one. Overview
With the progress of modernization, the nonlinear, impact and asymmetry loads are heavily connected to the grid, and the quality of power supply is becoming increasingly serious. Due to the high demands on quality of life and work efficiency, people are now paying more attention to power quality issues than ever before.
Power quality includes many aspects, such as grid voltage deviation, voltage harmonics, voltage fluctuations and flicker, three-phase voltage imbalance, etc., but voltage harmonics are the most important one in power quality. Harmonics are mainly caused by non-linear electrical loads (such as rectifiers, smelting furnaces, electrified locomotives, etc.) in the user. A user-induced harmonic not only affects itself, but also pollutes the grid and affects the grid. Other power users.
However, due to the extensive nature of the power grid and the universality of harmonics, the majority of power users, power production plants and power supply companies hope to understand the harmonics of the power grid anytime and anywhere. Therefore, through the monitoring of the harmonics of the power grid and the analysis of harmonics. It is of great significance to deal with the promotion of harmonics, improve the power quality of the power grid and strengthen the management of the power grid.
However, due to the extensive nature of the power grid and the universality of harmonics, the majority of power users, power production plants and power supply companies hope to understand the harmonics of the power grid anytime and anywhere. Therefore, through the monitoring of the harmonics of the power grid and the analysis of harmonics. It is of great significance to deal with the promotion of harmonics, improve the power quality of the power grid and strengthen the management of the power grid.
two. System characteristics
The main features of the grid harmonic voltage online monitoring system reflect the following aspects:
Comprehensiveness: the high-voltage busbars at all levels of the distribution network (measurement gateways) and the common connection points (including users) of harmonic sources connected to the public grid. The system can realize the harmonic online monitoring of a single substation, and can also realize the harmonic online monitoring of a regional substation.
Practicality: Long-term online monitoring, safe, reliable, easy to operate, and can be automated.
Economical: The instrument installed on site is simple in function, small in size, low in price, and can be used as a conventional instrument for display and harmonic over-limit alarm in normal times, which is convenient for promotion and popularization.
Security: This system adopts wireless communication mode to realize remote control or non-contact control mode of local wireless communication, which effectively ensures the safety of instruments and staff.
Anti-interference: There is strong electromagnetic interference at the site, and various measures are taken to improve the anti-interference ability of the instrument. Structurally, a shielded box structure is adopted. In hardware design, a watchdog circuit, a composite filter circuit and a signal isolation circuit are added; the software design uses digital filtering technology, data verification technology, real-time diagnosis technology, and the like.
Technical: The technical level of the harmonic measuring instrument used in this system is high, which facilitates the recording, analysis, statistics, storage and printing of digital signals transmitted in real-time monitoring at the receiving terminal; harmonic signal acquisition of high-voltage busbars The "High Voltage Harmonic Monitoring System" developed by Xi'an Yiwei Power Technology Development Co., Ltd. was the first in China; the software handled by the terminal of this system has strong functions and large capacity.
three. The purpose and basis of grid harmonic measurement
purpose
The supervision and management of power generation, power supply and electricity use shall ensure that the harmonic limit of the public power grid is within the limits prescribed by the national standards to ensure the normal production and product quality of the various sectors of the national economy and the quality of life of the people.
in accordance with
1. Measurement standard
The Ministry of Electric Power Industry Standard "Interim Provisions on Harmonic Management of Power Grids";
National Standard GB/T14549-93 "Power Quality Harmony of Utility Grid";
National Standard GB17625.7-1998 "Harmonic Current Limits from Low Voltage Electrical and Electronic Equipment";
National Standard GB17626.7-1998 "Guidelines for Measurement and Measurement Instruments for Harmonics and Interharmonics of Power Supply Systems and Connected Equipment".
2. Measuring condition
Select the minimum operating mode that the system may appear when the grid is normally powered, and during the period of harmonic generation during the harmonic source duty cycle.
When a power capacitor bank or harmonic filter is installed near the measurement point, a certain harmonic amplification or resonance may occur, and measurement should be performed in various combinations of operations.
3. Monitoring points
In principle, the harmonic source is selected to be connected to the public connection point of the public power grid, that is, the energy measurement point specified by the power supply protocol, and the harmonic voltage of the point and the harmonic source (the power device that interferes with the power quality) are injected into the harmonic of the utility grid. Current.
