Ungrounded Supplies; Low Frequency Harmonics; Micromaster Eco; Midimaster Eco - Siemens Midimaster Eco Reference Manual

ECO REFERENCE MANUAL

UNGROUNDED SUPPLIES

Certain installations need to operate with supplies
that are isolated from the protective earth (IT
supply). This permits equipment to continue to
run following a line to earth fault. However,
MICROMASTER Eco and MIDIMASTER Eco are
designed to normally operate on grounded
supplies and are fitted with interference
suppression capacitors between the supply and
ground. Preventative measures (see below)
should be used on ungrounded supplies. Please
consult Siemens for further clarification.

LOW FREQUENCY HARMONICS

The inverter converts the AC supply to DC using
an uncontrolled diode rectifier bridge. The DC link
voltage is close to the peak AC supply voltage, so
the diodes only conduct for a short time at the
peak of the AC waveform.
The current waveform therefore has a relatively
high RMS value as a high current flows from the
supply for a short time.
For typical harmonic details, refer to Section 15.

MICROMASTER Eco

MICROMASTER can be used on unearthed
supplies if connected through an isolating
transformer.
Alternatively they may also be connected directly
to the unearthed supply, but the inverter may then
shut down (F002) if an output earth fault
develops.

MIDIMASTER Eco

The 380/500V models are suitable for use on
unearthed supplies at a maximum switching
frequency of 2kHz (P076 = 6 or 7). This is to
prevent the input Y capacitors from overheating in
the event of an earth fault on the Eco output.
The MIDIMASTER Eco will continue to operate
normally under earth fault conditions at the
MIDIMASTER Eco input.
Earth fault monitoring on the input supply,
capable of detecting an earth fault on the motor
output, is recommended.
EMC FILTER RESTRICTIONS FOR
ALL PRODUCTS
The input RFI suppression filters cannot be used
on unearthed supplies since they are designed
for earthed supplies only. Many unearthed
supplies are only intended for industrial users
(particularly 500V ones), and EN61800-3 does
not impose any emissions limits in such
applications. Therefore a filter may not be
required in any case.
The EMC tests have been carried out according
to EN61800-3 on earthed supplies. The test
results will not be valid for unearthed supplies.
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