isolation between its input and output circuits.FUNCTIONAL GROUND An intentional impedance path from ground to a component or circuit in a PVarray and/or inverter circuit. Functio
7、nal grounding may be used during PV array isolation measurements.The intentional impedance path to ground may be a permanent or temporary connection. A permanent PVarray connection to ground without limiting impedance is not considered a functional ground.109 General109.1 These requirements cover PV
8、 inverters with transformer isolation, intended to be installed onground referenced AC output circuits and are intended for connection to ungrounded PV systems that donot have one of the PV source circuit conductors bonded / referenced to a grounding electrode conductorduring normal operation of pow
9、er export. Prior to power export during PV array isolation measurement thePV array is permitted to be temporarily referenced to ground.109.2 The requirements in sections 109 112 are in addition to the other requirements in UL 1741.Construction110 GeneralUL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FUR
10、THER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM UL110.1 Specific construction and operational requirements for isolated inverters intended for connection toungrounded PV systems are covered in sections 110 - 112.110.2 When an insulation resistance measurement circuit relies upon software or
11、 firmware to comply withthe requirements in sections 110-112 the software or firmware shall be evaluated for reliability inaccordance with the Standard for Software in Programmable Components, UL 1998.110.3 The insulation resistance measurement circuit shall have a built-in automatic self- test circ
12、uit toverify correct operation of the insulation resistance measurement. An automatic self-test feature shallverify the insulation resistance measurement circuit is functioning within its intended operating limits. If theinsulation resistance measurement circuit self-test circuit determines it is ou
13、tside its intended operatinglimits, the unit shall prevent the inverter from exporting AC power and indicate the fault.110.4 The self- test shall be performed prior to connection and export of energy to the EPS and at leastonce in each 24-hour period.110.5 Loss of power to the insulation resistance
14、measurement circuit shall result in cessation of AC powerexportation from the inverter.110.6 Components in an insulation resistance measurement circuit shall be analyzed to determine thepotential for a malfunction that could result in misoperation, the disabling of, or have a negative impact onthe i
15、ntended operation of the IMI monitoring system including control circuits, measuring circuits, or thepower supply to such circuits (e.g. capacitors, diodes, solid-state devices, current transformers, voltagemeasurement resistors, and similar components). Faults are to be short or open circuit of any
16、 twoterminals, one pair at a time. Critical components shall be identified by a failure mode and effects analysisin accordance with the Standard for Tests for Safety-Related Controls Employing Solid-State Devices, UL991.110.7 If the component analysis required in 110.6 shows that the malfunction of
17、one or more componentsmay render the insulation resistance measurement circuit inoperative, the components shall comply withsection 110.8.110.8 With reference to 110.7, the circuits and the identified components are to be subjected to thefollowing tests (to be run on IMI circuitry as a preconditioni
18、ng to the functionality tests), in accordance withthe methods described in Section 99, Tests for Safety-Related Controls:a) Surge withstand performance test as outlined in section 99.1;b) Protection from electromagnetic interference as outlined in section 99.1;c) Ramp Voltage Test (Verified operatio
19、n at extremes of PV and Utility ranges of operatingvoltages) as outlined in section 99.2;d) Electrostatic Discharge Test as outlined in section 99.3;e) Thermal Cycling Tests, Test performed at 20C to +85C or manufacturer specified storagetemperature range, whichever is most severe) as outlined in se
20、ction 99.4;f) Humidity cycling Test as outlined in section 99.5.Exception: Alternatively, circuits and components may comply with the equivalent requirements from theStandard for Test for Safety-Related Controls Employing Solid-State Devices, UL 991.STANDARD NUMBER: UL 1741 -2-UL COPYRIGHTED MATERIA
21、L NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM UL111 Insulation Resistance Detection of Ungrounded Arrays for Isolated Inverters111.1 Isolated inverters intended to be connected to ungrounded PV arrays shall have an insulationresistance detection means to measure th
22、e DC insulation resistance between the PV array input(s) andinverter ground connection. The unit shall:a) Measure the insulation resistance between the inverters PV array input circuit(s) to theinverter ground terminal prior to beginning the exportation of AC output current but no less thanonce per
23、24-hour period, andb) Be able to detect PV array circuit insulation resistance (R) values as calculated in 111.2.111.2 In reference to 111.1, when the measured DC insulation resistance values are less than as requiredin Table 111.1, the inverter shall take the following actions:a) Provide an indicat
24、ion of the isolation fault as required in 111.3 andb) Prevent the inverter from exportation of AC power.Table 111.1Minimum Allowable InsulationMinimum Allowed Insulation Resistance Inverter SizeR= 500ohms + (Voc/ 300mA) 30 kVAR= 500ohms + Voc/ (10mA*(Inverter kVA) 30 kVAWhere:R = Resistance in ohms
25、from the PV input to the inverter ground connectionVOC= Open circuit voltage of the PV array to be connected to the inverter in voltskVA = rated continuous output power in kVA of EUT111.3 The product shall indicate a fault when the DC insulation resistance measured is less than theminimum value as d
26、efined in 111.2. The fault indication means shall:a) Be integrated within the inverter and include a visible and/or audible indication that isdetectable external from the inverter, andb) Include a signal or provisions for connection to an electrical output circuit to provide for aremote fault indica
27、tion.111.4 In reference to 111.2, the product shall comply with the following section for Array InsulationResistance Measurement Test, Section 97.97 Array Insulation Resistance Measurement TestGeneral These tests are to evaluate an inverters ability to verify the PV array has the minimum levelof iso
28、lation resistance before it closes it critical isolation components in preparation to export power to theEPS.97.1 Ungrounded PV Arrays97.1.1 The inverter shall be tested as follows.STANDARD NUMBER: UL 1741 -3-UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERM
