Rectifier/transformer arrangement

Cathodic Protection Rectifier transformer-rectifier arrangement for supplying the direct current which flows between a groundbed and a buried structure which is receiving cathodic protection. 

A P=12 system can be formed by connecting two 6 pulse rectifiers on AC voltages shifted 30 degrees apart by means of Delta-Yie transformer arrangement, either a dual secondary transformer (Delta and Yie) or with two separate transformers in Delta-Delta and Delta-Yie. 

Various arrangements for the protection rectifier and its possible applications are described in Chapter 8. Large fluctuations of the protection current can be reduced by a current-reducing resistor, R (see Fig. 15-7). This means that the pipe/ soil potential in the middle becomes less negative. A current smoothing action can be achieved with rectifiers connected to the network or by reducing losses by an inductive resistance between the transformer and bridge rectifier (see Section 8.4). 

Six iron anodes are required for corrosion protection of each condenser, each weighing 13 kg. Every outflow chamber contains 14 titanium rod anodes, with a platinum coating 5 /tm thick and weighing 0.73 g. The mass loss rate for the anodes is 10 kg A a for Fe (see Table 7-1) and 10 mg A a for Pt (see Table 7-3). A protection current density of 0.1 A m is assumed for the coated condenser surfaces and 1 A m for the copper alloy tubes. This corresponds to a protection current of 27 A. An automatic potential-control transformer-rectifier with a capacity of 125 A/10 V is installed for each main condenser. Potential control and monitoring are provided by fixed zinc reference electrodes. Figure 21-2 shows the anode arrangement in the inlet chamber [9]. 

Figure 21 -3 shows a schematic diagram of the turbine in which the black areas are CrNi steel. The plate anodes are situated in the region of the suction manifold (A 1 to A3) in a triangular arrangement in the impeller ring (A4 to A6) and distributed in the vicinity of the segmented water inlet ring (A7 to A10) (see Fig. 21-4). These four anodes were individually connected to the transformer-rectifier with chloride-resistant pressure-resistant cable.

The full-wave rectifier just discussed requires a center-tapped transformer. An alternative implementation of the full-wave rectifier, as shown in Fig. 10.16 (a), is the bridge rectifier. This rectifier has four diodes arranged similar to Wheatstones bridge and does not require a center tapped transformer. 

From the other side power is supplied either from separate transformer/rectifier units for each electrolyzer or from one unit for two or more (up to six) electrolyzers in parallel. The switches are arranged close to the rectifiers. They are actuated automatically and connected to the common interlock system for safety reasons. 

---