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Electronic Based High Voltage Measuring Transformers

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Title: Electronic Based High Voltage Measuring Transformers


1
Electronic Based High Voltage Measuring
Transformers
  • Chen-Yu Hsieh /Xiao Nan Ma

2
Introduction
  • For electrical utilities in high-voltage
    networks, an important task is the voltage and
    energy measurement. Usually it is costly to get
    high accuracy transformers (up to 0.1) together
    with high voltages.
  • Without any auxiliary winding or double cores
    transformers, a compensation method is proposed
    to reduces the primary and secondary
    voltage-drops separately, the experimental result
    shows a reduction on the errors of a commercial
    voltage transformer.

3
Overview
  • The circuit consisting of 2 stages of
    compensating devices (primary secondary).
  • The main error source is the voltage drop in
    the series impedances of primary and secondary
    windings.

4
Primary side
  • At first, we look at the primary side and
    simulate the circuit to see that it actually
    compensate the voltage drop across the primary
    resistance and inductance.
  • The primary compensation device consists of
    1x high-pass filter 1x inverting amplifier.

5
Equivalent circuit (block compensate1)
  • The two OpAmps and the associated resistors is to
    compensate Rp, the capasitor C1 is to compensate
    Lp. The total series impedance now becomes zero
    and the error due to the voltage drop is
    cancelled.
  • V1-V2 ( -R1R3 /R2 j 1/?C)
  • -Rp -?L

6
Schematics (Primary side without compensation)
7
Schematics (Primary side with compensation)
  • The above 2 slides shows the voltage of the
    circuit with and without compensating device. And
    we see that the circuit with the compensating
    device actually compensates the voltages drop
    across the impedances, therefore its equivalent
    to almost no voltage lost in the primary
    impedance.

8
Primary side
  • So now we carry on to the secondary.

9
Secondary side
  • On the secondary side of the VT
  • Vm
  • Vi i(Rs- R4R6/R5)
  • di/dt (Ls-R4R6C2)
  • To get null series impedances, we design the
    circuit according to the ratio R5/R4 R6/Rs
  • and C2Ls/R4R6

10
Schematics (Secondary side without compensation)
11
Schematics (Secondary side with compensation)
  • From left, we can see that the voltage across the
    VT nearly equal to voltage across the load,
    therefore we know that the compensating is
    returning the voltage loss at the series
    impedances

12
Summary
  • Concluding from the previous slides, shows that
    the voltage drop happens severely without the
    compensating device. Therefore we construct a
    table with different values of source voltage
    range 12kv36kv to compare the voltage drop with
    and without the compensating device

13
Conclusion (Phase error)
Conditions Conditions Without Compensation With Compensation
Voltage (KV) Load (VA) Phase Error (mrad) Phase Error (mrad)
12 0 -64.425 13.7413
24 0 -51.324 3.93341
36 0 -45.321 -4.51435
36 15 -31.312 -8.23141
  • Varying the input voltage between 40 and 120 of
    the nominal voltage ,the ratio decreases from
    more than 1200 (µV/v) to less than -12 (µV/v),
    the phase displacement is reduced under -8(mrad)

14
Conclusion (Ratio error)
Conditions Conditions Without Compensation With Compensation
Voltage (KV) Load (VA) Ratio Error (µV/v) Ratio Error (µV/v)
12 0 1500 -12
24 0 1200 -1
36 0 900 10
36 15 -240 6
  • Errors in VT consist of the error under open
    circuit conditions when Z_load is infinite, and
    errors due to voltage drops as a result of the
    load current following through both windings.
  • N ratioxV(sec)-V(prime)/V(prime)

15
Application for the future device!
  • The proposed method can be applied to improve
    measurement quality in a high-voltage network,
    instead of replacing it by a large and costly
    high accuracy transformer.
  • Since the external electronic devices simulate
    negative impedances of the transformer, it can
    also be applied to in-service transformers.

16
REFERENCE
  • 1 G. Camilli, New developments in
    potential-transformer design, EE
  • Trans., vol. 62, pp. 483487, July 1943.
  • 2 T. A. Deacon and J. J. Hill, Two-stage
    inductive voltage dividers, Proc.
  • Inst. Elect. Eng., vol. 115, no. 6, pp. 888892,
    June 1968.
  • 3 D. Slomovitz, Electronic compensation of
    voltage transformer, IEEE
  • Trans. Instrum. Meas., vol. 37, pp. 652654, Dec.
    1988.
  • 4 , Electronic compensation of inductive
    voltage dividers and standard
  • voltage transformers, IEEE Trans. Instrum.
    Meas., vol. 47, pp.
  • 5 ,http//ieeexplore.ieee.org/Xplore/login.jsp?u
    rl/iel5/6870/18483/00851061.pdf
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