GB/Z 18039.2-2000 Evaluation of low-frequency conducted disturbance emission level of industrial equipment power supply in electromagnetic compatibility environment
Some standard content:
GB/7 18039.2-- 2000
This guidance technical document is equivalent to the IEC technical report IEC61000-2-6:1996 "Electromagnetic compatibility Part 2: Environment Part 6: Evaluation of low-frequency conducted disturbance emission levels of power supplies for industrial equipment". This guidance technical document recommends the evaluation method for the level of low-frequency conducted disturbance emission of power supplies for electrical and electronic equipment in industrial plants and mines. This guidance technical document is one of the "Electromagnetic Compatibility Environment" series of national standardization guidance technical documents. This series of national standardization guidance technical documents includes the following contents: Classification of competitive electromagnetic environment
GB/Z18039.1-2000 Electromagnetic compatibility
GB/Z18039.2-2000 Electromagnetic compatibility environment Evaluation of low-frequency conducted disturbance emission level of industrial equipment power supply This guidance technical document is for reference only. Suggestions and opinions on this guidance technical document should be reported to the standardization department of the State Council.
Appendix A, Appendix B, Appendix C, Appendix D and Appendix E of this guidance technical document are prompt appendices. This guidance technical document is proposed by the State Power Corporation. This guidance technical document is under the jurisdiction of the National Electromagnetic Compatibility Standardization Joint Working Group. The responsible drafting unit of this guidance technical document: Wuhan High Voltage Research Institute of State Power Corporation. The main drafters of this guidance technical document: Xiong, Lang Weichuan, Nie Dingzhen, Wan Baoquan, Jiang Hong, Fei Guangyu: GB/Z 18039. 2-2000
IEC Foreword
1) The International Electrotechnical Commission (IEC) is a global standardization organization composed of the National Electrotechnical Committees (IEC National Committees) of all participating countries. Its purpose is to promote international consensus on all questions concerning standardization in the field of electrical and electronic technology and, for this purpose, publishes, among other activities, International Standards, which are formulated by Technical Committees. Any IEC National Committee interested in the formulation of a project is called upon to participate, as are international organizations, governmental and non-governmental organizations in liaison with the IEC. The IEC cooperates closely with the International Organization for Standardization (ISO) on terms determined by negotiation between the two organizations. 2) Since each Technical Committee has representatives from all countries interested in the relevant formulation project, the formal decisions or agreements made by the IEC on the relevant technical content express international consensus as far as possible. 3) The documents produced may be published in the form of standards, technical reports or guidelines, recommended for international use and accepted by the National Committees in this sense.
4 ) To promote international consensus, IEC National Committees should, as far as possible, convert IFEC international standards into their national and regional standards. Any differences between the corresponding national or regional standards and IEC international standards should be clearly stated in the standards. The main task of IEC technical committees is to formulate international standards. In special cases, technical committees may publish one of the following types of technical reports.
· Type 1, when it cannot be published as an international standard despite repeated efforts; · Type 2, when the subject is still in the technical development stage, or for any other reason it cannot be agreed to be an international standard in the future:
· Type 3. When the technical committee collects various information in the routine process of publishing international standards, such as "scientific development trends\" Type 1 and 2 technical reports will be reviewed within three years from the time of publication to determine whether they can become international standards. Type 3 technical reports do not need to be reviewed until the information they provide is considered no longer valid or useful. IEC61000-2-6 is a Category 3 technical report developed by IEC Technical Committee 77 (Electromagnetic Compatibility) Subcommittee 77A (Low Frequency Phenomena):
The text of this technical report is based on the documents in the table below:CD
77A(Sec)94
77A(Sec)103
Full information on the vote to approve this report can be found in the voting report in the table above. Appendices A, B, C, D and E are for reference only. 68
Voting Report
77A/130
GB/Z 18039.2 --2000
IEC Introduction
This standard is part of the IEC61000 series of standards, which consists of: Part 1; General
General considerations (overview, basic principles)
Definitions, terms
Part 2: Environment
Description of environment
Classification of environment
Compatibility level
Part 3: Limits
Emission limits
Immunity limits (as they are not within the responsibility of the product committee) Part 4: Test and measurement techniques
Measurement techniques
Test techniques
Part 5: Installation and mitigation guidelines
Installation guidelines
Mitigation methods and devices
Part 6: Generic standards
Part 9: Others
Each part is divided into several subparts, which are published as International Standards or Technical Reports. These standards and reports will be published in chronological order and numbered accordingly. This subpart is a technical report.
