Welcome to the demonstrations at the high-voltage display.
Our demonstrations at the high-voltage display are the most viewed
here at the Deutsches Museum. We will show you a disruptive discharge through the air
a sliding discharge, the demonstration with the Faraday cage,
different transformers and artificially generated lightning.
Our demonstrations are unique in Germany;
you can see and experience them only here at the Deutsches Museum.
However, our demonstrations are partially extremely loud, so please hold
your ears covered precautiously, especially the children and young people.
Persons with pacemaker are advised not to take part at this demonstration,
as it occurs at your own risk. If you take a look to the top,
above the glassplate there are two tips at a distance of 80 cm (2,62 ft).
In the first demonstration we show you a disruptive discharge through the air.
Originating from the small tip passing over the glassplate to the other one facing
an alternating voltage of 280 000 Volt.
We will slowly turn up the voltage, until the sparkover takes place.
With the increasing of the voltage you can spot
a blueish sparkle at the small tip over the glassplate.
Here electricity leaks directly into the air.
This is a so-called corona.
In the second demonstration we willl show you a sliding discharge with a voltage of 160 000 Volt.
For this purpose we reduce the distance between the tips to 15 cm and place a glassplate in between as isolator.
The discharge doesn?t go through the glassplate,
but very effectively, making lots of noise over it.
In order to avoid sliding discharges over isolators,
we prolong the isolation path,
providing the insulator with numerous gills,
as you can see also on the isolators on our plant.
The sphere running down is completely made out of metal, it is the Faraday cage.
And as proof that inside this space enclosed by metal
there is no electric charge, when voltage is applied to this,
my colleague will take place inside the sphere.
And I will then apply a potential of about 220,000 Volt to this sphere.
The demonstration with the Faraday cage was carried out for the first time
by Michael Faraday in 1835, however he didn?t try the first experiment on himself.
He made the first experiment on his domestic animals,
then on his servant and just then did he try the first demonstration on himself.
The Faraday cage at the historical demonstration however, didn?t have
the form of a sphere, but of a cube.
As you have seen, the sphere is totally made up of metal,
the power feed takes place from bottom to top through the flexible supply line.
And as a proof that this 220,000 Volt high voltage passes over
the Faraday cage, during the demonstration you can see a standing sparkover
between these brass spheres above the cage.
The colleague can also touch the inside part of the sphere during the demonstration
without anything happening to him.
As you can see, nothing has happened to my colleague.
That arises out of the fact that the entire voltage is distributed
on the surface of the sphere, where it forms an electric field.
However, due to the metal shielding the inner space of the sphere remains completely fieldfree.
One person can stay inside the sphere.
The principle of the Faraday cage can be found for example in the car.
Inside you are very safe from a direct lightning stroke during a thunderstorm.
Next to the Faraday cage, that now goes back up,
you can see a trasformator with V-shaped disposed copper electrodes.
This is a horn transformer.
With the horn transformer we show you electric arches,
how they are generated for example at a horn overvoltage-protection.
For this purpose the horn transformator will transmit a voltage of 50,000 Volt
to the copper electrodes.
At the most narrow point a spark-over, more specifically an electric arc generates,
that moves upwards propelled by warmth and thermal forces,
until the air resistance becomes so strong, that it comes to a breakdown.
As long as the transformator is under tension,
always a new ignition takes place automatically.
In the next demonstration we show you now artificial lightning
and their effects on different earthed lightning rods.
We generate these bolts of lightning - or more precisely
voltage surge – with the surge generator.
The surge generator ist this big coloured tower,
where now the red light is illuminated.
Our surge generator is made up of 12 condensator units,
that are parallelly loaded with up to 100,000 Volt.
The discharge takes place serially whereby a maximal lightning voltage surge
of 1,2 milion Volts and a current strength of 3000 Ampere is reached.
In the first lightning demonstration we show you a discharge
into the church?s well earthed lightning rod on the model table.
The attempt shows you, that elevated spots with a good ground potential
are preferential impact spots for lightning.
A well earthed lightning rod is made up of three parts: the lightning rod,
that ist the tip on top of the building, the main generator lead and the so-called ring earthing.
A ring earthing is a metal band that in form of a ring runs around the protecting object.
But the house next to it is protected by a very well grounded lightning rod.
The next impact now takes place here, although top of the churchtower
still represents the highest spot on our model table.
When a house?s lightning rod is poorly earthed,
but inside the house there is a good ground,
it can happen that the lightning strikes the lightning rod,
but then is followed by a sparkover inside the house onto a good earth:
for example onto a water pipe.
Should it happen that there are highly flamable objects in close proximity
to the sparkover path, these can catch fire
and it can happen that inside this house a fire occurs.
Next to these buildings, the house and the church, you can see an overhead line.
The overhead line’s top cable is the lightning protection cable or earthing cable.
Its function is to protect the conductor rope from direct lightning strike.
The next discharge occurs on the earthing cable or lightning protection cable of the model overhead line.
In the last demonstration we want to show you lightning’s destructive forces.
Surely you have already seen, when lightning strikes a tree,
it was generally shattered.
This is because wood contains a certain amount of humidity,
that is brought to boil due to the lightning’s high energy.
Thereby vapor arises. The in turn arising pressure splinters
the wood. We want to show you a wood fissure test.
How far it succeeds, how strongly the woodstick is shattered,
it depends a lot on the fibre course, thus from the grain as from the interior residual humidity.
And with this we have reached the end of the demonstration.
We thank you for your visit, we hope you have enjoyed it,
we would be pleased to see you again once more and we wish you
furthermore a nice stay here at the Deutsches Museum.