Jameson

Health monitoring of solenoid valve electromagnetic coil insulation under thermal deterioration Jordan Jameson, Dr. Kai Wang, Dr. Carlos Morillo, Dr. Michael Azarian, and Prof. Michael Pecht 2016 Machinery Failure Prevention Technology (MFPT) Conference Dayton, OH

May 26, 2016 calce

Center for Advanced Life Cycle Engineering http://www.calce.umd.edu

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Introduction to Solenoid Valve • A solenoid-operated valve (SOV) is an electromechanical device used to control the flow of gas or liquid by passing an electric current through a coiled wire, thereby altering the plunger position and opening or closing the valve orifice. – Can be utilized to shut off, discharge, dose, allocate, or combine fluids. Two-way normally closed solenoid valve – Between 2% and 4% of solenoid (Ref. http://www.solenoid-valvevalves in a chemical plant are part info.com/) of a safety instrumented function (SIF), and as such, remain unused for long periods of time. § Their failure can result in failure of the SIF, which can result in damage to or catastrophic failure of the system/process § SOVs were shown to fail due to electrical coil turn-to-turn shorts and coil open calce


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Insulation Degradation Process Layer-to-layer

Expanded conductors

Power, environment

Turn-to-turn

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Insulation degradation

Mechanical and thermal stress on insulation

Turn-to-turn short

Break in insulation

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Oxidation, hydrolysis

Degradation + mechanical stress

Research Focus • In situ detection of degraded insulation is not well established – Provide ability to replace coils before insulation has failed (i.e., presence of short), while providing as much useful life as possible – Stone et al. [1] discuss several methods to measure insulation capacitance, insulation resistance, insulation dissipation factor § All methods required physical contact with the insulation – Coil impedance monitoring has been suggested as a possible method [2,3,4] § Not enough experimental evidence, nor any understanding of the physical significance (relationships to mechanical or chemical characteristics of insulation) 1. G. C. Stone, et al., Electrical Insulation for Rotating Machines: Design, Evaluation, Aging, Testing, and Repair. John Wiley & Sons, 2004. 2. F. Perisse, et al., “A new method for AC machine turn insulation diagnostic based on high frequency resonances,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 14, no. 5, pp. 1308–1315, Oct. 2007. 3. P. Werynski, et al., “Proposition of a new method for in-service monitoring of the aging of stator winding insulation in AC motors,” IEEE Transactions on Energy Conversion, vol. 21, no. 3, pp. 673–681, Sep. 2006. 4. K. Younsi, et al., “On-line capacitance and dissipation factor monitoring of AC stator insulation,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 17, no. 5, pp. 1441–1452, Oct. 2010.

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Impedance Monitoring of Electromagnetic Coil Insulation • Adopting a distributed parameter–motivated modeling perspective: 𝑍"#" = 𝑓 𝜔, 𝑹, 𝑳, 𝑮, 𝑪

• Impedance measurements can provide a bulk measurement of these parameters: changes in polymer insulation could be reflected in impedance as insulation degradation will cause changes in conductance (G) and capacitance (C) calce


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Experimental Setup • Aged two generic solenoid valves – DC resistance: 10.3Ω – Rated for 80°C – One tested at 80°C/85%RH; one at 80°C (uncontrolled humidity)

• Coils had different rates of degradation – Insulation failure determined by the formation of a turn-to-turn short – Coil exposed to 80°C/85%RH failed after ~1500 hours, while the coil exposed to 80°C did not fail after testing for ~1600 hours

• The valves were removed periodically and their impedance spectra were measured at room temperature – Measured at 501 distinct frequencies ranging from 20Hz-2MHz, equally spaced on base-10 logarithmic scale – Used Agilent E4980A LCR (inductance-capacitance-resistor) meter calce


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Magnet Wire Insulation Material AWG Size 26.5 Magnet Wire

Best match shows the insulation material to be PET/Polystyrene

Fourier transform infrared spectroscopy of neat insulation calce


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Understanding the Impedance Data • In general, the impedance data from the aging test is given as: 𝒕 = 𝑡. 𝑡/ 𝑍 𝑡. , 𝑓/ 𝑍 𝑡. , 𝑓0 𝒁 = 𝑍 𝑡. , 𝑓6 ⋮ 𝑍 𝑡. , 𝑓8

