Question

The harmonic restrained relay is used as protection for transformers having:
1. high fault settings and low operating speeds
2. low fault setting and high operating speeds
3. high fault setting and high operating speeds
4. low fault setting and low operating speeds

Answer 1

Correct Answer - Option 2 : low fault setting and high operating speeds

Harmonic current restraint can distinguish between differential current due to internal fault and that due to magnetizing inrush by their difference in the waveform.

• It is entirely current operated, there is no need for a potential transformer
• It has a high operating speed on the fault current & low current setting.
• It is entirely self-contained and the only moving part is the single relay armature which operates the tripping contacts.