National Standardization Guiding Technical Document of the People's Republic of China Electromagnetic compatibility environment
Low-frequency conducted disturbances in the power supply of industrial plants
Emission level assessment
Electromagnetic compatibility--Environment -Assessment of the emission levels in the power supply of industrialplants as regards low-frequency conducted disturbances1 Scope
GB/718039.2.--2000
idt IEC 61000-2-6:1996
This guiding technical condition recommends the procedure for assessing the level of disturbances emitted by devices, equipment and systems installed in non-public power grids in industrial environments, and is limited to low-frequency conducted disturbances in the power supply. On this basis, the relevant emission limits can be obtained. It is applicable to medium and low voltage non-public power grids of AC 50/60IIz. Power grids such as shipping, aviation, offshore platforms and railways are not within the scope of this guidance technical document.
This guidance technical document describes the low-frequency conducted disturbances emitted by equipment connected to the power supply. These disturbances include: harmonics and interharmonics:
unbalance;
voltage changes;
voltage sags.
2 Cited standards
The provisions contained in the following standards and standardized guidance technical documents constitute the provisions of this guidance technical document through reference in this guidance technical document. When this guidance technical document is revised, the versions shown are valid. All standards and standardized guidance technical documents will be revised. Parties using this guidance technical document should explore the possibility of using the latest versions of the following standards and standardized guidance technical documents.
GB/T43651995 Electromagnetic compatibility terminology (idtIEC60050 (61): 1990) GB17625.2--1999 Electromagnetic compatibility limit values for the limitation of voltage fluctuations and flickers in low voltage power supply systems for equipment with rated current not exceeding 16A (idtIEC61000-3-3: 1994) GB/Z17625.3--2000 Electromagnetic compatibility limit values for the limitation of voltage fluctuations and flickers in low voltage power supply systems for equipment with rated current greater than 16A (idtIEC6 1000-3-5:1996) IEC60146: Semiconductor converter
3 Overview
To achieve electromagnetic compatibility, the total value of the disturbance level at each coupling point should be limited, which means to control the emission of the disturbance load connected to the power supply
For low-voltage public power grids, the emission of equipment with a rated current of up to 16A installed in the power grid is strictly limited to control the disturbance. State Administration of Quality and Technical Supervision 2000-04-03 approved 69
2000-1201 implementation
GB/Z 18039.2--2000
level, these limits are determined by statistical studies of the following factors. Dispersion of equipment in the power grid;
Type of equipment used (simultaneous effect);
Power grid characteristics.
As long as the equipment meets the emission limits specified in the relevant standards, any equipment with a rated current of up to 16A can be connected to the power grid. This approach shows that for public power grids, strict coordination between different users and power supply companies is impossible. For factories and non-public power grids, the compatibility levels at different locations must be consistent. a) At the public power grid's point of public coupling (PCC), the total value of the equipment's emission to the public power grid must be appropriately limited according to the power supply company's requirements and the power grid conditions of the power supply.
b) At the internal coupling point (IIPC), the total value of the disturbance level generated by the industrial equipment and the disturbance level intruding the power supply will be limited to the compatibility level selected at the concerned IPC point. In order to make the emission limit of a single device meet the requirements of the above regulations, the following factors should be considered: ... the actual impedance of the power grid to which the device is connected; the combination of various devices actually existing in the factory; the actual use of the equipment related to the production process; the control and mitigation of interference can be achieved by taking preventive measures such as filtering or compensation devices, distributing loads to different power supplies, and dividing interference loads.
This method shows that for the factory, the interference loads in the design stage and the operation stage can be coordinated. In order to achieve the greatest economic benefits, the following factors are important for limiting the emission of a single device: the actual emission of a single device is largely related to the characteristics of the power grid; even if the emission level of low-power equipment is incompatible with the standards of the public power grid, in the case of strong interference equipment in the factory, its impact can be completely ignored;
-The synthesis method of interference caused by various sources mainly depends on the design of the equipment and the industrial process involved; to a certain extent, users can choose the appropriate electromagnetic compatibility level at the IPC point. In fact, this choice is a kind of compromise choice between the cost of limiting the emission level and the cost of reducing the disturbance level or improving the immunity through mitigation measures. 4 Coordination of emission limits and compatibility levels
The emission limits allowed by the equipment can be determined by a three-step procedure: a) Information between the power supply company and the user and between the user and the manufacturer. The power supply company is required to provide the user with at least the following information: · The total emission limit applicable to the factory;
The current and future expected disturbance levels at the PCC point, excluding the disturbance generated by the considered factory; - The range of the source impedance value at the coupling point is equally important as the disturbance assessment, and this range is related to the grid structure and frequency characteristics. The relevant information that the user is required to provide to the power supply department: - The characteristics of the equipment to be installed and its operating mode; - The characteristics of the power factor compensation equipment;
- The characteristics of the filter used for harmonic current compensation. The user is required to provide at least the following information to the manufacturer: - The characteristics of the installation plan and the connected equipment;
- The emission level of other equipment and the disturbance conducted by the power supply: The characteristics of the production process.
