Question

TEST RESULTS: QAD STEPS TORQUE 1 2 3 4 5 6 7 2 10 11 12 1710 1691 1678 1663 1645 16161605 1707 154 150 1949 1383 00 0.1 0.1 0.2 0.25 0.0.350.4 0.5 0.6 0.7 **** 0.8 10.700.76 0.78 0.82/0.91 18,98 1.05 1.12 1.25 142 45 1.85 TABLE 19-2 DE-BRIEFING The damper winding squirrel-cage) starts the rotor and gets it up to 90% synchronous speed. After DC is applied to the rotor field coil and the rotor pulls up to synchronous speed, what is the job of the damper winding? Explain 2. Why isn't DC applied to the rotor field coil right away instead of waiting until the rotor is up to speed? 3. What happened to rotor speed as you synchronized the rotor? What happened to stator current? Explain why rotor speed changed the way it did. What was the "pull-out torque" for this motor? (Pull-out torque is the maximum torque the motor will produce before dropping out of synchronism). 19-5

Answer 1

sweg: 1. After reaching 95% synchronous speed, the purpose of damper winding is to avoid oscillations with sudden change in toad . Explain: If load on machine changes, its power angle has to change accordingly, rotar starts swinging around the new power angle Now damper winding damps out the oscillations of rotor so that the rotor takes its new position quickly. 2. P DC applied to rotch at standstill, the revolving field passes the stationary field too fast to be locked. Hence fiast it is rotated to the full speed and then DC is applied as it creates magnetic locking. 3. As you synchronized the refer the rotor speed would be near to synchronous speed. If it reaches the yachronous Speed, the slip NS-Nr becomes new Sort becomes zero and and hence torane hence torque becomes zelo, heute motor would not rotate. What happened to stator Corrent: Here in this condition even the statos corrent becomes zelo as induction motor works on principle of induction, as rotor current is zero Stator current also becomes zero

why rotor speed changed the way it did The Walent in rotor is due to change in flus , when relative Speed between hotar & Stator flux is zero , change in rotor flun is ero, hence according to faraday's law no ens and corrent flowing through rotor bars, heuse No Speed ie, speed Changes its way When reaching synchronous speed. 4. Pull-out torque of this motor is 0.6 as manimum toague the motor will produce before dropping out of Synchronism as shown in the test genot Synchronous Speed 15008pm.