What is slope in differential relay?
The slope characteristic provides high sensitivity when low levels of current are flowing in the zone of protection but has less sensitivity when high levels of current are flowing and false differential current due to current transformer (CT) saturation is more likely.
How do you find the slope of a differential relay?
Once the differentially balanced through-current condition is established correctly, as in figure 7, the angle of one of the winding currents can be rolled until the relay trips. At this point, the slope can be calculated by dividing the differential current magnitude by the restraint current magnitude.
What is high set in relay?
The high-set instantaneous setting is typically for protecting a transmission line and is set at a margin below the maximum remote terminal fault magnitude so that it does not over-reach and trip for faults outside the line protection zone.
What is bias in differential protection?
The term biased-differential or percentage differential is based on the fact that the operating threshold increases with the through current. Biased-differential protection is an older design of protection than high impedance circulating current.
What is differential relay how it operates?
The differential relay is one that operates when there is a difference between two or more similar electrical quantities exceeds a predetermined value. In the current differential scheme, there are two sets of current transformer each connected to either side of the equipment protected by differential relay.
How do you test a differential relay?
Abstract and Figures
- Typical voltage and current reference direction for a power transformer.
- Power transformer differential protection scheme with interposing CTs.
- Positive Sequence External Fault test performed by the Wizard.
- Positive Sequence Internal Fault test performed by the Wizard.
What is ref protection transformer?
Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure.
What is spill current in relay?
At other tap positions, the current-transformer secondary currents will not balance. This causes spill currents in the relay-operate windings. This occurs when the tap changer is selected to maximum (or minimum) tap, coincident with the highest out-of-zone fault current flowing through the transformer.
What is low set and high set in relay?
The relay includes a high-set and low-set over current unit. When the phase currents exceed the set start value of low-set stage I>, the overcurrent unit will start to deliver a start signal after a ~55 ms’start time.