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Figure 3-22 Primary circuit of the precharge
User 3 phase power supply 380V
10kV transformer
MV input side
Phase-shifting
transformers
Transformer
secondary winding
Cell C1
Cell C2
Cell B1
Cell B2
Cell A1
Cell A2
Cell C7
Cell B7
Cell A7
Cell C8
Cell B8
Cell A8
Voltage
detection
380V
auxiliary
winding
VFD output side
“Cell detection” mode: The process of charging is the same as “percharge” mode. The only difference is that
the third stage charging will continue until the user presses the MV break button to stop charging, used for cell
detection.
Notes: To run the VFD unless remove the motor cables from the output chamber.
The precharge box is installed inside the VFD. The power, value and quantity of the resistor are matched with the
specifications of the VFD. The primary circuit of the precharge is shown in Figure 3-22.
3.2.7 Switchgears (optional)
For practice application, the switchgears (bypass cabinet and switch transfer cabinet) usually match the usage of
VFD.
The function of bypass cabinet is to switch motor working at industrial frequency when the VFD fails, and ensure
the continuity of manufacturing and also improve the reliability of system. There are two basic kinds of bypass
cabinet: manual bypass cabinet and auto-bypass cabinet. The manual bypass cabinet width is 0.8m; when
install it, VFD and switchgear should be interlocked. The auto-bypass cabinet width is 1m; when install it, VFD is
interlocked with KM1 contactor of input cables inside bypass cabinet.
When a bypass cabinet used, the primary cables from users (power inlet cables and motor outlet cables) normally
Three-phase electric power of cells input terminal are obtained by the secondary winding of phase-shifting
transformer. The output terminal of the precharge control system main circuit is connected to the auxiliary
winding (380V) of transformer. That is equivalent to supplying power to the auxiliary winding by user and then the
secondary winding will be DC capacitor on the cells for charging.
