Transformer Winding Configuration; Control Overview - Siemens 6SR41 series Product User Manual

Overview
2.3 Perfect Harmony Features
2.3.6

Transformer Winding Configuration

Each transformer secondary winding sees typical 6-Pulse Harmonics. The transformer
secondaries are wound with varying phase angles, resulting in a multi-pulse reaction. The
input transformer primary winding and the line sees between 18 to 48 Pulse Harmonics, as
defined by the power cell configuration. This patented topology results in nearly sinusoidal
current and a high, stable input power factor across the entire load range.
● Secondary Windings see Higher Harmonics
● Primary Winding sees Low Harmonics
The Perfect Harmony transformers are applied to motor drives using the rule of 1 kVA per
Hp (see below), resulting in a transformer utilization factor of 89%. The transformer is
unusual in that the secondary windings carry six pulse currents, while the primary carries
nearly perfect sine waves. The total VA of the secondary windings is greater than the VA of
the primary windings.
Rated Input Current (Amps) = [(kVA rating) x 802] ÷ [√3 x Rated Primary voltage x 0.96 x
0.94]
With following assumptions used for sizing purpose:
Motor efficiency
VFD efficiency at full load
Input power factor
Output power per Hp at shaft
Reducing this equation results in:
Rated Input Current (Amps) = [(kVA rating) ÷ (Rated primary voltage)] x 513.1
2.3.7

Control Overview

Perfect Harmony is a simple "synchronous" control. Basic operation is summarized as
follows:
● Control sends message to each power cell control via dedicated fiber links
● Cell executes request by firing one switch pair:
● Cell control confirms switch pair fired
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– Plurality of phase staggered delta or extended delta reduces current
– Harmonics reflect multi-pulse secondary configuration
= 93%
= 96%
= 94%
= 746 / 0.93 = 802
– Plus DC voltage
– Minus DC voltage
– Zero voltage
Operating Instructions, Version AE 12/2009, A5E01454341C
Product User Manual