Engr. Elmer M. Espiritu


                This research aimed at developing and designing a Portable Generator load Controller (PGLC)  as a protective device for portable generator. The PGLC is designed specifically to solve generator�s over-voltage and over-speeding that could possibly damage the generator unit itself and the other electrical loads connected to it by switching �ON� and �OFF� standby loads thereby maintaining the loading condition of the generator.

                The study includes determining the efficiency, effectiveness, reliability and cost of the said device. The PGLC has a rated voltage of 220 volts, 60 Hz with a rated capacity of 2.0 kVA. Analysis of data was done to determine whether the PGLC was associated with a favorable change on the generator�s performance with and without PGLC.

                Keywords: load controller, over-voltage, over-speeding, standby loads, loading condition

                An electrical generator unit is used primarily to supply a limited load up to specific capacity at a rated terminal voltage, speed and frequency. It is of greater use when there is power interruption or in areas where there are no power lines.

                During normal operation of an electric generator, the rotation motion of the rotor of the alternator is based on the principle in dynamics which states that to have a constants and uniform rotational motion the accelerating torque must be zero. To maintain this condition, the mechanical input of the prime mover to the alternator must always equal to the sum of the electrical output and rotational losses.

                When the alternator is operating at this condition, the machine is said to be operating a steady-state operation. In this study, the mechanical input to the alternator is considered constant at any given operating condition. This assumption is a fair one for the generator since a small capacity generator, which is the subject in this study, does not have governor or the so-called speed regulator that will automatically respond to any change in electrical output or electrical load connected to the machine.

                Some of the problems encountered in the operation of small capacity electric generator are the increase in the terminal voltage, varying frequency of the electric power supplied to the load and the increase in the rotational speed of the rotor. These problems are due primarily to the sudden loss or decrease in the electrical output of the machine.

                Should this situation happens, the rotating parts and bearings of the generator unit will be subjected to more wear and tear by the excessive friction, centrifugal force and vibration that are caused by the increased rotation of the rotor. The life span of the generator unit may be shortened; the maintenance and operating cost will be higher than usual. On the load side, electrical appliances connected on the generator will operate abnormally and could be damaged. The increase or decrease of the fuel input to the engine prime mover can control the generator to deliver its rated capacity at a rated frequency and speed.

                In this study, the Portable Generator Load Controller is expected to bring down excessive increase in the terminal voltage of the generator to its rated terminal voltage level. Thus, preventing a sudden decrease in electrical load that will cause imbalance in the mechanical input and electrical output thereby preventing an increase in terminal voltage. When the terminal voltage increases to a predetermined level, the PGLC will function by switching on a standby load so as to maintain the equilibrium between the input and output of the machine. With this equilibrium maintained, the terminal voltage of the generator will return to its former value together with the desired rotor speed and frequency.

                The PGLC functions automatically at the predetermined value of terminal voltage. This process will go �on� and �off� repeatedly depending on the decrease or increase of the loading condition of generator units.


                The experimental research was used in this study. Three generators having equal capacity of 2.0kVA at rated voltage of 220Volts, 60Hertz were used. A voltmeter, frequency meter and tachometer were used to measure the terminal voltage, frequency output and the rotational speed of the rotor of each of the three generators with and without the use of the Portable Generator Load Controller.

                In this study, the generator was tested at 100% or full load condition and then gradually the load was decreased down to 0% or no-load condition. The data gathered were given statistical treatments to determine if there was a significant difference between the generator�s outputs in terms of voltage, frequency, and speed with and without the use of PGLC.


                The Portable Generator Load Controller has high power efficiency during varying load conditions. As shown in Table 1, the loads connected were purely resistive load. The generator was loaded starting from 1950 watts, 1300watts, and 650watts and down to 0watts or no-load condition. The voltage current and power were measured both on the output terminals of the generator and the PGLC. In the test conducted, using the PGLC, it yielded an average power efficiency of 96.49%

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