Rectified current sources

A 120th of a second later, the direction of the AC flow will have reversed and it will originate at connection (2). Under this condition, the only path that it can take to reach connection (1) will be through rectifier leg (D), the external circuit, and rectifier (A). For either direction of AC flow, the DC flow through the external circuit is in one direction only. 

Rectifiers operate at less than 100 percent efficiency, meaning that the DC output power is less than the AC input power from the supply line. Rectifiers operate at maximum efficiency when operated at fullrated load. Where large rectifiers are used (as for large, bare structures), the rectifier rating should be selected so that it will operate at close to the full-load rating. 

The efficiency of a CP rectifier may be determined by measuring the AC power input with a watt meter, measuring the DC volts and amperes output, and calculating the efficiency as follows  

For example, a rectifier operating at 20 A and 32 V DC output is found to have an AC input of 940 W. The efficiency will then be (20 x 

---

Figure 7-9. Schematic of the rectifier and inverter circuit for a current source inverter.

In the direct current (DC) electrodeposition, the current source is a DC power source. A power source in the form of a battery or rectifier (which converts alternating current electricity to regulated low-voltage DC current) provides the necessary current. 

The most common source of electricity for impressed current systems is a local power utility. Power normally involves the DC rectifier arrangement. Remote locations can use solar cells, thermoelectric current sources, special fuel-driven electric generators, or even windmills. Impressed current systems are preferred when current requirements and electrolyte resistivity are high. These systems require an inexpensive source of electrical power, are well suited to long-time operation and large... 

By means of an external current source, usually a rectifier. A reference electrode may be used to control the current from the rectifier. 

Exact analysis of resonant converters is difficult due to the nonlinear loading on the resonant tanks. The rectifier-filter-load resistor block can be replaced by a square-wave voltage source (for SRC, Fig. 10.89(a)) or a square-wave current source (for PRC and SPRC, Fig. 10.88(b) and 10.88(c)). 

ICCP consists in polarizing the rebar with a DC current source (rectifier) to a cathodic potential where anodic dissolution of the rebar is minimized (Fig. 13.20). Three basic methods are available for controlling the output of a rectifier ... 

The current needed for cathodic protection by impressed current is supplied from rectifier units. In Germany, the public electricity supply grid is so extensive that the CP transformer-rectifier (T-R) can be connected to it in most cases. Solar cells, thermogenerators or, for low protection currents, batteries, are only used as a source of current in exceptional cases (e.g., in sparsely populated areas) where there is no public electricity supply. Figure 8-1 shows the construction of a cathodic impressed current protection station for a pipeline. Housing, design and circuitry of the rectifier are described in this chapter. Chapter 7 gives information on impressed current anodes. 

Another major source of noise is the loop consisting of the output rectifiers, the output filter capacitor, and the transformer secondary windings. Once again, high-peak valued trapezoidal current waveforms flow between these components. The output Alter capacitor and rectifier also want to be located as physically close to the transformer as possible to minimize the radiated noise. This source also generates common-mode conducted noise mainly on the output lines of the power supply. 

One subtle, but major noise source is the output rectifier. The shape of the reverse recovery characteristic of the rectifiers has a direct affect on the noise generated within the supply. The abruptness or sharpness of the reverse recovery current waveform is often a major source of high-frequency noise. An abrupt recovery diode may need a snubber placed in parallel with it in order to lower its high-frequency spectral characteristics. A snubber will cost the designer in efficiency. Finding a soft recovery rectifier will definitely be an advantage in the design. 

Direct Current (DC). This current is transmitted for industrial uses only in exceptional situations. The most common sources of direct current are storage batteries and industrial devices called rectifiers, in which alternating current is changed (rectified) to direct current, as is used in electrolytic cells for the manufacture of chlorine gas, magnesium, aluminum, and a few other chemicals. The direct current is flowing from the source through the user application and back to the source, in one direction. The motor is primarily used for speed control of selected equipment. 

The modern procedure to minimise corrosion losses on underground structures is to use protective coatings between the metal and soil and to apply cathodic protection to the metal structure (see Chapter 11). In this situation, soils influence the operation in a somewhat different manner than is the case with unprotected bare metal. A soil with moderately high salts content (low resistivity) is desirable for the location of the anodes. If the impressed potential is from a sacrificial metal, the effective potential and current available will depend upon soil properties such as pH, soluble salts and moisture present. When rectifiers are used as the source of the cathodic potential, soils of low electrical resistance are desirable for the location of the anode beds. A protective coating free from holidays and of uniformly high insulation value causes the electrical conducting properties of the soil to become of less significance in relation to corrosion rates (Section 15.8). 

The essential requirements for a constant-current electrolytic determination — a source of direct current (which may be a mains-operated unit producing a rectified smoothed output of 3-15 volts), a variable resistance, an ammeter (reading up to 10 amperes), a voltmeter (10-15 volts), and a pair of platinum electrodes — can be readily assembled in most laboratories, but if a number of determinations are to be performed a commercial electrolysis unit will doubtless be preferred. This will be equipped with rectifier, a motor drive for a paddle-type stirrer or with a magnetic stirrer, and a hotplate. 

The ED process is a reliable, membrane-based, electrically driven demineralization technology that is more than 50 years old. It is suitable for the production of basic pure water from lower TDS supply sources. Commercial ED units consist of hundreds of individual cells in a modular membrane sandwich arrangement, bounded by electrodes and linked to a direct current (DC) rectifier-controller. The total treated water flow is a function of the number of cells in the ED unit. 

---