NB/T 32004-2018 PDF English
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Technical specification of PV grid-connected inverter
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NB/T 32004-2018: Technical specification of PV grid-connected inverter---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/NBT32004-2018
NB
ENERGY INDUSTRY STANDARD OF
THE PEOPLE’S REPUBLIC OF CHINA
ICS 29.120.01
K 46
Filing number. 64298-2018
Replacing NB/T 32004-2013
Technical specification of PV grid-connected inverter
Issued on: APRIL 03, 2018
Implemented on: JULY 01, 2018
Issued by. National Energy Administration
Table of Contents
Foreword... 3
1 Scope... 8
2 Normative references... 8
3 Terms and definitions... 11
4 Inverter type... 22
5 Environmental and use requirements... 23
6 Safety requirements... 24
7 Basic functional requirements... 45
8 Performance requirements... 45
9 Protection requirements... 62
10 Identification and documentation... 65
11 Test method... 70
12 Inspection rules... 115
Appendix A (Normative) Symbols used on equipment identification... 119
Appendix B (Normative) Humidity preconditioning... 120
Appendix C (Informative) Measurement of inverter efficiency... 121
References... 128
1 Scope
This standard specifies the product types, technical requirements and test
methods of photovoltaic grid-connected inverters used in photovoltaic (PV)
power generation systems.
This standard applies to photovoltaic grid-connected inverters connected to the
PV source circuit whose voltage does not exceed 1500V DC and whose AC
output voltage does not exceed 1000V. The preparatory photovoltaic inverter
where the integrated step-up transformer is grid-connected to the grid of 35kV
and below voltage level can refer to this standard.
2 Normative references
The following documents are essential to the application of this document. For
the dated documents, only the versions with the dates indicated are applicable
to this document; for the undated documents, only the latest version (including
all the amendments) are applicable to this standard.
GB/T 2423.1-2008 Environmental testing - Part 2.Test methods - Tests A.
Cold
GB/T 2423.2-2008 Environmental testing - Part 2.Test methods - Tests B.
Dry heat
GB/T 2423.3-2016 Environmental testing - Part 2.Testing method - Test Cab.
Damp heat, steady state
GB/T 2423.4-2008 Environmental testing for electric and electronic products
- Part 2.Test method - Test Db. Damp heat, cyclic (12h+12h cycle)
GB/T 2423.10-2008 Environmental testing for electric and electronic
products - Part 2.Tests methods - Test Fc. Vibration (sinusoidal)
GB/T 2828.1-2012 Sampling procedures for inspection by attributes - Part 1.
Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot
inspection
GB/T 3805 Extra-low voltage (ELV) - Limit values
3 Terms and definitions
3.1
Photovoltaic grid-connected inverter
A device that converts the direct current output from the photovoltaic array
into alternating current and feeds it into the power grid.
Note 1.Inverters mentioned in this standard all refer to photovoltaic grid-
connected inverters.
Note 2.The technical requirements and test methods specified in this
standard are not applicable to inverters in AC components.
3.2
Preparatory photovoltaic inverter
Box-type or box-type combined photovoltaic grid-connected inverter devices
including inverters, power transformers, high and low voltage switchgear and
control equipment, including containerized type. The typical AC rated voltage
level at high-voltage side is between 3.6 kV and 40.5 kV.
3.3
Photovoltaic array simulator
A power source that simulates the static and dynamic current and voltage
characteristics of a photovoltaic array.
3.4
Inverter a.c. output terminal
The connection point for the external output power on the AC side of the
inverter.
3.5
Isolated inverter
An inverter with electrical isolation between the AC output circuit and the
photovoltaic DC input circuit.
Note. This kind of electrical isolation can be realized inside the inverter, or it
can be realized by a combination of external independent dedicated isolation
transformers on the AC side as required during use.
4 Inverter type
4.1 Classification by the number of output phases on the AC side
According to the number of output phases on the AC side, it can be divided into.
- Single-phase inverter;
- Three-phase inverter.
4.2 Classification by installation environment
According to the installation environment, it can be divided into.
