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)