CARRIAGE A 0837816 - Caterpillar

Voltage Droop
The method used to control the magnetizing power of an generator is called "voltage droop". It has been explained previously that speed droops in governors is used to divide the kilowatt loading of engine-driven generators. An engine that tends to speed up and carry more than its proportionate share of the load will, with a governor having speed droop, tend to speed up and again pick up its proportionate share of the load. Also, remember that active power (KW) loading is determined by the governor setting and the regulator should increase the magnetizing power in excess of its proportionate share for the system, it is necessary to reduce the exciter output of this unit to bring its level of magnetizing power back to the proper value.The increase in magnetizing power shows up as an increase in line amperes so the use of a circuit sensitive to line amperes should furnish the necessary control. This circuit should act to reduce the magnetizing level of the generator as the line amperes increase. Since, for an individually operating generator, this would cause a decrease in voltage, the circuit is called a "voltage droop" circuit. It generally operates as follows: An increase in line amperes causes a voltage to be generated in the secondary of a current transformer. This voltage is added to the generator voltage impressed on the regulator. The regulator senses the increase in voltage and acts as though the generator terminal voltage is too high. It reduces the magnetizing power of the exciter field by reducing the exciter voltage and correspondingly reducing the power to the generator field and the magnetizing power of this field. Since the voltage of a paralleled generator cannot change, but must remain the same as the bus voltage, the reduction in magnetizing power acts only to reduce the magnetizing amperes being furnished by the generator. Conversely, if the magnetizing power of the generator is too low, this circuit acts, within its capacity, to cause the voltage regulator to increase the magnetizing power of the paralleled generator so it will be furnishing its share of magnetizing power to the system. A voltage droop adjustment causing a 3% to 8% drop in voltage from no load to full load at rated power factor is usually required for satisfactory division of ampere loading. The largest amount of droop that can be tolerated by the load should be used to insure stable operation.Voltage droop circuits can mistakenly be connected in reverse. In this case, the voltage from the current transformer secondary subtracts from the voltage of the generator terminals. The regulator acts as though the generator voltage were too low and increases the magnetizing power of the generator. This causes the ampere output of the generator to become excessive. The increase in amperes acts to increase the voltage subtracting from the generator voltage impressed on the regulator and the regulator continues to act to increase the magnetizing power of the generator. This power can increase to the