Yes, it is a thing. All motors operate on a rotating magnetic field. The capacitor actually helps get the field rotating on start in single phase. A three phase does not need that help. But motors are designed to operate under specific conditions. There are engineering specifications to follow and there are rules of thumb to follow. What you worry about is how hot the winding's will get under load. And in general single phase motors dont like to be operated at conditions they were not designed for. So you can buy motors which are designed to be three phase and variable speed (which is what I did) or you can buy motors with larger horsepower and operate them at lower power ratings. You are doing the right thing (my opinion). All the vfd does is control the frequency of the rotating field. The starting phase single or three phase pretty much depends on what is available. If you do not have three phase its going to cost a lot to get it.
Whaaaat? Could it be?
- Thread starter Shopgeezer
- Start date
Help Support Home Model Engine Machinist Forum:
An aside: my first real experience of VFR was for Dinorwig Power Station that was being built in the 1970s. I designed all the steelwork supporting the starting busbars. The steel work had to resist the potential forces in case of a short circuit. But the interesting thing was the Variable speed drive: 2 versions: the simple one switched a pair of phases, coupling 2 turbo-generators, then by opening the water valve on one turbine, the generator started moving with variable frequency of output from 1/3 Hz up to 50Hz. This directly accelerated the other turbo-generator so when it reached 50Hz running speed it could be connected to the grid, and water valves opened so it could pump water to the top reservoir. The second method used was via a huge electronic VFR connected to the starting busbars, to start a turbo generator either rotating as a pump or the reverse direction as a generator.
Just FYI...
K2
Just FYI...
K2
awake !
With the circuit using thyristor: I haven't used it to control the 1 phase motor so I don't know
The output of a Triac is current / voltage AC partially trimmed, as shown below
( Triac is commonly used in Dimmer )
And currently I am using Dimmer to run a 110v - 1/2 hp motor with 220v voltage
With the circuit using thyristor: I haven't used it to control the 1 phase motor so I don't know
The output of a Triac is current / voltage AC partially trimmed, as shown below
( Triac is commonly used in Dimmer )
And currently I am using Dimmer to run a 110v - 1/2 hp motor with 220v voltage
Last edited:
ajoeiam
Well-Known Member
How many MW was that system?
Awake, As Minh-Thanh's diagram shows - a Triac simply switches on at some point and off again at each transit through zero volts - so it chops the power so that on average the voltage gets less as you dial it down.
This is a pretty blunt instrument but works fine on resistive loads like filament light bulbs which do not care how ratty the supply to them is.
Problem: It does not change the frequency (as a VFD does) so it can't change the speed of an induction motor. You might get it to hum, heat up, smoke or stall but never change its speed.
It can change the speed of a brushed / commutator type motor (A'La most hand held power tools) which are voltage dependent rather than frequency dependent.
But even here you will run into problems - like at 50% the voltage only turns on at what is its maximum - halfway through the wave - and that can pose considerable inrush current problems.
If you are on a 220V (RMS) system when the Triac switches on at 50% the instantaneous voltage is actually 311V and you are switching that into an inductive load with very low resistance and at switch on no other impedance as the magnetic field hasn't even got going yet - equals massive inrush. Worse the next cycle might run headfirst into the back EMF "outrush" from the first cycle. All in all, horrible.
Triac drives (light dimmers) should generally not be used for inductive loads for this reason.
Ditto for electronic devices which generally react badly to such "ratty" input voltages.
Regards, Ken
This is a pretty blunt instrument but works fine on resistive loads like filament light bulbs which do not care how ratty the supply to them is.
Problem: It does not change the frequency (as a VFD does) so it can't change the speed of an induction motor. You might get it to hum, heat up, smoke or stall but never change its speed.
It can change the speed of a brushed / commutator type motor (A'La most hand held power tools) which are voltage dependent rather than frequency dependent.
But even here you will run into problems - like at 50% the voltage only turns on at what is its maximum - halfway through the wave - and that can pose considerable inrush current problems.
If you are on a 220V (RMS) system when the Triac switches on at 50% the instantaneous voltage is actually 311V and you are switching that into an inductive load with very low resistance and at switch on no other impedance as the magnetic field hasn't even got going yet - equals massive inrush. Worse the next cycle might run headfirst into the back EMF "outrush" from the first cycle. All in all, horrible.
Triac drives (light dimmers) should generally not be used for inductive loads for this reason.
Ditto for electronic devices which generally react badly to such "ratty" input voltages.
