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Power Electronics:Thyristor Devices

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Power Electronics Introduction The modern age of power electronics began with the introduction of thyristors in the late 1950s [1]. There are now a number of power devices available for high-power and high-frequency applications. The most notable include: • Gat e turn-off (GTO) thyristor • Power Darlington transistor • Power MOSFET • I nsulated-gate bipolar transistor (IGBP) These power devices are used primarily as switches to convert energy from one form to another. They are used in motor control systems, uninterruptible power supplies, high-voltage dc transmission, ac-to-dc power supplies, induction heating, and other power-conversion applications. Thyristor Devices The thyristor, also called a silicon-controlled rectifier (SCR), is basically a four-layer three-junction pnpn device [1]. It has three terminals: anode, cathode, and gate. The device is turned on by applying a short pulse across the gate and cathode. After the device turns on, the gate loses its control t...
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Grounding Tower Elements:Facility Ground Interconnection.

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Facility Ground Interconnection Any radial that comes within 2 ft of a conductive structure must be tied into the ground system [1]. Bury the interconnecting wire, if possible, and approach the radial at a 45° angle, pointing toward the expected surge origin (usually the tower). Cadweld the conductor to the radial and to the structure. For large-base, self-supporting towers, the radials should be split among each leg pad, as shown in Figure 19.4. The radials may be brought up out of the soil (in air) and each attached at spaced locations around the foot pad. Some radials may have to be tied together first and then joined to the foot pad. Remember, if space between the radial lines can be maintained, less mutual inductance (coupling) will exist, and the system surge impedance will be lower. It is desirable to have a continuous one-piece ring with rods around the equipment building. Connect this ring to one, and only one, of the tower radials, thus forming no radial loops. (See Figure...
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Grounding Practices:Terms and Codes and The Need for Grounding.

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Introduction The attention given to the design and installation of a facility ground system is a key element in the day-to- day reliability of the plant. A well-designed and -installed ground network is invisible to the engineering staff. A marginal ground system, however, will cause problems on a regular basis. Grounding schemes can range from simple to complex, but any system serves three primary purposes: • Provides for operator safety • Protects electronic equipment from damage caused by transient disturbances • Diverts stray radio frequency energy from sensitive audio, video, control, and computer equipment Most engineers view grounding mainly as a method to protect equipment from damage or malfunction. However, the most important element is operator safety. The 120 or 208 Vac line current that powers most equipment can be dangerous — even deadly — if handled improperly. Grounding of equipment and structures provides protection against wiring errors or faults that could enda...
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