H - Electricity – 02 – P
Patent
H - Electricity
02
P
364/31, 318/57
H02P 3/20 (2006.01) H02P 3/24 (2006.01) H02P 23/06 (2006.01)
Patent
CA 1062383
ABSTRACT A hoist uses an alternating current three-phase variable speed reversible wound rotor motor to hoist and lower a load. An electromechanical brake and a tachometer generator are connected to the motor shaft. Controllable SCRs connected to the motor stator (primary) windings control motor direction and speed and motor braking in response to error signals resulting from comparison of reference signals from an operator's master control and feedback signals from the tachometer. During hoisting and lowering (when the electro- mechanical brake is released), direct current voltage derived from appropriate gating of the controllable SCRs is applied to the motor stator (primary) winding to effect direct current braking as required. This direct current flow is smoothed and rendered more effective by gating "on" a free-wheeling SCR which is connected across two of the motor stator (primary) windings. Emergency dynamic braking means operative in the event of failure of the electromechanical brake while the motor and control are deenergized but supporting a suspended load applies a rectified feedback signal from the tachometer to produce a magnetic field in the motor stator (primary) windings. A bridge rectifier is connected between the motor rotor (secondary) and stator (primary) windings. It produces a direct current voltage from the induced alter- nating current voltage in the rotor (secondary) which in turn provides additional direct current excitation to the stator to achieve emergency braking and slow descent of the load.
258579
Nash James N.
Price Lester A.
LandOfFree
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