Voltage class

Voltage, nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (as 120/240, 480Y/277, 600, etc.). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment. 

Simulation of disturbances (a) the voltage class of a generator station or a substation in which the disturbance was found (b) the cause of the disturbance (i.e., LS or SS) and (c) the impact of the disturbance, such as the breakdown of a diode or the freezing of control equipment... 

All the disturbances are in the voltage class of 154 kV and lower. The reason for this is estimated due to more coimtermeasures to reduce the surges in a higher voltage class. 

Generally, trees occur under the relatively high voltages associated with power cables (11—13). Trees can be classified in three classes electrical, water, and electrochemical. 

For lovv -voltage starters below 600 volts, the same starters are used for any voltage, since there is only one insulation class. 

Irrespective of the class of an insulation system and its quality, it will have some leakage current through its dielectric circuit on application of a high voltage. For all practical piiiposes. therefore, we can consider an insulation system as an imperfect capacitor. 

Measuring voltage transformers Standard accuracy class may be one of 0.1, 0.2, 0.5, I or 3. The recommended class of accuracy will depend upon the type of metering and generally as noted in Table 15.3. 

This class may be selected for protective devices that operate on the basis of phase relationship between the voltage and the current phasors, such as in a directional overcurreni protection, reverse power or directional distance protection. 

These are protection CTs lor special applications such as biased differential protection, restricted ground fault protection and distance protection schemes, where it is not possible to easily identify the elass of accuracy, the accuracy limit factor and the rated burden of the CTs and where a full primary fault current is required to be transformed to the secondary without saturation, to accurately monitor the level of fault and/or unbalance. The type of application tind the relay being used determine the knee point voltage. The knee point voltage and the excitation current of the CTs now form the basic design parameters for such CTs. They are classified as class PS CTs and can be identified by the following characteristics ... 

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 ... 

For this voltage, we have selected a Class 4 arrester, which has the nearest next higher rating as in Table 18.11 as... 

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