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Geoff_H

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Everything posted by Geoff_H

  1. Geoff_H
    Yes the speed of load rise depends upon the thermal inertia of the casing and the allowable rate of temperature rise. Derivatives are great for up to around 70MW. A 200MW stationary can get to 70MW around the same as a derivative (most stationary GTs meet the 10 minutes cold to full load). Below 60/70MW derivative makes the most sense from a cost point of view. Stationary GTs can quickly increase the load using water injection etc. Also stationary can immediately alter the set point on first stage inlet temperature, an increase in temperature instantly increases output at the cost of blade life. In a micro grid you always have enough reserve power to immediately replace the loss of the power being generated by the biggest loafed GT.
  2. Geoff_H
    Yes water cooling of the inlet air is common on stationary GTs. The compressors are density sensitive and produce less powe as the density drops. S&L GE aircraft derivatives are rated at around 60MW, but derated to around 50MW in the Goldfields. Super pure water is often injected just before the combusters. Is converts to steam (a steam turbines effect) and cools the combusted exhaust gas and allows more fuel to burn and a consequential power output. Some aircraft also do this to compensate for air density power loss in hot environments on take off. Super pure water is expensive to make so water injection is only used when an increased power is needed, or in power generation to the grid makes it economic. Walnut shells are often used in the air to clean blades.
  3. Geoff_H
    The smaller mines use 5MW diesel generators. But most large mines use GTs. Usually S&L GE aircraft derived 50/60MW with gearboxes to generators. A few Trent 70's exist and there redesigned to stationary generation rather poor (Rolls Royce aircraft derived). But most new installations are purposely generation designed GT'S of 100MW and combined cycle with steam turbines using Heat recovery (GT exhaust) steam generators and steam turbines 60%+ efficiency. GE have a steam cooled first stage turbine design that is rumoured to have 60% efficiency. Aircraft derived engines are not favoured for power generation as gearboxes above 60MW don't seem to exist. Power generation GTs run at 3000/3600RPM. However the GT that I worked on had Pratt and Whitney aircraft designed blades made under licence. Power Generation GTs of 400MW are now reasonably common.
  4. Geoff_H
    I worked on the design of 185MW gas turbine range in Florida in the early 90s. Gas turbines can be very efficient. In stationary situations 60% efficiency is easily obtained. In open cycle transport 35% is easily gained. The problem with gas turbines is that efficiency is directly proportional to installed cost. In another job I worked on with a 30% efficiency and 50MW output the replacement turbine first stage blades cost $5M and the overhaul of the combusters $4M, 15 years ago. OK stage that down to several hundred kW and the costs come much lower but still very expensive. GTs do have a longer life between overhauls. Large expense and long life between overhauls sounds just right to me for big trucks.
  5. Geoff_H
    The only thing that I can see that maybe a problem for an instructor (and I am not a person trained in law) is if instructors are responsible for the performance of his student. If the student lied and had a fit or something while flying and the instructor was held responsible then the instructor may wish to have a more rigorous medical certificate.
  6. Geoff_H
    Can be deterioration of O ring. Make sure that you are using correct fluid and O ring is correct type. If O ring gets wrong fluid rubber will expand and restrict piston movement. Just a thought.
  7. Geoff_H
    Just a reminder, do not remove oxide from electrical contract surfaces with carborundum (emery) it attaches small quantities to the surface and will oxidise with electrical current.
  8. Geoff_H
    In the 1970's when we first used computers in industry for control we would get many failures, almost always on computer board connections, we would always carry an ink rubber to remove oxides, more often happening in we weather. We were told by plug manufacturers that 30,000 psi connection pressure was needed to prevent high resistance connections. I believe that earth connections should be checked regularly, particularly after a wet period like the east coast is experiencing
  9. Geoff_H
    I think that you maybe right. Is there a difference between the shield and the ground plane. My experience is with instruments.
  10. Geoff_H
    It should have the shield wired to an instrument bus via a dedicated connection. However the installer may have connection the shied to earth at the aerial. The thing to do is only earth one shield end.
  11. Geoff_H
    Brendan the shield is best earthed at the tx/rx module. The antenna end shield is best isolated from the chassis of the aircraft. If the shield is earthed at both ends you will get an earth loop current in the shield, this loop current will radiate inside the aircraft and interfere with most devices. It is also recommended to check that an accidental earth is not happening at the antenna and a solid earth exists at the rx/tx module.
  12. Geoff_H
    Check your cable shields for earthing. Must be earthed solidly, and most importantly at one end only.
