Step-Up Transformers & Step-Down Transformers

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Step-Up Transformers:

No. of turns in the Sec. winding is more than the No. of turns in the Primary

It converts Low Voltage (High current) to High Voltage (Low Current)

i.e. Voltage is Stepped Up

Uses:  Power Plants, X-ray Machines, Micro-Oven

Step-Down Transformers:

No. of turns in the Sec. winding is less than the No. of turns in the Pri. winding

It converts High Voltage (Low current) to Low Voltage (High Current)

i.e. Voltage is Stepped Down

Uses:

(i) High Voltage (6.6 kV) to High Voltage (3.3 kV) – Step-Down Transformers

It is used to supply HV (3.3 kV) Electrical Loads (propulsion converter & motor)

 

(ii) HV (> 1 kV) to LV (440 V) – Step-Down Transformers

It is used to supply Low Voltage (440 V) Electrical Loads (Pump Motor, Heater)

(iii) LV (440 V) to LV  (220- V) – Step-Down Transformers

It is used to Supply Low Voltage (220 V) Electrical Loads (Lighting, Sockets, etc)

Transformer Equation

Relation between the Voltages, Currents  &  No. of Turns in the Windings

Efficiency of a Transformer = 95% to 99%

 

Efficiency = Output   =   Input – Losses  =   1 –  Losses

Input                Input                        Input

 

Transformers have No Mechanical Losses

Static Device – No Windage Loss [Air Resistance] or Friction Loss

Transformer have Only Electrical Losses

(i) Iron Losses (Core Losses)

(a) Eddy Current Loss

(b) Hysteresis Loss

(ii) Copper Loss (Winding Losses)

 

(i) Iron Losses (Core Losses)   [(a) Eddy Current Loss  & (b) Hysteresis Loss ]

These Losses depends upon the magnetic properties of the material (Steel/Iron) used for the construction of core

 

(a) Eddy Current Loss

Small part of the magnetic flux gets impinged / linked to Steel/Iron Core

This induces an emf in core causing a small circulating current in them

This current is called Eddy Current

Due to these Eddy Current some Energy will be Lost/Dissipated in the form of Heat

 

(b) Hysteresis Loss

This Loss is due to reversal of magnetization in the core

It depends upon the Volume and Grade of the Steel/Iron, Frequency of Magnetic Reversal and Value of Flux Density

 

(ii) Copper Loss

This Loss is due to Ohmic Resistance of the Windings

Copper Loss for primary winding is I12R1 & for secondary is I22R2

I1 & I2 are current in the primary & secondary windings

R1 & R2 are resistances of Primary & Secondary windings

Cu Loss varies with Load (Current (I) varies with Load)