Protective Elements
Z – Phase Distance Protection [21]
Available elements:
Z[1] ,Z[2]
The phase distance protection module, which is integrated in this relay, is intended to provide backup protection for
phase-to-phase faults on the electrical power system to which the generator set is connected. In case of a relay
failure on the power system the distance protection in the generator protection relay can work as a (remote) system
backup protection, backup protection for step-up transformer faults and sometimes backup protection for generator
internal faults as well.
Function
The device has two distance elements Z[1/2] with (independently configurable) MHO or polygon characteristics and
(independently settable) tripping timers, so that a two-zone phase distance protection scheme with different zone
reaches can be easily set up.
Fault Impedance Calculation
For the phase distance protection the three phase currents from the neutral (“W1”) CTs and the three voltages from
the terminal VTs are used to calculate the three phase-to-phase loop impedances (ZL1-L2, ZL2-L3,ZL3-L1).
However, impedance calculation is blocked as soon as the measured current drops below some (fixed device-
internal) limit, so that irrelevant calculation results can be excluded.
The relay takes corrections into account with the impedance calculation if there is a step-up transformer with
Delta/Star connection between generator and power system, as shown in the following diagram. These corrections
get activated if the Field Parameters of the Transformer are set to
»Phase Shift«
= 1, 5, 7 or 11. (The fault
impedance correction is not available for phase shift 3 and 9.)
Generator connected to the power system through a Δ/Y transformer.
815 MCDGV4 DOK-HB-MCDGV4-2E
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