bulbs blowing help please...

[stick insect]

I went past the shop and was pleased to see the pavement had been dug up and a sign with United Utilities on the apologies board. I spoke to the tenant and they said that The water main was being replaced......

Anyway on a positive note a mains voltage monitor has been left to check the mains.

The two properties are on the same phase and the supply is looped through from one to the other. the voltage is 242 volts. Keeping my fingers crossed.

David

 

[rumrunner]

just about the only thing that would cause a lamp to explode is if its getting 415,i heard about a thing called a swinging ground once ,cant remember exactly what it was but ,it had something to do with the supply transformer ,shorting out intermitedly ,could be it ,why not set up some sort of peak hold monitor or something ,
all the best now

Thats what it is spiritual power being induced,to much feng suie ****

Following up from the above ,can anyone explain the "third harmonic voltage " that is produced across the output terminals of the supply generator ,when there is a heavy earth fault ,i need to know if this causes a satuation of the transformer core or if it is caused by satuation of the core,and as far as i can deduce when the core is satuated this causes the voltage to multiply ,is this shunted via the generator windings ie path of least resistance ,where it is added to the voltage being generated and causes a peak on the line.
im a bit stuck ,cant find out much on line about 3rd harmonic voltage ,i did have it in a text book ,but thats with her to soon be divorced,so cant really ask her to look it up for me ,but i have a feeling thats whats up with mateys light bulbs,all and any ongoing dialouge on this subject is most wellcome
thanks in advance shake
atvbiotwww

just tried to find out more about 3rd harmonic voltage,it can be utilized to increse torque in electric motors ,does that mean its produced as a matter of cause,as with a slip ring motor that generates a voltage when running,or am i on the wrong track,and if 3rd harmonic is produced ,then why not other odd harmonics ,presuming the even ones are added,i cant get my head around where the unwanted voltage ends up
atvbitwww

 

[Shakey]

Following up from the above ,can anyone explain the "third harmonic voltage " that is produced across the output terminals of the supply generator ,when there is a heavy earth fault ,i need to know if this causes a satuation of the transformer core or if it is caused by satuation of the core,and as far as i can deduce when the core is satuated this causes the voltage to multiply ,is this shunted via the generator windings ie path of least resistance ,where it is added to the voltage being generated and causes a peak on the line.
im a bit stuck ,cant find out much on line about 3rd harmonic voltage ,i did have it in a text book ,but thats with her to soon be divorced,so cant really ask her to look it up for me ,but i have a feeling thats whats up with mateys light bulbs,all and any ongoing dialouge on this subject is most wellcome
thanks in advance shake
atvbiotwww

just tried to find out more about 3rd harmonic voltage,it can be utilized to increse torque in electric motors ,does that mean its produced as a matter of cause,as with a slip ring motor that generates a voltage when running,or am i on the wrong track,and if 3rd harmonic is produced ,then why not other odd harmonics ,presuming the even ones are added,i cant get my head around where the unwanted voltage ends up
atvbitwww

Ok, heavy stuff Rum,

I first got involved with harmonics because i have worked a lot with mobile and static generators

basically with normal resistive and inductive loads (and capacitive) the V & I relationships are linear. (ie the Xl will mean the current will lag the voltage in an inductive circuit because of CIVIL) but they will still be directly rpoprtional to each other in their magnitudes

now as seen as we introduce semi conductors to the load, the relationship becomes non-linear, i.e the current being drawn by the componenet does not follow the current sine wave that produced it. think of the main sine wave and then another 'spikey' sine wave superimposed over it, consisting of the original sine wave and the new spikey (non-linear) waveform. That is a current harmonic. Now when that harmonic current hits a linear load, that current produces a voltage drop, which, because the I producing it is non-linear, is also non-linear.

So you now have a non-linear harmonic voltage waveform superimposed on the original V sinewave.

Now imagine you have banks of semi conductors all switching on and off at different frequencies , a 'bandwidth' of harmincs will become your 2nd harmonics, then the next bandwidth the 3rd harmonic and so on. Each harmonic increasing in magnitude.

We used to hit this with generators supplying loads with a lot of thyristors in. Basically anything like that, particularly a thryristor because it would be pulse firing rapidly. End result was, that with a high 3rd harmonic current, we could be derating the genny output by as much as 50%.

