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Page 98

| Constant-Current Transformer |

| In the constant-current transformer, the primary and secondary coils are movable with respect to each other, the coils automatically taking the correct position to deliver the rated 6.6 ampere current continuously to the circuit. |

| Although many different mechanisms have been developed for the constant-current transformer, they all do essentially the same thing. The secondary coil moves up and down to vary the magnetic field (Fig. 6-10). The primary coil is usually fixed and the secondary floats. The latter is balanced by a weight which is proportional to the repulsion force of the rated current. If more than the rated secondary current flows, the repulsion becomes greater than the weight and pushes the secondary farther away from the primary. This automatically produces a greater leakage flux, which in turn automatically lowers the voltage, thus automatically lowering the current to its rated value again. |

| Hence, if part of the load is short-circuited or removed, the coils will move apart and the secondary current brought back to its normal value. Constant-current transformers are usually designed so that, with normal voltage on the primary, the secondary may be short-circuited without causing quite full separation of the coils. |

| Constant-current transformers differ in several important respects from the usual power and distribution transformers. Their load is a series of lamps |

| Figure 6-10 Constant current transformer. |

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