droop setting of governors
droop setting of governors
(OP)
I would appreciate, if any one can explain me exact meaning of droop in governor and how it is set along with setting range.
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RE: droop setting of governors
Droop allows generators operating in parallel to share load in proportion to their capacity. Voltage droop is used to provide reactive load sharing (kVAR), and frequency (speed) droop is used to provide real load (kW) sharing.
The concept of voltage droop: from a noload voltage condition, as reactive load is added the terminal voltage of the generator lowers due to the change in armature reaction. A voltage regulator causes the terminal voltage to lower linearly by controlling the rotor excitation. Voltage droop is usually expressed as the percent change in voltage from noload terminal voltage as the reactive load varies over the full reactive load range.
The concept of frequency or speed droop: from a noload frequency condition, as real load is added the the prime mover slows and the frequency lowers. A speed regulator causes the frequency to lower linearly by controlling the prime mover speed (governing). Frequency droop is usually expressed as the percent change in frequency from noload frequency as the real load varies over the full load range.
The generators I've worked with usually had less than 5% droop, and were fairly linear over the full load ranges.
Regulation allows load sharing by: (assume regulators for G1 and G2 are set equally as an initial condition)
As G1's voltage regulator is raised and G2's is lowered, G1 picks up more of the system's reactive load and G2 sheds reactive load while keeping the system voltage constant.
As G1's speed regulator is raised and G2's is lowered, G1 picks up more of the system's real load and G2 sheds real load while keeping the system frequency constant.
The load should be shared in proportion to the capacity of the generators. If G1's power rating is twice G2's, G1 should carry twothirds of the system's real and reactive load. This minimizes heating effects in each machine.
RE: droop setting of governors
Good explanation of droop, however, a good electrical operator or automatic system will manipulate the speed and voltage settings of both machines in parallel to maintain 60 hertz and rated output voltage on the buss. While the methodology of droop is to affect the machine's speed and voltage, the big picture is that the prime mover's (diesel, turbine, etc) power output and the field excitation are being adjusted proportionally to share the loads betwwen two connected machines.
Been there, done that.
Blacksmith
RE: droop setting of governors
RE: droop setting of governors
I assume I'll need a PID block with actual speed as PV and a speed setpoint SP. One of these terms is somehow modified by the droop variable, but I am not sure which or how.
The output of the PID block would be treated as a gate position setpoint. An inner control loop would position the gate to this setpoint using a hydraulic proportional valve.
Any thoughts?
Thank you
RE: droop setting of governors
It's right, you will use a PID algorithm, but not a compact one. For a electrohydraulic governor, we have a cascade loop, so the functions of the PID are distributed on the feedback reactions, depending on the regulating principle. The governor's droop can be defined either as a "power droop", when it operates on the generator's power feedback, either as an "opening droop" when the power signal from the generator is disconected and the droop is defined on the gate position. Assuming that the droop formula is (df/f0)/(dP/P0) where f0 and P0 are the rated values for the frequency and for the power, and df and dP are the variations at an arbitrary moment, that means you will take from the power signal only a part to compensate the frequency variation. The same applies for the gate position feedback. So when you write the PLC program you will multiply the power feedback with the droop value and sum the result with the frequncy error. The entire algorithm form depends on the way you design the speed governor.
Sorry for my english.
RE: droop setting of governors
I would calculate the Droop Adjustment as (%Droop) x (%Gate) so that as the Gate Position increases, I'll get a larger droop adjustment value. It is what I do next that I am confused about.
I assume that the PID block's setpoint (PV) input value should be actual speed (60HZ) and that I calculate the SP value by either adding or subtracting a value for Droop Adjustment from the desired speed setpoint (typically 60HZ).
Therefore the inputs to my PID block are as follows:
PV=actual measured speed (fixed by utility bus @60HZ)
SP=Desired Speed (60HZ) + (Max Droop Adjust  Calculated Droop Adjust)
I think I want the SP calculation as noted so that as load increases (gate %) the calc'd SP value gets smaller and approaches 60HZ, tending to balance out the PID equation. This way I am always trying to drive the unit towards full load (100% gate). But if all the connected generators produce to much power and the bus frequency speeds up, the unit will start to shut the gate as PV increases.
Comments and suggestions are greatly appreciated!
RE: droop setting of governors
RE: droop setting of governors
SPrpm= Desired Generator Speed in RPM entered by operator
PVrpm= Actual Generator Speed in RPM read from speed sensor
W= Actual Generator Output in Watts
F= Actual Generator Frequency in HZ(1800RPM=60HZ)
%Gate= Actual Gate Position from 0100%
%Droop= Droop setpoint from 05% entered by operator
The PLC program has a PID block with a setpoint (SP), present value (PV), and output (CV). The output (CV) will be fed as a setpoint to an inner loop (gate positioner) that will position the gate between 0100%.
I assume that I want the speed loop's SP=SPrpm as entered by the operator (typically 60HZ or 1800RPM). Therefore I believe that the "droop adjustment" should be made to the PV value. A formula of PV= PVrpm + (MaxDroopVal  DroopVal) should provide a PV of between 1800 and 1890RPM with 5% droop setpoint. As the actual %gate increased towards 100% (the unit is assuming more load), the PV value would decrease from 1890RPM (at 0% gate) to 1800RPM at 100% gate. Therefore the PID's blocks error signal would get smaller as the unit took on more load, therefore making it less likely to take on additional load. Am I on the right track?
Thanks again
RE: droop setting of governors
CV = [(df+dP*bp)(Kp+Ki/s)+df*Kd*s+setpoint]
where:
CV = the inner loop command
df = frequency error (desired frequency  actual frequency)
dP = power error (desired Power  actual power)
Kp = proportional gain
Ki = integral rate
Kd = derivative amplitude
setpoint = desired power
You can see that if the frequency error is zero, the power error is zero (so the frequency derivative is also zero) the gate positioner setpoint is zero for a steadystate opperation. You can also see that the PID is distributed on different terms so in your PLC you must use multiple calls to the PID routine (or function block) according to the mathematical operation you need in the loop.
RE: droop setting of governors
RE: droop setting of governors
bp  permanent droop
s  Laplacian operator
RE: droop setting of governors
RE: droop setting of governors
RE: droop setting of governors