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Online Monitoring of Dissipation Factor Dayashankar Dubey (MTech) Suhas P. Solanki, MTech Guide: Prof PC Pandey EE Dept, IIT Bombay. ABSTRACT - PowerPoint PPT Presentation
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Online Monitoring of Dissipation Factor
Dayashankar Dubey (MTech)Suhas P. Solanki, MTech
Guide: Prof PC Pandey
EE Dept, IIT Bombay
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ABSTRACTThe insulation status in HV equipment can be monitored by dissipation factor measurement. Online monitoring of dissipation factor is based on dividing the actual power by apparent power. Sampling rate lower than the power line frequency results in aliased periodic waveforms which retain the original phase relationship, and these waveforms can be processed at a relatively low computational speed. Numerical simulation has been carried out to study the effect of quantization error with different number of bits, for finding the effect of different filters used in processing, effect of harmonics, and variation in power line frequency.
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INTRODUCTIONLossy Capacitor Dissipation factor of lossy dielectric Loss angle = , dissipation factor = tan
Parallel model Series model
1 ωoCpRpC
IR
Iδtan ωoCsRsδtan
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Monitoring of dissipation factor
▪ Insulation deterioration → increase in
▪ Monitoring of or dissipation factor → safe & reliable operation of HV equipment
Online monitoring of dissipation factor
▪ HV equipment need not be removed from service
▪ Insulation deterioration between scheduled checks gets detected
▪ Monitoring under actual load & temperature conditions
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METHODOLOGYSignal Acquisition
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METHODOLOGY(contd..)
toωAt1s cos δ0.5πtoωBt2s cos
δ0.5ABt6s sin 20.5At7s
20.5Bt
8s δ
8s
7s
6st9s sin
For small , cos δ ≈ 1, s9 = sin δ ≈ tan δ
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ERROR ANALYSIS Assumption for theoretical analysis:
Error caused by quantization noise, Harmonics totally eliminated by LPF
RMS error in s9:
σ =2-L√(8γ/3)where L = no. of quantization bits& normalized cutoff frequency γ = fc/fs
For dissipation factor: 5 – 5010-3 & 1% resolution: σ = 50 10-6
L 8 12γ 6.1410-5 1.57 10-2
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IMPLEMENTATION Project objective: Verification of the technique Through,
Numerical Simulation Experimental setups
For two implementations High Sampling rate for fast updates Low sampling rate: low cost instrumentation for low update rate (based on aliasing of periodic waveforms)
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High sampling rate: Numerical simulation fs = 450 sa/s,: 0.005 - 0.05, γ=10-3 (for 8-bit), γ=15.53*10-4
(for 12-bit) (without band pass filter at the input)
IMPLEMENTATION (contd..)
L bits Filter Freq (Hz)
σ
(simulation)σ
(theoretical)8 IIR Butterworth 50 1e-10 to 1e-4 2e-4
IIR Chebychev-I 50 1e-7 to 4e-4 2e-4IIR Chebychev-II 50 1e-6 to 3.3e-4 2e-4
12 IIR Butterworth 50 2e-5 to 7e-5 4.9724e-5IIR Chebychev-I 50 8e-7 to 1e-5 4.9724e-5IIR Chebychev-II 50 7e-5 to 1e-4 4.9724e-5
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High sampling rate: Experimental setupsLow voltage setup (30 Vpp)
I/V converter & res. V-divider Acquisition with 8-bit 2-channel DSO, 5 k record length LPF: 1 k rect. FIR filter For D.F. of 1 - 20 10-3,
Best fit line: slope = 1.044, offset = 1.863 10-4
High voltage setup (600 V) Cap. divider for V & shunt resistor for I sensing Acquisition with 8-bit 2-channel DSO, 50 k record length LPF: 10 k rect. FIR filter For D.F. of 0.05 - 1 10-3
Best fit line: slope = 1.051, offset = 5.7 10-4
IMPLEMENTATION (contd..)
