Parameters that are related to PF regulation are listed below.
:01 - Generator Output Voltage
:02 - Ratio of Output Voltage to Sensing Voltage
:03 - Generator Type
:04 - Rated Generator Output Current
:05 - CT Voltage at Rated Generator Current
:31 - PF/KVAR Select
:32 - PF Reference
:33 - KVAR Reference
:36 - Paralleling Integral Gain
:37 - Paralleling Proportional Gain
:38 - PF Switch Point
Note: Parameters :36, :37 and :38 are only available on part number 155-xxxx or newer.
If a generator is connected in parallel with an infinite bus (utility), then the voltage of the generator is controlled by the infinite bus. The voltage of the generator will change as the infinite bus voltage changes. It is not possible to control the system voltage when the generator is connected to an infinite bus. In this instance, it is necessary for the digital voltage regulator to regulate the reactive power output which is supplied by the generator. There are two methods for regulating the reactive power output.
- KVAR Regulation
- Power Factor Regulation
Note: KVAR stands for kilo-Volt-Ampere-Reactive, which is the unit of measurement for reactive power.
If the digital voltage regulator is in the power factor operating mode, then it regulates so that the generator produces a constant power factor, regardless of the real power output of the generator. In this case, the reactive current will change when the real power output of the generator changes. A current transformer (CT) is necessary for this mode to work.
Operation of the power factor mode has changed a number of times. The power factor mode has changed in order to improve the behavior at low levels of real current. The first change took place when the "PROM ID" (parameter :91) changed to 1.03. The "PROM ID" change coincided with the new fault parameter methods. The second change took place when the part number for the regulator changed to 155-xxxx and the "PROM ID" changed to 1.05.
Original Power Factor Operation
If parameter :31 is set to zero, and the external switch on terminal 41 is closed, then the regulator will operate in "power factor control mode". The regulator assumes the generator is connected to an infinite bus, therefore, the voltage cannot be changed. In power factor mode the generator will supply a varying amount of reactive power (KVARs) based upon the real power output (kW) of the generator to obtain the desired power factor set in parameter :32 (or a remote rheostat).
PROM ID 1.03 Power Factor Operation
If parameter :31 is set to zero, and the external switch on terminal 41 is closed, then the regulator will start-up in the KVAR mode supplying 0 KVAR. When the real current measurement is equal to or above 10% of the rated generator output current, the regulator will switch operation to the power factor control mode. The rated generator output current is parameter :04. Thus, the generator set needs to provide a significant amount of real kW power before the digital voltage regulator will regulate in the power factor mode. The start-up value of 0 KVAR is a fixed value and cannot be adjusted.
While the measured real current is below 10%, the input of the remote rheostat will be ignored. Once the real generator output current exceeds 10%, the power factor will then be regulated according to parameter :32 (or a remote rheostat). In power factor mode the generator will supply a varying amount of reactive power (KVARs) based upon the real power output (kW) of the generator to obtain the desired power factor set in parameter :32 (or a remote rheostat). When the real current output of the generator decreases to 5% or less of the rated generator output current, the controller will switch back to regulating only KVARs as described above. The switch back point has hysteresis in order to avoid "ringing".
PROM ID 1.05 Power Factor Operation
When parameter :31 is set to zero, and the external switch on terminal 41 is closed, the regulator will start-up in the KVAR mode and will regulate according to the KVAR reference level which is set in parameter :33. When the real current measurement is equal to or above the percentage which is set in parameter :38, the regulator will switch operation to the power factor control mode. Thus, the generator set needs to provide a significant amount of real kW power before the digital voltage regulator will regulate in the power factor mode.
In the power factor mode the generator will supply a varying amount of reactive power (KVARs) based upon the real power output (kW) of the generator to obtain the desired power factor set in parameter :32 (or a remote rheostat). When the real current output of the generator becomes 5% less than the percentage configured in parameter :38, the controller will switch back to regulating only KVARs as described above. The actual switch back point has hysteresis. For further information, refer to the detailed explanation for parameter :38.
A remote PF/KVAR adjust rheostat may be connected in the power factor operating mode. When in the power factor mode (parameter :31 set to zero), the remote rheostat adjustment will override the PF reference in parameter :32, but at levels of current below the PF/KVAR switch point, the KVAR reference will be as set by parameter :33.
For stable operation of the generator in the power factor regulating mode, the generator must be connected to a utility or a system that is much larger than the generator. When the tie breaker is closed to the utility, use the external control switch contact at regulator terminal 41, via the gen/utility 52/a aux contact, to enable the power factor mode. When the terminal 41 contact logic is open, the regulator will be in a voltage control operating mode with or without droop or line loss compensation as previously described.