3.107 multiple mode inverter an inverter that operates in more than one mode, for example having grid-interactive functionality when mains voltage is present, and stand-alone functiona
Scope
Part 2 of IEC 62109 outlines specific safety requirements for d.c to a.c inverter products and devices that incorporate inverter functions alongside other capabilities, specifically designed for use in photovoltaic power systems.
Inverters that adhere to this standard can be grid-interactive, stand-alone, or operate in multiple modes They may be powered by single or multiple photovoltaic modules arranged in various configurations and are designed for use with batteries or other energy storage systems.
Inverters with multiple functions or modes shall be judged against all applicable requirements for each of those functions and modes
NOTE Throughout this standard where terms such as “grid-interactive inverter” are used, the meaning is either a grid-interactive inverter or a grid-interactive operating mode of a multi-mode inverter
This standard does not address grid interconnection requirements for grid-interactive inverters
The authors of Part 2 determined that incorporating grid interconnection requirements into this standard would be inappropriate and ineffective due to several reasons Firstly, grid interconnection standards encompass protection and power quality requirements, such as disconnection during abnormal voltage or frequency conditions, islanding protection, harmonic current limitations, and power factor considerations, which exceed the scope of a product safety standard Secondly, there is currently insufficient consensus among regulators regarding grid-interactive inverters, hindering the establishment of harmonized interconnection requirements For instance, while IEC 61727 outlines grid interconnection requirements, it has not achieved widespread acceptance, and the publication of EN 50438 necessitated country-specific deviations for numerous nations Lastly, the recently published IEC 62116 provides test methods specifically for islanding protection.
This standard does contain safety requirements specific to grid-interactive inverters that are similar to the safety aspects of some existing national grid interconnection standards
Users must recognize that in many regions permitting the grid interconnection of inverters, there are specific national or local regulations that need to be adhered to, such as EN 50438, IEEE 1547, and DIN VDE 0126-1-1.
This clause of Part 1 is applicable, with the following exception:
IEC 62109-1:2010, Safety of power converters for use in photovoltaic power systems – Part 1:
This clause of Part 1 is applicable, with the following exceptions:
3.100 functionally grounded array a PV array that has one conductor intentionally connected to earth for purposes other than safety, by means not complying with the requirements for protective bonding
NOTE 1 Such a system is not considered to be a grounded array – see 3.102
NOTE 2 Examples of functional array grounding include grounding one conductor through an impedance, or only temporarily grounding the array for functional or performance reasons
In an inverter designed for an un-grounded array, the resistive measurement network used to assess the array's impedance to ground does not qualify as functional grounding.
3.101 grid-interactive inverter an inverter or inverter function intended to export power to the grid
NOTE Also commonly referred to as “grid-connected”, “grid-tied”, “utility-interactive” Power exported may or may not be in excess of the local load
3.102 grounded array a PV array that has one conductor intentionally connected to earth by means complying with the requirements for protective bonding
In a non-isolated inverter system with an ungrounded array, connecting the mains circuit to earth does not establish a grounded array According to the standard, this configuration remains classified as an ungrounded array because the inverter electronics are part of the fault current path from the array to the mains grounding point, and they do not ensure reliable grounding for the array.
NOTE 2 This is not to be confused with protective earthing (equipment grounding) of the array frame
In certain local installation codes, grounded arrays may be permitted or mandated to disconnect from the earth during ground-fault conditions to interrupt fault current, effectively ungrounding the array temporarily Despite this, such configurations are still classified as grounded arrays according to the standard.
3.103 indicate a fault annunciate that a fault has occurred, in accordance with 13.9
3.104 inverter electric energy converter that changes direct electric current to single-phase or polyphase alternating current
3.105 inverter backfeed current the maximum current that can be impressed onto the PV array and its wiring from the inverter, under normal or single fault conditions
3.106 isolated inverter an inverter with at least simple separation between the mains and PV circuits
In inverters with multiple external circuits, there can be varying levels of isolation; for instance, an inverter may isolate the mains circuit from the PV circuit while allowing direct connection between the PV and battery circuits The term "isolated inverter" specifically refers to the separation between the mains and PV circuits When discussing other circuit combinations, additional clarification is provided to ensure accurate understanding.
For inverters lacking internal isolation between the mains and PV circuits, using a dedicated isolation transformer with no additional equipment on the inverter side allows the system to be considered as an isolated inverter Other configurations necessitate a system-level analysis, which exceeds the scope of this standard, although the principles outlined in this standard can still be applied in such analyses.
A 3.107 multiple mode inverter is a versatile device that functions in various modes, including grid-interactive operation when mains voltage is available and stand-alone functionality when the mains is disconnected or de-energized.
3.108 non-isolated inverter an inverter without at least simple separation between the mains and PV circuits
NOTE See the notes under 3.106 above
3.109 stand-alone inverter an inverter or inverter function intended to supply AC power to a load that is not connected to the mains
NOTE Stand-alone inverters may be designed to be paralleled with other non-mains sources (other inverters, rotating generators, etc.) Such a system does not constitute a grid-interactive system
This clause of Part 1 is applicable except as follows:
In IEC 62109-1 and Part 2, test requirements specific to individual hazards, such as shock or fire, are detailed in their respective clauses Conversely, Clause 4 encompasses test requirements that address multiple hazards, including testing under fault conditions, as well as general test conditions.
