Megger PVS 100i, User Manual

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3 Technical Description
3.1 General Description
Requirement Precise knowledge of the phase assignment in an electrical power network is an
essential condition for safe and reliable operation.
This is true for all levels from the distribution network to the transport network for high-
voltage transmission lines. Phase identification on live systems is necessary when
preparing and executing network restructuring, for recording, updating and revising
planning documentation, and for planning and setting up new network systems.
The PVS 100i system allows safe and reliable identification of the phasing on live
systems, so that the phases can be assigned and labelled in order to prevent operating
errors with serious consequences, for example during switching operations.
How it works The phases in a three-phase network are offset in time, as the following diagram shows:
If we observe the phase shift (120°) of each alternating current curve in a vector
diagram, the vectors form a symmetrical star:
Thus, by comparing the phasing, each phase can be clearly identified.
Due to the high propagation speed, the phase angle only drifts by about 1° in 8 km,
which means this comparison can be carried out even over long distances. In an
interconnected network, the load angle must also be taken into account. It is impossible
to forecast where the voltage to be measured is coming from. This means that in an
interconnected network, the phasing can be identified over distances of more than
50 km.
L1
L2
U
t
L1
L2
L3
L3