Bypass Circuits; Bypass Options; Basic 3-Contactor Bypass Functions; Contactor Operation - Danfoss VLT Option Panel Instruction Manual

Bypass Circuits

Two-contactor bypass. This bypass consists of
motor starter circuitry used in bypass, a bypass
contactor (M3) interlocked with a drive output
contactor (M2) mounted in the bypass enclosure.
For the electromechanical bypass (EMB), an
enclosure-mounted Drive/OFF/Bypass selector is
used to electrically select whether the motor is
controlled by the drive, connected to the full-speed
bypass, or disconnected from both. The contactor
and motor starter are controlled by this switch. A
light indicates when in bypass. For the electronically
controlled bypass (ECB), control selection is made
through the drive keypad by pressing the DRIVE
BYPASS key and selecting from the available
options shown. Display data indicates when in
bypass. A drive disconnect is also available with the
two-contactor bypass and is required for the option
panel components without bypass.
Three-contactor bypass. This bypass consists of
motor starter circuitry used in bypass, a bypass
contactor (M3) interlocked with a drive output
contactor (M2), a drive input contactor (M1), and an
overload relay mounted in the option panel. For the
Table 1-1. Contactor Operation
Contactor Drive Mode OFF
M1 Closed Open
M2 Closed Open
M3 Open Open
6
Bypass Mode Test Mode
Open Closed
Open Open
Closed Closed
Figure 1-1. Basic 3-contactor Bypass Functions
EMB, an enclosure mounted Drive/OFF/Bypass/
Test switch is used to electrically select whether the
motor is driven by the drive, connected to the full-
speed bypass, or disconnected from both. The test
position applies power to the motor through the
bypass (M3 closed) while removing power to the
motor (M2 open) but keeps the drive powered (M1
closed). A light indicates when in bypass. For the
ECB, control selection is made through the drive
keypad by pressing the DRIVE BYPASS key and
selecting from the available options shown. Display
data indicates when in bypass. The circuitry may be
supplied with either an input disconnect switch or
an input circuit breaker.

Bypass Options

Common run/stop with bypass. Allows a common
remote signal through the VFD input terminals to
initiate operation in either drive control or bypass. A
relay closure starts the motor(s) in drive or bypass,
depending upon the position of the bypass selector
switch.
Automatic bypass. Automatically transfers the
motor(s) from drive to bypass without operator
intervention when a fault condition trips the drive,
after a programmable time-out period. The VFD's
internal fault circuitry controls this action. The time
delay permits all automatically resettable faults to
clear prior to transfer to bypass. Run permissive or
safety circuit signals override the auto bypass
function and may prevent or delay running in
bypass.