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Low sampling rate
Sampling with fs< fo: aliasing of periodic V and I signals with frequency f = fo- fs, retaining the original phase relationship
Advantages
Low cost data acquisition systemDistributed signal acquisition units can transmit data over a serial link to central unit for processing
IMPLEMENTATION (contd..)
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Low sampling rate: Numerical simulation fs = 45 sa/s, : 0.005 - 0.05, γ=10-4 (for 8-bit), γ=2.48*10-4
(for 12-bit) (without band pass filter at the input)
IMPLEMENTATION (contd..)
L bits
Filter Freq (Hz)
σ
(simulation)σ
(theoretical)8 IIR Butterworth 50 5e-3 to 49e-3 0.6e-4
IIR Chebychev-I 50 1e-4 to 49e-3 6e-5IIR Chebychev-II 50 9e-5 to 1e-4 1e-4
12 IIR Butterworth 50 1e-5 to 4e-5 2e-5IIR Chebychev-I 50 8e-7 to 1e-5 1e-5IIR Chebychev-II 50 8e-7 to 1e-5 1e-5
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Low sampling rate: Signal acquisition card
IMPLEMENTATION (contd..)
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Low sampling rate: Experimental setupIMPLEMENTATION (contd..)
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EFFECT OF FREQUENCY VARIATION High sampling rate: Numerical simulation fs = 450 sa/s,: 0.005 - 0.05, L=12bit, γ=15.53*10-3
(without band pass filter at the input)Filter Freq (Hz)
σ
(theoretical)σ
(simulation)IIR Chebychev-I 48 5e-5 6e-6 to 5e-4
50 5e-5 6e-5 to 1e-452 5e-5 5.8e-5 to 6.1e-5
IIR Chebychev-II 48 5e-5 3e-5 to 5e-550 5e-5 7e-5 to 1e-452 5e-5 5e-4 to 5e-2
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Low sampling rate: Numerical simulation fs = 45 sa/s, : 0.005 - 0.05, γ=10-5,L= 12-bit (without band pass filter at the input)
EFFECT OF FREQUENCY VARIATION (contd..)
Filter Freq (Hz)
σ
(theoretical)σ
(simulation)IIR Chebychev-I 48 1e-5 4e-6 to 9e-4
50 1e-5 9e-5 to 1e-452 1e-5 3e-5 to 5e-5
IIR Chebychev-II 48 5e-5 3e-5 to 8e-550 5e-5 9e-5 to 1e-452 5e-5 2e-5 to 5e-5
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EFFECT OF HARMONICSTHD in power line is around 5%
mt
omω
mAtv φcos
mmt
omω
mBt i δφcos
m mm
2m
0.5B2m
0.5AmB
mAs sinδ
9
Harmonics filtering through
Band pass filter (BPF) (Using IIR Chebychev-I)
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EFFECT OF HARMONICS (contd..)
Low sampling rate: Numerical simulation fs = 45 sa/s, : 0.005 - 0.05, L= 12-bit, γ=10-5, σ = 1e-5 Freq With BPF σ Without BPF σ
48 1e-4 to 6e-5 5e-5 to 6e-550 1e-4 to 9e-5 9e-3 to 9e-5
High sampling rate: Numerical simulation fs = 450 sa/s, : 0.005 - 0.05, L=12bit, γ=15*10-3, σ = 5e-5
Freq With BPF σ Without BPF σ
48 1e-4 to 6e-5 5e-5 to 6e-550 1e-4 to 9e-5 9e-3 to 9e-5
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SUMMARY AND CONCLUSIONS Direct calculation algorithm for dissipation factor m/s verified for 0.005 - 0.05 range with resolution 1% (i.e.510-5) Implementation using high and low sampling rates IIR Chebychev filters for m/s insensitivity to power line drift Band pass filter for attenuating harmonics of power line freq.High sampling rate implementation For detecting incipient faults during tests/charging of HV equipment Instrumentation for m/s with high update rate (~10 s): DSP with two 12-bit simultaneous sampling ADCsLow sampling rate implementation For monitoring of HV equipment under normal aging process Instrumentation for m/s with low update rate (~10 min.): signal acquisition h/w with serial data link to central unit for pro.