  13. Geoff_H
    Not totally sure but I expect that it has to do with the on/off control circuit. The battery is one huge Capacitor. I expect that the others have a amperage demand circuit and use that to control. I think that the Capacitor one uses a simpler control circuit using the Capacitor and the resistance of the cables to the battery in an RC delay circuit that would give the frequency of the on/off operation. Why the control doesn't have an inbuilt Capacitor is don't know, but I am guessing it is to do with the size of the box
  14. Geoff_H
    I expect that the Capacitor is to give the MOSFET a voltage level at which to switch off. When the Capacitor discharges into the aircraft electrical system iits voltage will start to drop, the control circuit will see this and turn the MOSFET on. When the Capacitor reaches the voltage of the set voltage for aircraft operation the control system will turn the MOSFET off. This cycle continues as required.
  15. Geoff_H
    Another technique is the same as inverter technology. It uses switching using Mosfets. If you use resistance for control a large amount of heat will be produced. In essence the .Mosfet will switch on and when the output reaches the desired voltage the Mosfet will switch off. It does this as often as the time for the outlet voltage to drop to a predetermined value. On and off will be very quick at low power and very long at high voltage. Efficiency low at low power settings.
  16. Geoff_H
    Second sentence should read: The non permanent magnet alternator/ generators regulate the magnetic field strength of the rotating field to give a stator voltage of 12volt
  17. Geoff_H
    Not exactly the same. The non permanent magnet alternator/generators alternator the magnetic current of the rotating field. The stator voltage is then a function of rotating flux density and velocity. The relay was altering the field current. With a permanent magnet rotor the field flux is fixed, the velocity varies so the output voltage varies with rpm, so you have to convert the output voltage to 14volts (or 28volts depending on system). It is just the same as a phone charger that converts 110 or 240volts to 5/12volts automatically.
  18. Geoff_H
    Doesn't it depend upon whether the output from the alternator is below or above 14V?. I think that you are right but if you use straight resistance you may have a heat dissipation problem. Yes I agree that the oscillation frequency is high, that way only a small transformer is needed. In the 1970's I had a job that needed 5volts from a 24Volt supply. Two racks of many 2n3055's tied together, then switch mode became available, one small package 1/10 the panel space and no heat issues.
  19. Geoff_H
    If I understand it correctly the way a permanent magnet generator works is the same as a switch mode power supply. The AC voltage from the generator that will be speed dependent. This voltage is rectified and a large capacitor charged. A control circuit will turn a power transistor on and off through a transformer at a rate that will give an output at the aircraft system charging voltage the rectify this ac voltage and connect the rectified output to the system. Well in a similar way to this.
  20. Geoff_H
    I was thinking about buying an 80% complete Starlet, this would be like buying an advanced kit phone. Only 80% to go lol. So I looked at what needed to be purchased, cowling, fabric props fuel system radios paint, the 80% to go looked good. Then I priced these components, including freight, it would be cheaper to buy an already flying one.
  21. Geoff_H
    I have a Chinese lathe. A dead copy of an American lathe. However it needed adjusting of the lathe from new. The Chinese However did not know the material composition of the critical parts. A high tensile steel part was copied as mild steel, the zero backlash devise is now useless. Sorry I don't share your acceptance of the Chinese propaganda that they can make good things. Look at their NPT threads are NP no T.
  22. Geoff_H
    I would never put my life in the trust of a Chinese made product. I have too much crap that was made in China. Bought carbide tool system to curt thread on lathe. It broke 10 tips without a single pass ( some at only a few thou deep) in steel. Dis cut a thread in aluminium
  23. Geoff_H
    30 years ago I got mild co poisoning. I was the commissioning manager on a boiler plant that burnt CO to make it into CO2. The resultant heat was used to produce steam for a separate process. The plant was in the open, I wore a CO monitor. One day the CO alarm on the monitor went off, I was around 5 metres from the plant. I immediately ran in a direction away from the plant. I noticed that the reading was 100ppm. I ignored the event and continued my job. Two hours later I felt tired and decided to go home. I got more and more tired. When I got home I immediately went to sleep, I did not stir and woke up at 7am the next morning, with a headache. I was told that on the CO alarm I should have gone to first aid and sat on oxygen for several hours. So what is the flying take from this. The characteristic that one should look for is starting to get tired with muddled thinking, the get on the ground and out of the craft ASAP.
  24. Geoff_H
    An RCD, an RCCB and Earth leakage circuit Breaker are all the same device. They measure the current to the load, and the current from the load, if they are not equal the current that is different will magnetically open the circuit Breaker. Regularly test them by pressing the test button. If the current goes through you and returns through the earth there will be a residual current and trip, BUT if it goes back through the path leakage Breakers there is no residual then there is no trip. You are electrocuted.
  25. Geoff_H
    Electrocution active to neutral is not protected by an earth leakage circuit Breaker
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