- Indoor Type I (with temperature adjustment device);
- Indoor type II (without temperature adjustment device);
- Outdoor type.
4.3 Classification by electrical isolation
According to the electrical isolation, it can be divided into.
- Isolated type;
- Non-isolated type.
4.4 Classification by access voltage level
According to the access voltage level, it can be divided into.
- A type inverter.
Refers to photovoltaic inverters used in photovoltaic power stations that are
connected to the grid through voltage levels of 35 kV and above, or
connected to the public grid through voltage levels of 10 kV and above;
- Type B inverter.
Refers to photovoltaic inverters used in photovoltaic power generation
systems that are connected to the grid through a voltage level of 380 V and
connected to the user side of the grid through a voltage level of 10 kV and
below, including inverters used in residential environments and directly
connected to residential low-voltage power supply network facilities.
Note. In the electromagnetic compatibility test of the inverter connected to
the grid via an independent power transformer, the type A limit is adopted.
4.5 Classification by other factors
Other types not listed above but declared by the manufacturer.
5 Environmental and use requirements
5.1 Temperature
The ambient air temperature range of the indoor inverter. indoor type I. 0 °C ~
+40 °C; indoor type II. -20 °C ~ +40 °C.
The ambient air temperature range of the outdoor inverter. -25 °C ~ +60 °C.
5.2 Humidity
Indoor relative humidity range. Indoor type I. 5% ~ 85% without condensation;
Indoor type II. 5% ~ 95% without condensation.
Outdoor relative humidity range. 4% ~ 100%, with condensation.
5.3 Altitude
The altitude of the installation site does not exceed 2000 m. When the altitude
of the inverter installation site is greater than 2000 m, it shall consider the
decrease of electrical dielectric strength.
5.4 Shock and vibration
The inverter may be subject to shock and vibration during production,
transportation, installation, operation, maintenance. Reasonable precautions
are required to avoid damage. The method specified in 11.6.4 shall be used for
verification.
5.5 Transport and installation
For inverters above 50kg, it must indicate the center of gravity of the inverter
on the package to facilitate transportation and handling. If the transportation
and installation conditions of the inverter are different from those specified in
Chapter 5, the manufacturer and user shall reach a special agreement.
5.6 Enclosure protection
Outdoor inverters must meet the minimum IP54 requirements; indoor inverters
must meet the minimum IP20 requirements.
5.7 UV exposure
The polymer material of the outdoor inverter enclosure shall have sufficient
resistance to material aging caused by ultraviolet (UV) radiation; it needs to be
evaluated for resistance to ultraviolet radiation or provide a third-party qualified
test report. After the UV radiation test, the sample shall show no obvious signs
of deterioration, including cracks or breaks. If the degradation of the component
does not affect the protection it provides, the requirements of this clause can
be ignored.
6 Safety requirements
6.1 Temperature limit
The temperature of the materials and components used in the equipment must
not exceed the limits specified in Table 1 to Table 3.In general, if the inverter's
related components or their surface temperature does not change more than
1 °C/h, it is considered that the inverter has reached a thermally stable state.
Under full power conditions, the temperature rise test lasts for up to 7 hours
(simulating one day's sun exposure), except that if a longer test can prove that
it will produce greater danger.
6.2 Electric shock protection requirements
6.2.1 Direct contact protection requirements
6.2.1.1 General requirements
a) To prevent people from directly contacting live parts that cause harm to
people, the measures to prevent direct contact shall be achieved through
one or more of the measures specified in 6.2.1.2 or 6.2.1.3.
b) Open components and devices do not need to take protective measures
against direct contact, but their operating instructions must clearly require
the necessary protective measures to be provided after the installation of
the final product is completed.
c) Inverters scheduled to be installed in enclosed electrical operation areas
do not need to take protective measures against direct contact. If
maintenance personnel need to energize it during installation or
maintenance, the protective measures shall meet the requirements of
6.2.1.2.3.
