GB1060625A - Generator aggregate intended for variable speed operation - Google Patents

Abstract

1,060,625. Induction generators. ALLM€NNA SVENSKA ELEKTRISKA A.B. June 18, 1964 [June 20, 1963], No. 25215/64. Headings H2A and H2F. [Also in Division H3] An induction generator which provides a constant frequency at bus-bars 5 at variable speed by means of slip-frequency excitation supplied by an inverter system on the rotor, consists of an output machine 1, 2 and excitation machine 3, 4, wound with different polenumbers in the same stator and rotor cores. The inverter system is fed from D.C. bars 12, 13 connected, through rectifiers 14, to the exciter output windings U, V, W. The exciter field windings r, t, are energized from a source 7 which is controlled partly by a frequency picked up by winding S and partly by a comparison made at 11 between the generated frequency at 5 and a reference frequency. The magnetizing current fed to windings r and t is arranged to be inversely dependent on the rotor speed so that the rectified output at 12 and 13 is uniformly above the back-e.m.f. of windings R, S and T. Speed-sensing is done by means of a resistive shunt 30 across one phase u of the exciter rotor to produce a singlephase asymmetry which is picked up by stator winding s. The inverter is controlled by intermediate D.C. potentials at bars 20, 21, 22 derived from resistance divider 16, 17, 18, 19 the central bar being neutral. The inverter consists of six identical sections, one, 23R-28R, being typical: when the voltage generated by phase R is greater than the potential across capacitor 23R derived from line 21, current flows through diode 24R to the ignition electrode of thyristor 26R which then ignites to allow current to flow from bar 12 via diode 25R into the winding R in opposition to its generated voltage. The thyristor ceases to be conducting when its current is drawn off by operation of the next phase thyristor 265, and it cannot re-ignite until condenser 23R is recharged through resistor 27R and diode 28R.