Testing in single fault condition
Single fault conditions to be applied
4.4.4.15 Fault-tolerance of protection for grid-interactive inverters
4.4.4.15.1 Fault-tolerance of residual current monitoring
In accordance with section 4.8.3.5, a residual current monitoring system must effectively function with a single fault present or be capable of detecting any fault or loss of operability It should prompt the inverter to indicate a fault as specified in section 13.9 and ensure disconnection from, or prevention of connection to, the mains by the next attempted restart.
A PV inverter will attempt to restart no later than the morning after a fault occurs This brief period of less than one day is permissible, as it is highly unlikely for a fault in the monitoring system to coincide with a person encountering normally enclosed hazardous live parts of the PV system or a fire-hazardous ground fault on the same day.
Compliance is verified by testing the grid-interactive inverter under specified reference conditions outlined in Part 1 Each fault, such as those in the residual current monitoring circuit, control circuits, or power supply to these circuits, is applied individually to assess performance.
The inverter meets compliance for fault conditions if it either ceases operation and disconnects from the mains without reconnecting after power removal, or continues to operate while passing residual current monitoring tests under single fault conditions, or operates without residual current monitoring but does not reconnect after power removal.
PV power, AC power, or both, and indicates a fault in accordance with 13.9
4.4.4.15.2 Fault-tolerance of automatic disconnecting means
The means provided for automatic disconnection of a grid-interactive inverter from the mains shall:
To ensure safety, all grounded and ungrounded current-carrying conductors must be disconnected from the mains Additionally, the system should maintain at least basic insulation or simple separation between the photovoltaic (PV) array and the mains when a single fault occurs at the disconnection means or any other part of the inverter, particularly when the disconnecting means is in the open state.
4.4.4.15.2.2 Design of insulation or separation
The design of the basic insulation or simple separation referred to in 4.4.4.15.2.1 shall comply with the following:
The fundamental insulation or basic separation must be determined by the working voltage of the PV circuit, impulse withstand voltage, and temporary over-voltage, as outlined in section 7.3.7 of Part 1 It is also assumed that the mains are disconnected.
– the provisions of 7.3.7.1.2 g) of Part 1 may be applied if the design incorporates means to reduce impulse voltages, and where required by 7.3.7.1.2 of Part 1, monitoring of such means;
– in determining the clearance based on working voltage in 7.3.7 of Part 1, the values of column 3 of Table 13 of Part 1 shall be used
NOTE 1 These requirements are intended to protect workers who are servicing the AC mains system In that scenario the mains will be disconnected, and the hazard being protected against is the array voltage appearing on the disconnected mains wiring, either phase-to-phase, or phase-to-earth Therefore it is the PV array parameters (working voltage, impulse withstand voltage, and temporary over-voltage) that determine the required insulation or separation The worker may be in a different location than any PV disconnection means located between the array and the inverter, or may not have access, so the insulation or separation provided in the inverter must be relied on In a non-isolated inverter, only the required automatic disconnection means separates the mains service worker from the PV voltage In an isolated inverter, the isolation transformer and other isolation components are in series with the automatic disconnection means, and separate the worker from the PV voltage in the event of failure of the automatic disconnection means
NOTE 2 Example for a single-phase non-isolated inverter: Assume a non-isolated inverter rated for a floating array with a PV maximum input rating of 1 000 V d.c., and intended for use on a single-phase AC mains with an earthed neutral See Figure 20 below
Subclause 4.4.4.15.2.1 mandates the implementation of basic insulation to safeguard against shock hazards from PV voltage when working on mains circuits after a single fault occurs A widely used approach to ensure fault-tolerant automatic disconnection involves utilizing two relays (a1 and b1) in the ungrounded AC conductor and two additional relays (a2 and b2) in the grounded conductor This configuration allows for single-fault tolerance by employing two distinct relay control circuits (Control A and B), each managing one line relay and one neutral relay Consequently, in any single fault scenario affecting one control circuit or relay, at least one relay in both the line and neutral will remain operational, effectively isolating the mains circuit conductors from the inverter and the array.
In this scenario, the mains neutral is earthed, providing single fault protection against shock hazards between the neutral and earth, irrespective of the isolation between the mains, inverter, and PV array Consequently, the relays must safeguard against potential shock hazards from the mains line conductor to either earth or neutral.
In a single fault scenario, one pair of relays may fail to open, yet the other unaffected pair remains fully operational, ensuring the necessary basic insulation is maintained.
For a shock to occur, current must travel from the mains line conductor, through a person, to the earth or neutral, and return to the line conductor via the remaining relay gaps in series Thus, the essential insulation is ensured by the combined air gaps in the two remaining relays.
The impulse voltage withstand rating for a PV circuit system operating at 1000 V dc is 4,464 V, as indicated in Table 12 of Part 1 According to Table 13, the total required clearance is 3.58 mm, which should be evenly distributed between the air gaps of the two remaining relays, resulting in approximately 1.8 mm clearance for each relay Additionally, the necessary creepage across the open relays varies based on the pollution degree and material group, and is also determined for a voltage of 1000 V dc, divided between the air gaps in the two relays.
