19b_krueger-onsite measure ct and vt.pdf
TRANSCRIPT
A New Approach for On-Site Calibration of Voltage Transformers
Dr. Michael Krüger, Florian Predl, OMICON Austria
Content
> Measurement Methods • Conventional Measurement Method • Alternative Measurement Method (Using a Model)
> Case Studies • Onsite Measurement on a 66kV Reference VT • Measurement on a 66kV CVT
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Conventional Measurement Method
Source: IEC 61869-3
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Measurement Procedure
• 1. Measurement of short-circuit impedance
• 2. Measurement of secondary winding resistance
• 3. Measurement of secondary short-circuit impedance (only if more than one secondary winding)
• 4. Measurement of initial magnetization curve
• 5. Measurement of turns ratio correction
• 6. Calculation of voltage ratio error and phase displacement based on the equivalent circuit diagram
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1. Measurement of Short-Circuit Impedance Inductive Voltage Transformer
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1. Measurement of Short-Circuit Impedance Capacitive Voltage Transformer
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2. Measurement of Secondary Winding Resistance
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4. Measurement of the Magnetisation Curve
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4. Measurement of the Magnetization curve
Page 10 © OMICRON ↑↓↑↑⇒
⋅⋅=⇒
⋅⋅⋅⋅=
BfBVAfn
VB
AfBnV
C
C
C
or 2
ˆˆ
44,4
π
HC
BR Fl
ux d
ensi
ty B
[T]
Magnetic Force H [A/m]
5. Measurement of Turns Ratio Correction
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5. Measurement of Capacitive Ratio
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1st step: 2nd step:
5. Measurement of Turns Ratio Correction
• Measurement of capacitive ratio in two steps:
• 𝐾𝑡𝑡𝑡𝑡𝑡 = 𝑉𝑝𝑝𝑝𝑝𝑝
𝑉𝑠𝑠𝑠𝑝 𝐾𝑖𝑖𝑖 = 𝑉𝑝𝑝𝑝𝑝𝑝
𝑉𝑠𝑠𝑠𝑝
• Ratio of Ktotal to Kind is equal to capacitive ratio:
• 𝐾𝑐 = 𝐾𝑡𝑡𝑡𝑡𝑡𝐾𝑝𝑖𝑖
= 1 + 𝐶𝑝𝐶𝑝
• The total voltage ratio of a capacitive voltage transformer is equal to the product of capacitive ratio and inductive ratio obtained at higher voltages (3kV):
• 𝐾𝑡𝑡𝑡𝑡𝑡 = 𝐾𝑐 ∗ 𝐾𝑖𝑖𝑖@3𝑘𝑘
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5. Measurement of Turns Ratio Correction
Example for turns ratio correction from a 10kV reference VT (inductive VT)
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-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Volta
ge ra
tio e
rror
in %
Primary voltage in V
Ratio Error (V) [%]
Reference
Ratio Error without turns ratiocorrection correction
Ratio error with turns ratiocorrection
Case Study 66kV Reference VT
Nameplate data Secondary terminal box
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Case Study 66kV Reference VT
Obtained voltage ratio error of class ±0.03% ±1.5min reference VT
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Power Voltage ratio error in % of rated voltage
VA VA [%] cos phi 80% 100% 120%
1,0000 100,0% 1,0000 -0,0064% -0,0038% -0,0019%
0,0000 0,0% 1,0000 -0,0052% -0,0025% -0,0006%
Case Study 66kV reference VT
Obtained phase displacement of class ±0.03% ±1.5min reference VT
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Power Phase displacement table (min)
VA VA [%] cos phi 80% 100% 120%
1,0000 100,0% 1,0000 -2,5727 -2,5655 -2,5576
0,0000 0,0% 1,0000 -2,3296 -2,3225 -2,3146
Case Study 66kV Reference VT
Conclusions:
• Results have proven to be very stable over frequency range of 50Hz to 60Hz and for all successive measurement conducted
• The biggest absolute variance between all successive tests was ±0.001% in regards to the voltage ratio error and ±0.03min in regards to the phase displacement
• Voltage ratio error results were within the requirements of ±0.03%
• Phase displacement results were off the specs by -1min (still acceptible for calibrating class 0.1 metering VTs)
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Case Study Capacitive VT 66kV
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Capacitive Voltage Transformer (CVT)
VAfu [%]
Referencefu [%]
VOTANOphi [min]
Referencephi [min]VOTANO
25 0,08 0,11 -0,50 -0,43100 -0,22 -0,20 1,00 1,41
Conclusions:
• Voltage ratio error results are within ±0.03%
• Phase displacement results were ± 1min
