Section 1 Introduction; Purpose Of The Manual; Overview; Typical Bypass Operation - Danfoss VLT Option Panel Instruction Manual

Purpose of the manual

This manual is intended to provide detailed
information for the installation and operation of the
option panel used in conjunction with a Danfoss
variable frequency drive (VFD or drive). To enable
efficient handling of the equipment, requirements
are provided for installation of mechanical,
electrical, and control wiring, proper grounding, and
environmental considerations. Pre-start and start up
procedures are detailed. Also included is a detailed
overview of the option panel bypass function. In
addition, identification of other optional components
and their operation and start up troubleshooting
instructions are included. For the electronically
controlled bypass, additional programming and
operation information is provided.

Overview

A variable frequency drive regulates the speed and
operation of an electric motor(s). The drive is
programmable and offers many features and
savings compared to operating a motor from
unregulated line voltage. The option panel is a
protective enclosure in which the drive and various
optional components are assembled and mounted.
One of the most common functions of the option
panel is to allow switching between VFD control and
running in bypass. In bypass, the motor is operated
directly from line input power.
Two types of bypass options are available: the
electromechanical bypass (EMB) and electronically
controlled bypass (ECB). The EMB is operated by
selector switches on the front of the panel. The
EMB controls a motor(s) by switching between
drive control, operation in bypass, or off. In addition,
a test setting is available which disengages the
motor from the drive but keeps the drive operational
while the motor runs in bypass. The switching
Section 1
Introduction
function activates contactors that open or close to
provide power to the motor through the drive or
bypass circuitry, as required.
The ECB also uses contactors to provide power to
the motor through the drive or bypass circuitry.
However, the ECB contains a local processor which
interacts with the drive's control logic for
programmable options, remote inputs, and status
reporting. The VFD's logic circuitry is backed up by
an independent panel-mounted power supply so
that, even if the drive loses power, control and
communication functions are maintained.
Programming and display are provided by the
VFD's keypad. An important feature of the ECB is
the ability to accept commands from a building
automation system (BAS) and to report operational
status in return.
See more detailed descriptions of the EMB in
Sections 5 and ECB in Section 6 of this manual.

Typical bypass operation

With contactors M1 and M2 closed and contactor
M3 open (see Figure 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 configuration 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 the figure is
controlled by an ON/OFF disconnect on the bypass
panel.
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