how do you isolate the primary side of a power transformer?

Answer 1

Disconnect it from the electrical power supply, ideally by physically disconnecting rather than relying on a switch or circuit breaker which just might be faulty

Answer 2

isolate from what? the primary of the transformer receives power from the utility company, the secondary connects to the load.

in classical transformers, the primary or input winding is made of separate wires from the secondary so there is no electrical connection. energy is transfered by magnetic field only. The input and output circuits are electrically isolated at the transformer.

the autotransformer is a type that uses only one winding, which is tapped for input/output connections, thus there is a direct electrical path that is common to both. "adjustable" transformers are often of this contruction, and provides no isolation of source to load.

a transformer that provides single phase utility power to a house has an input winding that has a 'hot' side and the other is grounded which is also the return to the power station. the secondary winding has a center tap, which is the 'neutral'. both outer taps are 'hot' and carry current to the load. the neutral is connected to the building safety ground at the service entrance. thus there is this common connection exterior to the transformer between the primary and secondary. it would not be safe to break the secondary neutral connection for purposes of 'isolation' and in any case turning off the building main breakers does not disconnect this part of the circuit.

Answer 3

Power tranformer is isolated depending on the number of turns with respect to its functioning demands ie if 2000turns is for the transformer system and the valued turn is 150 in primary immediately at the 150th turn seperate the primary ones by forming a point or loop to isolate the couplings.