The manufacturer is required to provide the following information to the user at least: - the expected emission level of the equipment or system under specific operating conditions; GB/Z 18039.2--2000
- the sensitivity of the emission level to changes in source impedance, operating voltage, etc.; b) when there are different interference sources in the factory, select the appropriate superposition calculation rule; c) evaluate the total expected emission level of the factory at the PCC point and the total expected interference level at the IPC point. If the total emission value or expected interference level of the equipment exceeds the relevant compatibility level, taking into account the future development of the power grid and the possibility of an increase in factory interference sources, the following preventive measures should be considered: - adjust the power grid structure;
· change the characteristics of the interference equipment;
- use filters or compensation devices;
- tolerate the interference generated and improve the equipment's anti-interference level (this measure is not applicable to the PCC point, but only to the IPL point). Repeat the above process until all requirements are met. 5 Definitions
All terms are consistent with those in GB/T4365.1EC60146 and IEC61000-3 - 6 Overview of conducted emissions of industrial equipment
Table 1 lists an overview of the low-frequency conducted emission sources and their impact on the power supply. Table 1 Low-frequency conducted disturbance sources
Non-linear characteristics
Electronic device operating load
Operation load
7.1 Description of disturbance phenomena and disturbance sources
Magnetic saturation device, gas discharge lamp
Arc furnace, AC arc welding machine
Transformer closing
Converter, AC controller
Multi-cycle control device
Disturbance caused by capacitor, filter, induction motor closing ||tt ||Harmonics, interharmonics, voltage variations, unbalanced harmonics, voltage sags
Harmonics, interharmonics, voltage variations, unbalanced interharmonics, voltage sags
Harmonics in line current are mainly generated by the following methods. Other load characteristics are introduced in Appendix A. 7.1.1 Line current when the switching frequency of the electronic switch in the semiconductor converter is the line frequency or its multiple This function can be either controllable (such as thyristors) or uncontrollable (such as diodes). In most cases, this function is achieved by periodically switching the series impedance and voltage source between each phase. The harmonics generated in the converter generally have two characteristics: a) Periodic switching of the load, for example, the AC controller switches the load at a certain phase angle and switches the load when the current drops to zero. Figure 1a) is a schematic diagram of its arrangement. The amplitude and phase angle of the harmonic current depend on the angle when the line voltage is connected to the load, the voltage difference between the line voltage and the load voltage, and the series connection composed of the load impedance and the line impedance. Typical applications are:
Conduction heat, welding, smelting;
High-voltage DC power supply for electrostatic precipitator or transmitter tubes, high-current DC power supply for galvanizing or metal pickling; static VAR compensator:
Starter for AC motor
b) The impressed current is switched periodically between (large DC inductance). 692
Figure lb) is a simplified layout diagram.
Typical devices of this type are:
GB/Z 18039.2--2000
"Converters for feeding DC loads (e.g. DC drives, DC traction, DC power supplies for electrochemical and electrothermal treatment, DC excitation of motors or field coils, DC welding AC converters): --- AC converters with true current tie lines (e.g. AC drives with CSI or sub-string synchronous converters: point current sources of medium frequency converters for metal blast furnaces or induction furnaces). --- reversible converters, cycloconverters (e.g. AC drives. Low-frequency power supply for electric heating smelting), as shown in Figure A7 of Appendix A, the DC voltage is regularly connected and disconnected from the line through the impedance. The converter connected to the three-phase line is connected to the DC side at a certain phase angle from the phase with small DC inductance to another phase, and Figure 1b) is its equivalent circuit. The harmonic current generated is equivalent to the harmonic current of the AC controller. Here, the current drops to zero either when the subsequent phase is connected or when the current is small or the DC inductance is small. The output current and the voltage drop direction are the same and appear in advance. Typical devices of this type are converters connected to DC voltage (for example, drives connected to voltage source inverters (VSI), uninterruptible power supplies (UPS): DC power supplies for resonant converters suitable for metal heating or welding). Self-rectified converters (converters for drives and compensators that do not require reactive power or compensate it). 7.7.2 Nonlinear impedance limiting related to current and resistance (see Figure 1c)).