What this meant in reality was, we would size a genny at say 500Kva. Then when we accounted for the additional current taken by the harmonics we might need, say, a 1MW for the same supply

Cant see how saturation of the core would cause the V to multiply

We used to use saturable reactors as part of a transductor system for control windings for generators

Basically think of a normal transformer. This v & I rise and fall as a sinewave through the zero point. Now if you were to superimpose a DC control current to the winding, this would cause a 'constant' magnetic field at a set level around the zero line, so the AC could then only induce an putput at the parts of the sinewave above and below the DC level. Thus by controlling the DC level you could control the output.

The same is used with the old Robin RCD testers with the 'D' lock function, it just floods the RCD with DC and desensitizes it.

So, in basic terms.

A sudden fault on system would cause a sudden rapid change in current, this sudden rapid change would cause a corresponding voltage to appear (think of back EMF - which is where i think you were going with the slip ring motors analogy) which of course, because we are using Lenz' law would be greater than the force which created it. Thus we have the original V&I and the harmonic V&I caused by the collapsing fields ADDED to it

ok, me 'ed urts know, hope this has helped Rum, although i'm not sure it has

perhaps i'll try again after me second coffee......

 

[rumrunner]

Hi shakey
Of cause its helped ,i did a quick revision on lenz" law ,back emf ,and core satuation ,the web site i was on last nite when i was searching the net looking for "swinging grounds" was american and very dense ,i had trouble even reading it ,didnt understand hardly any of it ,but ill try again

one question thats arose from your excellent ,quite easy to understand answer,is
"if another sine wave is superimposed on the first then does that have the same effect as having 2 geneys on the line but out of sync"

i understand a voltage is produced due to a difference of potential between the waves ,secondly if this voltage is out of phase with the first does that cause a d.c effect when it reaches the transformer ,also if the fault was ,say,on the primary and was a swinging ground ,ie momentarially ,to earth does this have the same effect as opening the inductive circuit quickly.

im not trying to confuse your head shakey,really im not
atvbitwww

 

[Shakey]

Hi shakey
Of cause its helped ,i did a quick revision on lenz" law ,back emf ,and core satuation ,the web site i was on last nite when i was searching the net looking for "swinging grounds" was american and very dense ,i had trouble even reading it ,didnt understand hardly any of it ,but ill try again

one question thats arose from your excellent ,quite easy to understand answer,is
"if another sine wave is superimposed on the first then does that have the same effect as having 2 geneys on the line but out of sync"

i understand a voltage is produced due to a difference of potential between the waves ,secondly if this voltage is out of phase with the first does that cause a d.c effect when it reaches the transformer ,also if the fault was ,say,on the primary and was a swinging ground ,ie momentarially ,to earth does this have the same effect as opening the inductive circuit quickly.

im not trying to confuse your head shakey,really im not
atvbitwww

ok first point, not really, partly because the harmonic will be based around a sine wave, but will be changing in a non-linear fashion, unlike the linear sine wave, which sort of covers the second point as well. try and steer away from thinking of PD between the main sine wave and the harmonic wave, (we are not going to go into vectors!) and think of the harmonic as a seperate entity (which 'contains' the original sine wave)

to calculate harmonics i recall using Laplas transforms, and 2nd order differential equations, nor somewhere i want go this side of a stronbow based bank holiday!!!

and really, we tend to talk about harmincs in terms of effect of loads on supplys.

I have never really used them in terms of faults, where we should be dicussing power frequency fault voltages and the resultant power frequency stress voltages.

So, back to basics, - in any situation where you get rapidly changing currents (such as with a fault or highly inductive rapidly switched loads) you will get an element of harmonics

so your anology of the 'swinging ground' will include harmonics obviuosly. and try and think of harmincs as things that happen 'from' the supply (caused by the load) rather than 'to' the supply.

And your DC effect on the transformer, as i tried to state in my first bit, i think it will have the opposite effect. The constant DC 'stabilises' a proportion of the linear sine wave so it becomes non-effective for inductive (transformer) puropses.

So a harmonic will tend to INCREASE the amount of induced EMF's, both linear and non-linear, with the effect that with a step up, the harmonic effect would be increased (i think)

have you thought of using a HF digital ballast to counteract the harmonics

ok Rum, thats me done, i'll stop making things up about harmonics and get back to work.

