- #141
westom
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Why does that elecrostatic scrreen exist? Because electric fields (and other reasons) are never eliminated. The screen only reduces that current. Primary currents leak by various means into the secondary. An electrostatic shield only reduced currents from the 33,000 volts side appearing on the secondary. Does not eliminate it.sophiecentaur said:Even a half decent transformer in a low power equipment power supply will have an electrostatic screen.
Second, all wires can have two different voltages. Demonstrated were different currents creating 240 volts and 33,000 volts on the same secondary wire. To better understand this, learn two basic electrical concepts - longitudinal and transverse currents.
So that 33,000 volts does not appear on the 240/120 secondary, the secondary must be earthed somewhere.
Third, another example. Suppose lightning strikes the primary (33,000 volt) system. This is a lower energy event. That lightning strike can short transformer primary to secondary. The resulting plasma leaves utility 33,000 volts shorted directly to 240/120 volt power consumers. This 'follow-through' current means high energy connects into a homes and factories. Lightning is the low energy event. A high energy source that may cause much more damage exists if the transformer is not properly earthed.
If a plasma short is not created, then currents on the primary side are not shorted to wires on the secondary side. Another example of why earthing is essential for protection - in this case for lightning protection.
Fourth, earthing a secondary is necesary for numerous reasons both for normal operation and for safety during fault conditions. Elecricians, for example, would not know this. These installers spend years learning only what must be connected to what. Code also only says what must be connected to what. Neither would learn or say "why" this connection is made. Neither would know or discuss two important concepts - longitudinal and transverse currents.
Studiot kept asking "why" a transformer must be earthed. Instead, with frustration, he got "what" must be earthed. If a secondary is not earthed, then 33,000 volts will exist on same wires that also provide 120 volts.
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