Typical devices of this type are:
—- Electric arc furnace (AC arc for melting metal). AC welding machine (welding arc powered by high-resistance transformer) - Fluorescent lamps and gas discharge lamps for public lighting. 1.3 Closing of saturated inductance (e.g. closing of induction motors and transformers) Magnetic saturation can produce transient current components. Closing of resonant circuits with inductance and capacitance will produce transient resonance in the power grid (e.g. when a filter or capacitor is closed, transient resonance will occur between the filter capacitor and the filter and line inductance). Figure 1c shows its equivalent circuit.
7.2 Typical emission data
The range of typical emission data for the most common loads that produce harmonic line currents is given in Appendix A. It is given for guidance only. Reliable data for disturbance assessment should be obtained by the manufacturer based on actual design parameters and his experience with similar equipment. 7.3 Influence of operating and installation conditions on emissions For emissions generated by various loads (e.g. converters), the magnitude and phase angle of the harmonic currents will be estimated, the connection of converters to transformers, simultaneous and single or random operation of converter loads must be considered. The disturbance in the supply system can be determined by the presence of harmonic components in the line voltage, i.e. the voltage drop caused by the harmonic currents across the line impedance. This line impedance is determined by all the impedances connected in series and parallel with the high-voltage network, all loads, compensation and filtering elements, taking into account that this impedance applies to all frequencies (see Figure 2a). Therefore, possible resonances must be verified and taken into account. Further information is given in Appendix B.
7.4 Superposition of harmonics
When there are several devices generating harmonic currents in the same plant, the harmonic currents in the line and the harmonic voltages at the relevant points (IPC or PCC) depend on the superposition effect caused by the different magnitudes and phase angles of the currents emitted by the different sources. The exact calculation of the harmonic resultant voltage (vector sum) is limited to a few special cases. Although taking the algebraic sum of the effects of each harmonic source can reflect the worst case, this method often results in very high data that are inconsistent with reality, especially for higher harmonics. In most cases, an approximate calculation method is sufficient. There are several methods for approximate calculation of harmonic synthesis, see the relevant literature in Appendix F [4[5][6].
7.4.1 Harmonic voltage at the point of interest
GB/Z 18039.2-2000
UA= Uho + ZUh
The hth harmonic voltage U at the point of interest (IPC or PCC) can be obtained from the following formula (see Figure 2b)): Where: Uh--the hth harmonic voltage of the power supply network when the influence of related sources is not considered (background disturbance) Un is the hth harmonic voltage caused by the injection source i. (1)
Assuming that all transfer impedances between the source connection point and the point of interest are equal for all disturbance sources (see Figure 2b)), then (: is obtained by the following formula:
Uh = Uho + ZZla
Where: Equivalent harmonic impedance seen from the point of interest 7.4.2 Superposition of harmonic voltages
7.4.2.1 Calculation principle
Since the permissible emission level is related to the grid structure, the problem of selecting harmonics arises when studying the connection of new industrial loads that generate harmonics. Harmonics are the sum of harmonics generated by existing loads and future loads. Due to the lack of data and the variability of all loads that generate harmonics, it is necessary to use statistical methods to calculate Synthesized harmonic vector. In the statistical method, each harmonic source is represented by a random time-varying vector, the amplitude and phase angle of these vectors are simulated according to the distribution law. In order to obtain a simple law in practical application, the difference factor K is used: K
K is defined as the ratio of the vector sum (actual or expected) of all harmonic sources acting alone to the algebraic sum. This action is caused by emissions related to the design operating characteristics of the equipment in question. With the help of the difference factor K, the total disturbance U can be estimated as follows: U, Uhol + The difference factor KZIUh
is influenced mainly by the following factors: - Type of disturbance load, for example in the case of converters: · Controllable or uncontrollable converter;
. Inductive or capacitive smoother;
· Type of load (resistive, inductive, motor); · Number of converters operating simultaneously;
Mode of operation of the various disturbance sources (coordinated or independent operation): - Variability of the load;
- Harmonic order considered.