– Similar analysis can be done for other system and inverter topologies
Figure 20 – Example system discussed in Note 2 above
4.4.4.15.2.3 Automatic checking of the disconnect means
For non-isolated inverters, it is essential to automatically verify the isolation provided by the disconnection means before the inverter begins operation If the isolation check fails, any operational disconnection means must remain open, ensuring that at least basic insulation or simple separation is upheld between the photovoltaic (PV) input and the mains Consequently, the inverter will not initiate operation and must indicate a fault as specified in section 13.9.
Compliance with sections 4.4.4.15.2.1 to 4.4.4.15.2.3 is verified through the inspection of the PCE and schematics, assessment of the insulation or separation offered by components, and for non-isolated inverters, by conducting a specific test.
Electrical ratings tests
Measurement requirements for AC output ports for stand-alone
Measurements of the AC output voltage and current on a stand-alone inverter shall be made with a meter that indicates the true RMS value
NOTE Some non-sinusoidal inverter output waveforms will not be properly measured if an average responding meter is used.
Stand-alone Inverter AC output voltage and frequency
The AC output voltage and frequency of a stand-alone inverter, or multi-mode inverter operating in stand-alone mode, shall comply with the requirements of 4.7.4.2 to 4.7.4.5
4.7.4.2 Steady state output voltage at nominal DC input
The steady-state AC output voltage must remain between 90% and 110% of the rated nominal voltage when the inverter is provided with its nominal DC input voltage.
Compliance is verified by measuring the AC output voltage of the inverter under no load conditions and then again with a resistive load that matches the inverter's rated maximum continuous output power in stand-alone mode The AC output voltage is recorded once any transient effects from loading or unloading have stabilized.
4.7.4.3 Steady state output voltage across the DC input range
The steady-state AC output voltage must remain between 85% and 110% of the rated nominal voltage, regardless of the DC input voltage value within the specified range supplied to the inverter.
Compliance is assessed by measuring the AC output voltage under four specific conditions: when the inverter operates with no load and when it supplies a resistive load equal to its maximum continuous output power in stand-alone mode, at both the minimum and maximum rated DC input voltages The AC output voltage is recorded after any transient effects from load application or removal have stabilized.
4.7.4.4 Load step response of the output voltage at nominal DC input
The AC output voltage must remain between 85% and 110% of the rated nominal voltage for no longer than 1.5 seconds after a resistive load, equal to the inverter's maximum continuous output power in stand-alone mode, is applied or removed, while the inverter is supplied with its nominal DC input voltage.
Compliance is evaluated by measuring the AC output voltage following a resistive load step, transitioning from no load to maximum continuous output power and back to no load The RMS output voltage is recorded during the first complete cycle after \( t = 1.5 \) seconds, where \( t \) represents the time elapsed since the load step change was applied.
The steady-state AC output frequency shall not vary from the nominal value by more than +4 % or –6 %
Compliance is assessed by measuring the AC output frequency under four specific conditions: when the inverter operates with no load and when it supplies a resistive load equal to its maximum continuous output power in stand-alone mode This evaluation occurs at both the minimum and maximum rated DC input voltages The AC output frequency is recorded after any transient effects from load application or removal have dissipated.
Stand-alone inverter output voltage waveform
The AC output voltage waveform of a stand-alone or multi-mode inverter in stand-alone mode must meet the specifications outlined in section 4.7.5.2 for sinusoidal outputs, or sections 4.7.5.3 and 4.7.5.4 for intentionally non-sinusoidal outputs, as well as the dedicated load requirements specified in section 4.7.5.5.
4.7.5.2 Sinusoidal output voltage waveform requirements
The AC output waveform of a sinusoidal output stand-alone inverter shall have a total harmonic distortion (THD) not exceeding of 10 % and no individual harmonic at a level exceeding 6 %
Compliance is checked by measuring the THD and the individual harmonic voltages with the inverter delivering 5 % power or the lowest continuous available output power greater than
The inverter operates at 5%, 50%, and 100% of its continuous rated output power with a resistive load, using nominal DC input voltage The specified limits pertain to the magnitude of the fundamental component at each load level The Total Harmonic Distortion (THD) measuring instrument will calculate the sum of harmonics from n=2 to n@ as a percentage of the fundamental (n=1) component.
4.7.5.3 Non-sinusoidal output waveform requirements
The AC output voltage waveform of a non-sinusoidal output stand-alone inverter shall comply with the requirements of 4.7.5.3.2 to 4.7.5.3.4
The total harmonic distortion (THD) of the voltage waveform shall not exceed 40 %
The slope of the rising and falling edges of the voltage waveform must not exceed 10 V/µs This measurement is taken between the points where the waveform reaches 10% and 90% of the peak voltage for each half-cycle.
The peak voltage of both the positive and negative half-cycles of the waveform must not exceed 1.414 times 110% of the RMS value of the rated nominal AC output voltage.
To ensure compliance with sections 4.7.5.3.2 through 4.7.5.3.4, the total harmonic distortion (THD), slopes, and peak voltages of the inverter's output voltage waveform must be measured while delivering 5% power or the lowest continuous output power above 5%, as well as at 50% and 100% of its rated output power into a resistive load Each measurement should be conducted at the DC input voltage that presents the worst-case scenario for the inverter within its rated range The THD measurement instrument must quantify the sum of harmonics from \( n=2 \) to \( n@ \) as a percentage of the fundamental component (\( n=1 \)).