29、ISSION FROM ULa) A test resistance is to be connected between the PV array input terminal of the inverter andground. The value of the test resistance is to be less than the value of resistance required byTable 90.1.b) The inverter is to be connected to its rated input and output sources as required
30、by themanufacturers installation instructions.c) The inverter shall indicate the PV array isolation fault and prohibit closing of the criticalisolation components that connect the inverter to the EPS.d) The procedure shall be repeated for each PV input terminal.e) If the unit has multiple PV input s
31、ource circuit connections, the test shall be repeated foreach terminal of each PV input source circuit.Exception: If analysis of the PV input terminals of the inverter under test can show that one or moreterminals can be expected to have an similar available current (e.g. PV string inputs connected
32、in parallel)then testing of each PV input terminal is not required.97.2 Functionally Grounded PV Arrays97.2.1 The inverter is to be tested as follows.a) A test resistance is to be connected between each PV array input terminal of the inverterand ground as noted below. The value of the test resistanc
33、e connected is to be equal to or lessthan the calculated value.b) The externally applied test resistance (Rtest) is to be adjusted to result in a total combinedparallel resistance of less than 80% of the minimum design resistance for the inverter ascalculated according to 91.1 A. This value is desig
34、nated below as RTotal, which consists of theparallel combination of the following items:1) The test resistance.2) The pre-existing inherent insulation resistance of the PV array simulated supplysource and,3) The inverter actual design resistance Rdesignc) The test resistance is to be connected from
35、one of the PV input source terminals to ground.d) The inverter is to be connected to its rated input and output sources as required by themanufacturers installation instructions.e) The inverter shall indicate the PV array isolation fault and prohibit closing of the criticalisolation components that
36、connect the inverter to the EPS.f) The procedure shall be repeated for each PV input terminal.g) If the unit has multiple PV input source circuit connections, the test shall be repeated foreach terminal of each PV input source circuit.STANDARD NUMBER: UL 1741 -4-UL COPYRIGHTED MATERIAL NOT AUTHORIZE
37、D FOR FURTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM ULThis is generated text for figtxt.97.2.2 During the test the inverters resistance measurement circuit may optionally be disengaged (i.e. notconnected between PV inputs and ground) during the test if the combination of all other resi
38、stances whichare present in the circuit during test meet the above requirement for RTotal.NOTE: The test resistance for these tests, when connected to the inverter terminal(s) will be in parallelwith respect to the pre-existing inherent insulation resistance of the PV array or other supply source be
39、ingused for the test. As such, the test resistor value cannot be sized directly from Table 90.1 but must takeinto account the total resistance of the test circuit with the application of the external resistor. It may benecessary to modify the test array circuit to increase the initial insulation res
40、istance to a large enoughresistance value to perform the test.112 Markings and Installation Manual Requirements112.1 The following markings shall be provided in addition to the markings required elsewhere in UL 1741.Figure 97.1STANDARD NUMBER: UL 1741 -5-UL COPYRIGHTED MATERIAL NOT AUTHORIZED FOR FU
41、RTHER REPRODUCTION ORDISTRIBUTION WITHOUT PERMISSION FROM UL112.2 Products intended for connection to ungrounded arrays shall be marked as follows: “WARNING:ELECTRIC SHOCK HAZARD. THE DC CONDUCTORS OF THIS PHOTOVOLTAIC SYSTEM AREUNGROUNDED AND MAY BE ENERGIZED.” This marking is required to be in a l
42、ocation that is readilyvisible after installation of the inverter.112.3 Inverters with a permanent or intermittent array functional grounding feature shall be marked asfollows: “WARNING: Electric Shock Hazard. The DC conductors of this photovoltaic system are normallyungrounded but will become inter
43、mittently grounded without indication when the inverter measures the PVarray isolation.” This marking is required to be in a location that is readily visible after installation of theinverter.112.4 The installation manual for products intended for connection to ungrounded arrays shall state thatthe
44、inverter is to be installed in accordance with NFPA 70, including Sec. 690.35 with an ungrounded PVarray.112.5 Visual indicators used to comply with 111.2(a) shall include a marking stating WARNING and DCGround Fault or the equivalent.112.6 If an audible indicator is used to comply with 111.2(a), a
45、marking on the inverter shall indicateWARNING, a description of the audible signal, and explain that the signal indicates a DC Ground Faultor the equivalent.Exception: Units that include a visual DC ground fault indicator and are marked with 112.5 are notrequired to include the marking in 112.6.112.
46、7 The installation instructions shall be provided with details on the connection method and circuitparameters for the remote isolation fault indicator or signal required in 111.2(b).RATIONALE FOR DECISION:A certification requirement decision (CRD) to UL 1741 was issued for non-isolated inverters for
47、 connectionto ungrounded PV systems on April 26, 2010. However these requirements do not address isolatedproducts (e.g. inverters which employ the use of an interconnection transformer) for use on ungroundedPV systems. This CRD defines requirements for isolated inverters intended for connection to u
48、ngroundedPV systems and it augments the April 26, 2010 UL1741 CRD published for non-isolated inverters forconnection to ungrounded PV systems. The NEC includes requirements for the installation of ungroundedPV systems and this document provides a means to evaluate equipment for this application.Copy
49、right 2012 Underwriters Laboratories Inc.UL, in performing its functions in accordance with its objectives, does not guarantee or warrant thecorrectness of Certification Requirement Decisions it may issue or that they will be recognized or adoptedby anyone. Certification Requirement Decisions are the opinion of Underwriters Laboratories Inc. inpractically applying the requirements of the standard. They do not represent formal interpretations of thestandard under American National Standards Institute (ANSI) processes. UL shall not be responsible toany
