Introduction
Operating instructions RHF
15
ELTROPLAN
-
REVCON
Elektrotechnische Anlagen GmbH
The configuration of the distribution system and the relevant impedances must be
known to calculate the distortion in the PCC.
A commonly used term to describe the impedance of a grid is the short circuit ra-
tio Rsce, defined as the ratio between the short circuit apparent power of the
supply at the PCC (S
sc
) and the rated apparent power of the load (S
equ
).
=
/
with
=
/
and
=
×
3.2 The negative effect of harmonics is twofold
•
Harmonic currents contribute to system losses (power cable, transformer etc.)
•
Harmonic voltage distortion causes disturbances to other loads and increase
losses in other loads
3.3 Harmonic limitation standards and requirements
The requirements for harmonic limitation are:
•
Application specific requirements
•
Requirements from standards that have to be observed
The application specific requirements are related to a specific installation with
technical reasons for limiting the harmonics.
For example: A 250kVA transformer is connected with two 110kW motors. One is
connected direct and the other motor is supplied by a frequency converter.
If the other motor should also be supplied by a frequency converter, the trans-
former will, in this case, sized too small.
If the system should be retrofitted without changing the transformer, the harmonic
distortion caused by two drives must be mitigated using RHF filters.