Let me first say that I'm not an electrician or engineer but read the forums to further my knowledge in how electricity works and how to stay safe around it.

Recently a question was asked about the effects of 50hz vs. 60hz power. What problems would occurs in running an inductive motor, filament or appliance that was designed for 50hz and run on 60hz or visa-versa. We were talking about voltages of 220-250v.

Thanks to all the pros of the board.

Joe

My South African (230V, 50Hz) bench drill and grinder run 20% faster - induction motors. The grinder sounds sweeter at 3450 rpm rather than 2850 rpm (I suspect this is its original 60 Hz design spec) and I have a conversion table posted above the drill for the speed increase.

B&D hammer drill, sander etc. (brush motors)
run no different, likewise heaters and lights. TV's, HiFi's and other electronics that step down their supply internally appear unaffected electrically - they generate low V DC (there are other isues regarding PAL/NTSC and the preset bandwidths on FM, MW and SW that differ between 60 Hz land and 50 Hz land!).

There are problems with timers and oscillators that use the line frequency as internal clocks. Household white-goods (dishwashers/washing machines etc.) are a no go.

There are, I believe, induction/capacitance issues with transformers - but I'll let the pro's tackle that.


[This message has been edited by Hutch (edited 12-01-2002).]

Joe,

As mentioned by Hutch, there are a few situations which arrise when using Equipment built for one certain Frequency on a higher or lower Frequency.
I'll briefly cover some stuff here.

***Induction Motors [Squirrel Cage Rotor & Wound Rotor]: Full-Load RPMs are effected on these Motors. The most obvious change in speed will be seen on Motors with a "Set Speed".
A simple example: Two Pole Squirrel Cage Rotor Induction Motor. 1 HP - 3,450 RPM @ 60 HZ [Rotor speed slips to apx. 3,450 RPM when developing maximum HP].
No Load RPM @ 60 HZ = 3,600 RPM
At 50 HZ, no load RPM = 3,000 RPM, and slips to somewhere around 2,895 RPM at full load.
Same applies in reverse when HZ is increased.

An Induction Motor's speed is related to the Syncronous Frequency.
So to make an Induction Motor run at 1/2 speed [1800 RPM instead of 3600 RPM], the poles are doubled. 3600 RPM for 2 pole motor, 1800 RPM for 4 pole motor.

These are very basic examples for Induction Motors. Many other examples and factors have not been shown, but are important to the overall performance and design.

***Syncronous Motors: These should run at the Line Frequency of the Power System which they are connected to. Once again, design per anticipated HZ will be a key issue.

***Incandescent Lamps: No changes in output should be seen. If the HZ falls to like 25 HZ and lower, there may be noticable flashing from dips in light intensity while current passes the "Zero Line"

***Ballasts: Lamps running at Line HZ may show higher flickering / pulsing when driven at lower frequencies. Ballasts may tolerate slight HZ variations, but should be used on Frequencies which they are designed for. [see transformers]

***Transformers: Transformers may be used between 50 HZ and 60 HZ without too much of an effect - provided they are lightly used. Voltages will be mostly effected.
As with all Inductive items, the lower frequency results in larger cores / windings.
Reactances [XL for Inductive Reactance, XC for Capacitive Reactance, "X" for Total Reactance] change with Frequency.
This can be a really lengthy and in-depth discussion, so I'll stop here!.

***Switch-Mode Power Supplies: These usually Rectify the input AC to Pulsating DC, so in the most point they shouldn't be effected.

Sure hope this answers your questions!

Scott s.e.t.

When I was bouncing around the world (while in the USAF), I had to explain to over a hundred persons that there was noting wrong with the clock puchased in the US that suddenly lost 10 min every hour in coutries that supplied 50 cycle power. And no the step down transformer does nothing about that problem.

A friend for Germany, who brough many of his
appliances with him, had only two troubles,
his airless sprayer, whose mechanism works horribly at 60Hz, and his air compressor,
which had a 3 phase motor, him having only single phase at his Canadain farm (where
3 phase was the norm in Germany).

It's a pity really that the world ended up with these two different frequency standards. Voltage differences are easy to adapt, but not so frequencies.

A couple of other notes to add to the comprehensive list above:

The induction motors in some devices such as record turntables will run quite happily at either frequency, but obviously at a different speed. In these cases the pulley needs to be changed for one of a different diameter so as to adjust the ratio and get the turntable revolving at the correct speed.

Modern digital clocks aren't generally a problem as they are timed from an internal crystal reference, but some of the earlier digital clocks (say early/mid 1970s) took their reference from the AC line, so will also run fast or slow.

The frequency difference must be quite a problem for anyone who travels regularly between islands in the Carribean where both 50 and 60Hz are employed.