4.7.5.4 Information requirements for non-sinusoidal waveforms
The instructions provided with a stand-alone inverter not complying with 4.7.5.2 shall include the information in 5.3.2.6
4.7.5.5 Output voltage waveform requirements for inverters for dedicated loads
For an inverter that is intended only for use with a known dedicated load, the following requirements may be used as an alternative to the waveform requirements in 4.7.5.2 to 4.7.5.3
It is essential to assess the integration of the inverter with the dedicated load to ensure that the output waveform remains safe for both the load equipment and the inverter, preventing any potential hazards and ensuring compliance with relevant product safety standards.
Compliance is verified through testing and analysis to ensure that the inverter output waveform meets applicable standards Required tests must be conducted on dedicated load equipment to assess compliance However, a specific test may be excluded if an analysis indicates that the output waveform does not impact safety-related parameters.
The output waveform can lead to various effects, including heating, clearance issues related to the inverter's peak voltage, increased input current, and potential breakdown of solid insulation or components due to excessive peak voltages or rapid rise times Additionally, these factors may cause misoperation of control circuits, especially protective circuitry.
The inverter shall be marked with symbols 9 and 15 of Table C.1 of Part 1
The installation instructions provided with the inverter shall include the information in 5.3.2.13
Additional tests for grid-interactive inverters
General requirements regarding inverter isolation and array
Inverters can either offer galvanic isolation from the mains to the photovoltaic (PV) array or not, and the array may have one side of the circuit grounded or not It is essential for inverters to meet the specifications outlined in Table 30, depending on the specific combination of inverter isolation and array grounding.
Table 30 – Requirements based on inverter isolation and array grounding 1)
Array grounding: Ungrounded a or functionally grounded Ungrounded or functionally grounded Grounded
Inverter isolation: Non-isolated Isolated Isolated
The article discusses the testing of basic or reinforced b insulation, focusing on leakage current type testing as outlined in sections 4.8.3.2 and 4.8.3.3 These tests are essential for assessing shock and fire hazards, specifically to establish the necessary requirements for array ground insulation resistance and array residual current detection.
Array ground insulation resistance measurement
Before starting operation, per 4.8.2.1 or 4.8.2.2
Action on fault: indicate a fault in accordance with 13.9, and do not connect to the mains
Before starting operation, per 4.8.2.1 or 4.8.2.2
For inverters with isolation complying with the leakage current limits for both shock and fire hazards under “Minimum inverter isolation requirements” above, indicate a fault in accordance with 13.9
For inverters with isolation not complying with the above minimum leakage current values, indicate a fault in accordance with 13.9, and do not connect to the mains
Either a) 30 mA RCD c between the inverter and the mains per 4.8.3.4, or b) monitoring for both continuous excessive residual current per 4.8.3.5.1 a) and excessive sudden changes per 4.8.3.5.1 b)
Action on fault: shut down the inverter, disconnect from the mains, and indicate a fault in accordance with 13.9
Not applicable for inverters with isolation complying with the leakage current limits for both shock and fire hazards under
“Minimum inverter isolation requirements” above
Inverters that do not meet the leakage current limits for shock hazards must monitor sudden changes in residual current or utilize a Residual Current Device (RCD) Similarly, inverters failing to comply with leakage current limits for fire hazards require monitoring of excessive continuous residual current or the use of an RCD In the event of a fault, it is essential to shut down the inverter, disconnect it from the mains, and indicate the fault as specified.
Non-isolated inverter topologies with a grounded array are feasible, but IEC 60364-7-712 mandates simple separation between the mains and the PV system if the array is grounded Such inverters are permitted as long as the design prevents current flow on grounding conductors under normal conditions, except for expected leakage current, ensuring that the functionality of any residual current device (RCD) remains intact If the array's only ground connection is on the mains side of the inverter, it is deemed ungrounded Inverters used with arrays classified under decisive voltage classification DVC-A must incorporate reinforced insulation between the array and DVC-B and -C circuits, including the mains Certain inverter types also necessitate a type B RCD Recent findings suggest that grounded arrays could greatly benefit from array ground insulation resistance measurement prior to grid connection, as this additional protection can significantly mitigate fire hazards associated with ground faults due to improper installation, commissioning, or maintenance, which may lead to undetected initial ground faults followed by further faults.
1) As noted in the Foreword, the numbering of tables and figures in this Part 2 continues the existing numbering scheme in Part 1 to avoid any confusion that might arise from identical numbering between the two parts inverters for grounded arrays, but an IEC 62109-2 amendment is planned for the near future and requirements are under consideration for improved ground fault protection for grounded arrays At that time IEC 62109-2 will also be coordinated with the system protection requirements in IEC 62548 currently under development.
Array insulation resistance detection for inverters for ungrounded and
The requirements for detecting and responding to abnormal array insulation resistance to ground aim to mitigate fire and shock hazards from unintended connections between the array and ground In non-isolated inverters, a ground fault can lead to dangerous current flow upon connection to the mains due to the earthed neutral, necessitating that the inverter does not connect to the mains Conversely, in isolated inverters, while the detection of the first ground fault is essential, the inverter can still connect and operate safely, as the isolation prevents the earthed neutral from providing a return current path for fault currents.
4.8.2.1 Array insulation resistance detection for inverters for ungrounded arrays
Inverters designed for ungrounded arrays must include a method to measure the DC insulation resistance from the photovoltaic (PV) input to ground prior to operation, or they should come with installation instructions that comply with section 5.3.2.11.
