Typical Bypass Operation; Bypass Circuits; Bypass Options - Danfoss VLT FC Series Operating Instructions Manual

Introduction

1.1.4 Typical Bypass Operation

With contactors M1 and M2 closed and contactor M3 open
(see Illustration 1.1), the motor is running in drive control.
Opening contactor M2 removes power to the motor but
allows the drive to remain under power. This is the test
mode and only available in the three-contactor configu-
ration shown. With contactors M1 and M2 open and
contactor M3 closed, the motor is running in bypass from
the line input. For a two-contactor configuration, M1 is
absent. In this case, contactors M2 and M3 control the
options for running in drive or bypass mode. The drive
disconnect and fuses shown in Illustration 1.1 are
controlled by an ON/OFF disconnect on the bypass panel.

1.2 Bypass Circuits

1.2.1 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 LCP by pressing [Drive Bypass] 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 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 fullspeed bypass, or discon-
nected 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 LCP 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.
Option Panel Operating Instructions
Contactor
M1
M2
M3
Table 1.1 Contactor Operation
Illustration 1.1 Basic 3-contactor Bypass Functions

1.3 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 before
transfer to bypass. Run permissive or safety circuit signals
override the auto bypass function and may prevent or
delay running in bypass.
Run permissive in bypass
With run permissive active, the drive sends a run request
and waits for a remote response to before notifying the
motor to start. The response indicates the system is safe to
operate.
Basic fire mode in bypass
This option switches the panel to bypass whenever a
remote fire mode command is given to the VFD through
the input terminals. In either drive or bypass, fire mode is
intended to ignore common safety and overload inputs in
emergency situations. The motor will continue to run in
bypass until fire mode is removed or the drive or option
panel fail. External safety signals and motor overload are
ignored when in fire mode.
Advanced fire mode in bypass
The advanced fire mode allows for a variety of
programmable responses to an external fire mode
command signal. Bypass options are programmed through
the drive's fire mode parameters. See fire mode section of
the drive manual and support materials for available
options.
®
MG14I102 - VLT is a registered Danfoss trademark
Drive Mode OFF Bypass
Mode
Closed Open Open
Closed Open Open
Open Open Closed
1 1
Test Mode
Closed
Open
Closed
5