Engineering Guide CDA3000
3-17
3 Selection of inverter module
DE
EN
1
2
3
4
5
6
7
A
Second letter - Link from the bodies of the electrical system to ground:
T
Body grounded directly, regardless of any grounding of a point of
the supply system
N
Body grounded directly with the grounded point of the supply
system (in AC systems the grounded point is generally the center
point or, if there is no center point, an outer conductor).
Voltage conditions in the IT system
In an IT system the voltages of the outer conductors are adjusted against
ground according to the voltage distribution by the discharge imped-
ances. These impedances comprise the capacitors of the conductors and
those of the equipment against ground, and the parallel switched insula-
tion resistors. If the said discharge impedances are equally large for every
conductor, all outer conductors likewise conduct the same voltage against
ground. High-resistance voltmeters connected between the outer conduc-
tor and ground display the same value. In three-phase AC systems this is
the star voltage; in AC systems half the conductor voltage is displayed.
Insulation monitors should therefore be connected symmetrically. If a
ground fault occurs on a conductor, its voltage to ground collapses. How-
ever, because the voltage between the conductors is maintained the
healthy conductors are raised to the conductor voltage against ground.
It should be considered that in the event of a ground fault on a conductor
in ungrounded systems the center point of the transformer takes on
phase voltage and the non-faulty outer conductors are raised to the outer
conductor voltage against ground.
This increased voltage load may result in puncture at a point with low
electrical insulation resistance, and this cause a double short circuit to
frame.
Содержание CDA3000
Страница 62: ...Engineering Guide CDA3000 2 29 2 Drive definition DE EN 1 2 3 4 5 6 7 A Notes ...
Страница 315: ...A 24 Engineering Guide CDA3000 Appendix A Formula bank Movement by rack Movement by cable reel Movement by spindle ...
Страница 317: ...A 26 Engineering Guide CDA3000 Appendix A Formula bank Indexing table with eccentric loads ...
Страница 336: ...Engineering Guide CDA3000 A 45 DE EN FR 1 2 3 4 5 6 A Appendix B Practical working aids for the project engineer ...