Step–up transformer

 A transformer that increases the voltage from primary to secondary… or from the lesson plan:

If secondary windings are more than primary, flux will cut more coils in the secondary and induce higher voltage;

Step–down transformer

 A transformer that decreases the voltage from primary to secondary… or from the lesson plan:

If there are fewer secondary windings than primary windings, less voltage will be induced than is applied.

Primary winding

Turns ratio

Vp/Np= Vs/Ns

Vp is primary voltage.

Np is number of primary winding turns.

Vs is induced secondary voltage.

Ns is number of secondary winding turns.

Describe the operation of a transformer during no load conditions.

Describe the relationship between current and the number of turns in a loaded transformer.

Ip*Np=Is*Ns

Ip = Primary current

Np = # of Primary turns

Is = Secondary current

Ns = # of Secondary turns

Vp*Ip = Vs*Is 

Vp = Primary voltage

Ip = Primary current

Vs = Secondary voltage

Is = Secondary current

They allow alternating electrical energy to be transferred between circuits, raising or lowering the voltage as necessary.  High voltage and low current transmission lines have greatly reduced (I²R) losses.  Less current is required at a high voltage than a low voltage to transmit a given amount of power.

Transformer capacity is rated in apparent power(VA).  Output rating is based on maximum current without exceeding design temperature.  Transformers and AC machines in general are rated in volt-amperes to preclude using power factor.

P_real=P_apparent*power factor

Real power is denoted in Watts

Apparent power is denoted in VA

Describe the five losses that occur in a transformer

1)  I²R losses in the form of heat from current flow in the windings.

2) Magnetic flux leakage is any flux that does not link the primary and secondary and is wasted.

3) Third loss is eddy currents, limited by laminating the core.

4) Fourth loss is hysteresis loss, high quality soft iron or silicon iron minimizes resistance of the core to realigning of domains.

5) Fifth loss is saturation loss, by ensuring capacity of the transformer is greater than maximum input power; the core will not become saturated.

Single Phase transformer Connections, Describe methods to supply a residential customer with 120 VAC and 240 VAC from a single distribution transformer.

Local transformers that supply single-phase, relatively low voltage power, to residential and small industrial loads are distribution transformers.  Usually are supplied from one leg of a three phase line.  Secondary has a center-tap and two end connections.

Describe the advantages and disadvantages of a three–phase transformer compared to a bank of three single–phase transformers.

1) ADV: Three-phase transformers occupy less space than three single-phase transformers of the same rating.

2) ADV: Three-phase transformers are slightly more efficient and have a lower initial cost.

3) DISADV: Three single-phase transformers, If one transformer fails, the other two phases will still be supplied.

OA

Transformer Cooling

OA w/radiators

 transformer Cooling

Same as above, but with radiators that take advantage of natural air movement to cool the oil.

OA/FA

 Transformer Cooling

FOA

Transformer Cooling

Transformers in an oil bath with forced air and forced oil(oil pumps) circulation for the most available cooling(similar to the main transformer)