If the insulation resistance is less than R = (V MAX PV /30 mA) ohms, the inverter:
Isolated inverters must indicate a fault as per section 13.9, while still allowing operation This fault indication should remain until the array's insulation resistance improves to a value exceeding the specified limit.
Non-isolated inverters, or those failing to meet the leakage current limits specified in Table 30, must signal a fault as per section 13.9 and are prohibited from connecting to the mains However, if the insulation resistance of the array improves to a level above the required limit, the inverter may cease fault indication and reconnect to the mains while continuing to perform measurements.
The measurement circuit shall be capable of detecting insulation resistance below the limit above, under normal conditions and with a ground fault in the PV array
Compliance is checked by analysis of the design and by testing, as follows:
To ensure compliance with current values, an RMS meter must be utilized, capable of measuring both AC and DC components of the current, with a minimum bandwidth of 2 kHz.
The inverter must be connected to both PV and AC sources as outlined in the reference test conditions in Part 1, with the PV voltage set below the minimum operating voltage necessary for the inverter to initiate operation A resistance 10% lower than the specified limit should be connected between ground and each PV input terminal sequentially, after which the PV input voltage should be increased sufficiently for the inverter to attempt to start The inverter will indicate a fault as per section 13.9 and will take the appropriate action, whether to operate or not, as required.
Testing all PV input terminals is unnecessary if the design analysis suggests that some terminals will yield identical results, such as in cases where multiple PV string inputs are connected in parallel.
When conducting tests on the inverter, it is crucial to consider the resistance to ground of the DC supply or simulated array used for powering the inverter, unless this resistance is sufficiently large to have a negligible impact on the test results.
4.8.2.2 Array insulation resistance detection for inverters for functionally grounded arrays
Inverters that functionally ground the array through an intentional resistance integral to the inverter, shall meet the requirements in a) and c), or b) and c) below:
System designers must evaluate the potential shock hazard on the array when using resistance between the array and ground that is not integral to the inverter This assessment should consider factors such as array design, resistance value, and protection against direct contact Since the inverter does not provide the resistance, it is not responsible for the hazard The total resistance, including intentional resistance for functional grounding and expected insulation resistance, must not be lower than \( R = \frac{V_{\text{MAX PV}}}{30 \, \text{mA}} \) ohms The expected insulation resistance should be calculated based on an insulation resistance of 40 MΩ per m², using the panel surface area determined by the inverter power rating and the efficiency of the worst-case panels.
Designers must incorporate a design margin to account for factors like panel aging, which can diminish the array insulation resistance over time, and the AC leakage current due to array capacitance to ground The insulation resistance measurement will verify that the total resistance remains at a safe level; however, if the design margin is insufficient, the system will not connect after the insulation resistance check.
The installation instructions must include the requirements specified in section 5.3.2.12 Alternatively, if a lower resistor value is utilized, the inverter must be equipped to detect during operation whether the total current through the resistor and any parallel networks exceeds the residual current values and times outlined in Table 31 In such cases, the inverter should either disconnect the resistor or limit the current through other means Additionally, if the inverter is non-isolated or does not meet the leakage current limits defined in Table 30, it must disconnect from the mains.
The inverter may attempt to resume normal operation if the array insulation resistance has recovered to a value higher than the limit in 4.8.2.1
To ensure accurate measurement of array insulation resistance as specified in section 4.8.2.1, it is essential that the array functional grounding resistor remains disconnected, or that current limiting measures are maintained, until the insulation resistance measurement is completed.
Compliance is verified through design analysis and, for case b), by testing for sudden changes in residual current as outlined in section 4.8.3.5.3 Additionally, the inverter must be equipped to measure the DC insulation resistance from the PV input to ground prior to operation, in accordance with section 4.8.2.1.
Array residual current detection
Ungrounded arrays operating at DVC-B and DVC-C voltages pose a shock hazard if live parts are touched and a return path for touch current exists In non-isolated inverters, or those with insufficient isolation, connecting the mains to earth can create a return path for touch current if a person contacts live parts and earth simultaneously To enhance safety against this shock hazard, the application of residual current detectors (RCDs) or monitoring for sudden changes in residual current is recommended, except in isolated inverters where the isolation limits the available touch current to less than 30 mA.
Ungrounded and grounded arrays pose a fire risk if a ground fault permits excessive current to flow through unintended conductive parts or structures To mitigate this hazard, additional protection measures are outlined, including the use of Residual Current Devices (RCDs) as specified in section 4.8.3.4, or monitoring for continuous excessive residual current as per section 4.8.3.5 However, these requirements do not apply to isolated inverters, where the isolation limits the available current to a safe level.
– 300 mA RMS for inverters with rated continuous output power ≤ 30 kVA, or
– 10 mA RMS per kVA of rated continuous output power for inverters with rated continuous output power rating > 30 kVA when tested in accordance with 4.8.3.3
In the preceding sections and subsequent tests, the definition of current varies The 30 mA threshold for touch currents is evaluated through a human body model touch current test circuit, as this limit pertains to shock hazards Conversely, the current limit for fire hazard assessments is determined using a standard ammeter without a human body model circuit, since fire hazards are associated with current flowing through unintended conductors rather than through the human body.
