Harmonics protection

Induction motor fed from a voltage source inverter Eiltering of Power Line Harmonics Protection, Alarms and Indication References... 

Snubber circuii More conventional protection from high dvidi is to provide an R-C circuit across each device, as shown in Figure 6.37. The circuit provides a low impedance path to all the harmonic quantities and draws large charging currents and absorbs the energy released, Q, and in turn damps dvIdi within safe limits across each device. Now Q = C idu/di)... 

Excessive harmonics may also make the protective devices behave erratically or render them inoperative. Filter circuits would suppress the harmonics and eliminate these effects. 

Noie The proleclive devices which ineasure r.m.s. values ot current also detect the hannonic contents and provide automatic protection for the machine against harmonic disorders. But in... 

Such relays are normally instantaneous, highly sensitive and operate at low spill cuiTents. Since they detect the residual current of the system, the current may contain third-harmonic components (Section 23.6) and operate the highly sensitive relay in a healthy condition. To avoid operation of the relay under such conditions, it is a normal practice to supply the relay coil with a tuned filter, i.e. a series L-C circuit to filter out the third-harmonic components. The capacitance of the filter circuit may also tame a steep rising TRV (Section 17.10.3) during a momentary transient condition and protect the relay. 

Referring to the data available from experiments, as shi)wn in Table 23.1, it hits been estimated that a Vp, of I. Hj should be sufficient to account for the harmonic effects. For this dielectric strength is designed a capacitor unit and selected a switching or protective device. 

Based on the system studies carried out and Table 23.1, it has been assessed that in actual operation, effective current through a capacitor circuit may increase up to 1.3 limes its rated cunent, /,., i.e. = 1.3 /, to account for all the harmonic effects (V, - Jf. equation (23.4)). A capacitor unit is thus designed for at least M)9r continuous overload capacity (Section 25.6). Its switching and protective devices are selected along similar lines. 

It is desirable to contain the harmonic effects as far as practicable to protect the capacitors as well as inductive loads connected on the system and the communication network, if running in the vicinity. 

As noted from general experience, except for specific large inductive loads such as of furnace or rectifiers, the fundamental content of the load current is high compared to the individual harmonic contents. In all such cases, it is not necessary to provide a filter-circuit for each harmonic unless the current is required to be as close to a sinusoidal waveform as possible, to cater to certain critical loads or instruments and devices or protective schemes operating in the system, where a small amount of harmonics may lead to malfunctioning of such loads and devices. Otherwise only the p.f. needs be improved to the desired level. Also to eliminate a parallel resonance with the... 

The protection current produced by the usual full-wave rectifier has a 100-Hz alternating component of 48%. There are receivers with selective transmission filters for 100 Hz, which corresponds to the first harmonic of the cathodic protection currents [45]. With such a low-frequency test current, an inductive coupling with neighboring pipelines and cables is avoided, which leads to more exact defect location. 

Differential relaying is the universal bus and transformer protection scheme. The inrush current associated with power transformers rec uires a special differential relay utilizing filters to provide harmonic restraint to differentiate between energizing current and fault current. 

The EU laws follow three principles related to consumer health (1) protection, (2) fraud prevention, and (3) trade barriers. The union tried to harmonize the laws of different countries, particularly in recent years when the enlargement of the European Community became dynamic. Color Directive 94/36/EC contains horizontal provisions that refer to common laws in different countries and vertical directives that apply to specific foods. The EU directives take into account the recommendations of the Scientific Committee for Food (SCF), the Codex AUmen-tarius Commission, and the Joint Food and Agriculture OrganizationAVorld Health Organization (FAOAVHO) Expert Committee on Food Additives (JECFA). 

In order to set up a harmonized framework for the regulation of plant protection products in the EC, Council Directive 91/414/EEC of 15 July 1991 concerning the placing of plant protection products on the market was adopted and implemented in all Member States. Six annexes were established within this Directive, providing the basis for the harmonization of registration procedures and regulatory decisions (Table 1). 

Legislation for pesticide residues, including the setting of MRLs in food commodities, is a shared responsibility between the Commission and the Member States. To date, Community MRLs have been established for about 130 pesticide a.i. For pesticides and commodities where no Community MRL exists, the situation is not harmonized and the Member States may set MRLs at national levels to protect the health of its citizens. 

Analytical methods submitted by applicants are evaluated using harmonized criteria (see Section 2.5). The following presentation provides a brief overview of the validation parameters used in the registration of plant protection products and their a.i. These parameters are as follows ... 

Until 1991, manufacturers seeking authorizations for pesticides had to fulfil country-specific requirements of validation of enforcement methods. The term enforcement method means analytical methods which are developed for post-registration control and monitoring purposes. The harmonization of these requirements was initiated with the European Economic Community (EEC) Council Directive 91/414/EEC and temporarily finalized with the Guidance Document on Residue Analytical Methods SANCO/825/00 rev. 6, dated 20 June 2000 [Santd et Protection des Consommateurs (SANCO)]. The evaluation of validation studies by the competent authority is conducted by comparison of these European Union (EU) requirements with the study results and most often without any practical experience of the method. Some details of this evaluation are discussed below. 

United States Environmental Protection Agency, Harmonization and Regulatory Coordination, US Government Printing Office, Washington, DC. Also available on the World Wide Web http //www.epa.gov/oppfeadMntemational/harmonization.html. 

Those activities are generally conducted during the course of official registration of a plant-protection product. Because, according to Council Directive 91/414/EEC, the registration procedures and evaluation criteria are currently harmonized between the member states of the European Union, the objective of this paper is to contribute to the discussion about a future Union-wide evaluation and assessment scheme for re-entry exposure. 

EPA, U.S. Environmental Protection Agency, Prenatal Developmental Toxicity Study, Health Effects Test Guidelines, OPPTS 870.3700, EPA 712-C-98-207,1998a. http //www. epa.gov/opptsfrs/OPPTS Harmonized/870 Health Effects Test Guidelines/Series/870-6300.pdf... 

Electrostatic axially harmonic orbital trapping, 15 662-663 Electrostatic discharge-protection circuits, for LEDs, 14 863... 

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