7.4.2.2 Practical application of the calculation
(4)
Based on the knowledge of the harmonic effects of all devices in the industrial power grid and the required accuracy of the harmonic composite voltage at the point of interest, two methods for calculating the difference factor K are proposed here. In particular, method 1 is related to special equipment groups; while method 2 involves statistical considerations. Method 1
This method gives suitable difference factors for first approximations or for relevant The harmonic synthesis voltage at the noted point is effective and has a large safety margin for the compatible level, and is applicable to low-order harmonics of subh≤7. The difference factor K can be obtained by the following formula:
ZK,Uml
Several different K can be used in a factory equipment. According to the literature in Appendix E [131, Table 2 gives the difference factors for each load and different harmonic orders. 1691
（5）
GB/Z18039.2-- 2000
Table 2 Difference factors K5 for various X values and harmonic orders
Note: X is the ratio of the load of the considered device to the total disturbance load of the plant Note: If the equipment group is an uncontrolled rectifier converter, K, -0.97
In addition, if the uncontrolled rectifier has the same load cycle, K, 1.0.11
The difference factors in the table take into account the phase angle increment of higher harmonics^ (see data related to method 2). Method 2
This method is based on the statistical method and takes into account that the compatibility level must meet the probability of 95% and above. It is required to understand the amplitude and phase angle changes of a single harmonic effect: K
where: S(Uh(p))-
has a statistical loss with a probability not exceeding 95%,
the difference factor K, which is related to the changes in the harmonic voltage amplitude and phase angle and the number of harmonic sources N, can be obtained according to the method of the literature [in Appendix E:
KZIUh/ = b(ZIUh [\)Va
Table 3 lists the typical values of α and 6, which are applicable to values with a probability not exceeding 95%. Table 3 applies to α and b values with uniform amplitude and phase angle distribution (maximum amplitudes are all equal)
Phase angle distribution range
0°~-360°
0°～270°
0°~180″
0°~90°
Amplitude distribution range
AU/Umax
Note: The formula given above is applicable only when there is no harmonic source greater than 50% of the algebraic sum of the harmonic voltages being considered. Otherwise, refer to the method!. In general, the applicable range is as follows:
3rd, 5th and 7th harmonics, phase angle within 90°. 2.0
GB/Z 18039. 2--2000
-11.13th harmonic, phase angle within 270°. -13th and above harmonics, phase angle within 360°, for vectors with different maximum amplitudes, these coefficients have sufficient accuracy. If the result exceeds the algebraic sum, the algebraic sum is used instead. In special cases, when the result is less than the largest single component, the latter is used. If in the equipment, some converters are connected by phase-shifting transformers (Y connection), while: · This is connected by non-shifting transformers】Y or D/D connection), when the converters are operated under similar conditions, the resulting 5 The 1st and 7th harmonic currents tend to cancel out the 8th interharmonic wave
8.1 Sources of harmonic currents and voltages
Most of the interharmonic currents and voltages in the power supply are generated by static frequency converters. Rotating motors without converters can also generate interharmonic voltages, but they are related to the interharmonic waves generated by the converter. Since their amplitude is very small, they can be ignored. Regarding the harmonics injected into the power supply, such as ripple control, their emissions are well known and therefore will not be discussed here. The mechanism for generating interharmonic frequencies depends on the type of converter. Table 4 gives the static frequency converter as a source of interharmonic waves. Table 4 Interharmonics generated by converters
Converter installation
Load side
Grid-commutated inverter
Grid-commutated inverter and DC tie line
Self-commutated inverter
Resonant inverter
Self-commutated inverter and DC tie line
Direct converter (cycloconverter)
Typical PWM
Variable speed drive, power exchange between grids, subsynchronous cascade
Variable speed drive, UPS
Induction heating
Variable speed Drive
Energy storage
Variable frequency, super synchronous series low speed variable speed drive for traction and electrothermal process
AC arc furnace is also a source of interharmonic wave. In addition, any converter or nonlinear device under non-steady-state operating conditions can generate interharmonic current,
8.2 Interharmonic line current of indirect converter The indirect converter consists of a grid-commutated converter on the AC power supply side, which is connected to another converter for motor commutation, resonant commutation or self-commutation through a DC interconnection line.
The ripple current of the DC interconnection line contains the current of the following frequency: fi = npuft.