4.8.3.2 30 mA touch current type test for isolated inverters
To ensure compliance with the 30 mA limit outlined in section 4.8.3.1, testing is conducted with the inverter operational under specified reference conditions, where the DC supply is isolated from earth and one pole of the mains supply is earthed It may be necessary to disable array insulation resistance detection functions during this procedure The touch current measurement circuit, as per IEC 60990, Figure 4, is connected to each terminal of the array sequentially, and the measured touch current is documented and assessed against the 30 mA threshold This evaluation determines the necessary requirements for array ground insulation resistance and array residual current detection as specified in Table 30.
NOTE 1 For convenience, IEC 60990 test figure 4 is reproduced in Annex H of Part 1
NOTE 2 Consideration should be given to the impact on the touch current measurement that capacitance between external test sources and earth could have on the result (for example a d.c supply with capacitors to earth can increase the measured touch current unless the d.c supply is not earthed to the same earth as the PCE under test)
4.8.3.3 Fire hazard residual current type test for isolated inverters
To ensure compliance with the 300 mA or 10 mA per kVA limit outlined in section 4.8.3.1, testing is conducted with the inverter operational under specified reference conditions During this process, the DC supply to the inverter must remain ungrounded, while one pole of the mains supply should be earthed It may be necessary to disable array insulation resistance detection functions for this test An RMS ammeter, capable of measuring both AC and DC current components, is connected sequentially from each PV input terminal of the inverter to ground.
The current is recorded and compared to the limit in 4.8.3.1, to determine the requirements for array ground insulation resistance and array residual current detection in Table 30
When measuring current, it is crucial to consider how capacitance between external test sources and earth may affect the results For instance, a DC supply with capacitors connected to earth can lead to an increase in the measured current, particularly if the DC supply is grounded to the same earth as the PCE being tested.
4.8.3.4 Protection by application of RCD’s
To meet the additional protection requirement outlined in section 4.8.3.1, an RCD with a residual current setting of 30 mA should be installed between the inverter and the mains It is essential to select the appropriate RCD type for compatibility with the inverter, following the guidelines specified in Part 1 The RCD can either be integrated into the inverter or installed separately by the installer, provided that the installation instructions include details on the rating, type, and location of the RCD as per section 5.3.2.9.
4.8.3.5 Protection by residual current monitoring
In accordance with Table 30, the inverter must include residual current monitoring that operates whenever it is connected to the mains with the automatic disconnection means engaged This monitoring system is required to measure the total RMS current, encompassing both alternating current (a.c.) and direct current (d.c.) components.
Table 30 outlines the necessary detection requirements for various inverter types, array configurations, and isolation levels It specifies that detection is needed for excessive continuous residual current, sudden changes in residual current, or both Specifically, if the continuous residual current exceeds the defined limits, the inverter must disconnect within 0.3 seconds and indicate a fault as per section 13.9.
– maximum 300 mA for inverters with continuous output power rating ≤ 30 kVA;
– maximum 10 mA per kVA of rated continuous output power for inverters with continuous output power rating > 30 kVA
The inverter will attempt to reconnect if the array insulation resistance complies with the specified limits Additionally, in the event of a sudden increase in RMS residual current that exceeds the threshold outlined in Table 31, the inverter must disconnect from the mains within the designated timeframe and indicate a fault as per section 13.9.
Table 31 – Response time limits for sudden changes in residual current
Residual current sudden change Max time to inverter disconnection from the mains
NOTE These values of residual current and time are based on the RCD standard IEC 61008-1
– monitoring for the continuous condition in a) is not required for an inverter with isolation complying with 4.8.3.3;
– monitoring for the sudden changes in b) is not required for an inverter with isolation complying with 4.8.3.2
The inverter may attempt to re-connect if the array insulation resistance meets the limit in 4.8.2
Compliance with sections a) and b) is verified through tests 4.8.3.5.2 and 4.8.3.5.3 The current values must be measured using an RMS meter capable of detecting both AC and DC components, with a minimum bandwidth of 2 kHz An illustrative test circuit is provided in Figure 21 below.
PV-pole(s) the test circuit may be duplicated or moved
Test circuit for testing the PV-pole
In the continuous residual current test, R1 sets a baseline current slightly below the trip point, while R2 is activated to increase the current beyond the trip point, with capacitor C1 being excluded from the process.
For the sudden change residual current test, C1 establishes a baseline current and R1 or R2 is switched in to cause the desired value of sudden change The other resistor is not used
Figure 21 – Example test circuit for residual current detection testing
4.8.3.5.2 Test for detection of excessive continuous residual current
An external adjustable resistance is connected from ground to one PV input terminal of the inverter, which is gradually lowered to exceed the specified residual current limit, causing the inverter to disconnect This process establishes the actual trip level of the sample, ensuring it remains within the continuous residual current limit To evaluate the trip time, the test resistance is set to create a residual current approximately 10 mA below the trip level A second external resistance is then introduced, adjusted to generate around 20 mA of residual current, and connected via a switch to the same PV input terminal Upon closing the switch, the residual current surpasses the previously determined trip level, and the time is recorded from the connection of the second resistance until the inverter disconnects, indicated by the inverter output current dropping to zero.
This test shall be repeated 5 times, and for all 5 tests the time to disconnect shall not exceed 0,3 s
The test is conducted for each PV input terminal, but it is not necessary to test all terminals if the design analysis suggests that some terminals will yield the same results, such as in cases where multiple PV string inputs are connected in parallel.