 

[rumrunner]

Cheers pall,excellent answer ,top marks, i think i am begining to understand it a bit better now,still dont know why his bulbs exploded ,maybee he should have used an hf digital ballast.
enjoy your afternoon and your weekend on the bow,you deserve it after those answers
atvbitwww

 

[Bane]

Didn't he do well.

 

[wayne]

i think an applause is in order for both rr &shakey ,now im going for a beer and some migraine tablets

 

[rumrunner]

[

So a harmonic will tend to INCREASE the amount of induced EMF's, both linear and non-linear, with the effect that with a step up, the harmonic effect would be increased (i think)

If the above is so ,then a "swinging ground" ,which as far as i can tell is the partial breakdown of the insulation in the transformer ,whitch induces more emf ,due to the harmonics caused by the rapid decline in the voltage in the inductive circuit,momentarally,
which then flows around the circuit and blows the bulbs(weakest part of circuit)

have i got it right this time shaker

 

[MacSparky]

Wow!! I wish my wife had this sort of knowledge........i'd probably listen more
Fantastic posts guys...loving it

 

[Shakey]

[

So a harmonic will tend to INCREASE the amount of induced EMF's, both linear and non-linear, with the effect that with a step up, the harmonic effect would be increased (i think)

If the above is so ,then a "swinging ground" ,which as far as i can tell is the partial breakdown of the insulation in the transformer ,whitch induces more emf ,due to the harmonics caused by the rapid decline in the voltage in the inductive circuit,momentarally,
which then flows around the circuit and blows the bulbs(weakest part of circuit)

have i got it right this time shaker

sort of, but the bulbs blowing is an effect of something happening momentarily rather than permanently, and i ten to think of (even a partial) breakdown of the insualtion as a permanent thing.

A fault to earth on the HV side would cause a power frequency fault voltage (yes, rapid collapse of fields, harmonics etc) this would cause a power frequency stress voltage on the LV side (because its a massive step down) which would certainly pop bulbs

but as i said, i tend to think of this as a 'one off' event rather than an occasional event, which is what i think that chap is describing.

although you could use the same analogies for faulty connections etc on the HV side causing harmonics on the LV side. And remember, we are stepping down, so....

the induced voltage would be stepped down, therfore the current is stepped up (because power out = power in as you well know!!!)

but if that is a harmonic current, then that PRODUCES a harmonic voltage, which of course, thanks to mister Lenz could be great in magnitude, AND non-linear (ie a voltage spike)

job done

off to the 'bow have fun guys

and cheers Rum, its good to talk!

 

[rumrunner]

Yeah thanks Shakey i enjoyed that ,bit more pain than a visit to miss whiplash ,but 200 quid cheaper,we should do it more often,

i agree that even a partial breakdown of the transformer insulation would be a perminent
situation

now is it possable that a factory ,say using some inverters or machines which are turned off quickly puts the harmonics on the line
if it is harmonics that are to blame anyway

ive got a feeling we will never know ,it might not ever happen again ,i doubt if the electric board will commit huge resorces to investigate the matter,its a shame i dont like not knowing whats wrong with something

enjoy your holiday ,all the vb

 

[Shakey]

Yeah thanks Shakey i enjoyed that ,bit more pain than a visit to miss whiplash ,but 200 quid cheaper,we should do it more often,

i agree that even a partial breakdown of the transformer insulation would be a perminent
situation

now is it possable that a factory ,say using some inverters or machines which are turned off quickly puts the harmonics on the line
if it is harmonics that are to blame anyway

ive got a feeling we will never know ,it might not ever happen again ,i doubt if the electric board will commit huge resorces to investigate the matter,its a shame i dont like not knowing whats wrong with something

enjoy your holiday ,all the vb

i dont think the factory would cause the problem elsewhere, because:

they wouldnt 'put harmonics on the line'

the harmonic current would be caused by the machines, in the cables carrying current TO the machines. And rememebr the harmonic voltages are a PRODUCT of the harmonic current not the other way around, so i dont think the harmonic would travel 'back up' the line and then go elsewhere

its only my opinoin though, and i make most of this stuff up anyway!

have a good one Rum

 

[rumrunner]

YouTube - Lenz's Law Demo 2 heres a short vid i found whilst researching lens law ,i think it explains it almost as well as shake
atvbitwww

YouTube - Lenz's Law Demo 2 heres a short vid i found whilst researching lens law ,i think it explains it almost as well as shake