Dayashankar Dubey (MTech) Online Monitoring of Dissipation Factor Dayashankar Dubey (MTech) Suhas P. Solanki, MTech Guide: Prof PC Pandey EE Dept, IIT Bombay

ABSTRACT The 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.

INTRODUCTION Lossy Capacitor Dissipation factor of lossy dielectric Loss angle = , dissipation factor = tan Parallel model Series model

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

METHODOLOGY Signal Acquisition

METHODOLOGY(contd..) For small , cos δ ≈ 1, s9 = sin δ ≈ tan δ

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 – 5010-3 & 1% resolution: σ = 50 10-6 L 8 12 γ 6.1410-5 1.57 10-2

Project objective: Verification of the technique 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)

IMPLEMENTATION (contd..) 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) L bits Filter Freq (Hz) σ (simulation) (theoretical) 8 IIR Butterworth 50 1e-10 to 1e-4 2e-4 IIR Chebychev-I 1e-7 to 4e-4 IIR Chebychev-II 1e-6 to 3.3e-4 12 2e-5 to 7e-5 4.9724e-5 8e-7 to 1e-5 7e-5 to 1e-4

IMPLEMENTATION (contd..) High sampling rate: Experimental setups Low 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..) 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 system Distributed signal acquisition units can transmit data over a serial link to central unit for processing

IMPLEMENTATION (contd..) 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) L bits Filter Freq (Hz) σ (simulation) (theoretical) 8 IIR Butterworth 50 5e-3 to 49e-3 0.6e-4 IIR Chebychev-I 1e-4 to 49e-3 6e-5 IIR Chebychev-II 9e-5 to 1e-4 1e-4 12 1e-5 to 4e-5 2e-5 8e-7 to 1e-5 1e-5

IMPLEMENTATION (contd..) Low sampling rate: Signal acquisition card

IMPLEMENTATION (contd..) Low sampling rate: Experimental setup

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) (simulation) IIR Chebychev-I 48 5e-5 6e-6 to 5e-4 50 6e-5 to 1e-4 52 5.8e-5 to 6.1e-5 IIR Chebychev-II 3e-5 to 5e-5 7e-5 to 1e-4 5e-4 to 5e-2

EFFECT OF FREQUENCY VARIATION (contd..) 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) Filter Freq (Hz) σ (theoretical) (simulation) IIR Chebychev-I 48 1e-5 4e-6 to 9e-4 50 9e-5 to 1e-4 52 3e-5 to 5e-5 IIR Chebychev-II 5e-5 3e-5 to 8e-5 2e-5 to 5e-5

EFFECT OF HARMONICS THD in power line is around 5% Harmonics filtering through Band pass filter (BPF) (Using IIR Chebychev-I)

EFFECT OF HARMONICS (contd..) 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-5 50 1e-4 to 9e-5 9e-3 to 9e-5 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-5 50 1e-4 to 9e-5 9e-3 to 9e-5

SUMMARY AND CONCLUSIONS Direct calculation algorithm for dissipation factor m/s verified for 0.005 - 0.05 range with resolution 1% (i.e.510-5) 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 ADCs Low 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.