摘要:

Studies of the effects of environment on the mechanical and electrical properties of surface films on contact metals involve many measurements of properties, such as contact resistance, for a range of loads applied both with and without an associated surface traction (wipe). It is impracticable, and wasteful of effort, to do such work manually. The machine described does it automatically: ten loads are available and a plate two inches square can be tested at a thousand different places, each observation occupying eight seconds.The test sequence at each place is as follows. A probe is lowered gently on to the plate, and when stationary, the contact resistance is measured and classified automatically. The probe is then ‘wiped’ and, again when stationary, a similar evaluation is made. This procedure is repeated for each of seven loads (10, 20, 50, 100, 200, 500 and 1000 g) or until one or other of the two sets of contact resistances falls within a specified range. The remaining three loads can be applied manually when it is necessary to explore a particular load interval in detail.Resistance measurements are made with a 4-terminal bridge arranged so that the open-circuit voltage at the source is about 40–50 mV. A switching unit takes the place of the variable arm in the bridge, and substitutes, in turn, one resistor from a group of five. When the bridge condition passes through a balance as a consequence of bringing a particular resistor into circuit, the event is recorded on one of a group of five meters corresponding to the resistance classifications used.

DOI:10.1049/pi-a.1962.0035

出版商:IEE    

年代:1962

数据来源: IET

摘要:

In light-duty contacts failure is caused less frequently by erosion than by high resistance due to contamination of the surface. The best guide to the degree of contamination of a contact is obtained by measuring its resistance in such a way as to avoid damaging the surface film, even if the normal use of the contact may entail such damage. A 4-terminal method of measurement should be used in order separate the resistance of the contact from that of the switching device as a whole and its connections to the measuring network. The conditions in which the separation is physically meaningful are considered, and a simple calculation indicates where the connections should made in a typical case.Theoretical arguments, supported by experiment, are given for limiting the test voltage to 10mV. The current need not be limited provided that the circuit is de-energized during make and break prevent damage to surface films by inductive voltage peaks. If this not done the current must be limited to a very small value, with serious loss in sensitivity.

DOI:10.1049/pi-a.1962.0036

出版商:IEE    

年代:1962

数据来源: IET

摘要:

The manner in which an initially sound compression joint fails in service is discussed, and it is suggested that one of the most important parameters affecting the life is the running temperature of the joint. It is the temperature near the contact areas which is vital, and this can, under certain circumstances, differ markedly from the bulk temperature of the joint. It is shown that in a typical joint the regions near the contact areas within which the dangerous local high temperatures occur are so small that the temperature follows the oscillations of a 50c/s current.

DOI:10.1049/pi-a.1962.0037

出版商:IEE    

年代:1962

数据来源: IET

摘要:

In noise problems the limitation of structure-borne vibration is often important. Properly designed resilient mountings can be employed to give the required isolation; these may take the form of unit mountings used as point supports or pads of sheet-like material cut to the required size. Anti-vibration mountings employing pads of material in sheet form will often be suitable and are usually cheaper than unit mountings.Information on the attenuation to be expected from such materials is not usually available from the manufacturers. The paper gives details of a simple method which may be employed to give useful and reliable information on the dynamic performance of such materials.

DOI:10.1049/pi-a.1962.0039

出版商:IEE    

年代:1962

数据来源: IET

摘要:

Overhead-transmission-line conductors are peculiarly prone to aeolian vibration generated by eddy vortices formed as the wind passes across the conductor. Unless steps are taken to reduce this vibration, failure of the conductor by fatigue wear at the clamp may occur after a few years' service.The various methods of detecting vibration are reviewed. These include vibrating-mass recorders, directly-coupled pen recorders, electromagnetic transducers, resistance and piezo-electric strain gauges, and piezo-electric accelerometers. The dampers described include:(a) Tuned dampers: pneumatic, hydraulic, spring and suspended-weight (Stockbridge) types.(b) Impact dampers: vibrating-pad, vibrating-lever, plastic-tube and plastic-spiral types.(c) Reinforcing devices: armour rods, festoons, cable absorbers, tape and springs.(d) Special conductors.Details are given of experimental work performed on 33, 132, and 275/380kV lines to detect and damp vibration. For convenience, vibrating-mass recorders were used. The damping efficiencies of several types of damper are given, the vibration of twin-conductor bundles is compared with that of single similar conductors, and the vibration characteristics of special steel-cored-aluminium conductors are examined. Data are also given on the effectiveness of various arrangements of dampers fitted to the very long spans across the Rivers Usk and Severn, and a method is suggested for damping such long spans with multiple Stockbridge dampers.

DOI:10.1049/pi-a.1962.0040

出版商:IEE    

年代:1962

数据来源: IET