6.2.1.2 Enclosure and barrier protection
6.2.1.2.1 General requirements
Provide a protective enclosure and safety barrier; its parts shall not be
disassembled without tools. Polymer materials that meet these requirements
shall meet the requirements of 6.1 and 6.5 at the same time. When the inverter
is used outdoors, the polymer enclosure of the inverter must meet the
requirements of 5.7 when exposed to sunlight.
6.2.1.2.2 Requirements for protection against contact
a) After passing the enclosure and safety protection, the distance between
people and live parts must meet the following requirements.
1) The voltage of live parts is less than or equal to the specified safe
voltage - It is accessible;
2) The voltage of live parts is greater than the specified safe voltage - It is
not accessible, meanwhile there must be sufficient electrical clearance
between the live parts.
Note. The safety voltage limit is specified in accordance with the requirements
of the standard GB/T 3805.
b) The inverter adopts enclosure or shielding protection; it shall be inspected
according to the method of 11.2.2.1, to prevent the dangerous live parts
from being touched.
6.2.1.2.3 Maintenance personnel contact area
When the enclosure needs to be opened during installation or maintenance,
meanwhile the inverter needs to be energized, protection against contact shall
be provided for live parts with a voltage greater than the specified safe voltage
that may be unintentionally touched during the maintenance process. The
protection requirements shall be inspected according to the method of 11.2.2.1.
6.2.1.3 Insulation protection of live parts
Insulation shall be determined according to the impulse voltage, temporary
overvoltage or working voltage of the inverter; the most severe condition shall
be selected according to the requirements of 6.2.3.Without the use of tools, the
insulation protection shall not be removed.
6.2.2 Requirements for indirect contact protection
6.2.2.1 General requirements
a) In the case where the insulation between the contactable conductor and
the live parts of the inverter fails, in order to prevent contact with the
current that has the risk of electric shock, protection of indirect contact is
required. There are generally 2 ways of indirect contact protection.
Protective class I. Basic insulation and protective grounding;
Protective class II. Double insulation or reinforced insulation.
b) If the indirect contact protection depends on the installation method, the
installation manual shall clearly indicate the relevant hazards and specify
the installation method in detail.
c) Circuits that use insulation for indirect protection shall meet the
requirements of 6.2.3.
d) For the part whose voltage is less than the specified safe voltage [see a)
1) in 6.2.1.2.2], this kind of circuit does not have the risk of electric shock.
6.2.2.2 Protective connection and grounding
The inverter shall provide a reliable protective connection and protective
grounding, to ensure the electrical connection between accessible conductive
parts and with the external grounding conductor. Figure 1 shows an example of
the inverter and its related protective connections and grounding.
Description.
7 Basic functional requirements
7.1 Automatic ON/OFF
The inverter shall be able to realize the corresponding automatic ON/OFF
operations according to the voltage input conditions, or failures and post-failure
recovery.
7.2 Communication function
The inverter shall be equipped with a local communication interface; the
communication interface shall have fixation measures, to ensure the validity of
its connection. The electromagnetic compatibility of the communication port
shall meet the requirements of 8.4; meanwhile it shall be easy to form a network.
Communication can choose RS485, optical cable, PLC power carrier, Ethernet,
wireless and other methods for communication. The communication content
shall include inverter operation status, fault alarm and other related information.
The photovoltaic power station's power control system can communicate the
active power control, reactive power control and other control requirements to
the inverter; the communication protocol should match the communication
protocol of the photovoltaic power station.
8 Performance requirements
8.1 Electrical parameters
8.1.1 Input requirements
When the inverter is working within the normal input working voltage range, the
Sudden change of residual current
mA
The longest time the inverter is disconnected from grid
measured continuous maximum input current or power shall not exceed 110%
of the nominal maximum input value; the measured inverter working voltage
range shall not exceed the value declared by the manufacturer plus the voltage
control accuracy declared by the manufacturer.
8.1.2 Output requirements
When the inverter is working within the normal input and output operating
voltage range, the continuous output current of the inverter shall not exceed
110% of the nominal maximum continuous output current. At this time, the over-
current protection device and the over-temperature protection device shall not
act.
