||The resistance of the winding in each of the saturable reactors of Example 7-1 is 35 ohms and the resistance of the noninductive load is 140 ohms.
- The max value of the current.
- The rms value of the current.
- The power output.
- The efficiency of the frequency tripler. Neglect core losses.
|| Explain why a magnetic frequency multiplier operating on the principles discussed in Section 7-1 requires an odd number rather than an even number of saturable reactors.
|| A 120-v, 60-cycle, single-core saturable reactor has a d-c control winding of 900 turns and an a-c output winding of 225 turns. The load is a noninductive resistance of 59.5 ohms and the resistances are Rc = 10.0 ohms and RG = 0.5 ohm for the control winding and output winding respectively. Assume the a-c flux density to be just below the saturated value and calculate the self-inductance of a choke in the control circuit such that the alternating current induced in the control winding is not to exceed 0.25 amp when the pre-magnetization is zero. Neglect the resistance of the control circuit.
|| Calculate the amplitude of the flux when the saturable reactor of Problem 7-3 is operated in series with the 59.5-ohm resistor from a 120-v, 60-cycle source with its control circuit open-circuited. Assume the shape of the magnetization curve in Fig. 7-3(b) for the core material.
|| Plot the wave form of the output current if the saturable reactor in Problems 7-3 and 7-4 is operated in series with the 59.5-ohm resistor from a 130-v, 60-cycle source with its control circuit open-circuited. What is the amplitude of the current?
|| Assume the choke in the control circuit of the saturable reactor in Problems 7-3 and 7-4 to have infinite inductive reactance.
- Calculate the output current if the premagnetization is of a value such that the core remains saturated throughout the entire voltage cycle, while the reactor is operated with its connected load from a 120-v, 60-cycle source.
- What is the minimum value of premagnetizing current for this condition?
- Calculate the angle α2 at which the saturable reactor of Problems 7-3
and 7-4 becomes unsaturated when supplying the 59.5-ohm resistance load from a 120-v, 60-cycle source with a control current of 0.354 amp.
- Estimate the value of the firing angle at. Assume an infinite choke in the control circuit.
|| The core in the reactor of Problem 7-4 has a net cross-sectional area of 2.25 sq in. and a mean length of 11.75 in. Assume the hysteresis loop to be rectangular and the coercive force to be 72 amp turns per m for the material in the core, and calculate the current when the reactor operates with its connected load of 59.5 ohms from a 120-v, 60-cycle source with zero premagnetization, Plot the approximate wave form of the current.
|| The saturable reactor of Problems 7-3 and 7-4 is to operate from a 400-cycle system with the amplitude of the a-c flux just below the saturated value at zero premagnetization. Calculate
(a) The voltage of the source.
(b) The value of the noninductive load resistance if the current range is to be the same as for 60-cycle operation. What is the ratio of maximum power output to that for 60-cycle operation?
|| The saturable reactor of Problems 7-3 and 7-4 is to be rewound for operation at 120 v and 400 cps with the load specified in Problem 7-3.
(a) What changes, if any, should be made in one or both windings?
(b) How would the current rating be changed?
(c) How does the power output rating compare with that of Problem 7-9?
|| The cores in a 2-core saturable reactor are toroids of the following dimensions: ID = 2 1/2in., OD = 5 in., and height = 2 in. The stacking factor is 0.80. The number of turns NC in the control winding on each core is 900 turns. The core is assumed to saturate abruptly at Bs = 90000 lines per sq in. and the magnetization curve to be horizontal in the saturated region and vertical in the unsaturated region. The control windings are connected in series. The gate windings are connected in parallel for operation from a 120-v, 60-cycle source. The rated value of the output current is 2 amp (average value, not rms). Calculate
(a) The number of turns in each gate winding if the flux density is just below saturated value at zero premagnetization.
(b) The rms value of rated current.
(c) The resistance of the load if the firing angle α is zero at rated output for a 60-cycle emf of 120 v if the resistance of the gate windings is neglected.
(d) The average value and rms value of the rated current of the control winding on the basis of (c).
|| The 2-core saturable reactor in Problem 7-11 is delivering rated current at 120 v, 60 cps to a noninductive resistance of 50 ohms. The resistance of the gate windings may be neglected. Calculate
(a) The firing angle α.
(b) The control current.
(c) The output current if the control current remains at the value in (b) while the load resistance is reduced to 10 ohms.
(d) The firing angle α for (c).
(e) The form factor for (a) and (c).
|| The reactor in Problem 7-12 is operating with a choke in its control circuit of such size that the free even-harmonics in the control circuit are negligible.
Neglect the resistance of the gate windings and calculate
(a) The maximum value of resistance for rectangular wave form of output current from a 120-v, 60-cycle supply.
(b) The voltage across the choke in the control circuit.
|| A 2-core saturable reactor is used in an arc welder. The number of turns on each core are NC = 300 and NG = 20. The gate windings are series-connected and supplied from a 90-v, 60-cycle source. The control windings are also series-connected and receive their current from a 30-v d-c source with a potentiometer voltage divider to adjust the control current. The voltage across the welding arc is nearly constant at 25 v rms. Calculate
(a) The d-c value of the control current for a welding current of 200 amp rms. (Assume sinusoidal current wave form.)
(b) The rms value of the control current.
(c) The amplitude of the voltage wave if the impedance of the control circuit is negligible.
(d) The power gain if the voltage applied to the control windings is 28 v and the arc voltage is 25 v. Neglect losses in the voltage divider and assume the arc voltage to be in phase with the arc current.
(e) The ampere turn gain.
(f) The current gain.
|| A d-c transformer, as shown in Fig. 7-11(d), for measuring direct currents up to 2000 amp has a rated output of 1 amp d-c.
(a) Calculate the number of turns in each gate winding.
(b) The a-c supply is 120 v, 60cps. Estimate the cross-sectional area of the core in square inches. Assume a stacking factor of 0.80.