Let me trow my two cents in.
Generally speaking, electrical machines designed for 50 Hz will not have problems operating at 60 Hz. On the contrary, machines designed for 60 Hz will most probably have problems running at 50 Hz due to increased flux and will have to be derated.
Dan

Paul UK:
"Modern digital clocks aren't generally a problem as they are timed from an internal crystal reference,"

---------------

The cheap digital clocks that come with those $10-$15 clock-radio combos you buy in a drug store or discount store still take their reference off the line frequency.

I have two 220 Volt/50 hertz digital-clock radios (one is a Malaysian Grundig and the other is a Roberts for the UK market).

Both clocks run fast when plugged into a 220 volt/60 hertz source (I run them through a small step-up transformer). Too bad... I like the Grundig's tuner and sound quality but it's no good for waking me up in the morning.

I once saw a no-name generic clock radio with a 50/60 hertz switch next to the 110/220 volt switch...that seemed like a good idea. Wonder how that worked....there was no crystal inside the clock section (I bought it and took it apart).

Japan also has both 50 hertz and 60 hertz power supplies (depending on what half of the country you're in).

Northern Japan (Tokyo, Sapporo, Kawasaki, etc.) has 100 volts/50 hertz and Southern Japan (Osaka,Hiroshima, etc.) is at 100 volts/60 hertz.

[This message has been edited by SvenNYC (edited 12-02-2002).]

Wow, there are still some digital clocks taking the AC line as a reference? I haven't come across one in quite a while.

If there's a switch to allow operation on either 50 or 60Hz, then it probably just alters the division/N-count on a binary counter so that the output is always 1 pulse per second.

May I respectfully suggest that you use caution when running those bench or pedestal grinders at increased speed, the abrasive (grinding) wheel could explode sending shrapnel at you at very high velocities.

Each wheel is marked, usually on the blotter, (that’s the thin cardboard like oversized washer which fits between the wheel and the mounting flange) with a maximum rpm. If it was originally matched to the spindle speed of the motor then increasing the motor speed would result in exceeding the maximum allowable wheel speed which is a very hazardous condition.

Good luck and be safe!

Prof,

I knew that a velocity increase was in order. The first thing I did, before connecting the machinery was to check the specs on the wheels. They read "Max 4200 r.p.m.". I took that to be fine at 118% of idle speed.

I am assuming that equipment can be run to the rating displayed and that additional safety factors are built in above that by the manufacturer. What does OSHA say regarding maximum speeds versus posted ratings - should additional safety factors be built in?

Hutch,

I don’t know exactly what you mean by 118% of idle speed however what OSHA says is that the wheel can not be run at a velocity (rpm) which exceeds the marked maximum rpm on the wheel, No need to calculate anything just read the maximum wheel speed and be sure the spindle speed does not exceed that (rpm higher than the wheel rpm) don’t spin it faster than that. I have seen too many accidents and fatalities which resulted from wheels exploding due to excessive speeds.

You can see all the entire OSHA regulations also called “Standards” at the OSHA website: www.osha.gov

more specifically the regulation on abrasive wheels is codified 1910.215 and is located at :
http://osha.gov/pls/oshaweb/owadisp...S&p_id=9839&p_text_version=FALSE

The specific reference state on this issue states

“1910.215(d)(1)

Inspection. Immediately before mounting, all wheels shall be closely inspected and sounded by the user (ring test) to make sure they have not been damaged in transit, storage, or otherwise. The spindle speed of the machine shall be checked before mounting of the wheel to be certain that it does not exceed the maximum operating speed marked on the wheel. Wheels should be tapped gently with a light nonmetallic implement, such as the handle of a screwdriver for light wheels, or a wooden mallet for heavier wheels. If they sound cracked (dead), they shall not be used. This is known as the "Ring Test".”


Additionally many accidents result from missing guards particularly the tongue guard which must be adjusted to within 1//4 inch of the periphery of the wheel (obviously needs to be readjusted as the wheel wears).

The other most frequently found problem is the work rest which must be adjusted to within 1/8 inch of the periphery of the wheel.

BTW the “ring test” is used to detect unseen cracks in the wheel which would also cause the wheel to explode upon starting. When tapped with a wooden dowel the wheel should have a distinctive ring or resonance not a dull thud . A dull thud would indicate a crack or cracks in the wheel and the wheel should not be used. Also never stand directly in front of the wheel / grinder when turning it on the first time after mounting. This is the most likely time that the wheel will explode if anything is wrong (cracks in wheel, incorrect mounting etc) .

And that’s the gospel according to OSHA, hope this helps. OSHA Professor – Grizzy