PFC-Projective fault current

PSCC-Short Circuit

PEFC-Earth Fault

So when selecting projective devices we may need a CPD with a higher breaking capacity if it is 3Ø because VL (400v) will increase the fault current. (PSCC)

 

Inductors are coils

when a magnetic current flows a magnetic field is created.

the coil shape helps to increase the magnetic field. 

they often have a soft iron core which also works to increase the magnetic field

some inductors are better than others.

 

Capacitors have two plates with insulation in between. the insulation is called dielectric. 

When a voltage is applied, charge is stored. Positive chage on one plate. negative on the other. 

 

Some capacitors are better than others at storingcharge, this is measures by CAPACITANCE

 

Len's law says that this voltage will be in the opposite direction to the original voltage that created it.

This is why the induced voltage is called back-emf

Back-emf means the induced current will also be in the opposite direction. 

It takes energy for capacitors to store charge

If the capacitor is part of a circuit and we remove the voltage. the capacitor will discharge. 

Electrons on one plate will flow around the circuit to cancel out the positive charge on the other plate. 

This current is driven by a voltage also obeying Lenz's law

The voltage is also a back emf so id in the opposite dicrection to the original voltage that created it. 

The current will also be in the opposite direction. 

 

If we connect an inductor or capacitor to an AC supply, it means the supply voltage will be constantly changing. one moment theres a voltage, the necxt moment, nothing. 

Inductors will be continuously charging and discharging. There will be mments when the supply voltage will be driving current one way, and the back emf will be driving the other way, the effect of the suply voltage is being reduced by the back emf.

 

Effective voltage = Supply voltage - back emf. 

 

So if we have less voltage we will have less current. The same effect as if we increased resistance. 

We can say that by including an inductor or capacitor in an AC Circuit we are introducing something that has the same effect as some kind of extra resistance. 
This is called reactance. 

 

Quantity: Reactance (x) Units: Ohms 

So the amount of current in such a circuit is affected by the actual resistance of the circuit and the reactance of the inductor or capacitor.