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AC Voltage Regulators

Discussion in 'Electronic Design' started by Myauk, Nov 6, 2006.

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  1. Myauk

    Myauk Guest

    In my country, I took part in design and construction of Auto
    Transformer AC Voltage Regulators with automatic control of tap
    changing with electromechanical relays.

    Since my country is less developing country in Electrical and
    Electronics product development, I would like to know if these
    Electromechanical Relay Type-Automativ AC Voltage Regulators with Auto
    Transformers are obselete or not.

    Are they still required for certain applications?

    If it is not useful anymore, I would study
    solid-state-relay-auto-transformer type regulators, and PWM control
    type, Servo motor control type AC regulator designs!

    More over I would like to know how to study and analyze relay
    connection scheme for such regulators. ( I mean we use up to five SPDT
    relays to change six different tapping for auto-transformer to provide
    six different turn ratios, one step down, five step up between the ac
    input and output. I would like to study different combinations of relay
    contact points to provide a good voltage regulation scheme)
     
  2. Ken Smith

    Ken Smith Guest

    They also make electro-mechanical ones that don't use relays. These may
    be a better thing for you to think about. Imagine an object that looks
    mechanically like an AC motor.

    The stator is much as you would expect in the AC motor.

    The rotor has a winding on it that is only part of the secondary turns.

    If you imagine the stator and rotor windings connected in series, you will
    see how turning the shaft will vary the turns ratio from less than 1:1 to
    more than 1:1.

    To remove the leakage inductance, a heavy copper strap is used to act as a
    shorted turn to the leakage.

    Ones like these are still in use here and there in China. They are
    extremely robust but they don't remove sudden pulses of power. They are
    still worth knowing about because the theory they work on may be adapted
    to something more modern.


    All such devices make matters worse for others. When the mains voltage is
    low, they draw more current and when it goes high they draw less current.
    This makes the variations worse. For this reason, they con only be used
    on a small fraction of the loads if you want the power system to be
    stable.
     
  3. Sola "Adjust-A-Volt"
    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  4. Myauk

    Myauk Guest

    Can you show me the link so that I could understand more and study the
    schematic?
     
  5. AFAIK they are still used for electrical distribution systems.
     
  6. Eeyore

    Eeyore Guest

    Don't you also get motor driven variacs ?

    Graham
     
  7. Ross Herbert

    Ross Herbert Guest

    The relay system you describe would appear to me capable of only
    producing step-incremental voltage changes, - not what I would term a
    "good voltage regulation scheme".

    High power systems which I saw used around the 1970's, employed motor
    driven variacs which produced a much smoother response than relay
    switched schemes.
     
  8. Not for mains electrical systems. N. America seems to use a lot more smaller
    pole transformers from 11 Kv. I've lived where step selected transformers
    were in use - you can see the lights change brightness as the transformer
    steps up or down.
     
  9. Borat

    Borat Guest

    20+ yrs ago they used a motor driven system in the front end of
    telecommunications rectifiers (mains AC --> 48Vdc) for regulation. Perhaps
    someone remembers more about them than me?
     
  10. Ross Herbert

    Ross Herbert Guest

    That's exactly the units I was referring to (at Pier Exchange in
    Perth) but it was a lot earlier than the 80's. Several 48Vdc/1000A
    rectifiers for battery charging.
     
  11. John Perry

    John Perry Guest

  12. I've seen my share of CVTs, however I only once ever worked on a system with
    a magnetic amplifier and I don't know anyone else who has.
     
  13. John Perry

    John Perry Guest

    This is not a magnetic amplifier. This is a variable transformer
    similar to what was described in my attribution, which you deleted.

    The variable transformer adds a controllable small AC voltage to the
    line voltage, with consequent smooth sine wave output.

    Magnetic amplifier operation is very similar in operation to an SCR
    power controller. In an SCR controller, the control signal causes the
    semiconductor to be an open circuit until conditions cause it to switch
    to a low resistance, with consequent waveform chopping. In a magnetic
    amplifier, the control signal causes the inductor to be a high reactance
    until conditions cause the core to saturate, switching to a low
    reactance, with consequent waveform chopping.

    jp
     
  14. It was just an observation.
    But isn't this basically a CVT?
     
  15. Eeyore

    Eeyore Guest

    I don't know if it counts as a 'magnetic amplifier' but ~ 32 yrs ago I saw a
    theatre light dimmer pack that used a DC control current in one winding of a
    saturable reactor that controlled the AC load.

    Quite neat really and no triac style EMI !

    Graham
     
  16. Yep, same thing.
     
  17. Myauk

    Myauk Guest

    What is CVT?
    for voltage regulation is no longer useful in General Electrical
    Applications except in some light dimming schemes, battery charging and
    Generator Sets, am I right?

    Has a magnetic amplifier been still being used until now? From the
    point of view of power quality, I think it is a better solution
    providing a good regulator with less spikes and surges, am I right?

    Can anybody show me the link to the general circuit design for servo
    motor controls for such moter driven voltage regulators.:- I have one
    schematic by some China Company but I still need more schematics so
    that I could compare the design to understand more about it!

    Please explain a little bit about them for the newcomer like me, who
    actually is just a few years old in Electronics Design Field. :)


    Regards
     
  18. Last one I saw was in a sewage pumping station about 40 years ago. It was
    controlling a DC pump motor and we connected it to a depth gauge to control
    the depth in the holding tanks.
     
  19. Jamie

    Jamie Guest

    yes, it has a 3 pole core. very common in the old days for variable
    control from a low power source of DC>
     
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