An absolute charge sensor of fluid electrification measurements

Abstract

A new instrument, the Absolute Charge Sensor (ACS), has been developed that measures the net charge density entrdned in a fluid flow, independent of the fluid's electrical properties, velocity, and any electrification processes within the instrument. Through a shielded sampling probe, the ACS periodically transfers a small volume of charged fluid to an electrically isolated Faraday cage with no fluid exiting. The charge density is calculated from the known filling flow rate and either the current or voltage, respectively measured by low or high impedance electrometers connected to the electrically isolated Faraday cage. The ACS overcomes the ambiguity in current or voltage measurements of probes placed into the fluid flow where it is impossible to separate contributions from impacting charge in the flow from charge separated at the probe interface by the very charge generation and transport processes that are under study. The instrument is typically operated to measure charge densities as low as a few pC/m3 using a sampling flow rate of 0.18 cm3 with a sampling period on the order of 1 min. A Couette charger apparatus that simulates flow electrification processes in transformers and fuel pumps has been used to test the ACS using transformer oil or gasoline. Results show good correlation between the ACS and continuous flow measurements. In preparation for field tests of electrification charging of transformer components, laboratory tests were also performed in a pump driven flow loop. ACS measurements of charge density were made at the inlet and outlet of an oil drum electrically grounded through an electrometer. Charge density measurements in flows having Reynolds numbers as high as 3000 were in good agreement with the charge conservation law, i.e. the difference in convection currents into and out of the grounded oil drum equal the measured current through the electrometer. 0018-9367/01/0400-181$1.00 0 1991 IEEE Authorized licensed use limited to: MIT Libraries. Downloaded on January 22, 2009 at 16:38 from IEEE Xplore. Restrictions apply. that can rise in potential can lead to significant ohmic Authorized licensed use limited to: MIT Libraries. Downloaded on January 22, 2009 at 16:38 from IEEE Xplore. Restrictions apply. i , , , closer to i~ listed in Table 1. Thus at 20 and 70 Authorized licensed use limited to: MIT Libraries. Downloaded on January 22, 2009 at 16:38 from IEEE Xplore. Restrictions apply.

Streaming electrification of mineral insulating oil and synthetic ester MIDEL 7131

“…They include the pipe flow system [8] and Oommen mini-tester [9,10], Couette system of rotating cylinders [11,12] and rotating disc system [13]. Another group of small systems for both, laboratory and diagnostic tests are the charge volume density sensor built at MIT, so called ACS (Absolute Charge Sensor) [14] and a system with double Nelson chamber [15]. The scope of ECT tests included, among others, the effect of flow velocity [16], temperature [17], thermal aging [18].…”

Optical, electrical and electromechanical measurement methodologies of field, charge and polarization in dielectrics

“…To overcome measurement uncertainties from charge separation at surfaces of charge measuring devices, an absolute charge senso (ACS) using Faraday cage principles has been developed that provides an absolute measurement of the charge density that is independent of the fluid's electrical properties, the velocity of the fluid, and any electrification process within the instrument [46]. A schematic of the ACS is illustrated in Figure 40.…”

Electrostatic charging in transformer oils. Testing and assessment

“…The identification and quantification of charge separation at the interface between various transformer materials has been investigated successfully by the use of Couette chargers [118,119].…”