Thyristor Controllers

Thyristor controlled variable reactor (TCR) 0 (i) A few fixed capacitor banks that may be normally ON. 

Reactive control is also possible through synchronous condensers. As they rotate, the rotor stores kinetic energy which tends to absorb sudden Huctuations in the supply system, such as sudden loadings. They are. however, sluggish in operation and very expensive compared to thyristor controls. Their rotating masses add inertia, contribute to the transient oscillations and add to the fault level of the system. All these factors render them less suitable for such applications. Their application is therefore gradually disappearing. 

Heating mantles. These consist of a flexible knitted fibre glass sheath which fits snugly around a flask and contains an electrical heating element which operates at black heat. The mantle may be supported in an aluminium case which stands on the bench, but for use with suspended vessels the mantle is supplied without a case. Electric power is supplied to the heating element through a control unit which may be either a continuously variable transformer or a thyristor controller, and so the operating temperature of the mantle can be smoothly adjusted... 

A plasma torch is based on arc ignition between a thermionic tungsten cathode and a co-axial copper anode both water-cooled anode and cathode are immersed in an axial magnetic field. Nitrogen is generally chosen as the plasma gas. Air or steam can be injected into the plasma to increase the enthalpy and to produce sub-stoichiometric incineration. The torch is powered by a thyristor-controlled rectifier, which has controls to match the torch impedance. 

Each of the evaporators is electrically heated by use of a high current, some 100 A, which is fed at a low alternating potential of approximately 10 V. This is achieved by using high-current transformers with a thyristor-controlled primary current. Layer thickness monitors, positioned over the width of the web at the same dis-... 

A power converter generates a pulsating DC voltage from the three-phase mains. DC motor speed is determined by the amount of DC voltage generated that can be altered via the thyristor control angle of the power converter. 

Copper is generally the preferred material for cable conductors used in the oil industry. Aluminium is seldom choseu for conductors. It is sometimes used for the armouring of single-core cables that carry AC, or DC, if a substantial AC ripple is present e.g., DC, motors fed from a thyristor controlled power source. 

Most power systems in the oil industry do not have variable speed drives and so the AC supply is a highly dependable and simple source of sinusoidal voltage and current. Little or no harmonics are present. If a large variable speed drive is required, and an inverter or thyristor controller of some form is used, then the combination of these equipments will cause harmonic currents to be drawn from the supply. 

A special AC power system is required that will contain thyristor controllers, inverters or the like, that will produce harmonics. 

Continuously by using some form of thyristor controller which will allow feedback action in the form of closed loop control to be used to accurately regulate the speed. However, if such a scheme is used then it is the customary practice to adjust the applied frequency so as to maintain a constant air-gap flux, see 14.3.2 and 14.6. 

The very flexible nature of the thyristor controller allows the motor to have accurate control plus excellent overload protection. Most thyristor controllers are furnished with maximum current limits for motor armature current and for short-circuit current protection. During conditions of rapid acceleration or heavy load the armature current will rapidly become high and so the maximum current limiter will automatically hold the armature current until the duty is reduced. Thyristor controllers also make it possible to gain accurate control of the torque or load at zero speed. This is very desirable when handling anchors and the drill string. 

Standard belt widths are 1.0, 1.5, 2.0, 3.0 and 4.0 m with a length/width ratio in the range 4-15. H0 values of the latter rates lead to higher belt speeds with associated wear and tear. Low speeds tend to have higher belt costs and process liquor distribution difficulties. Thyristor-controlled drive units may be used for belt eed control—usually in the range of 3-30 m/min. 

Chromium plating from chromic acid baths is more sensitive to the source of current than most other processes, sufficiently so for commercial operators to use at least three-phase rectifiers as a rule, and to take precautions against any temporary break of current during voltage regulation. A recent investigation showed that the ripple introduced by thyristor control of rectifiers was detrimental to chromium electrodeposits. 

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