Where: -
fhkpafA
The frequency of the harmonic component in the intermediate interconnection line current. Hz; the number of pulses of the converter on the AC power supply side;
ft\. Line frequency,Hz;
Integer 0,1,2,3.·
Number of pulses of load-side inverter;
-load frequency, Hz. When the load is a motor, this frequency is related to the actual speed of the motor. Abzxz.net
In steady state, the current has the following frequency: fu = fi(1 t np) -kpaf.
Where: .fh.----Line current frequency component, Hz. s
GB/Z 18039.2--2000
When Table II 0 (equivalent to the DC component in the DC tie line current), this formula gives the characteristic harmonics in the line current. When Table III), this formula gives the interharmonic frequency
The interharmonic frequency with the highest amplitude is:
Jmh =(f± paTA)
(10）
Figure 3a) and Figure 3b) give an overview of the frequency components. The number under the frequency trace is the coefficient G, that is, the ratio of the line current to the corresponding tie line current at each frequency component.
Appendix C gives the formula used in the preliminary approximation of the interharmonic current, which is also an application example of Figure 3b). More detailed information can be provided by the manufacturer.
8.3 Interharmonic currents generated by direct converters Direct converters are frequency converters without intermediate tie lines and energy storage. They convert line frequencies in the range of 0 (DC) to about 40% of the line frequency.
Three-phase to three-phase converters are called cycloconverters. They can control both frequency and voltage amplitude. They are mainly used for speed control of large three-phase rotating machines, either by processing the total energy of the transfer device or by processing the slip energy. In the second case, the converter is connected to the induction motor via a slip ring, and its speed control is limited to a narrow range close to the synchronous speed (cycloconverter grade). Typical applications for direct conversion from three phases to single phase are, for example, tie lines between the public supply and the railway single-phase supply, or AC supplies such as certain metallurgical processes that require very low frequencies. The spectrum of the supply current is determined by the characteristic harmonics: fh = (1 ± npr)fi.
In addition, there are sideband frequencies. They are given by the following equations: Single-phase load (see Figure 4): J = 2 kfA Three-phase load (cycloconverter, see Figure 4): fh = 6 k/A Where: - Characteristic frequency corresponding to the number of pulses of the power converter; / Output frequency of the cycloconverter.
Figures 4, 5 and 6 show the influence of different load parameters, such as: - High and low load frequency;
6, 12 pulse configuration.
The amplitude of the interharmonic current depends mainly on:
Load current;
Load power factor
- Motor voltage (related to the actual speed) - Converter control method, such as sinusoidal control, irregular trapezoidal control, etc., 8.4 times synchronous cascade
This type of slip control is implemented by a simple indirect converter and is often used to adjust the speed of medium-power induction motors, approximately controlling the speed in the range of 60% to near synchronous speed. The rotor winding returns energy to the AC power supply side (through the rectifier, DC tie line and inverter), and the harmonic currents generated by the rectifier and inverter flow into the power supply grid. In addition, the harmonic currents generated by the rotor-side rectifier hit the rotation of the winding and cause the frequency to change.
Figure 7 shows the frequency fh· generated in the line current as a function of speed. The following equation is then obtained:
Determined action
Rotor action
fh(土kSP)fi
fh=(1+nPi±SP)f)
Where: I-the pulse number of the converter connected to the AC power supply side; (12)
GB/Z 18039.2 --2000
P,-the pulse number of the rotor-side rectifier P.=6; step speed;
UA actual speed;
S slip rate
Figure 8 shows an example of supersynchronous and subsynchronous cascades, in which the slip energy is controlled by a cycloconverter. 8.5 Line-side self-commutated converter
If the beat frequency is not an integer multiple of the line frequency, interharmonic voltages or currents will be generated. 8.6 Arc furnace
Arc furnaces generate harmonics and interharmonic frequencies. Converters produce discrete frequency spectra, while arc furnaces produce continuous frequency spectra. In this case, the harmonic spectral density should be considered.
Figure 9 gives an example of this.
8.7 Selection of interharmonic frequency components
Only in exceptional cases and for a short period of time do the interharmonic components have the same frequency. Therefore, superposition of interharmonics is only possible in these cases.
9 Three-phase unbalance
9.1 Description of disturbance sources
9.1.1 Overview
When an unbalanced load is connected to the power system, an unbalanced three-phase voltage appears. The current absorbed by the unbalanced load has an amplitude or phase angle of two phases that is not uniform
Loads (such as three-phase AC motors, generators and converters) generally do not cause unbalance during normal operation. However, due to imperfect design, there may be minor imbalances, but these are usually negligible and cannot be calculated using general rules. Unbalanced voltages may also be caused by symmetrical currents in power systems with unbalanced line impedances, but this is beyond the scope of this technical guidance document.
