2 Engineering
2.9 Single-phase AC motors
44
DC1-S…20…, DC1-S…OE1 Variable Frequency Drives
05/21 MN040058EN
www.eaton.com
2.9.6 Three-phase motors run from a single-phase supply (Steinmetz connection)
Figure 18: Running a three-phase motor on a single-phase supply (example: delta circuit)
Using a Steinmetz connection makes it possible to operate three-phase
asynchronous motors on a single-phase AC supply system. Depending on
the mains voltage and motor voltage, the connection needs to be
implemented with a wye or delta circuit.
The three windings, which are displaced in space by 120° relative to each
other, are connected (U, V) directly to the AC supply system. The remaining
terminal (W) is powered through a run capacitor, with the corresponding
reactive current producing the required phase difference. Within this context,
the capacitor connection is what determines the operating direction,
meaning that it is possible to switch operating direction without having to
swap windings.
When using a single-phase mains connection with a Steinmetz circuit, only
about 2/3 of the three-phase motor output will be produced. This motor will
have a lower output and torque (approx. 40 - 70 %) than PSC motors
(
section 2.9.4, “Capacitor motor (PSC-Motor)”, page 42), and also
requires a capacitor with greater capacitance (approx. 70
μ
F per kW).
When using direct starting, the inrush currents will be around 3 to 4.5 times
the rated operational current.
The good efficiency and quietness of this configuration mean that it can be
used for a wide variety of applications involving small drives with
compressors in refrigerators and deep freezers, circulation pumps in heating
systems and swimming pools, and drives for roller shutters and awnings.
U
U
V
U
U
V
Summary of Contents for PowerXL
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