Which of the following devices contributes to the safety of electrical systems?

Protective relays play a crucial role in the safety of electrical systems by monitoring the electrical parameters and providing equipment protection. They are designed to detect abnormal conditions, such as overcurrent, overvoltage, or ground faults, and initiate actions to disconnect the affected circuit or equipment from the power source. This rapid response helps to prevent damage to electrical components, reduces the risk of electrical fires, and enhances the overall safety of the electrical system. By ensuring that faults are isolated quickly, protective relays help to maintain system stability and protect both personnel and equipment.

While power lines, transformers, and batteries each have their roles in the electrical system, they do not directly contribute to safety in the way that protective relays do, which are specifically engineered to prevent hazardous situations.