·Unbalanced harmonics may appear in the system in general, but they are not discussed here. This technical guidance document only deals with fundamental voltage and current imbalances.
9.1.2 Examples of unbalanced loads
All single-phase loads, whether connected by phase neutral or by phase one, are unbalanced. Typical examples are:
Heating equipment
—lighting equipment,
single-phase converters and rectifiers;
AC controllers;
—AC traction equipment;
welding machines.
These loads should be distributed as evenly as possible on the three phases to reduce the overall imbalance. Even though the arc furnace is a three-phase device, it can still have a large imbalance.
9.2 Emission characteristics
9.2.1 Symmetrical component method
Using the symmetrical component method, the unbalanced system can be decomposed into three components, namely positive sequence, negative sequence and zero sequence components. Note: Zero sequence components are beyond the scope of this guidance technical document and have no effect on the load connected between phases. Zero sequence components exist in the line-to-ground voltage of any system. Even if the neutral point is not grounded, they can also exist in the line current. This current can flow into the ground through the line-to-ground capacitance6!s
In addition, there are sideband frequencies. They are given by the following formula: Single-phase load (see Figure 4): J = 2kfA Three-phase load (cycloconverter, see Figure 4): fh = 6k/A Where: - Characteristic frequency corresponding to the number of pulses of the power converter; / Output frequency of the cycloconverter.
Figures 4, 5 and 6 show the influence of different load parameters, such as: - High and low load frequency;
6, 12 pulse configuration.
The amplitude of the interharmonic current depends mainly on:
Load current;
Load power factor
—Motor voltage (related to actual speed)—Converter control method, such as sinusoidal control, irregular trapezoidal control, etc. 8.4-second synchronous series
This type of slip control is implemented by a simple indirect converter and is often used to adjust the speed of medium-power induction motors, approximately controlling the speed within a range of 60% to near synchronous speed. The rotor winding returns energy to the AC power supply side (through rectifiers, DC interconnects and inverters), and the harmonic currents generated by the rectifiers and inverters flow into the power supply grid. In addition, the harmonic currents generated by the rotor-side rectifiers are affected by the rotation of the windings and cause the frequency to change.
Figure 7 shows the frequency fh· generated in the line current as a function of speed. The following equation is then obtained:
Determined action
Rotor action
fh(土kSP)fi
fh=(1+nPi±SP)f)
Where: I-the pulse number of the converter connected to the AC power supply side; (12)
GB/Z 18039.2 --2000
P,-the pulse number of the rotor-side rectifier P.=6; step speed;
UA actual speed;
S slip rate
Figure 8 shows an example of supersynchronous and subsynchronous cascades, in which the slip energy is controlled by a cycloconverter. 8.5 Line-side self-commutated converter
If the beat frequency is not an integer multiple of the line frequency, interharmonic voltages or currents will be generated. 8.6 Arc furnace
Arc furnaces generate harmonics and interharmonic frequencies. Converters produce discrete frequency spectra, while arc furnaces produce continuous frequency spectra. In this case, the harmonic spectral density should be considered.
Figure 9 gives an example of this.
8.7 Selection of interharmonic frequency components
Only in exceptional cases and for a short period of time do the interharmonic components have the same frequency. Therefore, superposition of interharmonics is only possible in these cases.
9 Three-phase unbalance
9.1 Description of disturbance sources
9.1.1 Overview
When an unbalanced load is connected to the power system, an unbalanced three-phase voltage appears. The current absorbed by the unbalanced load has an amplitude or phase angle of two phases that is not uniform
Loads (such as three-phase AC motors, generators and converters) generally do not cause unbalance during normal operation. However, due to imperfect design, there may be minor imbalances, but these are usually negligible and cannot be calculated using general rules. Unbalanced voltages may also be caused by symmetrical currents in power systems with unbalanced line impedances, but this is beyond the scope of this technical guidance document.
·Unbalanced harmonics may appear in the system in general, but they are not discussed here. This technical guidance document only deals with fundamental voltage and current imbalances.
9.1.2 Examples of unbalanced loads
All single-phase loads, whether connected by phase neutral or by phase one, are unbalanced. Typical examples are:
Heating equipment
—lighting equipment,
single-phase converters and rectifiers;
AC controllers;
—AC traction equipment;
welding machines.
