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What is the function of governors?
control the speed of the prime mover driving the generator by controllingthe flow of steam or fuel to the prime mover under any load up to the capacity of the prime mover
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What are the two types of governors?
- mechanical (or hydraulic)
- electrohydraulic load sensing
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Mechanical governor
can operate in isochronously or droop
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What is isochronous?
- use when operating singly
- no change in speed as the load changes
- gen immediately takes on its portion of the load and the gen is in parallel
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What is droop?
speed changes as the load changes in order to get proportional division of load between generators
set at 3.3%, max 5%, between generator to provide good load division
gen takes part of the load but the speed potentiameter is manually adjust to make oncoming generator share the load equally
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Electrodydraulic Load Sensing
- better transient response than mechanical-hydraulic type
- allows associated generators to operate in isochronous
- does not require operator to adjust freg as the load changes
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How does the EH governor works?
EH receives eletric signals (speed and load), compares them to a reference, and any difference becomes a signal for a hydraulic system to change the throttle setting
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What are the basic elements of EH?
- PMA: permanent magnetic alternator
- speed sensing circuitry
- load sensor
- actuator
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How does the PMA workds?
measures prime mover speed and its output freq is converted to a voltage and compared to a freq reference
it also supplies power for the brushless exciter
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How does the speed sensing circuitry works?
it receives the speed signal, converts it to a voltage, compares it to a reference voltage (set with petentiameter), and produces an output to control the fuel or steam valves to provide the desired speed output.
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How does Load Sensor works?
comprised of xformer, diodes, and potentiameter
converts its gererator's voltage and current signal to a dc voltage signal proportional to load.
in isochronous mode: output of one gen load sensor is compared to an equivalent output of another gen. difference is fed into the basic sensing ckt of each gen to equalize loads automatically
in droop mode: outputs of load sensors are not compared.
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How does an actuator works?
controlled by the speed and load sensor circuitry
controls the fuel or steam, as required, to control the output speed of the prime mover
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Operation of governor
- automatically takes over speed control when the speed gets to 80% synchronous speed
- normal procedure: isochronous mode,
use droop: when paralleling with other gen set or shore power
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Maintenance
Hydraulic actuator: sensitive to oil and moisture, which can cause corrosion
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Troubleshooting
trouble in the governor can be located by measuing various dc signals to the actuator speed sensing and load division circuits.
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