Regards, Ken
ajoeiam - 300MW per set (6 sets)
But the starting busbars could not carry that power. That was the power per set of Main Connection busbars. The Starting busbars only carried power to get a single set started from rest to synchronous speed (50Hz.). This could be done with the water turbine spinning "In-air" or "In water" - but not against the head of the High pressure water. I can't remember all the operational modes. Starting by external supply through the VFD would be "in-air" to get the pump-generator up to pumping speed, when it would be synchronised and connected to main busbars before introducing water from the lower low-pressure tunnel and as pressure was developed the high pressure valve would be opened to permit pumping of water to the top reservoir. Of course, for generation, the turbine (at rest) could have the low pressure valve opened to flood the turbine, then the high pressure valve opened to start the generator and when at synchronous speed the circuit breakers could be closed onto the main connections to generate power. (This takes 90 seconds or so I think?).
I understand that when on "stand-by" - e.g. for the half -time kettles to be switched ON in a cup match, all sets would be spinning "in-air" and synchronised to the grid, ready for the low pressure and high pressure valves to be opened and generation would be brought up to full load in 30 seconds, or so, but in emergency (Spinning in water? - Low pressure valve opened?): the whole power station can be brought on line - 0 to 1,320 MW in 12 seconds! (I understand the limitation is the acceleration of the hundreds of tons of water in the high pressure water column and low pressure pipe from rest to full velocity!). Similarly shut-off (close high pressure valve and blow-down the turbine with air). Of course, steam turbine power plant is much quicker to react as the mass of steam to be accelerated from "spinning at no load" to "Full load" is 1000 times less than the mass of water in a hydro-station. But the expense of holding a reservoir of water compared to a boiler full of steam is a bit different, and the rapid thermal loading on the steam turbines is not very clever.
Here's a link to the Power Station site... It can tell you more than I remember.
https://en.wikipedia.org/wiki/Dinorwig_Power_Stationhttps://www.electricmountain.co.uk/About-Pumped-Storage
I just worked on the 18kV Main and Starting connection Busbars and associated plant. - A curiosity: The thickness of "rock" - with lining - for the high pressure water side, was about the same as the rock and lining for the low pressure side - although the low pressure tunnel ID was larger: This same cross section was carried through the space require for the 18kV Busbars, between switchgear, the 440kV busbars, between switchgear, the 440V underground cables - and then the 440kV Overground power lines (which require a lot of air space to insulate 440kV!). Seems with "the whit of man" there is an "economical space" required through which we transmit power....??
K2
But the starting busbars could not carry that power. That was the power per set of Main Connection busbars. The Starting busbars only carried power to get a single set started from rest to synchronous speed (50Hz.). This could be done with the water turbine spinning "In-air" or "In water" - but not against the head of the High pressure water. I can't remember all the operational modes. Starting by external supply through the VFD would be "in-air" to get the pump-generator up to pumping speed, when it would be synchronised and connected to main busbars before introducing water from the lower low-pressure tunnel and as pressure was developed the high pressure valve would be opened to permit pumping of water to the top reservoir. Of course, for generation, the turbine (at rest) could have the low pressure valve opened to flood the turbine, then the high pressure valve opened to start the generator and when at synchronous speed the circuit breakers could be closed onto the main connections to generate power. (This takes 90 seconds or so I think?).
I understand that when on "stand-by" - e.g. for the half -time kettles to be switched ON in a cup match, all sets would be spinning "in-air" and synchronised to the grid, ready for the low pressure and high pressure valves to be opened and generation would be brought up to full load in 30 seconds, or so, but in emergency (Spinning in water? - Low pressure valve opened?): the whole power station can be brought on line - 0 to 1,320 MW in 12 seconds! (I understand the limitation is the acceleration of the hundreds of tons of water in the high pressure water column and low pressure pipe from rest to full velocity!). Similarly shut-off (close high pressure valve and blow-down the turbine with air). Of course, steam turbine power plant is much quicker to react as the mass of steam to be accelerated from "spinning at no load" to "Full load" is 1000 times less than the mass of water in a hydro-station. But the expense of holding a reservoir of water compared to a boiler full of steam is a bit different, and the rapid thermal loading on the steam turbines is not very clever.
Here's a link to the Power Station site... It can tell you more than I remember.
https://en.wikipedia.org/wiki/Dinorwig_Power_Stationhttps://www.electricmountain.co.uk/About-Pumped-Storage
I just worked on the 18kV Main and Starting connection Busbars and associated plant. - A curiosity: The thickness of "rock" - with lining - for the high pressure water side, was about the same as the rock and lining for the low pressure side - although the low pressure tunnel ID was larger: This same cross section was carried through the space require for the 18kV Busbars, between switchgear, the 440kV busbars, between switchgear, the 440V underground cables - and then the 440kV Overground power lines (which require a lot of air space to insulate 440kV!). Seems with "the whit of man" there is an "economical space" required through which we transmit power....??