These loads should be distributed as evenly as possible on the three phases to reduce the overall imbalance. Even though the arc furnace is a three-phase device, it can still have a large imbalance.
9.2 Emission characteristics
9.2.1 Symmetrical component method
Using the symmetrical component method, the unbalanced system can be decomposed into three components, namely positive sequence, negative sequence and zero sequence components. Note: Zero sequence components are beyond the scope of this guidance technical document and have no effect on the load connected between phases. Zero sequence components exist in the line-to-ground voltage of any system. Even if the neutral point is not grounded, they can also exist in the line current. This current can flow into the ground through the line-to-ground capacitance6!s
In addition, there are sideband frequencies. They are given by the following formula: Single-phase load (see Figure 4): J = 2kfA Three-phase load (cycloconverter, see Figure 4): fh = 6k/A Where: - Characteristic frequency corresponding to the number of pulses of the power converter; / Output frequency of the cycloconverter.
Figures 4, 5 and 6 show the influence of different load parameters, such as: - High and low load frequency;
6, 12 pulse configuration.
The amplitude of the interharmonic current depends mainly on:
Load current;
Load power factor
—Motor voltage (related to actual speed)—Converter control method, such as sinusoidal control, irregular trapezoidal control, etc. 8.4-second synchronous series
This type of slip control is implemented by a simple indirect converter and is often used to adjust the speed of medium-power induction motors, approximately controlling the speed within a range of 60% to near synchronous speed. The rotor winding returns energy to the AC power supply side (through rectifiers, DC interconnects and inverters), and the harmonic currents generated by the rectifiers and inverters flow into the power supply grid. In addition, the harmonic currents generated by the rotor-side rectifiers are affected by the rotation of the windings and cause the frequency to change.
Figure 7 shows the frequency fh· generated in the line current as a function of speed. The following equation is then obtained:
Determined action
Rotor action
fh(土kSP)fi
fh=(1+nPi±SP)f)
Where: I-the pulse number of the converter connected to the AC power supply side; (12)
GB/Z 18039.2 --2000
P,-the pulse number of the rotor-side rectifier P.=6; step speed;
UA actual speed;
S slip rate
Figure 8 shows an example of supersynchronous and subsynchronous cascades, in which the slip energy is controlled by a cycloconverter. 8.5 Line-side self-commutated converter
If the beat frequency is not an integer multiple of the line frequency, interharmonic voltages or currents will be generated. 8.6 Arc furnace
Arc furnaces generate harmonics and interharmonic frequencies. Converters produce discrete frequency spectra, while arc furnaces produce continuous frequency spectra. In this case, the harmonic spectral density should be considered.
Figure 9 gives an example of this.
8.7 Selection of interharmonic frequency components
Only in exceptional cases and for a short period of time do the interharmonic components have the same frequency. Therefore, superposition of interharmonics is only possible in these cases.
9 Three-phase unbalance
9.1 Description of disturbance sources
9.1.1 Overview
When an unbalanced load is connected to the power system, an unbalanced three-phase voltage appears. The current absorbed by the unbalanced load has an amplitude or phase angle of two phases that is not uniform
Loads (such as three-phase AC motors, generators and converters) generally do not cause unbalance during normal operation. However, due to imperfect design, there may be minor imbalances, but these are usually negligible and cannot be calculated using general rules. Unbalanced voltages may also be caused by symmetrical currents in power systems with unbalanced line impedances, but this is beyond the scope of this technical guidance document.
·Unbalanced harmonics may appear in the system in general, but they are not discussed here. This technical guidance document only deals with fundamental voltage and current imbalances.
9.1.2 Examples of unbalanced loads
All single-phase loads, whether connected by phase neutral or by phase one, are unbalanced. Typical examples are:
Heating equipment
—lighting equipment,
single-phase converters and rectifiers;
AC controllers;
—AC traction equipment;
welding machines.
These loads should be distributed as evenly as possible on the three phases to reduce the overall imbalance. Even though the arc furnace is a three-phase device, it can still have a large imbalance.
9.2 Emission characteristics
9.2.1 Symmetrical component method
Using the symmetrical component method, the unbalanced system can be decomposed into three components, namely positive sequence, negative sequence and zero sequence components. Note: Zero sequence components are beyond the scope of this guidance technical document and have no effect on the load connected between phases. Zero sequence components exist in the line-to-ground voltage of any system. Even if the neutral point is not grounded, they can also exist in the line current. This current can flow into the ground through the line-to-ground capacitance6!s
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