Rectifier/transformer thyristor rectifiers

Cuncnt imiisieiits A similar situation will arise wheti a switching ON operation of the rectifier unit occurs hen it is a thyristor rectifier. Under load conditions, the stored magnetic energy in the incoming supply system, which can be the feeding transformer and the line reactances similar to a fault condition discussed earlier, may cause a current transient which can be expressed by... 

Solid-State DC Drives. The controlled-thyristor rectifier and separate-field DC motor is the solid-state motor drive in greatest use. The combination provides control over at least a 10 1 speed range, plus an additional two to three times by field weakening. Depending upon the power level, the rectifier is operated directly from the AC supply lines, or via a transformer. Typical speed regulation of 2% can be accomplished with a single control system. The horsepower and speed limitations are set by the DC motor, not by the semiconductor rectifiers. The DC motor and rectifier can be combined to any required power level. 

As in the case of power stations, where there is known to be considerable variation in operating conditions due to tidal changes, or in estuary waters variations in salinity, automatic control systems may be desirable. For such systems the current output of the transformer-rectifier is controlled by thyristor or transductors. Sensing electrodes are permanently installed on selected piles and transmit the electrode potential of the steel back to the controlling device. This type of system enables the most economic amount of current to be provided under all operating conditions. 

The transformer-rectifiers are either thyristor or transductor controlled and operate in a similar manner to that described for power stations. 

In the case of rectifying elements, the total installed cost of a thyristor system is usually less than that of one based on diodes. Operating costs also are lower. Maintenance costs, as we saw in Section 8.3.1.2B, are lower because of the use of static, solid-state control devices rather than the mechanical switchgear of a tap changer. Rectification efficiency might be expected to suffer from the loss of part of the sine wave before firing, but this loss usually is comparable to the inefficiencies of the regulating transformers and the saturable reactors in a diode system. 

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