K2
ajoeiam
Well-Known Member
Interesting information on the hydro stuff.
Got a tourist view (look from a distance) of Itapu, AIUI the world's highest power production dam system (yes bigger than the 3 Gorges), where they 'only' have 20 - 800 MW turbines.
I worked some doing maintenance in steam turbine coal fired plants - - - - the whole plant was less than 800 MW !!!!!!!!!!! (Quite a number of locations in fact.)
For a running steam turbine you might be able to play very hard but even there I doubt it.
Know that starting from black (cold) it was around 24 hours to get to production. (Metals just don't like high levels of temperature change per hour!)
There were times when there was a small leak where rather than cool the whole thing off completely that the boiler was partially cooled and then some very well paid guy went in to fix (not me - - - - I wasn't that good!) this would shorten the boiler outage by maybe 24 hours if not more. (That would be added cooling time and then the slow re-heat.)
As I understand it - - - - from off to full bore a hydro power system is the fastest of all power production. (Even a gasoline engine needs more time - - - got to warm it up before you put the boots to her!)
Also - - - - the world - - - or most of it- - - believes that power from coal is B A D !!!!!!!!!
Really not true - - - - if you check looking for ultra-supercritical fluidized bed combustion you will see that it is possible to burn coal AND have cleaner outputs than from even natural gas. These plants are not cheap though - - - - specialized materials in lots of places. There are a few in the world - - - - one operating from some time in the late 80's in Japan IIRC. Plants built in Canada into the late oughts (one I think finished 2009) were not using this technology - - - I think because no one asked them to and because it might have added another 2 to 3 hundred million to the already $1.6 billion canuckistani smackers of plant cost.
An odd thing about Coal fired Power Stations that people sometimes forget. They want to make as much electricity as possible from each ounce of coal. So mostly it is burned in Babcock style water tube boilers, with feed-water pre-heaters air pre-heaters (Economisers), superheaters - so the dry steam is utilised at over 600 degrees C in the turbines - and leaves dry at over 150 deg.C. But the "odd" thing is the combustion method: To burn the coal it is ground into "dust" and blown into the boiler in huge volumes of air, so there is almost no Hydrocarbon or Carbon monoxide in the exhaust. It's just like a big blow-lamp! I'm not sure the fluidised bed actually improves on this - as I remember it was mentioned frequently in my Dad's monthly "Power News" (magazine of the CEGB), but I don't know of any Fluidised Bed large boilers? - I suspect the "dust blowers" do the same job as effectively? The xhaust from "dust blowers" does produce exhaust full of "fly-ash". But the post combustion precipitators clean the exhaust gasses so particulates are kept to levels as low as modern Petrol vehicles - or lower - depending on the country. Light-beam(or maybe lazer scattering?) particle detectors are used in the stack to constantly monitor the cleanliness of the exhaust for particulates. Any Sulphur products may be allowed by local legislation to go up the flue, but in many modern countries they are not allowed, so Magnesium oxide (??) (Milk-of-magnesia? / indigestion tablets?) is sprayed into the exhaust to neutralise the sulphur and it is collected in separate precipitators (Magnesium Sulphate - Epsom salts?- as used in the washing powder industry? - or whatever?). So the gaseous exhaust is CO2 and H2O.... A pity the CO2 is banned in many places. The CO2 can be sequestered (not sure of the chemistry?) but that process makes the electricity a bit more expensive, and with fossil fuels being banned within the 40 year lifetime of a modern power station's life, the whole thing has been made to be uneconomic in some countries. (maybe not China? - The world's biggest population, growth region and burner of fossil fuels?).
I guess that no-one in their right mind models modern coal-fired power stations - I.C engines are much simpler?
K2
I guess that no-one in their right mind models modern coal-fired power stations - I.C engines are much simpler?
K2
That is so amazing. Sounds like late development railroad steam engine design. Nineteenth century innovation running steam turbines to this day.
I worked in a Power Station for 39 years. Eraring P.S. in NSW Australia It was one of the largest . Four 660 MW turbines The boilers were 80 mtrs tall with a single drum in each one. We burned Pulverised coal that was such a poor quality, it had to be blended to become flammable . All the high quality stuff went for export. Your description is a very good one.
