Surge load experiment design and results analysis of relay
Due to the transient overvoltage or overcurrent when relay's contacts switch different loads, the relay's contacts are damaged by transient arc erosion of electrical-over-stress, which influences the reliability of relay seriously. Firstly, according to the life test requirements of one type of electromagnetic relay with permanent magnets, the load circuit and the testing program are designed, which has characteristic of adjustable surge current time. Secondly, the contacts' breaking arc and closing bounce under 2A resistive load, 5A resistive load and surge load are analyzed. The influence of surge load on relay's electrical life is studied with increasing of test cycles. Finally, based on the testing data, the optimal design of relay has been modified and the results have been analyzed, which is helpful for improving the life of the relay.
Arc discharge and surge suppression during a breaking operation of a magnetic relay
In a switching circuit with an inductive load, arc discharge and surge generated during a breaking operation are big problems. We proposed an electric method for arc discharge suppression using a timely controlled transient current switch and a capacitor arranged in parallel to the energizing switch. In this paper, we propose an improvement. We replaced the capacitor with two capacitors. One to suppress arc ignition and the other is to suppress surge. Using electrical measurements of the relay contact operation, adequate capacitance values and series resistance were derived numerically. The capacitance to suppress arc ignition does not depend on load inductance but only on load resistance. However, the capacitance and its series resistance to suppress surge depend on the load inductance and its resistance. For the break operation (50 V/8 A) of a conventional magnetic relay (HH62P) with an inductive load (84 mH), a 1muF capacitor can suppress arc ignition and a 100 muF capacitor and a resistance of 8Omega is sufficient to suppress surge. No arc ignition and surge controlled to less than 30 V were confirmed experimentally.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.