ac line frequency

i am puzzle by this .
if a device ( fridge , TV , washing machine , etc) is specified to be
connected to
a 240V 60Hz point , will it cause problem if it is plugged into
[1] a 240V 50Hz source ?
[2] a 220V 50Hz source
[3] a 220V 60Hz source
what about the case of a 240V 50Hz device connect to a 240V 60 Hz
source ?
generally , i wanted to know will it damage the device , can the house
get over-heated , etc.
thanks .
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[3] should be fine. The difference between 220v and 240v ratings is small enough to be ignored for domestic appliances.
[1] and [2] depend very much on the type of equipment. Equipment with a motor such as a vacuum cleaner washing machine etc may or may not run slightly slower on 50 Hz than on 60 Hz. A digital clock or other timer meant for 60 Hz which counts the cycles of the AC will lose time on 50 Hz.
TVs and electronic equipment may well work just fine, but other problems from the location may loom larger - 50 Hz countries tend to use the PAL TV system, while 60 Hz countries often use NTSC. Similarly, an FM radio or tuner may have problems with different channel spacings. If a record player uses a synchronous motor, it will turn at the wrong speed. If it uses a DC motor with electronic speed control, as many do, it may be OK.
A 240v 60 Hz supply is often used in the USA for heavy current applications such as air conditioners and cookers, and you would not want to plug them into a 13 Amp 230v European socket, for various reasons. You would be crazy to bring them across the Atlantic. The only safe way to know is to contact the manufacturer.
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There are motors, and there are devices like TVs that use the AC to create their own DC power using an internal converter (power supply). The latter usually doesn't care much about frequency, and they operate in broad voltage ranges e.g., 100-140 volts, and 200-250 volts.
While the actual "motor engineering" can be more complicated, and there are several kinds of motors, the basics are usually enough to get close if you slap on a small safety factor, and they go like this:
Basically, when an engineer designs a motor or its application, he considers primarily two things - heat and torque - and secondarily the insulation value for voltage at heat and power. (For all intents and purposes, the insulation voltage capacity is not a factor for most motors, but the heat rating of the insulation is.) Power follows torque and rpm.
Heat is the result of inefficiency.
A motor can be run at any voltage and any frequency - but obviously not as efficiently when run at a voltage and frequency other than its design voltage and frequency. So when an engineer uses a motor, especially other than at its rated parameters, he primarily considers that heat.
The motor puts out torque - power is torque times rpm, so a motor designed to handle the heat from the rated power out from 50X rpm at its rated torque may not have the capacity to handle the heat from a motor putting out 20% more power - e.g., at 60X rpm at rated torque. Motors designed for 60 hz operation normally have no problem handling 50hz - but because the torque available is primarily a function of the voltage applied (which drives the amps that makes the field), then for the same voltage, a 60 hz motor runs on 50 hz power delivers 14% less power, and thus less heat. (There are also motors that really don't care what the frequncy is, because they convert the frequency internally to DC) So you can run a motor at 120 cycles as long as you lower the voltage in order to lower the torque and not exceed the heat capacity - that is the basics of variable speed motor controllers
Another thing to look at is that motors respond to the load by using a multiplicand(?) of volts and amps. For a given load, if you lower the voltage, the amps go up. So if you need to run the washer motor with 10 amps at 240vac, and you lower the voltage to 220vac, it will draw 11 amps to do the same job.
And if you run a 60 hz washer at 50 hz, it will run slower.
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Not if the motor has electronic speed control.
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hi there, i like to thank all those who responded . all your answers are certainly very helpful, and educational. --------------------------------------------------
amos wrote:
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For induction motors the main problem is at reduced frequencies rather than increased frequencies.
The main problem in using a 60Hz motor at 50Hz is that the exciting current goes up sharply as the iron will saturate. This also leads to overheating although the peak torque available will also increase at the lower frequency (I'm talking induction motors which are in the majority). Running a 240V 60Hz motor at 240V 50 Hz is asking for overheating. For those reasons variable speed controls set the voltage proportional to the frequency- keeping flux density constant. Of the combinations shown, the most suitable to a 240V 60Hz motor, the 220V 50 Hz is the best fit.
