A new life-test equipment designed for medium-duty electromagnetic contactors
In this study, a new test equipment, which is capable of performing arc-erosion experiments of electrical contacts on a medium-duty contactor, was designed and manufactured. The current load value of the system was gradually adjustable up to 30 A via control buttons located on the device. The make/break counts (cycle) and delay times of electrical contacts were adjusted by an electronic flasher. The number of operations was readily adjusted to desired counts before tests, and was monitored along the whole test on the LCD display of up/down counter. Inductive loads consisting transformers were used to achieve real-life operating conditions. A contactor having pole number of 3, switching power of 37 kW, and switching current of 75 A was used to conduct arc-erosion experiments. The test conditions for this contactor were 220 V operating voltage, 50 Hz frequency, and 20 A switching current. The switching frequency and delay time were selected as 1,000 times per hour and 2.6 s, respectively. Arc-erosion experiments were carried out by using the contactor up to 40,000 operations. The contact surfaces were analyzed by using scanning electron microscopy. The chemical compositions nearby arc were determined by energy dispersive x-ray spectroscopy. The experimental results showed that the contact surfaces were reasonably affected by the arc-erosion, which leads to mass loss by material migration and/or evaporation. Arc-affected zones were enlarged with the increasing operation number. It was concluded that the stationary contacts underwent major erosion.
Investigation of the Effect of Different Current Loads on the Arc-Erosion Performance of Electrical Contacts
In this study, arc-erosion experiments using contactors were performed under inductive loads for up to 40000 switching operations to investigate the effect of different current loads on the arc-erosion performance of electrical contacts. Determination of the mass loss was performed after every 5000 operations. The arc-eroded surfaces were examined using scanning electron microscopy. The chemical composition near the arc was determined by energy dispersive X-ray spectroscopy. The results show that the contact surfaces are greatly affected by arc-erosion, resulting in mass loss due to material migration and/or evaporation. In addition, the arc-affected zones become bigger with the increase in the number of switching operations, especially at 20 A. However, electrical cleaning improves the contact performance by reducing the contact resistance due to breakdown of the non-conducting oxide films formed between 20000 and 25000 switching operations at 20 A. The stationary contacts experience major erosion, whereas the movable contacts suffered less contact erosion under each current load.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.