Harmonics suppression

A phasor diagram (Figure 23.18(c)) illustrates the reduction in the actual loading and enhanced load transfer capacity of the network which can be achieved with the help of harmonic suppressions. For even better utilization, the system may be tuned for higher harmonic disorders also. 

Solving the matrix set (4.293) at various frequencies, one finds that the harmonic suppression effect is most pronounced under the adiabatic condition cox —> 0. Henceforth, we focus on it. In this limit, suppression of a kth harmonic means its complete vanishing the value of p) turns into zero. In... 

In our model with the aid of parameter e we continuously pass from a zero bistable potential (magnetically isotropic particle) to a pair of symmetric wells of infinite depth (highly anisotropic particle). For the magnetic case, as for those of Refs. 21 and 22, a crucial circumstance enabling the harmonic suppression is that an antisymmetric contribution (bias) should be present in the potential. On the other hand, the presence of a symmetric contribution turns out to be an... 

Figure 9.5 XANES scan at the Lm edge of platinum with K2Pt(CN)4 as sample measured on DORIS with a Si (220) double crystal, harmonic suppressing monochromator with 0.7 eV bandwidth. A large jump in the absorbed intensity (white line) is seen very close to the absorption edge. Estimates of/" (in e-) are given at specific points. From Helliwell, Phillips and Sid-dons (unpublished). See also figure 9.8.

A. McLean, K. McLeay and A. Sheldrake, Harmonic suppression filter for offshore interconnected power system. lEE Colleqium, 14 June 1993. 

Suppressing the harmonics (in phase-controiied rectifier units)... 

The inductor on the input side also suppresses the harmonics in the incoming supply, as high Lj will provide a high impedance path to higher harmonics. For suppression of harmonics, where the supply system is already substtintially distorted, tiddilional L-C... 

To reduce the no-load iron losses caused by such harmonics the machine core may be formed of thinner low-loss laminates (see also Section 1.6,2(A-iv)). When the machine has already been manufactured and there is a need to suppress these harmonics, filter circuits may be employed along the lines discussed in Section 23.9. 

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

This can be defined by the most severe external fault at which the schetne will remain inoperative. It should also remain inoperative in healthy conditions. That is it should be immune to the momentary voltage or current transients and normal harmonic contents in the circulating current. Series LC-filter circuits are generally provided with the relay coil to suppress the harmonics and to detect the fault current more precisely. 

Filter circuits suppress harmonics in a power network 23/745... 

In an HT system, either the star is not grounded or it is a delta-connected system and hence the third harmonic is mostly absent, while the content of the. second harmonic nuiy be too small to be of any significance. For this purpose, where harmonic analysis is not possible, or for a new installation where the content of harmonies is not known, it is common practice to use a series reactor of 6% of the reactive value of the capacitors installed. This will suppress most of the harmonics by making the circuit inductive, up to almost the fourth harmonic, as derived subsequently. Where, however, second harmonics are significant, the circuit may be tuned for just below the second harmonic. To arrive at a more accurate choice of filters, it is better to conduct a harmonic analysis of the system through a harmonic analyser and ascertain the actual harmonic quantities and their magnitudes present in the system, and provide a correct series or parallel filter-circuits for each harmonic. 

If there are many large or small consumers that a distribution line is feeding, it is possible that the voltage of the network may be distorted beyond acceptable limits. In this case it is advisable to suppress these harmonics from the system before they damage the loads connected in the system. Preferable locations where the series inductor or the filter-circuits can be installed are ... 

Refer to Table 23.1, which shows the average cumulative effect of all the harmonics that may be present in a power system. If we can provide a series reactor of 6% of the total kVAr of the capacitor banks connected on the system, most of the harmonics present in the. system can be suppressed. With this reactance, the system would be tuned to below the fifth harmonic (at 204 Hz) for a 50 Hz system as derived below. 

When such a reactance is used to suppress the system harmonics it will resonate at a frequency /, such that... 

Similarly, the third harmonic may also be suppressed by grounding the generator or the transformer neutral through a suitable impedance (LC circuit), as discussed in Section 23.5.2(e) and equation (23.6). 

When a capacitor circuit is compensated through a series reaetor. either to suppress the system harmonics or to limit the switching inrush currents (Section 23.11) or both, it will require suitable adjustment in its voltage and capacitive ratings, fhe series reactor will dampen the switching currents but consume an inductively reactive power and offset an equivalent amount of capacitive kVAr. and require compensation. The following example w ill elucidate this. 

From the above it can be inferred that for an accurate analysis of a system, particularly where the loads are of varying nature or have non-linear characteristics it is necessary to conduct a harmonic analysis. The above corrective measures will provide a reasonably stable network, operat-ing at high p.f. with the harmonics greatly suppressed. The improved actual line loading, eliminating the fifth harmonic component, which is compensated,... 

In HT systems, where a series reactor is already being used, to suppress the system harmonics this would also serve to limit the switching inrush currents and no separate reactor would be necessary,... 

A few TCRs to balance the reactive power supply. They may generate harmonics, which must be suppressed to avoid any resonance. T.SCs and TCRs are monitored through a feedback control system,... 

Now filler circuits would also be on to suppress harmonics and absorb capacitive MVAr. . Net maximum reactive support available... 

For syslems prone 10 generating excessive harmonics, and when the size of the reactor, if used, is not sufficient to suppress these, ratings up to 200% are recommended. 

For suppressing harmonics since on an LT system, the capacilor banks are normally small, there is generally no need to provide a reactance to suppress the harmonics. It is, however, advisable to provide this for larger banks above 500 kVAr to contain the overvoltages on account of this, to save the other devices also operating on the same system. For the likely magnitudes of harmonics on an LT system, refer to Table 23.1. 

For larger units they i may be rated lor 69c or so for the suppression of harmonics. Now they i would be able to signifi-j canily add lo ihe impedance of the cireuil and diminish the fault level of the system, which they can withstand. 

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