Evaluation of modern measuring devices power quality indicators

The measurement and analysis of the quality of electrical energy in electric grids. The characteristics of the main tools for measuring power quality, the requirements on the measurement of power quality. Instruments to measure the indicators of quality.

Рубрика Физика и энергетика
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Язык английский
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Omsk State Technical University

EVALUATION OF MODERN MEASURING DEVICES POWER QUALITY INDICATORS

Kalimullin A.T., Leskov I.A., Temnikov E.A.

Abstract

quality electrical energy measurement

The article deals with topical issues such as the measurement and analysis of the quality of electrical energy in electric grids, for power quality has a significant impact on the reliability of the electrical equipment and the technical and economic indicators. Power quality, going beyond the limits, in combination with other factors result in economic losses. The article also evaluated the characteristics of the main tools for measuring power quality, the requirements on the measurement of power quality. Comparative characteristics of domestic and foreign instruments to measure the indicators of quality of electric energy.

Keywords: power quality indicators, measuring power quality, power quality.

Аннотация

ОЦЕНКА СОВРЕМЕННЫХ СРЕДСТВ ИЗМЕРЕНИЯ ПОКАЗАТЕЛЕЙ КАЧЕСТВА ЭЛЕКТРОЭНЕРГИИ

В статье рассмотрены такие актуальные вопросы, как измерение и анализ качества электрической энергии в электрических сетях, ведь качество электроэнергии оказывает значительное влияние на надежность работы электрооборудования и технико-экономические показатели. Показатели качества электроэнергии, выходя за допустимые пределы, в совокупности с другими факторами приводят к экономическим потерям. Также в статье произведена оценка характеристик основных средств измерения показателей качества электроэнергии, требования, предъявляемые Стандартом по измерениям качества электроэнергии. Дана сравнительная характеристика отечественных и зарубежных приборов по измерению показателей качества электрической энергии.

Ключевые слова: показатели качества электроэнергии, средства измерения показателей качества электроэнергии, качество электроэнергии.

Main text

Power quality - this is a question the economic and at the same time, the issue of cultural production and consumption - quality of life of society. Electrical energy today is increasingly becoming a commodity, and where the goods there and the quality of goods.

During the operation of electrical networks there are changes of parameters such as the rated frequency, rated sinusoidal voltage and current on the requirements, which are characterized by readings of power quality (PQP). The deterioration of the PQP not only leads to failure of the equipment, its accelerated wear, but also to the loss of information, failures of processes among consumers, the damage from which can sometimes reach up to one million rubles at a time. Poor quality also leads to a direct increase in electricity losses during transmission and consumption. Therefore, the question of adequate QP is now being given more attention [3]. The result was the emergence of new types of instruments for measuring the PQP and executed on the basis of modern microprocessor, as well as development of various PQP monitoring systems.

To ensure the perfect quality of electric energy in real operating conditions, when increasing the share of electricity consumers, which are widely used power semiconductor devices, there is a constant input of new capacities, introduction of energy systems (SES) of alternative energy sources (wind, solar power plants, power plants in the thermal waters), etc., is virtually impossible. Since this will lead to high material costs on continuous monitoring, carry out the necessary measures, the purchase of modern PQP measurements [6]. In this regard, the state standards set permissible levels of some deterioration of the PQP, which largely does not affect the operation of electrical receivers of consumers.

Nomenclature of parameters measured in Russia, describing the PQ, sets GOST 32144-2013. It includes proper PQP (normalized and not normalized) and auxiliary parameters of electric energy.

The standard establishes the following indicators of quality of electric power [2]:

· steady-state voltage deviation дUу;

· alteration voltage range дUt;

· flicker dose Pt;

· THD voltage KU;

· ratio of the n-th harmonic component of the voltage KU(n);

· ratio of voltage unbalance on the reverse sequence K2U;

· voltage unbalance factor for residual K0U;

· frequency deviation Дf;

· the duration of a voltage dip tп;

· impulse voltage Uимп;

· relation of temporary overvoltage Kпер

In determining the values used by the PQP following auxiliary power options:

· repetition rate of voltage change ;

· interval between voltage changes ;

· voltage dip depth ;

· relative frequency of occurrence of voltage dips ;

· pulse duration at the level of 0.5 of its amplitude ;

· duration of the temporary overvoltage.