𝑍 𝑡/ , 𝑓/ 𝑍 𝑡/ , 𝑓0 𝑍 𝑡/ , 𝑓6 ⋮ 𝑍 𝑡/ , 𝑓8

𝑡0 ⋯ 𝑡 23/ 𝑡 2

𝑍 𝑡0 , 𝑓/ 𝑍 𝑡0 , 𝑓0 𝑍 𝑡0 , 𝑓6 ⋮ 𝑍 𝑡0 , 𝑓8

⋯ ⋯ ⋯ ⋱ ⋯

𝑍 𝑡 23/ , 𝑓/ 𝑍 𝑡 23/ , 𝑓0 𝑍 𝑡 23/ , 𝑓6 ⋮ 𝑍 𝑡 23/ , 𝑓8

1 𝑋 = 2𝜋𝑓𝐿 − = 𝑋D + 𝑋E 2𝜋𝑓𝐶

𝑍 𝑡 2 , 𝑓/ 𝑍 𝑡 2, 𝑓0 𝑍 𝑡 2, 𝑓6 ⋮ 𝑍 𝑡 2 , 𝑓8

Resistance

• Reactance is made up of inductive and capacitive components – Positive reactance is inductive; negative is capacitive calce


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= 𝑹 + 𝑗𝑿

Reactance

Impedance Spectra – 80°C/85%RH • The resistance and reactance spectra over the lifetime of the coil are shown Initial resonance: 257.7kHz

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Impedance Spectra – 80°C • The resistance and reactance spectra over the test time of the coil are shown Initial resonance: 257.7kHz

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Spearman Rank Correlation Coefficient • Some frequencies better reflect the aging condition of the coil – One measure of this reflection is the monotonic trends of impedance measurements at certain frequencies over the aging period – In this analysis, time was correlated with impedance data

• The Spearman correlation coefficient, ρ, ranges between –1 and +1, such that when ρ = +1 (–1), each of the variables is a perfect monotone increasing (decreasing) function of the other. – Pearson correlation coefficient for ranked data – For a sample size n, the raw samples, Xi and Yi, are converted to ranks xi and yi, and ρ is computed by: N

𝜌GH

6 0 K =1− 𝑑 M 𝑛 𝑛0 − 1 MO/

where di is the statistical difference between ranks: 𝑑M = 𝑥M − 𝑦M calce


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Spearman Correlation Diagram – Resistance • Each row of the resistance matrix was correlated with the time vector. Values closer to ±1 indicate that the impedance at that frequency is monotonically correlated over the degradation period.

80°C 80°C/85%RH

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High Correlated Resistance – 80°C/85%RH • The time series of the frequencies with high correlation are shown below

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High Correlated Resistance – 80°C • The time series of the frequencies with high correlation are shown below

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Spearman Correlation Diagram – Reactance • Each row of the reactance matrix was correlated with the time vector. Values closer to ±1 indicate that the impedance at that frequency is monotonically correlated over the degradation period.

80°C 80°C/85%RH

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High Correlated Reactance – 80°C/85%RH • The time series of the frequencies with high correlation are shown below

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High Correlated Reactance – 80°C • The time series frequencies of the regions with high correlation are shown below

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Hypothesized Failure Mechanism • It has been hypothesized that the expansion of the conductor places a mechanical stress on the insulation, which fails due to loss of mechanical strength [5,6] – One method to test this hypothesis is by using the fracture toughness of the insulating material. – Fracture toughness is generally considered a function of the ratio of elastic modulus to hardness 𝐸⁄𝐻 – These mechanical properties (elastic modulus and hardness) of the insulation materials were measured using nano indentation

5. S. V. Angadi, et al., “Reliability and life study of hydraulic solenoid valve. Part 1: A multi- physics finite element model,” Engineering Failure Analysis, vol. 16, no. 3, pp. 874–887, Apr. 2009. 6. S. V. Angadi, et al., “Reliability and life study of hydraulic solenoid valve. Part 2: Experimental study,” Engineering Failure Analysis, vol. 16, no. 3, pp. 944–963, Apr. 2009.

