Choke coil

Reducing the residual ripple from single-phase rectifiers for currents up to about 20 A and voltages of up to about 20 V can be achieved by filter circuits of choke coils and condensers. For greater output and constant residual ripple independent of load, the only possibility is the three-phase bridge circuit. It is always more satisfactory than a filter circuit. 

Current fluctuations are damped by means of choking coil D connected in series. The rectifier starts operating by means of auxiliary electrode H which is connected to anode. 1, over the resistance W. When the rectifier is started it must be tilted so that the two pools of mercury accumulated at H and K merge into one. On restoring the rectifier to its normal position the pool of mercury is divided once again in two parts and gives rise to an electrical spark at the point of interruption the heat evolved by the spark causes that a certain amount of mercury, sufficient to ignite the arc, evaporates. 

On the top of the chamber there is a cylindrical extension C which is cooled in order to effect condensation of mercury vapour. Six iron anodes A (there may be twelve or even eighteen of them) are suspended from ring R which covers the top of the chamber. Current for the rectifier is supplied by a three-phase transformer the secondary windings of which have their middles connected in a neutral point in this way the secondary windings have six ends connected to six anodes A by choking coils D in series. 

The size of a switching amplifier is not only determined by its efficiency, but also by the applied electrical reactive elements (choke coil, capacitor, filter). So, one will choose a high switching frequency to keep the energy that... 

Even though they do not form as strong a magnet as their ferromagnetic cousins, the ferrites, as this class of ceramics is called, are very important technologically because they are also insulators. Because they do not conduct electricity, they may be used as cores for transformers or choke coils in high frequency radio or microwave applications where losses from induced eddy currents must be avoided. 

Nai] Naitoh, Y., Bitoh, X, Hatanai, X, Makino, A., Inoue, A., Application of Nanocrystalline Soft Magnetic Fe-M-B (M = Zr, Nb) Alloys to Choke Coils , J. Appl. Phys., 83(11), 6332-6334 (1998) (Experimental, Magn. Prop., 6)... 

Figure 5-1 shows a typical LTX process. The inlet gas stream is choked at the well to 2,000 to 3,000 psi or until the temperature declines to approximately 120°F, which is well above the hydrate formation temperature. The inlet stream next enters a coil in the bottom of the low temperature separator. The stream is then cooled to just above the hydrate formation temperature with the outlet gas coming off the low temperature separator. This assures the lowest possible temperature for the inlet stream when it enters the vessel after the choke. This choke is mounted in the vessel itself. When the pressure drop is taken, the temperature will... 

As shown in Figure 5-2, the wellstreain enters the first coil at its flowing-tubing temperature and pressure. Alternatively, it could be choked at the wellhead to a lower pressure, as long as its temperature remains above hydrate temperature. 

To calculate the heat duty it must be remembered that the pressure drop through the choke is instantaneous. That is, no heat is absorbed or lost, but there is a temperature change. This is an adiabatic expansion of the gas w ith no change in enthalpy. Flow through the coils is a constant pressure process, except for the small amount of pressure drop due to friction. Thus, the change in enthalpy of the gas is equal to the heat absorbed. 

In order to choose the coil length and diameter, a temperature must first be chosen upstream of the choke the higher Tj, the longer the coil L and the shorter the coil L2. In Chapter 2 we showed that the greater the LMTD between the gas and the bath temperature, the greater the heat transfer per unit area, that is, the greater the LMTD, the smaller the coil surface area needed for the same heat transfer. The bath temperature is constant, and the gas will be coldest downstream of the choke. Therefore, the shortest total coil length (L[ -I- L2) will occur when L is as small as possible (that is, Tj is as low as possible). 

Although the total coil length is always smaller when there is no upstream coil (Lj = 0), the temperature could be so low at the outlet of the choke under these conditions that hydrates will form quickly and will partially plug the choke. In addition, the steel temperature in the choke body may become so cold that special steels are required. Therefore, some guidelines are necessary to choose Tj for an economical design. 

After the minimum inside diameter and the required wall thickness, a coil diameter and wall thickness may be selected. Very often, the coil length downstream of the choke (L2) is of a different diameter and wall thickness than the length upstream of the choke (L,). 

For a given shell length the number of pas.ses for each coil can be determined. Since the number of passes both upstream and downstream of the choke must be an even integer, actual Tj and T2 may differ slightly from that assumed in the calculation. The actual values of Tj and T2 can be calculated from actual coil lengths L, and L2. 

Heat duty for a single pass coil downstream of choke. 

Fluorescent light fittings contain a choke or inductive coil in series with the tube and starter lamp. The starter lamp switches on and off very quickly, causing... 

Use small parasitic chokes in the plate lead as shown in Fig. 5.63(b). The size of the coil will vary considerably depending on the tube and circuit layout. A coil of 4-10 turns measuring approximately 1/2-in diameter is typical. The presence of the choke in the frequency determining part of the circuit... 

In the lefthand circuit diagram, a piezo actuator is connected as a load. The coil (choke) protects it from rectangular switching voltages, but not from force impulses due to high peaks that can occur in the triangular current-... 

DuPont s Zenite 7130, an LCP reinforced by 30% glass fibre which features a HDT of 289 and low creep at high temperatures, is used by Epcos, for coil bobbins in its range of transformers, chokes and other surface mount devices. Another LCP glass reinforced compound, Zenite 6130L, is used by the Swiss Sonceboz company for coil bobbins and the over-moulding of the stator of its 4000-Series of torque motors. 

---