Hopkinson Test

Hopkinson Test Points : Hopkinson Test The back to back test for dc machines was devised in its original form by Hopkinson and is similar to the Sumpner’s test for transformers. In practice the modification of the original Hopkinson test by Kapp is employed and it is usually called the Hopkinson test. Two dc shunt machines are mechanically coupled and losses are supplied electrically.

Machine M is started with the help of a starter as a dc shunt motor and brought to speed with switch SW open. Since both the machines M and G are mechanically coupled, both the machines run at the same speed. The field current of the machine G is adjusted till the meter V₁ reads zero and the switch is then closed. Under this condition the generator will float neither taking nor giving current to supply. Any desired load can be put on the generator by increasing the value of its induced emf; this in turn can be accomplished either by increasing the generator exciting current or by decreasing the exciting current of the motor or both adjustments may be made. The machine with lower field current will act as motor and the other will work as generator. The power supplied from the mains is only the power required to supply the losses of the two machines. At the end of the test,