IIT Bombay AIM , IIT Bombay, 27 June ’03 1 Online Monitoring of Dissipation Factor Dayashankar Dubey (MTech) Suhas P. Solanki, MTech Guide: Prof PC Pandey EE Dept, IIT Bombay

IIT Bombay AIM , IIT Bombay, 27 June ’03 2 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.

IIT Bombay AIM , IIT Bombay, 27 June ’03 3 INTRODUCTION  Lossy Capacitor Dissipation factor of lossy dielectric Loss angle = , dissipation factor = tan  Parallel model Series model

IIT Bombay AIM , IIT Bombay, 27 June ’03 4  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

IIT Bombay AIM , IIT Bombay, 27 June ’03 5 METHODOLOGY  Signal Acquisition

IIT Bombay AIM , IIT Bombay, 27 June ’03 6 METHODOLOGY( contd.. ) For small , cos δ ≈ 1, s9 = sin δ ≈ tan δ

IIT Bombay AIM , IIT Bombay, 27 June ’03 7 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  & 1% resolution: σ = 50  L812 γ 6.14   10 -2

IIT Bombay AIM , IIT Bombay, 27 June ’03 8 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)

IIT Bombay AIM , IIT Bombay, 27 June ’03 9  High sampling rate: Numerical simulation f s = 450 sa/s,  : , γ=10 -3 (for 8-bit), γ=15.53*10 -4 (for 12-bit) (without band pass filter at the input) IMPLEMENTATION (contd..) L bitsFilterFreq (Hz) σ (simulation) σ (theoretical) 8IIR Butterworth501e-10 to 1e-42e-4 IIR Chebychev-I501e-7 to 4e-42e-4 IIR Chebychev-II501e-6 to 3.3e-42e-4 12IIR Butterworth502e-5 to 7e e-5 IIR Chebychev-I508e-7 to 1e e-5 IIR Chebychev-II507e-5 to 1e e-5

IIT Bombay AIM , IIT Bombay, 27 June ’03 10  High sampling rate: Experimental setups Low voltage setup (30 V pp )  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  10 -3, Best fit line: slope = 1.044, offset =  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  Best fit line: slope = 1.051, offset = 5.7  IMPLEMENTATION (contd..)

IIT Bombay AIM , IIT Bombay, 27 June ’03 11  Low sampling rate  Sampling with f s < f o : aliasing of periodic V and I signals with frequency f = f o - f s, 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..)

IIT Bombay AIM , IIT Bombay, 27 June ’03 12  Low sampling rate: Numerical simulation f s = 45 sa/s,  : , 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 FilterFreq (Hz) σ (simulation) σ (theoretical) 8IIR Butterworth505e-3 to 49e-30.6e-4 IIR Chebychev-I501e-4 to 49e-36e-5 IIR Chebychev-II509e-5 to 1e-41e-4 12IIR Butterworth501e-5 to 4e-52e-5 IIR Chebychev-I508e-7 to 1e-51e-5 IIR Chebychev-II508e-7 to 1e-51e-5

IIT Bombay AIM , IIT Bombay, 27 June ’03 13  Low sampling rate: Signal acquisition card IMPLEMENTATION (contd..)

IIT Bombay AIM , IIT Bombay, 27 June ’03 14  Low sampling rate: Experimental setup IMPLEMENTATION (contd..)

IIT Bombay AIM , IIT Bombay, 27 June ’03 15 EFFECT OF FREQUENCY VARIATION  High sampling rate: Numerical simulation f s = 450 sa/s,  : , L=12bit, γ=15.53*10 -3 (without band pass filter at the input) FilterFreq (Hz) σ (theoretical) σ (simulation) IIR Chebychev-I485e-56e-6 to 5e-4 505e-56e-5 to 1e-4 525e-55.8e-5 to 6.1e-5 IIR Chebychev-II485e-53e-5 to 5e-5 505e-57e-5 to 1e-4 525e-55e-4 to 5e-2

IIT Bombay AIM , IIT Bombay, 27 June ’03 16  Low sampling rate: Numerical simulation f s = 45 sa/s,  : , γ=10 -5,L= 12-bit (without band pass filter at the input) EFFECT OF FREQUENCY VARIATION (contd..) FilterFreq (Hz) σ (theoretical) σ (simulation) IIR Chebychev-I481e-54e-6 to 9e-4 501e-59e-5 to 1e-4 521e-53e-5 to 5e-5 IIR Chebychev-II485e-53e-5 to 8e-5 505e-59e-5 to 1e-4 525e-52e-5 to 5e-5

IIT Bombay AIM , IIT Bombay, 27 June ’03 17 EFFECT OF HARMONICS  THD in power line is around 5%  Harmonics filtering through Band pass filter (BPF) (Using IIR Chebychev-I)

IIT Bombay AIM , IIT Bombay, 27 June ’03 18 EFFECT OF HARMONICS (contd..)  Low sampling rate: Numerical simulation f s = 45 sa/s,  : , L= 12-bit, γ=10 -5, σ = 1e-5 FreqWith BPF σWithout BPF σ 481e-4 to 6e-55e-5 to 6e-5 501e-4 to 9e-59e-3 to 9e-5  High sampling rate: Numerical simulation f s = 450 sa/s,  : , L=12bit, γ=15*10 -3, σ = 5e-5 FreqWith BPF σWithout BPF σ 481e-4 to 6e-55e-5 to 6e-5 501e-4 to 9e-59e-3 to 9e-5

IIT Bombay AIM , IIT Bombay, 27 June ’03 19 SUMMARY AND CONCLUSIONS  Direct calculation algorithm for dissipation factor m/s verified for range with resolution 1% (i.e.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.