When the inverter is working within the normal input and output working voltage
range, it can continuously output the nominal rated power, meanwhile it shall
not exceed 110% of the nominal rated output power. At this time, the over-
current protection and over-temperature protection devices shall not operate.
8.2 Efficiency requirements
For the inverter, the efficiency of its energy conversion is determined by
dynamic MPPT efficiency, static MPPT efficiency and conversion efficiency.
The maximum conversion efficiency ηmax and the average weighted total
efficiency ηt,c of the inverter shall not be lower than the requirements in Table
15.It is required that the dynamic MPPT efficiency calculated by the test shall
not be less than 90%. Among them, the average weighted total efficiency is the
average weighted efficiency of static MPPT efficiency and conversion efficiency
under different voltages calculated according to the efficiency weighting
coefficients of typical solar resource areas in China.
The conversion efficiency includes all auxiliary power and control power losses.
For inverters with external independent dedicated isolation transformers, they
may be assessed according to the conversion efficiency limits of non-isolated
inverters without transformers; they can also be assessed according to the
conversion efficiency limits of isolated inverters with isolation transformers. The
loss includes loss of the isolation transformer. The conversion efficiency limit of
the preparatory photovoltaic grid-connected inverter device can refer to the limit
of the isolated inverter, which needs to include the loss of the isolation
transformer.
9 Protection requirements
9.1 Over/under voltage protection
9.1.1 Overvoltage protection at DC input side
When the input voltage on the DC side is higher than the maximum value of the
DC array access voltage allowed by the inverter, the inverter must not start and
a warning signal will be issued at the same time. After the DC side voltage is
restored to the allowable working range of the inverter, the inverter shall be able
to start normally.
9.1.2 Over/under voltage protection at AC output side
For Class B inverters, when the grid-connected point's voltage exceeds the
voltage range as specified in Table 1 of GB/T 29319-2012, see Table 32; it shall
stop transmitting power to the grid lines within a corresponding period of time.
This requirement applies to any phases in a multi-phase system.
Note. The manufacturer can declare the upper limit of normal working voltage
between 110%UN and 135%UN and indicate it in the manual.
9.2 Over/under frequency protection
For Class B inverters, when the grid-connected point frequency exceeds the
operating range of 47.5Hz ~ 50.2Hz, it shall stop supplying power to the grid
within 0.2s. When the grid frequency is lower than 49.5 Hz, or higher than 50.2
Hz, the inverters that are out of service must not be connected to the grid at this
time. The inverter shall be able to restart operation when the grid frequency is
restored to the allowed grid frequency.
For Class A inverters, the frequency protection configuration shall meet the
requirements of 8.3.6.
9.3 Incorrect phase sequence or polarity
9.3.1 Polarity misconnection
The inverter can automatically protect when the DC input or AC output polarity
of the inverter is incorrectly connected. When the polarity and phase sequence
are correctly connected, the inverter shall be able to work normally.
9.3.2 AC phase loss protection
When the AC output phase of the inverter is missing, the inverter will
automatically protect and stop working. The inverter shall be able to operate
normally after correct connection.
9.4 DC input overload protection
9.4.1 If the inverter's input terminal does not have the power limiting function,
protection is required when the inverter's input power exceeds 1.1 times the
nominal maximum DC input power.
9.4.2 If the inverter's input terminal has a power limiting function, when the
output power of the photovoltaic array exceeds the maximum DC input power
allowed by the inverter, the inverter shall automatically limit the current and work
at the maximum AC output power allowed.
9.5 Output short circuit protection
When the inverter is turned on or running, if a short circuit on the output side is
detected, the inverter shall be able to automatically protect. It is required that
there is no electric shock hazard in the accessible conductive parts, meanwhile
the parts with electric hazard and mechanical hazard shall not be touched. If
the recorded short-circuit current exceeds the maximum rated current of the
circuit, the measured maximum short-circuit current must be written in the
installation manual.
9.6 Reverse discharge protection
When the DC side voltage of the inverter is lower than the allowable working
range or is in the shutdown state, there shall be no reverse current flowing out
of the inverter DC side.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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