What is the difference between high impedance and low impedance differential protection?
High impedance differential protection
The basic principle of the high impedance protection is the same as the low impedance principal, it sums up all currents measured by the CT’s surrounding the bus. The biggest difference is how the high impedance principle handles the problem of CT saturation on external faults.
What is low impedance bus differential protection?
The low- impedance bus differential scheme typically has one set of current inputs for each phase from every set of CTs in the scheme. … A single low- impedance bus differential relay can provide protection for a single phase, two phases, or all three phases, depending on the number of relay current inputs.
Is lower impedance better for headphones?
Most headphones with low impedance (less than 25 ohms, approximately) require little power to deliver high audio levels. … Headphones with higher impedance (25 ohms and over, approximately) demand more power to deliver high audio levels. As a result, they are protected from damage caused by overloading.
How does high impedance busbar protection work?
High impedance protection system is a simple technique which requires that all CTs used in the protection scheme have relatively high knee point voltage, similar magnetizing characteristic and the same ratio. These CTs shall be installed in all ends of the protected object.
What happens in a differential relay when the saturation is too high?
The effect of CT saturation on transformer differential protection is double-edged. Although, the percentage restraint reduce the effect of the unbalanced differential current, in the case of an external faults, the resulting differential current which may be of very high magnitude can lead to a relay male-operation!
What is meant by high impedance state in TTL?
Hi-Z (or High-Z or high impedance) refers to an output signal state in which the signal is not being driven. The signal is left open, so that another output pin (e.g. elsewhere on a bus) can drive the signal or the signal level can be determined by a passive device (typically, a pull-up resistor). Synonyms.