4. Test volume
The harmonic order of harmonic voltage and harmonic current is generally measured 2-25 times, the harmonic voltage is expressed by the content rate (), the harmonic current is represented by the effective value (A), and the total harmonic distortion rate is represented by THD(). .
5. Measurement interval and duration
For harmonic sources with fast load changes (such as: electric arc furnace, rolling mill, electric locomotive, etc.), the measurement interval is not more than 2 points, and the number of measurements is not less than 30 times.
For harmonic sources with slow load changes (such as chemical rectifiers, DC transmission converter stations, etc.), the measurement interval and duration are not specified.
6. Processing of measurement data and determination of harmonic level values
The standard stipulates: take the 95 probability value of the measured value in the continuous measurement process of each phase in the measurement period, and take the value of the largest phase in the three phases as the harmonic level value of the test period, and use this as the judgment whether the harmonic is exceeding the standard. in accordance with.
four. Regulation of harmonic measurement methods
1. Harmonic measurement method
The provisions of the International Electrotechnical Commission (IEC) standards classify harmonics into four categories according to their speed and nature:
(1) quasi-steady state (slow change) harmonics;
(2) Fluctuating harmonics;
(3) rapidly changing harmonics;
(4) Interharmonics and their virtual parts.
The harmonics specified in the standard mainly refer to the first three categories, and the following suggestions are proposed for the measurement interval of different fluctuation properties, that is, the measurement period and the method of determining the harmonic value from the measured value:
(1) Very short interval: TVS=3s;
(2) Short interval: TSH = 10 min;
(3) Long interval: TL = 1h;
(4) Day interval: TD=24h;
(5) Week interval: TW=7d.
2. Lowest operating rate of grid power quality
Table 2: Allowable values ​​of harmonic current injected into the common connection point
| Standard Voltage kV | Reference short circuit capacity MVA | ||||||||||||
| 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | |||||
| 0.38 | 10 | ||||||||||||
| 6 | 100 | ||||||||||||
| 10 | 100 | ||||||||||||
| 35 | 250 | ||||||||||||
| 66 | 500 | ||||||||||||
| 110 | 750 |
| Standard Voltage kV | Reference short circuit capacity MVA | ||||||||||||
| 14 | 15 | 16 | 17 | 18 | 19 | 20 | twenty one | twenty two | 25 | ||||
| 0.38 | 10 | 12 | |||||||||||
| 6 | 100 | 6.8 | |||||||||||
| 10 | 100 | 4.1 | |||||||||||
| 35 | 250 | 2.5 | |||||||||||
| 66 | 500 | ||||||||||||
| 110 | 750 | 1.9 |
Table 3: Single harmonic voltage limits for low and medium voltage distribution systems
| Odd harmonic (not 3 multiples) | Odd harmonic (3 times) | Even harmonic | |||
| Harmonic number | Harmonic voltage () | Harmonic number | Harmonic voltage () | Harmonic number | Harmonic voltage () |
| 5 | 6 | 3 | 5 | 2 | 2 |
| 7 | 5 | 9 | 1.5 | 4 | 1 |
| 11 | 3.5 | 15 | 0.5 | 6-24 | 0.5 |
| 13 | 3 | twenty one | 0.5 | ||
| 17 | 2 | ||||
| 19 | 1.5 | ||||
| twenty three | 1.5 | ||||
| 25 | 1.5 |
/> five. Harmonic measuring instrument function and accuracy
1. Harmonic measuring instrument
1.1 Status of harmonic measuring instruments
The harmonic test analyzer is a special instrument for measuring the harmonic severity of the power grid. As far as the harmonic test analyzer is concerned, there are many manufacturers and products at home and abroad, such as the F40/41 handheld power harmonic analysis of the US FLUKE company. Instrument, Japan HIOKI 3195 and 3166 portable power analyzer, UK VOLTECH PM3000/300/100 power analyzer, Sweden UNIPOWER company Unilyzer900F power test analyzer and China Anhui Zhenxing company PS series power quality analyzer. Through comparative analysis, it is not difficult to find that these instruments have the following general characteristics:
(1) Multi-function, high performance, high price;
(2) Laboratory or indoor use, suitable for scientific research, short-term power test, power grid inspection or temporary monitoring;
(3) Dedicated test instruments for independent use, managed and used by special personnel.
However, due to the extensive nature of the power grid and the universality of harmonics, the power generation, power supply, and power utilities all want to understand the harmonics of the power grid anytime and anywhere. Only specialized harmonic test management organizations and scientific and technical personnel can not meet the requirements. High-priced test analyzers cannot be promoted and popularized.
