Measuring voltage transformers

X6/1987 Measuring voltage transformers Protective voltage transformers Capacitor voltage transformers. "1156-2/1992. 1156-3/1992 3156-4/1992 BS 7729/1995 BS 7625/1993 ... 

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 is not material in voltage transformers, as neither the voltage measuring instruments nor the protective relays will carry any inrush current during a switching operation or a fault. No short-time rating is thus assigned to such transformers. 

The residual voltage may also be measured by a residual voltage transformer (RVT) (Figure 20.10). Refer to Section 15.4.1 for more details. 

The instmments discussed above (and many of the others which follow) act in response to the system voltage and/or current. In most cases, the values of these two parameters are very high, which presents problems in the design of the insulation and current-carrying capabilities of the instmment. In these instances, the instmment is supplied with a known fraction of the measured quantity using a voltage transformer or a current transformer, as appropriate. 

The DPET s electrodes are in the form of concentric cylindrical plates suspended from the top of the vessel and are connected to a high-voltage transformer such that adjacent plates are given opposite charges. As the oil passes through the electrodes, water droplets are influenced by the field to create a sinusoidal migration between plates of opposite charge. This motion serves two purposes to restrict the upward flow of the water in relation to the oil and to enhance the rate of collision of water droplets, which are distorted to form dipoles under the electric field, and thereby increase the rate of coalescence. Clean oil leaves from the top of the vessel, while water is drained out from the bottom. Instrumentation available on this unit permits pressure and temperature measurement of both the feed and vessel conditions and the treated oil and outlet water flow rates. 

The terminal voltage of the main generator is measured by the use of a voltage transformer connected across two of the stator lines, e.g. LI and L2. The signal is then rectified and smoothed in the automatic voltage regulator (AVR), by a circuit that incurs a small time constant Tr. ... 

The FT technique has been applied in a multitude of different areas. Starting at low frequencies, FT methods have been used for dielectric response spectroscopy of solids (sometimes called time domain reflectometry). A short picosecond voltage pulse is applied to a dielectric and the current response is measured. Fourier transformation of the current gives the dielectric response function, s v), which is typically interpreted as the Debye relaxation of dipoles. 

Taking the Laplace transform gives for the measured voltage... 

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