Impressed current system transformer

Impressed-current systems for power stations are somewhat more sophisticated than those required for pipelines or marine structures inasmuch that a large number of items of plant, with a wide range of current requirements, are protected by one transformer-rectifier. Each section of every water box in order to provide even current distribution requires one or more anodes. In the case of a large circulating water pump as many as 30 anodes may be required to provide the current distribution necessary. Three types of system should be considered as follows ... 

Impressed current systems require low-voltage high-current DC power. The voltages are typically 12, 25 and 50 volts. The currents are typically 100 to 800 amperes from one unit. The power is supplied by transformer rectifier units in which the transformer coils and the power rectifier are usually immersed in insulating oil to improve heat removal. The AC supply is usually three phase at LV voltage, e.g. 380 to 440 volts, and the supply power factor is about 0.75 lagging. 

In contrast to the galvanic anode system, the flow of current from the anode to the cathode is forced from a DC source in the impressed current system. Thus, whereas the current is provided by the corrosion of the electrode in the anodic galvanic system, the electrode acts as a conductor and hardly corrodes in the impressed system and the AC input is transformed and rectified to a varying DC voltage. A transformer rectifier is the most important component of the system. 

Impressed current system A cathodic protection system which receives the required current for protection from a transformer-rectifier. 

In addition, the pulsing process requires sophisticated electronics which must prove durable over many years. They are likely to be less reliable than transformer rectifier systems providing straight DC for impressed current cathodic protection. 

With a frequency converter, stator voltage and frequency of the asynchronous motor can be varied infinitely. This transforms a standard motor into a variable speed drive system. An asynchronous motor equipped with a rotor position sensor, magnetization calculation, and the impression of the corresponding stator currents (vector regulation) has the properties of a servo drive. 

Nevertheless, there are two important issues that can arise following the use of sparteine in any particular transformation. Firstly, although (-h)-sparteine also occurs naturally it is much less easily obtained and so for a specific application if (-)-sparteine leads to the undesired enantiomer, then it is currently difficult, even despite an impressive recent total synthesis of (-h)-sparteine [66], to find a substitute for (-)-sparteine that will allow access to the desired enantiomer. A recent example is found in work by Clarke and Travers towards insecticidal 4-alkynyloxazohnes, which used a novel sparteine-mediated enantioselective deprotonation-alkylation of propargyhc amide systems (Scheme 20), and unfortunately did not lead to the biologically relevant enantiomer [67]. 

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