To evaluate compliance with PQP standards specified GOST set minimum billing period is 24 hours, and the recommended period - 7 days. The use of existing means of measurement (MD) allows PQP to solve current problems in the monitoring of the PQP.

MD PQP requirements [7]:

- The ability to use MD in industrial (hard) conditions;

- The ability to control the three-phase (phase-phase) voltage at the same time;

- Additional opportunity to control the phase currents;

- The presence of the recording properties;

- In some cases - the requirements of the relevant Standards.

Values PQ indicators of measurement error should be in the range bounded by the maximum permissible values (Table. 1), the establishment of standards [2].

Table 1

Measurement error for MD PQP

Power quality, the unit of measurement

Standards PQ (standard items)

The limits of the permissible measurement error PQ index

normally admissible

limits

absolute

relative, %

steady-state voltage deviation dUy,%

±5

(5.2.1)

±10

(5.2.1)

±0,5

--

alteration voltage range dUt,%

--

Curves 1 and 2 in Figure 1 (5.3.1, 5.3.2)

--

±8

Flicker, rel. units:

short Pst

long PLt

--

--

1,38; 1,0

1,0; 0,74

(5.3.3, 5.3.4)

--

--

± 5

± 5

THD voltage КU %

According to table 1 (5.4.1)

According to table 1 (5.4.1)

--

±10

ratio of the n-th harmonic component of the voltage КU(п), %

According to table 2 (5.4.2)

According to table 2

(5.4.2)

± 0,05 at

КU(п) < 1,0

± 5 at

КU(п) і1,0

ratio of voltage unbalance on the reverse sequence K2U, %

2 (5.5.1)

4 (5.5.1)

±0,3

--

voltage unbalance factor for residual K0U, %

2 (5.5.2)

4 (5.5.2)

±0,5

--

frequency deviation Df, Hz

±0,2(5.6.1)

±0,4(5.6.1)

±0,03

--

the duration of a voltage dip Dtп, s

--

30 (5.7.1)

± 0,01

--

impulse voltage Uимп, kilovolt

--

--

--

±10

ratio of temporary overvoltage Kпер U, relative units

--

--

--

±10

Generalized measurement purposes, we distinguish between three [7]:

- express - examination of the electrical network (audit);

- continuous monitoring of the PQP (monitoring);

- survey electrical network in order to identify the causes of decline in the quality of power supply and make necessary recommendations for its improvement.

Audit requires a relatively simple and inexpensive MD PQP. This portable MD. Audit task - identifying anomalies stable electrical networks, those such which occur at relatively short observation time (minutes to several hours).

Monitoring more difficult and requires, in general, more expensive hardware and software solutions. This spatially distributed, as a rule, measurement and information networks with centralized management and monitoring (measuring-computing complexes).

The specialized firms having necessary licenses for carrying out such works conduct examination. They require much more sophisticated, precision, “thin” and feature-rich, much more expensive tools.

In all developed countries, many companies produce electricity grids MD parameters that we can refer to the PQP. These include specialized multimeters, spectrum analyzers, loggers, measuring systems, and more. Table. 2 shows the characteristics of both domestic and foreign MD PQP.

Table 2

Measured values MD PQP in accordance with GOST 32144-2013

Obviously, all the variety of devices has the right to be represented in our market. A number of foreign instruments already has Russian certificates. Domestic appliances are usually intellectually and functionally more complex devices. They immediately developed to meet the Standard. However, their price for our customers is that large.

Consider the generalized structural MD PQP scheme (Figure 1).

Fig. 1 Generalized structure MD PQP

A - device adaptation of the input signals to a digital environment; B - the device is the digital processing of the primary information (computer); O - on the display device; P - device registration information; T - device information broadcast; M - modification of the device operating mode; У - control device; П - power device.