Marking
Equipment ratings
In addition to the markings specified in other sections of Part 1 and throughout Part 2, the ratings listed in Table 32 must be clearly and permanently displayed on the inverter, ensuring they are easily visible post-installation Only the ratings relevant to the specific type of inverter are mandatory.
AC input quantities are necessary only for inverters that feature an AC input port alongside an AC output port, or for those with a single AC port capable of functioning as an input in multiple modes.
Table 32 – Inverter ratings – Marking requirements
Isc PV a (absolute maximum) d.c A a.c output ratings:
Frequency (nominal or range) Hz
Power (maximum continuous) W or VA
Power factor range a.c input ratings:
Frequency (nominal or range) Hz d.c input (other than PV) ratings:
Current (maximum continuous) d.c A d.c output ratings:
Protective class a (I, II, or III)
Ingress protection a (IP) rating per Part 1 a These terms are defined in Clause 3 of Part 1
An inverter designed for multiple nominal output voltages must be clearly marked to indicate the specific voltage setting at the time of factory shipment This marking can be provided through a removable tag or another non-permanent method.
Warning markings
Content for warning markings
5.2.2.6 Inverters for closed electrical operating areas
In accordance with section 4.8.3.6, inverters lacking comprehensive shock hazard protection for the photovoltaic (PV) array must display a warning indicating that they are intended solely for use in a confined electrical operating environment, and users should consult the installation instructions.
Documentation
Information related to installation
Subclause 5.3.2 of Part 1 requires the documentation to include ratings information for each input and output For inverters this information shall be as in Table 33 below Only those ratings that are applicable based on the type of inverter are required
Table 33 – Inverter ratings – Documentation requirements
PV input operating voltage range d.c V
Maximum operating PV input current d.c A
Max inverter backfeed current to the array a.c or d.c A a.c output quantities:
Current (inrush) a.c A (peak and duration)
Frequency (nominal or range) Hz
Power (maximum continuous) W or VA
Power factor range Maximum output fault current a.c A (peak and duration), or
RMS b Maximum output overcurrent protection a.c A a.c input quantities:
Current (inrush) a.c A (peak and duration)
Frequency (nominal or range) Hz d.c input (other than PV) quantities:
Current (maximum continuous) d.c A d.c output quantities:
Protective class a (I, II, or III)
Ingress Protection (IP) ratings are defined in Part 1, Section 3, which outlines the criteria for these classifications Additionally, the output short circuit test section in Part 1 details the measurement types and required units for determining the IP rating.
For grid-interactive units featuring adjustable trip points, trip times, or reconnect times, it is essential that the documentation for the Power Control Equipment (PCE) includes details on the presence of these controls, methods for adjustment, factory default values, and the limits of adjustability This information should also be accessible in alternative formats, such as on a website.
Certain local interconnect standards mandate that modifications to setpoints must be secured by a password or rendered inaccessible to users This requirement emphasizes the importance of safeguarding sensitive adjustments in the documentation.
“means for adjustment” is not meant to require the documentation to disclose the password or other security feature
The settings of field adjustable setpoints shall be accessible from the PCE , for example on a display panel, user interface, or communications port
An inverter must include details for the installer about the presence of an internal isolation transformer and its insulation level (functional, basic, reinforced, or double) Additionally, the instructions should specify the installation requirements, including whether to earth the array, the need for external residual current detection devices, and the necessity of an external isolation transformer.
5.3.2.4 Transformers required but not provided
An inverter that necessitates an external isolation transformer, which is not included with the unit, must come with clear instructions detailing the required configuration type, electrical ratings, and environmental ratings for the compatible external isolation transformer.
5.3.2.5 PV modules for non-isolated inverters
Non-isolated inverters must include installation instructions specifying the use of PV modules with an IEC 61730 Class A rating If the maximum AC mains operating voltage exceeds the PV array's maximum system voltage, the instructions should mandate PV modules with a maximum system voltage rating aligned with the AC mains voltage.
5.3.2.6 Non-sinusoidal output waveform information
The instruction manual for non-compliant stand-alone inverters must include a warning about the non-sinusoidal waveform, indicating that certain loads may experience increased heating Users are advised to consult the manufacturers of their equipment before using it with the inverter Additionally, the inverter manufacturer is required to provide information on which load types may overheat, recommendations for maximum operating durations with these loads, and details on the total harmonic distortion (THD), slope, and peak voltage of the waveforms as determined by specific testing standards.
5.3.2.7 Systems located in closed electrical operating areas
In accordance with section 4.8.3.6, if an inverter lacks comprehensive shock hazard protection for the photovoltaic (PV) array, it must come with installation instructions These instructions should mandate that both the inverter and the array be installed in enclosed electrical operating areas Additionally, they must specify the types of shock hazard protection that are included with the inverter, such as a residual current device (RCD), an isolation transformer that meets the 30 mA touch current limit, or residual current monitoring for sudden fluctuations.
5.3.2.8 Stand-alone inverter output circuit bonding
Where required by 7.3.10, the documentation for an inverter shall include the following:
If output circuit bonding is necessary but not included as part of the inverter, the installation instructions must specify the required bonding means This includes identifying the conductor that needs to be bonded and detailing the necessary current-carrying capacity or cross-section of the bonding method.
