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| Illustration 1 | g01012488 |
The parameters that are related to the loading and stopping profile are listed below.
- Generator output voltage
- Knee frequency
- Decreasing V/Hz slope 1
- Decreasing V/Hz slope 2
- Minimum voltage
- Under frequency 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. The Volts/Hz regulators provide an automatic means for the engine to recover from a large block load. The functionality of the DVR allows the configuration of the block load recovery performance. The functionality allows field optimization 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 is required for the following:
- Time for the engine to recover
- Time for the generator to recover
- Increases the ability to pick up large loads
As a large load is applied, the engine speed will begin to drop (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.
If the frequency decrease continues beyond the knee frequency minus 5 Hz, then the voltage reference will decrease. The decrease will follow a Volts/Hz slope according to the decreasing slope 2 value until the minimum voltage level is reached. The DVR will try to regulate the generator output voltage at the minimum voltage. Minimum voltage regulation will continue unless the under frequency point is reached where 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 the voltage decreased. The the reverse order will be true unless the frequency dropped below the under frequency point. If the frequency dropped below the under frequency point, the startup profile will be used for the recovery.
In some applications, a constant voltage is desirable even at the possible sacrifice of a larger frequency dip during load transients. The digital voltage regulator can accommodate these applications if the knee frequency 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. Small load transients 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. The control will respond to the load to produce the additional power requirement by burning more fuel. If the regulator is set to act as a V/Hz type, the regulator will reduce the output voltage. The output voltage will be reduced 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. That is, the regulator will not reduce the output voltage for a change in speed even with the addition of block load. Therefore, a longer time will be needed for the engine 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. The block load applications must be kept small enough so that the engine can recover in acceptable time.