High Field Characterization

Extensive facilities are available for characterizing the electrical properties of insulating materials used in electrical apparatus including distribution and transmission networks, rotating machinery component, electrostatic/electro-responsive devices, capacitive energy storages, etc. These facilities include:


Broadband Dielectric Spectroscope
Combining the time-domain technique with frequency-domain spectroscope comprises a Broadband Dielectric Spectroscope System for measuring various polarization/relaxation processes, conductivity and electrochemical impedance over a wide range of frequency and temperature (10-4 Hz – 1 GHz, -70oC-300oC). The Time Domain Technique (10-4 Hz to 10 kHz) provides one of the best ways of measuring the conductivity of polymeric samples, with a lower limit in the range of 10-15 to 10-16 S/m over the above temperature range, while frequency domain impedance analyzers extend the measurement frequency range to 1GHz (Hioki 3532-50/Agilent 4285A/HP4191).


Ferroelectric Tester 
A modified Sawyer-Tower ferroelectric tester is available for the measurement of the P-E loop of a ferroelectric device, i.e., the charge or polarization developed against the electric field at a given frequency. The setup is designed for polarization study under high electric field (+/-10kV) at frequency up to 1kHz.


High Field Conduction — Pulsed Electroacoustic Space Charge Profiling
Charge injection and transport under high electric field play a key role in the ageing and ultimate failure of engineering dielectrics (breakdown). Quantitative measurement of high field conduction is essential for new material development. The application of a voltage pulse with nanosecond rise time to a dielectric sample under high field induces a transient displacement of space charge by the Coulomb effect which in turn generates an acoustic pressure wave propagating across the sample. The intensity and temporal information of the pressure wave signal detected by piezoelectric sensor at the opposite electrode is de-convoluted into spatial information of space charge (and polarization) by using signal processing. This Pulsed Electroacoustic Space Charge Profiling technique can measure high field charge injection and conduction for both flat coupon and cylindrical sample (power cables) with a spatial resolution of 5 micron. Higher resolution can be achieved with lithium niobate based sensory.


High Field Conduction — Guarded Needle
Carrier mobility-related prebreakdown phenomena can only be studied within microscopic dimensions, as the power dissipation would cause thermal runaway for a macroscopic geometry. The guarded needle apparatus is designed for such measurement, using a sharp metal needle to create local high electrical field, which induces carrier mobility. A guarded needle electrode with a tip radius in the range of 5 µm and an electrical guard which extends to within about 35 µm of the tip provides the basis for measuring high-field mobility as the resistive current can be measured independent of the displacement current with a background noise level in the 5 fC range. Thus, the guarded needle measurement provides a level of quantitative detail that cannot be achieved through simpler measurements.


High Voltage Test Transformers
General purpose high voltage transformers are available for AC (100kV, Pheonix), DC (100kV, Spellman) and impulse (10kV) tests, with various electrode configurations/accessories. In addition, a special purpose Baur dielectric fluid tester is available for automated dielectric fluid test up to 100kV. This setup has embedded partial discharge coupler for prebreakdown activity sensing.


Partial Discharge System
Partial discharge generally refers to the localized electrical discharge activities within a power apparatus that only partially bridges the insulation between conductors. High frequency partial discharge signals are coupled inductively or capacitively and fed into an analyzer for phase-resolved analysis to provide insight into the nature and the location of defects. Partial discharge technique has been used extensively in condition monitoring of various power apparatus including generators, transformers, substation, power cables. A noise-gating, high resolution partial discharge measurement system located in an EMI shielded room with noise level of <5pC is available for research and engineering development.


High Frequency/High Temperature Aging 
High frequency, high temperature aging is an effective tool for new dielectric materials development as they provide accelerated life assessment of materials under development. In addition, on-line Lock-in amplifier based circuit has been development to monitor the dielectric dissipation factor growth over the course of aging at high electric field in controlled environmental chamber. The test can be conducted at ac with high frequency of 1 kHZ or under pulse width modulated conditions for variable speed drive application.


Tracking Resistance
An inclined plane tester is available for the measurement of the resistance of polymer materials to dry arc erosion and tracking caused by surface discharges.



HV Switchers for Pulse Discharge Energy Density Characterization 
A discharge energy measurement circuit is available for capacitive energy storage device characterization with maximum rating of 10 kVDC and 10 kA peak repetitive current. This special purpose switcher is developed to measure the discharge energy density of capacitors as a function of discharge time constant, for various film, nonlinear/ferroelectrics capacitors. This fast rise time (nanosecond), HV switch has been adopted by US Army, Navy, and Air Force research laboratories for pulse power, directed energy research.



Automatic Film Breakdown Tester
A Labview controlled tester has been developed to utilize metalized films as electrodes and rewind/renew automatically the film sample along with electrodes after each breakdown. This tester makes it possible to perform hundreds of ramp-to-failure tests or time-to-failure tests for novel capacitor film development, and provide an effective means to evaluate the low probability film breakdown strength that is most relevant to capacitor design.



Other Equipment 
  • Digital (Stanford Research Systems SR830) and Analog Lock-in Amplifiers
  • High voltage Capacitance and Tan-delta Bridge
  • Salt-Fog and Clean-Fog Chamber
  • Tektronics Oscilloscopes (200 MHz to 1 GHz)
  • Keithley fA meters