# Step up and step down transformer

May 6, 2017 # Step up and step down transformer

These two types of transformers .. step up and step down transformer are used to step up voltage from low value  to high value  according to turns ratio of primary and secondary windings.

## Step up transformer:

This transformer has less primary winding than secondary winding so, we find that the current that flows through primary winding greater than secondary winding according to this equation P= V * I      (for ideal transformer that means no losses in power )

Such that :

P : power in watt

V: Voltage in volt

I : Current in Ampere

So , Power in primary = Power in secondary  (for ideal transformer)

Vp * Ip = Vs* Is

Vp : primary voltage of transformer

Vs : secondary Voltage of Transformer

Ip : Primary current of transformer

Is : secondary current of transformer

As example :

If I have single phase  ideal transformer 100 watt  with primary winding of 5 turns and secondary winding of 20 turns and primary voltage of 100 volt .. calculate currents at primary and secondary sides and voltage at secondary side .

Solution:

P = V * I

100 = 100 * Ip

Then …. Ip = 1 ampere

For

So ,  Vs = 400 volt

For ideal transformer :

Power in primary = Power in secondary  (for ideal transformer)

Vp * Ip = Vs* Is

100 * 1 = 400 * Is

So,   Is = 0.25 Ampere

According to what we explain; you must deduce that step up transformer mightily presents near power plants which operate megawatts of power, also in machines which require high voltage to work like X-ray and micro-wave.

## Step down transformer:

This transformer has greater primary winding than secondary winding … So, we find that the current that flows through primary winding less than secondary winding and the primary voltage is higher than the secondary voltage which make step up transformer the best in domestic consumption. Now you may think about Can we use the same transformer as step up or step down transformer at the same time ?? that means if I have step up transformer can I use it as step down transformer and vice versa ?

As we mention before that main task of transformer is stepping up or stepping down voltage from primary side to secondary side assuming that losses are eligible .. I will drive with equations that step up transformer can’t used as step down transformer and vice versa So,

If any transformer designed as step up transformer .. Its primary and secondary winding designed to carry specified current so, if I have step up transformer 1000 watt with these parameter :

Vp = 100 volt , Np = 100 Turns , Ns = 1000 turns

So ,

P = V * I

1000 = 100 * Ip

Then …. Ip = 10 ampere  ( so we use wires for these winding with cross section area withstand this current )

For

Vp/Vs = Np/Ns

100/Vs = 100/1000

So ,  Vs = 1000 volt

For ideal transformer :

Power in primary = Power in secondary  (for ideal transformer)

Vp * Ip = Vs* Is

100 * 10 = 1000 * Is

So,   Is = 1 Ampere (so we use wires for these winding with cross section area withstand this current  )

From previous example we conclude that if I use step up transformer as step down transformer secondary winding (now it primary) will burned because these winding are designed to withstand less current .

So,  we can’t use step up transformer as step down transformer and vice versa

##### Applications of step up and step down transformer :
• Step up transformer used at power plant to decrease currents before transmission process along transmission lines
• Step down transformer used at substations that used to decrease voltage to distribute on customers .