Excitation unit outlet device 3BSE004214R1

Excitation unit outlet device 3BSE004214R1

Excitation unit outlet device 3BSE004214R1

Negative sequence polarization has the following advantages compared to zero sequence polarization: • on solidly earthed systems U2 may be larger than U0 .

If the bus behind the IED location is a strong zero-sequence source, the negative sequence voltage available at the IED location is higher than the zero-sequence voltage.

• negative sequence polarization is not affected by zero sequence mutual coupling (zero sequence polarized directional elements may misoperate in parallel lines with high zero-sequence mutual coupling and isolated zero sequence sources).

• negative sequence polarization is less affected by the effects of VT neutral shift (possible caused by unearthed or multiple earths on the supplying VT neutral)

• no open-delta winding is needed in VTs as only 2 VTs are required (U2 = (UL12 – a · UL23)/3) The zero sequence current polarized earth directional unit compares zero sequence current I0 of the line with some reference zero-sequence current, for example the current in the neutral of a power transformer.

The relay characteristic AngleRCA is fixed and equals 0 degrees. Care must be taken to ensure that neutral current direction remains unchanged during all network configurations and faults, and therefore all transformer configurations/constructions are not suitable for polarization.

In dual polarization, zero sequence voltage polarization and zero sequence current polarization elements function in a “one-out-of-two mode”