The correct answer is: C. constantly the electrical quantities which differ during normal and abnormal conditions.
Protective relays are devices that detect abnormal conditions in electrical circuits and take action to protect the circuit from damage. They do this by measuring electrical quantities such as current, voltage, and power, and comparing them to pre-set values. If the measured values exceed the pre-set values, the relay will trip, which will cause the circuit to be shut down.
The electrical quantities that are measured by protective relays can vary depending on the type of relay and the type of circuit being protected. However, some of the most common electrical quantities that are measured include current, voltage, power, frequency, and phase angle.
Protective relays are an essential part of electrical safety. They help to protect people and equipment from the dangers of electrical faults. Without protective relays, electrical faults could cause fires, explosions, and other serious damage.
Here is a brief explanation of each option:
- Option A: Current during abnormal condition. This is not the correct answer because protective relays measure electrical quantities constantly, not just during abnormal conditions.
- Option B: Voltage during abnormal condition. This is not the correct answer because protective relays measure electrical quantities constantly, not just during abnormal conditions.
- Option C: Constantly the electrical quantities which differ during normal and abnormal conditions. This is the correct answer because protective relays measure electrical quantities constantly and compare them to pre-set values to detect abnormal conditions.
- Option D: None of the above. This is not the correct answer because one of the options is correct.