The main purpose of the MD PQP - separated from the original signals PQP itself. The information obtained or used on-site by the operator O, or passed to the upper level system through T or P is registered for the purpose of deferred consumption. All these functions can in some cases can be performed simultaneously [7].

Structural products scheme supplemented “parasitic” element - the “environment”. The most critical part of any MD and MD PQP, in particular, - the measuring channel. It is usually referred to as a group of structural elements, i.e. measurement. In this example, A+B. Where A performs an initial conversion of the input analog signal to a digital - provides the primary input signal into a digital environment. Element B processes the digitized values ??in order to extract information - indicators of quality of electric energy [7].

Measuring channel determines the metrological properties of the MD. In this case, the element A its “saturates” the structure is mainly an instrumental component of the error, and the element B - methodical.

Naturally, figure 1 at different stages of the design will become more complex.

Catering for MD PQP requires separate serious consideration. The underestimation of the problem can lead to unreliable operation of the product or a substantial reduction in application properties. It should be borne in mind when designing schemes of power that modern power converters are a source of interference for internal MD PQP schemes (especially analog), and for the environment.

The technical side of the problem of expanding the range of MD PQP, as well as a systematic approach to improving the MD situation in the consumer market are given in [7].

International Electrotechnical Commission, in 2008, two instruments operating in the field of PQ were presented [4, 5]:

1. IEC 6100-4-30:2008. Electromagnetic compatibility. Methods of testing and measurement. PQ measurement methods.

2. IEC 6100-4-7:2002. Amendment 1 (2008). Electromagnetic compatibility. Methods of testing and measurement. General guidance on the measurement of harmonics and interharmonics and instrumentation for power supply systems and equipment connected to it.

Currently issued on the basis of standards of GOST Р 51317.4.30-2008 and GOST Р 51317.4.7-2008. Under these standards, two classes characterize the measurement process of the PQP:

- class A (advanced);

- class S (observation).

The standard provides PQP measurement ranges separately for MD PQP Class A and Class S. A comparison on a number of PQP reflected in [1]. Based on the above it can be concluded that the Russian market MD PQP although saturated, but slow and expensive devices mainly. The main problems: high price, low level of technical support, and poor theoretical training of technical personnel. An additional difficulty - the virtual absence of literature on the issue is not the quality of electric power, nomenclature and the practice of the MD PQP. MD PQP market is not yet formed and waiting for affordable, reliable and convenient products.

References

1. Safonov, D. G. Analysis of the main characteristics of the modern means of measuring the power quality // D. G. Safonov, C. H. Turakhanov. Omsk Scientific Bulletin №1 (27) 2010. С. 144.

2. GOST 32144-2013. Electric Energy. Compatibility of technical equipment. Power quality limits in public electrical systems. M.: Standartinform, 2014. С. 33.

3. Investments. [Electronic resource] - Access mode - URL: http://www.alfar.ru/smart/3/507/ (date of the application: 25.04.2016).

4. IEC 6100-4-30:2008. Electromagnetic compatibility (EMC). Part 4-30. Methods of testing and measurement. Quality measurement methods of electrical energy, 2008. С. 40.

5. IEC 6100-4-7:2002. Electromagnetic compatibility (EMC). Part 4-7. Methods of testing and measurement. General guidance on the measurement of harmonics and interharmonics and instrumentation for power supply systems and equipment connected to them, 2008. С. 42.

6. Povoroznyuk, N. I. Power Quality Monitoring System // N. I. Povoroznyuk, D. P. Bilyuba. Vestnik NTU “KPI”. Special Issue: Information and simulation. Kharkov: NTU “KPI” - 2011. № 36. С. 135 - 139.

7. Makarychev, P. C. The measuring power quality. The principles and design issues // P. C. Makarychev. Moscow Power Engineering Institute (Technical University), Russia, Institute of energy efficiency problems (IPEEF) STRC ETT.

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