Chapter 19, Problem 4DP

An open-circuit voltage of 240 V appears across the slip-rings of a wound-rotor in- duction motor when the rotor is locked. The stator has 6 poles and is excited by a 60 Hz source. If the rotor is driven by a variable-speed dc motor, calculate the open-circuit voltage and frequency across the slip-rings if the dc motor turns a. At 600 r/min, in the same direction as the rotating field b. At 900 r/min, in the same direction as the rotating field c. At 3600 r/min, opposite to the rotating field

If we double the number of poles on the stator of an induction motor, will its syn- chronous speed also double? The rotor of an induction should never be locked while full voltage is being applied to the stator. Explain. Why does the rotor of an induction motor turn slower than the revolving field?

a. Calculate the synchronous speed of a 3-phase, 12-pole induction motor that is excited by a 60 Hz source. b. What is the nominal speed if the slip at full-load is 6 percent?

A 3-phase, 75 hp, 440 V induction motor has a full-load efficiency of 91 percent and a power factor of 83 percent. Calculate the nominal current per phase.

Please answer all the questions  a) What is the minimum required transformer rating for each transformer in kVA? b) Find the voltage required at Bus 1.  c) The loadcentre is to be powered by PV panels that have the same I-V curve (ISC = 120 A, VOC = 60 V). Identify the configuration that uses the minimum number of panels to provide enough power to Bus 1. You can assume that the inverter converts the power at 95% efficiency and requires V DC input to generate the same VRMS AC output.

What happens to the rotor speed and rotor current when the mechanical load on an in- duction motor increases? Would you recommend using a 50 hp in- duction motor to drive a 10 hp load? Explain. Give two advantages of a wound-rotor mo- tor over a squirrel-cage motor. Both the voltage and frequency induced in the rotor of an induction motor decrease as the rotor speeds up. Explain.

What would the electropneumatic diagram of a circuit with the sequence a+b+c+(a-b-c-) look like?

### What would the electropneumatic diagram of a circuit with the sequence a+b+c+(a-b-c-) look like, with a counter, in the fluidsim?

You are asked to design a unit to condense ammonia. The required condensation rate is 0.09kg/s. Saturated ammonia at 30 o C is passed over a vertical plate (10 cm high and 25 cm wide).The properties of ammonia at the saturation temperature of 30°C are hfg = 1144 ́10^3 J/kg andrv = 9.055 kg/m 3 . Use the properties of liquid ammonia at the film temperature of 20°C (Ts =10 o C):Pr = 1.463 rho_l= 610.2 kf/m^3 liquid viscosity= 1.519*10^-4 kg/ ms kinematic viscosity= 2.489*10^-7 m^2/s Cpl= 4745 J/kg C kl=0.4927 W/m CCalculate the surface temperature required to achieve the desired condensation rate of 0.09 kg/s( should be 688 degrees C) a) Show that if you use a bigger vertical plate (2.5 m-wide and 0.8 m-height), the requiredsurface temperature would be now 20 o C. You may use all the properties given as an initialguess. No need to iterate to correct for Tf. b) What if you still want to use small plates because of the space constrains? One way to getaround this problem is to use small…