SECTION SIXACCESSORIES (all in terminal box except hand trimmer)HAND TRIMMERS FOR REMOTE CONTROL (SC MACHINES ONLY)A remote hand trimmer can be provided to give fine adjustment to the output voltage of approx. 6%. The hand trimmerworks in conjunction with the range control fitted to the A.V.R. to give the voltage range specified in Section One.Resistance value- 4.7 k ohms.Fig. 14. Wiring detailsFig. 15. Fitting detailsPARALLEL OPERATION (SC MACHINES ONLY)There are two important rules to bear in mind when paralleling two or more generators.1.It is the engine that controls the kW load sharing.2.It is the generator A.V.R. that controls the kVAr load sharing.If the engine governors are not electrically interconnected and generator excitation systems are not electricallyinterconnected, then the larger the engine speed droop when kW load is applied and the larger the generator voltagedroop with circulating current, the more flexible and stable the system becomes to obtain load sharing when thegenerators are in parallel. If closer control of both engine speed and generator voltage is required, then some form ofcross connection is required between the governor systems and generator excitation systems.The standard machine is fitted with a fully interconnected damper winding and the standard phase sequence is UVWwhen rotating clockwise viewed from the drive end. When paralleling Stamford a.c. generators, the neutrals can beconnected but when paralleling dissimilar machines it is recommended that the neutrals are not connected as differencesin waveform may result in harmonic currents.Two paralleling systems can be supplied for the Stamford 'C' range a.c. generators.Quadrature Droop- For both similar and dissimilar control systems provided, a droop circuit is fittedto all machines.Quadrature Droop KitThis is the most widely used and simple of paralleling systems and comprises a current transformer (C.T.) and burdenresistor (see Fig. 16), or a current transformer (C.T.) and burden choke (see Fig. 17).35
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