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Nano Indentation Theory • Nano indentation is a technique where, using load displacement data and contact mechanics, some mechanical properties of the sample can be computed. stiffness

correction factor

𝑑𝑃 2 𝑆= = 𝛽𝐸 𝐴 𝑑ℎ 𝜋 Z

Projected area of indentation at contact depth 𝐴 = 24.56ℎ0d Poisson’s ratio

1 1 − 𝜈M0 1 − 𝜈]0 = − 𝐸Z 𝐸M 𝐸] hardness calce

𝑃^_` 𝐻= 𝐴

Modulus of elasticity


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Fracture Toughness Measurement • According to Lawn-Evans-Marshall (LEM) model, fracture toughness is proportional to the ratio of modulus of elasticity and hardness [7,8]. 𝑃^_` 𝐸 𝐾d = 𝛼 6/0 𝑐 𝐻

• 𝛼: calibration constant; 𝑐: distance from the center of contact to the end of a corner radial crack; 𝑃^_`: maximum load placed on the sample. • Other analyses have yielded different equations, however, the proportionality of fracture toughness to modulus of elasticity divided by hardness remains in most models. • Took 7-8 indentation measurements on each piece of insulation and used 𝐸 ⁄𝐻 as a proxy for fracture toughness 7. G. Evans and E. A. Charles, “Fracture Toughness Determinations by Indentation,” Journal of the American Ceramic Society, vol. 59, no. 7–8, pp. 371–372, Jul. 1976. 8. B. Lawn and R. Wilshaw, “Indentation fracture: principles and applications,” J Mater Sci, vol. 10, no. 6, pp. 1049– 1081, Jun. 1975.

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Mechanical Properties • The modulus of elasticity, hardness, and ratio of 𝐸 ⁄𝐻 are shown below

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Nano Indentation Discussion • Modulus of elasticity much higher in sample exposed to 80°C/85%RH – Sample aged in temperature alone still higher than neat sample

• Hardness of both aged samples higher than the neat sample – Sample exposed to 80°C/85%RH has a wider variance in hardness

• Present analysis does not support the hypothesis that insulation failure is due to decreased fracture toughness. There may be several shortcomings of this approach that cause it to not fit with expectations. – 𝐸⁄𝐻 as a proxy for fracture toughness measurement using nano indentation is still under investigation at CALCE, in addition to continued investigation into the brittle behavior of polymers in electronic applications. – The nano indentation measurement of mechanical properties may be complicated further due to the insulation material being a polymer. – Unable to measure the mechanical properties of the insulation in situ. calce


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Solenoid Valve Testing Observations • Humidity plays a significant role in the reliability of electromagnetic coils – Coil with same material and same rating failed with 85%RH while the coil without humidity survived (both held at the same temperature)

• The Spearman correlation-frequency diagram can be used to differentiate degradation environments – Differences can be observed by looking at the absolute value (indicating strength of correlation) and sign (indicating direction of migration) of the Spearman correlation coefficient at the various measured frequencies

• Mechanical testing revealed differences in modulus of elasticity between the neat insulation and the samples exposed to high temperature and high humidity

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Comparison with Existing Technology • Few other researchers have attempted to use coil impedance measurements as health indicators [2,10] – Used resonant frequency as the health indicator – Decided to set a threshold for replacement at 95% of initial impedance resonance

• In the cases presented here: – The resonant frequency of the coil subjected to 80°C experienced no shift in resonant frequency – The resonant frequency of the coil subjected to 80°C/85%RH shifted 12.2% higher before returning to the original, then shifting 4.5% lower before a short was formed

• Focusing on specific frequencies leads to greater sensitivity and insight into the degradation process 2. 9.

F. Perisse, et al., “A New Method for AC Machine Turn Insulation Diagnostic Based on High Frequency Resonances,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 14, no. 5, pp. 1308–1315, Oct. 2007. F. Perisse, et al., “Robust diagnostics of stator insulation based on high frequency resonances measurements,” IEEE Transactions on Dielectrics and Electrical Insulation, vol. 16, no. 5, pp. 1496–1502, Oct. 2009.

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Thank you!

Questions? email: [email protected]

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