 | |
| Illustration 1 | g00609389 |
Diagram of the Generator Set Load Sensor | |
Note: For a description of the circuit functions of the engine speed control governor, see the appropriate manuals.
The basic circuits of the generator set load sensor are listed below.
- power supply
- power sensor
- controller
- summing point
The Power Supply Circuit
The power supply circuit is connected internally to the terminals of a potential transformer. The power supply circuit does not require any additional, external power supply. Installation of the jumpers provides either 95 to 130 or 190 to 260 potential transformer voltage to the internal power supply. The frequency in this case can be from 50 to 400 Hz. The power supply regulates a DC voltage for all load sensor circuits.
The Power Sensor Circuit
The generator kilowatt load is measured by the power sensor circuit that has connections to the current and potential transformers. The power sensor provides the controller circuit with a filtered load signal. At the controller, the load signal is adjusted with the load gain potentiometer to a specific voltage at full load. This specific voltage is equal to a load gain voltage. All other controls in the system are similarly adjusted. This load gain voltage is always proportional to the generator load and decreases proportionally from full load to no load.
In an isochronous load sharing system, the load gain voltage is shared with all other controls through paralleling lines. The load gain voltage provides an average load gain signal which is used by the controller circuits.
The Controller Circuit
By comparing the paralleling line voltage to the load gain voltage, the controller calculates an output in order to raise the engine speed or lower the engine speed. This will make the load gain voltage of the unit equal to the paralleling line voltage. The output of the generator set load sensor directly biases the circuit of the speed loop controller of the engine speed control governor. This affects the actuator fuel level setting and precisely maintains the proportional share of system load. Also, a fixed frequency is maintained.
Note: In an isochronous load sharing system the engine speed control's governing function is fully utilized. It responds normally to all speed changes and maintains constant system frequency regardless of load changes within its capacity because the load sensor output is determined by comparing actual system and unit loads. However, in a droop paralleling system the common load signal of the paralleling line is not used. The load sensor's droop function is derived from a voltage which represents load sensor output to the speed control. However, circuit functions remain essentially the same whether operating isochronously or with droop.
The droop potentiometer adjusts a voltage that is used to change the output of the load sensor. As the unit load changes, controller circuit output is biased by the droop function. The output of the load sensor and actuator terminal shaft position are reduced according to the desired droop slope which maintains the unit's load. Note that this would allow the frequency of a single isolated unit to vary proportionally with load. In droop paralleled systems, however, the system frequency is dependent upon the frequency of the one isochronous unit in the system. The isochronous unit will accept all load changes within the capacity. The isochronous unit will maintain system frequency. When droop operating controls are paralleled to an infinite bus, the infinite bus regulates the system frequency. The droop adjustment in this case adjusts the amount of load assumed by the generator.
The Summing Point
The generator load sensor controller circuit output connects to the internal summing point. The summing point allows an optional Service Program Module Synchronizer to control the engine speed governor for automatic synchronization to the bus.
The generator set load sensor output is used with 524, 1724, 2301A and 701 speed controls. The output is an analog voltage signal that increases or decreases to affect the speed control.