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| Illustration 1 | g00538141 |
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Illustration Of The Loading And Stopping Profile | |
The parameters that are related to the loading and the stopping profile are listed below.
01 - Generator Output Voltage
03 - Generator Type
06 - Knee Frequency
07 - Decreasing V/Hz Slope 1
08 - Decreasing V/Hz Slope 2
09 - Minimum Voltage
10 - Underfrequency Point
Voltage regulators are generally of the volts per hertz type or the constant voltage type. The digital voltage regulator can perform as a constant voltage regulator or a volts per hertz type regulator depending on user configuration. Volts per hertz type regulators are commonly used with reciprocating internal combustion engine driven generator sets because the regulators provide an automatic means for the engine to recover from a large block load. In the digital voltage regulator, the block load recovery performance is configurable so that it may be field optimized for each specific application.
When the generator is running and if a large load is applied, the frequency and voltage will drop. The loading/stopping function minimizes the amount of time that it takes the engine and generator to recover and increases the ability to pick up large loads. After the knee frequency has been reached on start-up, this function will modify the voltage reference based upon the frequency of the generator.
As a large load is applied, the engine speed will begin to drop, that is, the generator frequency decreases. As the frequency decreases below the knee frequency, the voltage reference will decrease on a Volts/Hz slope according to the decreasing slope 1 value (parameter :07). If the frequency decrease continues beyond the knee frequency minus 5 Hz, then the voltage reference will decrease on a Volts/Hz slope according to the decreasing slope 2 value (parameter :08) until the minimum voltage level (parameter :09) is reached. The digital voltage regulator will try to regulate the generator output voltage at the minimum voltage, unless the underfrequency point (parameter :10) is reached at the point the generator output voltage will decrease to a minimum value.
As the engine recovers from the load increase, the voltage will increase in the reverse order as it decreased, unless the frequency dropped below the underfrequency point. If the frequency dropped below the underfrequency point, the start-up profile will be used for the recovery.
In some applications it is preferable to maintain a constant voltage at the possible sacrifice of a larger frequency dip during load transients. The digital voltage regulator can accommodate these applications if the knee frequency (parameter :06) is configured for a lower value than normal. The actual value will depend on the specific application. When used in this application, the load transients must be kept small in order to allow the engine to recover without dropping below the knee frequency.
When a large block load is switched on to the system, the engine speed temporarily decreases as the engine produces the additional power requirement by burning more fuel. If the regulator is set to act as a volts per hertz type, it will reduce the output voltage according to the slope of the V/Hz curve. The reduction in voltage reduces the power requirement of the load, thus allowing the engine to recover faster for a given block load.
If the regulator is set to act as a constant voltage type, the regulator will not reduce the output voltage for a change in speed (addition of block load). Therefore, it will take the engine a longer time to regain speed and supply the total power requirement of the load. If the regulator is set to act as a constant voltage type, care must be taken to keep block load applications small enough so that the engine can recover in acceptable time.