What is a transformer?
A transformer is a passive device that is designed to convert one voltage to another through the magnetic induction.

What is an isolation transformer?
An isolation transformer is referred to a transformer that has its primary and secondary windings separated.

What is an autotransformer?
As opposed to an isolation transformer, an autotransformer has a common winding for primary and secondary.

What is a control transformer?
A transformer intended for power supply of control circuit is a control transformer. It is designed to provide high stability (regulation) during a short period of overload condition typically referred to as inrush.
 
Can a transformer be connected reversely?
Yes, a transformer can be connected reversely. However, the output voltage will be less than the rated voltage due to the compensation factor of the windings.

What is voltage regulation?
Voltage regulation is the ability to provide constant secondary voltage given a constant primary voltage over a wide range of load conditions.
Voltage regulation is defined as:
Regulation%= Vno-load- Vfull-loadVfull-load x100

What is intermittent rating?
A transformer can be operated in continuous or intermittent mode. When a transformer is operating in an intermittent duty cycle, the maximum power can be increase significantly during that short period of time.
Intermittent power can be calculated using the following formula:
P= p operation time total duty cycle (operation+pause)

What is the effect of using a transformer in high altitude?
Dry type transformers used above 1000 metres require derating due to the reduced cooling capacity of the less dense air. The capacity of the transformer should be derated 0.3% for every 100 metres above 1000 metres.