1. a. Differentiate between a AC and Dc machine b). State types of DC machines that you understand (4mks) c). with help of diagram, describe the following types of single-phase motors in terms of their construction and principle of operation. i). capacitor start induction motors ii). Split phase induction motors (6mks) d). Explain three characteristics of three phase induction motor and why they are preferred in industries (6mks) 2. As a technician in industry, your supervisor instructs you to install a motor that can be used to lift a load and move across in a mechanical workshop to and from one point to another point laterally. a). which motor starting method will you advice on and use b). Name the installation requirements for the installation of the motor using the method above. c). Draw a labelled wiring diagram for a control circuit for forward reverse motor starter. Explain the principle of its operation. mks) (20 3. a). State and explain ways of improving power factor. mks) (10 b). A 800KVA transformer is operating at 0.90 power factor. Calculate Useful power and reactive power produced from this arrangement. (6mks) c). with the help of a diagram, explain how three phase power is produced (4mks) 4. a). Identify the phase sequence of a three -phase power, explain b). With help of a drawing, highlight two ways through which three phase power can be connected (8mks) c). Explain two ways of power measurements in a three-phase system (4mks) d). Three coils each having resistance 3Omega and inductive reactance 4Omega connected (i) in star and (ii) in delta to a 415V, 3-phase supply. Calculate for each connection (I) the line and phase voltages (II) the phase and line currents. (4mks) (8mks)

1. a. AC machines operate on the principle of alternating current, where the direction of current changes periodically, while DC machines operate on the principle of direct current, where the direction of current remains constant.<br /><br />b. Types of DC machines include:<br /> - Series DC Motor<br /> - Shunt DC Motor<br /> - Compound DC Motor<br /><br />c. i) Capacitor start induction motors use a capacitor to provide a phase shift in the starting winding, resulting in a rotating magnetic field that starts the motor. The capacitor is disconnected once the motor reaches a certain speed.<br /><br /> ii) Split phase induction motors have two windings, a main winding and an auxiliary winding. The auxiliary winding is connected in parallel with the main winding and is out of phase with it, creating a rotating magnetic field that starts the motor.<br /><br />d. Three characteristics of three-phase induction motors are:<br /> - High efficiency: They have high power factor and low losses.<br /> - Reliable: They have fewer moving parts and are less prone to mechanical failures.<br /> - Constant speed: They have a constant speed regardless of load variations.<br /><br />2. a) For lifting and moving loads laterally, a star-delta starter or a soft starter would be suitable.<br /><br /> b) Installation requirements include:<br /> - Adequate ventilation for cooling<br /> - Proper wiring and grounding<br /> - Protection from mechanical and electrical hazards<br /><br /> c) The control circuit for a forward reverse motor starter consists of a contactor for each direction, a switch to select the direction, and overload relays. The principle of operation involves closing the contactor for the selected direction to start the motor, and opening it to stop the motor.<br /><br />3. a) Ways of improving power factor include:<br /> - Adding capacitors or inductors to the circuit<br /> - Using power factor correction equipment<br /><br /> b) Useful power = 800 x 0.90 = 720 kW<br /> Reactive power = 800 x (1 - 0.90^2) = 48 kVAR<br /><br /> c) Three-phase power is produced by three coils or windings connected in a way that their magnetic fields add up to produce a rotating magnetic field.<br /><br />4. a) The phase sequence of a three-phase power is typically ABC or ACB, where A, B, and C represent the three phases.<br /><br /> b) Two ways of connecting three-phase power are:<br /> - Star connection<br /> - Delta connection<br /><br /> c) Two ways of power measurements in a three-phase system are:<br /> - Using wattmeters<br /> - Using kilowatt-hour meters<br /><br /> d) (I) Line voltage = √3 x Phase voltage = √3 x 415V = 720V<br /> Phase voltage = 415V<br /><br /> (II) Phase current = Line current = 415V / √3 = 238A<br /> Line current = 238A