The mishap occurred in the morning hours when a boiler attached to a transformer in the plant caught fire, apparently due to short circuit, causing the explosion, they said.
The injured were identified as Ashok, Vijay and Srikanth who all are employed by a private contractor.
They were rushed to a corporate hospital at Visakhapatnam and are out of danger.
Workers blamed the management for not taking adequate measures for the safety of workers.
Repeated efforts to contact Aurobindo officials did not yield any results.