Voltage rating

These ratings can be enhanced by connecting them in series-parallel combinations. In scries to enhance the voltage rating and in parallel to enhance the cuiTcnl rating. Bui the controls may not be so accurate as with a single device. 

Rated voltage Rated frequency Rated insulation level... 

Rotating electrical machines lEC standard voltages, rating and performance A122im2l 325/1996 BSEN 60034-/1995 -... 

Voltage ratings for a.c. electrical systems and equipment above 230 kV Insulation coordination, definitions, principles and rules... 

Electric power systems and equipment - Voltage ratings (60 Hz )... 

If relays, instruments and other auxiliary apparatus, have a voltage other than the main voltage, they should be disconnected from the main circuit, while conducting this test and tested separately, according to their voltage rating as shown in Table 14.3. 

To provide a reference for those working on power projects or at sites, we provide some important data on different types of LT and HT power cables in this appendix. The cables described here are in use for all kinds of power distribution applications. Of these, XLPE cables are also used for power transmission applictiiions. To help a user to select the most appropriate types of cables, we also provide a brief comparative chart of the various types of cables being manufactured. Tables giving the technical particulars of such cables in all voltage ratings have also been provided. 

The choice of any of the cables mentioned in Table A16.1 w ill depend upon the site conditions, fault level and the voltage rating of the system. A brief comparison of all these insulating systems is given in Table A16.2... 

We have reproduced in a few Tables (AI6.3-AI6.15) for cables that are used more com-nionly in all voltage ratings and with aluminium conductors. For other cables and copper conductor cables, refer to the manufacturers of their catalogues. 

As a result of a better insulation and insulating medium of an LT interrupting device, compared to its voltage rating, there are no restrikes of the contact gap after a current zero. The TRV is insufficient to establish an arc. 

Select the nearest voltage rating of a station class surge arrester (see also Section 18.8) from the manufacturer s catalogue, (Table 18.8) as 6 kV which has the following protective levels ... 

System voltage Rated voltage Max. MCOy cont. as in operating ANSI voltage tests (coy) TOV capability for Maximum residual voltage with current wave ... 

In lower voltage ratings, as noted above, the puffer technique is quite prevalent and is adopted by all leading manufacturers. For constructional details and more information on this mechanism, refer to the manufacturers catalogues. Figure 19.18 illustrates a typical pole assembly of a 12 kV, SFft circuit breaker. 

When selecting the voltage of the capacitor units care must be taken that during operation the voltage across the capacitor units does not fluctuate beyond 10%. If this happens the voltage rating of the capacitor units must be chosen so that the variation across the units under unfavourable operating conditions does not exceed 10%. 

For higher system voltages, it is common practice to use more than one lower voltage rating, identical capacitor units in series, to obtain the required voltage. With the use of a number of such series connected units in parallel, one can make any size and voltage capacitor banks. The following are a few more common practices ... 

With adjustment in the voltage rating of the 11 kV capacitor units, the bank may be made suitable for the required system... 

The harmonic content may be measured through harmonic analysers and expressed as a percentage of the fundamental component. The cuiTent and voltage ratings of the reactors will depend upon their application. A series reactor connected permanently in the circuit, for instance, will be rated continuously and for full system voltage, whereas a reactor used in the ground circuit may be short-time rated and rated for the likely maximum ground fault current. 

Nominal voltage Rated current f/J Non-s U gregated phase system Segregated phase system isolated phase system... 

Nominal system voltage Rated max. system voltage One-minute power frequency voltage withstand at a frequency between 45 and 65 Hz for LT and 25 and 100 Hz for HT systems Standard lightning impulse, 1.2/50 fis voltage withstand (phase to ground)... 

For application of isolated phase bus to generator, the following voltage ratings will apply. ... 

For dc input voltages that are more than 100 VDC, a layer of Mylar tape should be placed between primary and the secondary(ies) and between any multiple secondaries. One should not completely trust the insulation breakdown voltage rating of the magnet wire since it could nick during the winding process. 

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