– if the output circuit is intended to be floating, the documentation for the inverter shall indicate that the output is floating
5.3.2.9 Protection by application of RCD’s
To comply with the requirements of section 4.8.3.1, installations must include a Residual Current Device (RCD) that is not integrated into the inverter, as permitted by section 4.8.3.4 The installation instructions must clearly indicate the necessity of the RCD and provide details on its rating, type, and the specific location within the circuit.
The installation instructions shall include an explanation of how to properly make connections to (where applicable), and use, the electrical or electronic fault indication required by 13.9
5.3.2.11 External array insulation resistance measurement and response
The installation instructions for an inverter for use with ungrounded arrays that does not incorporate all the aspects of the insulation resistance measurement and response requirements in 4.8.2.1, must include:
Isolated inverters require careful consideration of array insulation resistance measurement and response, as certain aspects may not be fully addressed It is essential to consult local regulations to ascertain whether any additional functions are necessary for compliance and safety.
• an explanation of what external equipment must be provided in the system, and
• what the setpoints and response implemented by that equipment must be, and
• how that equipment is to be interfaced with the rest of the system
When utilizing approach a) of section 4.8.2.2, the inverter installation instructions must encompass several critical elements: the total resistance between the PV circuit and ground integral to the inverter, the minimum array insulation resistance to ground that the system designer or installer must adhere to when selecting the PV panel and system design, and the minimum total resistance value calculated as R = V_{\text{MAX PV}} / 30 mA Additionally, it is essential to provide a clear explanation of how to compute this total resistance Furthermore, a warning should be included to highlight the potential shock hazard if the minimum resistance requirements are not satisfied.
5.3.2.13 Stand-alone inverters for dedicated loads
The installation instructions for the inverter must include a warning that it is intended solely for use with the specific dedicated load for which it was evaluated, and this dedicated load should be clearly specified.
An inverter equipped with firmware for protective functions must include a method to identify the firmware version This identification can be achieved through a physical marking, a display panel, a communications port, or any other user interface.
This clause of Part 1 is applicable
7 Protection against electric shock and energy hazards
This clause of Part 1 is applicable with the following exceptions:
Protection against electric shock
Additional requirements for stand-alone inverters
The output circuit of a stand-alone inverter may need one conductor bonded to earth, depending on the supply earthing system it is designed for, to establish a grounded conductor and an earthed system.
NOTE In single-phase and star-connected (wye-connected) three-phase systems this grounded conductor is also referred to as an earthed neutral
The method for connecting the grounded conductor to protective earth can either be included within the inverter or be part of the installation process If the inverter does not include this feature, the necessary connection methods must be detailed in the installation instructions according to section 5.3.2.8.
The bonding of the grounded conductor to protective earth must adhere to the protective bonding requirements outlined in Part 1 However, if the bond is designed solely to carry fault currents in stand-alone mode, the maximum current for the bond is dictated by the inverter's maximum output fault current.
Output circuit bonding configurations must guarantee that the grounded circuit conductor is bonded to earth at only one location during any operational mode If switching arrangements are implemented, the switching device must undergo a bond impedance test in conjunction with the entire bonding path.
Inverters intended to have a circuit conductor bonded to earth shall not impose any normal current on the bond except for leakage current
Outputs that are intentionally floating and lack a circuit conductor bonded to ground must not present any voltages that pose a shock hazard, in compliance with Clause 7 of Parts 1 and 2 Additionally, the inverter's documentation must clearly state that the output is floating, as specified in section 5.3.2.8.
Functionally grounded arrays
All PV conductors in a functionally grounded array shall be treated as being live parts with respect to protection against electric shock
The purpose of this requirement is to clarify that the functionally grounded conductor should not be considered at ground potential when assessing insulation coordination factors, such as clearance to ground This is due to its connection to ground not meeting the protective bonding standards outlined in Part 1.
This clause of Part 1 is applicable
This clause of Part 1 is applicable with the following exceptions:
Short-circuit and overcurrent protection
Inverter backfeed current onto the array
The backfeed current testing and documentation requirements in Part 1 apply, including but not limited to the following
Testing will be conducted to assess the current flowing from the inverter's PV input terminals when a fault occurs in the inverter or the PV input wiring Considered faults include short circuits affecting all or part of the array, as well as any inverter malfunctions that could allow energy from external sources, such as the mains or a battery, to affect the PV array wiring Current measurements will exclude transients caused by short circuits that originate from discharging storage elements other than batteries.
This inverter backfeed current value shall be provided in the installation instructions regardless of the value of the current, in accordance with Table 33
To prevent overloading of array wiring due to backfeed currents from the inverter, it is essential to limit these currents to the maximum normal current that the array can source Backfeed currents may occur during fault conditions, allowing currents from other sources, such as the mains or a battery, to flow out of the PV input terminals If the backfeed current is controlled, the wiring and devices in the current path will be adequately sized to handle it without risk of overload However, if the backfeed current exceeds this limit, it is crucial to provide the maximum current value to the installer to determine if larger wiring sizes or additional overcurrent protection is necessary.
10 Protection against sonic pressure hazards
This clause of Part 1 is applicable
This clause of Part 1 is applicable
This clause of Part 1 is applicable
This clause of Part 1 is applicable with the following exception: