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Control type of hydropower governor and traffic lights

Short answer

The governor system is a closed-loop control that measures turbine speed and adjusts water flow to keep frequency at 50 Hz despite load changes. The traffic light system is open-loop, using preset timers without measuring traffic flow, so no feedback corrects the output.

What kind of control system could have been in the following? Illustrate with necessary blocks and variables. i) Governor system of Hydropower Station ii) Traffic light system of Kathmandu

i) Governor system of a hydropower station: closed-loop control

The governor keeps the turbine-generator speed (hence frequency, 50 Hz) constant while the electrical load changes. It measures the actual speed and corrects the water flow, so it is a closed-loop (feedback) system.

 Nref +   e   +---------+ u +--------+ q +-------+ N  
 ---->(Σ)---->|Governor |-->|Servo + |-->|Turbine|-+->
      ^ -     |(PID)    |   |gate    |   |+ Gen. | |
      |       +---------+   +--------+   +-------+ |
      |                            load ΔPL -->    |
      +------------[Speed sensor / PMG]<-----------+
Variable / blockMeaning
NrefN_{ref}reference speed (synchronous speed, 50 Hz)
Speed sensormeasures actual speed NN (tachogenerator, PMG, frequency transducer)
eespeed error Nref−NN_{ref} - N
Governorcontroller (PID / droop) giving signal uu
Servomotor + gateactuator; sets wicket gate / needle opening, i.e. water flow qq
Turbine-generatorplant; mechanical power and speed NN
ΔPL\Delta P_Ldisturbance: change in electrical load

When load rises, speed falls, ee becomes positive, the gate opens and the turbine power increases until speed returns to normal.

ii) Traffic light system of Kathmandu: open-loop control

The lights change according to preset timers; no measurement of traffic is fed back.

 preset   +-----------+ signal +---------+ vehicle flow
 timing ->| Timer /   |------->| Traffic |------------->
          | controller|        | junction|
          +-----------+        +---------+
                                   ^ disturbance:
                                   | traffic volume
Variable / blockMeaning
Inputpreset green/amber/red durations
Controllertimer / sequencer circuit
Actuatorsignal lamps
Plantroad junction and vehicles
Outputvehicle flow / queue length
Disturbancevarying traffic volume, accidents

Because the output (queue length) never affects the controller, the system is open loop. It can be made closed loop by adding vehicle detectors or cameras whose data adjust the green time.

✓ Answer checked by Claude Opus 5.5 (high effort)

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