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    Chapiter2 1

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    hassen miber
    This document discusses potential dividers and Rogowski coils used for measuring high voltages and currents. It addresses: 1) Potential dividers at voltages over 100kV must be treated as distributed networks rather than lumped resistors due to their large size. Stray capacitances can distort measurements but guard rings can reduce this. 2) Rogowski coils induce voltages proportional to the rate of change of the measured current. Properly designed coils and integrating circuits can accurately measure impulse currents up to 100MHz, such as those needed in exercises 2-4. 3) Exercises 2-4 provide examples of calculating component values for Rogowski coils and shunts to measure specific impulse currents within given measurement parameters.

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    Chapiter2 1

    Uploaded by

    hassen miber
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    This document discusses potential dividers and Rogowski coils used for measuring high voltages and currents. It addresses: 1) Potential dividers at voltages over 100kV must be treated as distributed networks rather than lumped resistors due to their large size. Stray capacitances can distort measurements but guard rings can reduce this. 2) Rogowski coils induce voltages proportional to the rate of change of the measured current. Properly designed coils and integrating circuits can accurately measure impulse currents up to 100MHz, such as those needed in exercises 2-4. 3) Exercises 2-4 provide examples of calculating component values for Rogowski coils and shunts to measure specific impulse currents within given measurement parameters.

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    This document discusses potential dividers and Rogowski coils used for measuring high voltages and currents. It addresses: 1) Potential dividers at voltages over 100kV must be treated as distributed networks rather than lumped resistors due to their large size. Stray capacitances can distort measurements but guard rings can reduce this. 2) Rogowski coils induce voltages proportional to the rate of change of the measured current. Properly designed coils and integrating circuits can accurately measure impulse currents up to 100MHz, such as those needed in exercises 2-4. 3) Exercises 2-4 provide examples of calculating component values for Rogowski coils and shunts to measure specific impulse currents within given measurement parameters.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    3 views10 pages

    Chapiter2 1

    Uploaded by

    hassen miber
    This document discusses potential dividers and Rogowski coils used for measuring high voltages and currents. It addresses: 1) Potential dividers at voltages over 100kV must be treated as distributed networks rather than lumped resistors due to their large size. Stray capacitances can distort measurements but guard rings can reduce this. 2) Rogowski coils induce voltages proportional to the rate of change of the measured current. Properly designed coils and integrating circuits can accurately measure impulse currents up to 100MHz, such as those needed in exercises 2-4. 3) Exercises 2-4 provide examples of calculating component values for Rogowski coils and shunts to measure specific impulse currents within given measurement parameters.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 10

    Chapter 2.

    2: Measurement of High voltage


    and Current
    IV- Potential Dividers Used for High Voltage Impulse
    Measurements

    In a resistance potential divider, R1 and R2 are


    considered as resistors of small dimensions in the
    previous section. For voltages above 100 kV, R1 is no
    longer small in dimension and is usually made of a
    number of sections. Hence the divider is no longer a
    small resistor of lumped parameters, but has to be
    considered as an equivalent distributed network with
    its terminal to ground capacitances and
    intersectional series capacitances as shown in Fig.
    7.26. The total series resistance R1 is made of n
    resistors of value R'1 and R = nR'1. Cg is the terminal
    to ground capacitance of each of the
    resistor elements R'1, and Cs is the capacitance
    between the terminals of each section. The
    inductance of each element (L'1) is not shown in the
    figure as it is usually small compared to the other
    elements (i.e. R'1, Cs and Cg). This type of divider
    produces a non-linear voltage distribution along its
    length and also acts like an R-C filter for applied
    voltages. The output of such a divider for various
    values of Cg/Cs ratio is shown in Fig. 7.27 for a step
    input. By arranging guard rings at various elemental
    points, the equivalent circuit can be modified as
    shown in Fig. 7.28, where Ch, represents the stray
    capacitance introduced between the high voltage lead
    and the guard elements. This reduces the distortion
    introduced by the original divider.
    Exercise 1:

    The H. V. arm of R -C, divider has 15 numbers of 120


    ohm resistors with a 20 pF capacitor to ground from
    each of the junction points. The L.V. arm resistance
    is 5 ohms. Determine the capacitance needed in the
    L.V. arm for correct compensation.
    V- Measurement of High Impulse Currents Using Magnetic
    Potentiometers (Rogowskl Colls) and Magnetic Links

    If a coil is placed surrounding a current carrying


    conductor, the voltage signal induced in the coil is
    vi(t)=MdI(t)/dt where M is the mutual inductance
    between the conductor and the coil, and I(t) is the
    current flowing in the conductor. Usually, the coil is
    wound on a nonmagnetic former of toroidal shape and
    is coaxially placed surrounding the current carrying
    conductor. The number of turns on the coil is chosen
    to be large, to get enough signal induced. The coil is
    wound cross-wise to reduce the leakage inductance.
    Usually an integrating circuit (see Fig. 7.52) is
    employed to get the output signal voltage proportional
    to the current to be measured. The output voltage is
    given by

    Rogowski coils with electronic or active integrator


    circuits have large bandwidths (about 100 MHz). At
    frequencies greater than 100 MHz the response is
    affected by the skin effect, the capacitance distributed
    per unit length along the coil, and due to the
    electromagnetic interferences. However, miniature
    probes having nanosecond response time are made
    using very few turns of copper strips for UHF
    measurements.

    Exercise 2
    A Rogowski coil is to be designed to measure impulse
    currents of10 kA having a rate of change of current of
    1011 A/s. The current is read by a VTVM as a potential
    drop across the integrating circuit connected to the
    secondary. Estimate the values of mutual inductance,
    resistance, and capacitance to be connected, if the
    meter reading is to be 10 V for full-scale deflection.
    Exercise 3:
    If the coil in Exercise 2 is to be used for measuring
    impulse current of 8/20 μs wave and of the same
    peak current, what should be the R-C integrating
    circuit
    Exercise 4:

    A coaxial shunt is to be designed to measure an


    impulse current of 5O kA. If the bandwidth of the
    shunt is to be at least 10 MHz and if the voltage drop
    across the shunt should not exceed 5O V, find the
    ohmic value of the shunt and its dimensions.

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