31
6 Reflected
Harmonics
Rectification:
The standard A77 comes in single and 3-Phase versions having a typical total harmonic distortion between
25
33% ATHD.
12-Pulse Rectification
(OPT17B)
A77 3-Phase chargers may optionally be equipped with 12-Pulse rectification. 12-Pulse rectification provides
greatly reduced harmonic content as observed by the commercial 3-Phase source. 12-Pulse also presents less
ripple stress to the battery and internal capacitors which provides better transient response.
Using a proprietary phase shifting power transformer, the two independent SCR rectifier bridges operate 30°
apart from each other. The unique SCR firing board and other proprietary circuitry maintain approximately ½
the total DC load current through each rectifier bridge. The phase shifted DC current from each rectifier bridge
summed in the Inter-Phase Transformer (IPT) where much of the harmonic cancellation takes place. Typically
the 5
th
, 7
th
, 17
th
and 19
th
harmonics are nearly entirely canceled, resulting in typically
≤
10%ATHD.
Related Components:
Phase Shifting Power Transformer: SPT-**
12-Pulse SCR Firing Board: P24S-12P60HZ-**
Dual Current Sensor Board: S2A-418S-****
Inter-Phase Transformer: “IPT” SCH-**
Dual Independent Rectifier Bridges: S1E-12P**
12-Pulse Rectification With 5%ATHD Option
(OPT17B & OPT535)
A77 3-Phase 12-Pulse chargers may also be equipped with Option 535 to further reduce the line current
distortion to
≤
5%ATHD. This option consists of an additional line filter added to the charger between the AC-
breaker and the primary of the phase-shifting power transformer. The line filter incorporates a 3-phase
capacitor, which must be replaced on a 7-year interval following the standard La Marche recommended
maintenance schedule.
Related Components:
All 12-Pulse components listed above in (OPT17B)
Line Filter: P24L-LF**
3-Phase Capacitor: P24-P2A-480-**
Design
Typical THD
A77 Standard 3-Phase
25-30%
12-Pulse Option
10%
12-Pulse 5% THD Option
≤
5%
Summary of Contents for A77
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