1.2 Monitoring methods and instrument selection
The important PCC (current quality control) adopts continuous monitoring mode and sends the data to the upper-level power quality monitoring center in time. Generally, the instrument is connected to the monitoring point for continuous online detection and the instrument networking of multiple detection points in the area. The harmonic monitoring network is formed; the general PCC adopts the timing monitoring method and sends the data to the upper-level power quality monitoring center. Generally, the portable harmonic analyzer and the fixed-point detecting instrument are combined to detect the multi-point timing tour; Phase PCC, according to the need for detection, that is, random monitoring mode, generally use the pocket harmonic analyzer to meet the detection requirements.
1.3 Measuring instruments used in the system:
(1) HVHe type high voltage harmonic monitor:
The HVHe series high voltage harmonic monitor (hereinafter referred to as high voltage harmonic meter) consists of three parts: signal measurement system, signal transmission system and signal processing system. The high-voltage harmonic monitor is an intelligent harmonic measurement and recording instrument, which realizes real-time monitoring of voltage and voltage harmonics of high-voltage power grids (10, 35, 110, 220, 330, 500kV) and harmonics. The wave is recorded in the time limit and processed.
(2) Harmonic measurement table
The harmonic measurement meter can be divided into a harmonic voltage measurement table and a harmonic current measurement table in terms of functions, and can be divided into a simple type and an advanced type in terms of performance.
LVHv type harmonic voltage measurement meter and LVHa type harmonic current measurement meter are simple type, which is used for 0.38kV, 6(10)kV user substation, filter device, power distribution cabinet, rectifier cabinet, etc. High-order harmonic voltage and current, monitoring and digital display of harmonic voltage and current total distortion rate, and contact output for users to alarm or control the protection loop. In addition to the simple functions, the advanced harmonic measurement meter can also record and store signals. If the signal is transmitted to the terminal, it can also be analyzed and counted.
2. measurement accuracy
The accuracy of harmonic measuring instruments is A and B. On-line monitoring of power grid harmonics is generally possible with Class B. It is mainly used to measure harmonic magnitude, and phase angle accuracy is not specified. The instrument can guarantee normal operation under the condition that the rated voltage is 15∽-15 and the total voltage distortion rate does not exceed 8.
Maximum allowable error of harmonic measuring instruments
| parameter | |||
| Uh≥1Un | 5Un | ||
| Uh<1Un | 0.05Un | ||
| Ih≥3In | 5In | ||
| Ih<3In | 0.05In | ||
| Uh≥3Un | 5Un | ||
| Uh<3Un | 0.15Un | ||
| Ih≥3In | 5In | ||
| Ih<3In | 0.50In |
/>
/> Six. Principle of grid harmonic online monitoring system
The grid harmonic online monitoring system includes a single substation (single user) grid harmonic online monitoring system, and a regional substation (multi-user) grid harmonic online monitoring system, and multiple systems can be combined to achieve remote harmonic online monitoring. The system has convenient scalability so that users do not have to worry about adding monitoring points and system upgrades in the future. Various types of combinations make the system more flexible. The data analysis and processing system is tailored to meet the needs of users.
The grid harmonic online monitoring system includes a single substation (single user) grid harmonic online monitoring system, and a regional substation (multi-user) grid harmonic online monitoring system, and multiple systems can be combined to achieve remote harmonic online monitoring. The system has convenient scalability so that users do not have to worry about adding monitoring points and system upgrades in the future. Various types of combinations make the system more flexible. The data analysis and processing system is tailored to meet the needs of users.
Seven. solution
Technical Support:
The project is planned for the user in advance according to the needs.
Program development:
We set up a project team for each project, equipped with technical and business professionals to create a comprehensive solution for the user.
Project management:
The contract management department creates a project file for the user by a well-trained contract manager to handle all aspects of the project. From the terms of the contract, payment to construction, through the standardized process and strict management at all levels to ensure the effective implementation of the contract.
On-site installation and project commissioning:
Our expertise and experience will complete the system installation and commissioning.
Regular on-site maintenance:
We will go to the site to perform system maintenance on a regular basis to ensure that the system is performing well in daily operation.
Fast on-site repair:
As long as the user needs, we can quickly assign experienced engineers to the user site at any time.
System Upgrade:
With the help of experts, your system upgrade will be more timely and convenient.
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