Going from 50 to 60Hz is easier as then the exciting current drops. Available peak torque also drops. The motor will have a higher slip to develop rated torque and could put out more than rated power at that torque without overheating because the current will be about the same (V/Z and Z increases with frequency). Starting current and torque will be lower because the reactance is higher.
The actual torque is determined by the load's torque speed characteristic which generally increases with speed so that this could cause an increase in current and heating. As is the usual case- it depends.
Don Kelly remove the X to answer
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Don Kelly
| hob wrote: | | |> And if you run a 60 hz washer at 50 hz, it will run slower. |> | | Not if the motor has electronic speed control.
And how many actually have such a feature when for most sold in the markets they are intended for would have no need for this?
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Get up to date!
Electronic speed control has been the norm in Europe for some time, and is becoming mainstream in the USA.
Motors are driving demand for electricity, accounting for about half of the electricity we consume, according to the Electric Power Research Institute (EPRI).
Two appliances undergoing an energy-efficiency design upgrade are washing machines and dishwashers. While last year's worldwide washer market-about 70 million units-grew modestly at 3.6% from the prior year,
[emphasis] the number of electronically controlled washers grew at a rate of 23% to 15 million units, [emphasis]
driven by tighter standards, growing regulations, and the emergence of the environmentally conscious consumer. To meet the need, appliance design engineers are working hard to reduce the machine's energy consumption, water use, weight, and cycle time, while delivering added benefits such as better cleaning, more productive spin cycles, and improved fabric care.
One trend in washing machine design is to replace the machine's traditional drive system with an electronically controlled brushless alternative. In the past, washing machine designs employed either a two-speed single-phase ac induction motor with electromechanical controls or a universal brushed motor with triac-switch-phase control.
The new electronic control systems are enabling features that were once too costly or impossible to implement.
[emphasis] As these new features have gained popularity, manufacturers have even begun to design them into their midrange or lower-end models. [emphasis]
Lower raw-material prices are making permanent-magnet synchronous (PMS) motors more attractive than induction and universal motors, nullifying the cost impact of electronic-component additions for the control system. At the same time, other components have been eliminated, such as gearboxes and pulleys required in a mechanical control scheme and sensors needed for rotor position feedback. The results are a smaller and lighter motor and a drive system with greater capability, higher reliability, and improved energy efficiency.
In Europe, where I live, horizontal axis drums are the norm, and they are catching on fast in the USA. They require fast torque response from the controller to manage load conditions that are constantly changing. Higher spinning speeds require better balancing of the drum to prevent washing machine vibration, associated noise, and higher stress on bearings and dampers.
Preventing machine wear and tear, new control systems can detect, assess, and even predict possible out-of-balance conditions and dynamically correct for them. The task requires high torque at low speeds and low torque at high speeds, using artificial field weakening.
Drum-spinning speed itself has become a significant design consideration and important product differentiator. Today's European washing machines advertise spinning speeds of up to 2,000 rpm.
With variable-speed motor control systems in place, washing programs can be expanded to accommodate previously nonwashable fabrics and protect the environment further by reducing the amount of detergent required. A final trend, found at the core of variable-speed motion control systems, is the move to sinusoidal drive schemes to minimize audible noise.
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All european washing machines for at least the last 30 years.
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Andrew Gabriel
That long? I didn't realise, although i can believe it. I used to work in the UK for a charity which reconditioned unwanted washing machines and either gave or sold them at low prices to people on benefits, and the guy who did the reconditioning work told me that "these days" (around 1990) all the broken washing machines we got donated seemed to have circuit boards for motor control. Not like the old days when it was all contactors and split windings. He built up a stock of working modules from machines which were deemed unsuitable for reconditioning for various reasons such as corroded casings. We used about 6 main brands and a surprising amount of stuff was common.
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I see phil-news has decided that discretion is the better part of valour...
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