Rectifier mercury arc

Rectifiers without moving parts are aluminium or tantalum rectifiers, vacuum tube rectifiers, contact rectifiers and mercury-arc rectifiers. The first two types of rectifiers, the function of which has already been described in the theoretical section of this book are suitable for laboratory purposes only. Likewise vacuum tube rectifiers can also be used where a medium output is required these tubes act as valves allowing the alternating current to pass through in one direction only they are built for both low (up to 100 V) and high voltage (up to 10 000 V). 

For large electrochemical installations mercury-arc rectifiers are used whioh have proved valuable whereever strong direct current and relatively high voltage is required (above 300 V). In this case there is a loss of energy whioh is in proportion to the voltage necessary to overcome the arc resistance (20 to 30 V). As this voltage depends neither on the current nor on the total output... 

Fig. 55 is a schematic diagram of a single-phase mercury-arc rectifier fed from an autotransformer the terminals of which are marked U and v on the... 

G— Single phaeo mercury-arc rectifier, Ax A, — Anodes, K — Cathode, , t> — Alternating current Input, +,-----Direct current output, D — Chok-... 

When mercury-arc rectifiers were first introduced into industry some time ago many difficulties arose due to so called backfiring this phenomenon is caused by one anode suddenly starting to work as a cathode and so giving rise to a double short circuit. This was overcome by taking meticulous care to see that the anode material was kept free of any impurities capable of emitting electrons. 

Before the 1970 s, if a winder was powered by a DC motor or motors, the control of the motor(s) would have been almost exclusively by MG sets operating on the Ward Leonard principle. English Electric and AEI did, however build a limited number of winder drives using mercury arc rectifiers. Preference by some mine operators for Ward Leonard drives even lasted well into the 1980 s and many of those winders are still rendering sterling service today. 

Cathode in the electrolytic production of chlorine and caustic soda lamps arc rectifiers mercury cells switches thermometers barometers laboratory apparatus dental amalgams raw material for various mercury compounds fungicides antiseptics preservatives pharmaceuticals electrodes reagents... 

The electrical discharge in a mercury-are rectifier tube is an important example of a vacuum arc. Here the metal... 

Current fluctuations are damped by means of choking coil D connected in series. The rectifier starts operating by means of auxiliary electrode H which is connected to anode. 1, over the resistance W. When the rectifier is started it must be tilted so that the two pools of mercury accumulated at H and K merge into one. On restoring the rectifier to its normal position the pool of mercury is divided once again in two parts and gives rise to an electrical spark at the point of interruption the heat evolved by the spark causes that a certain amount of mercury, sufficient to ignite the arc, evaporates. 

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