Automatic Backup Of Fan Motors - Remak AERO MASTER XP Series Installation And Operating Instructions Manual

Automatic Backup of Fan Motors

A fan section, respectively a built-in fan assembly, with a backup motor
(drive) for the "backup" function is equipped with two motors situated in one
fan section; each motor belt drive leads to the common shaft of the fan. The
backup function is designed so that the main motor runs in basic mode while
the second/backup motor will only run if the main motor fails.(1
The backup is ensured by automatic start-up of the backup motor if the main
fan motor has failed.
The backup mode will be activated if the air flow (supply) is interrupted dur-
ing the air-handling unit operation, which can be caused by the following
reasons:
a) The main motor belt has broken – air flow failure.
b) The main motor has failed – overheating,
open thermo-contacts, shorted motor, etc.
c) The frequency inverter has failed (if equipped).
Due to application purposes (i.e. guaranteed air-handling unit operation), the
fans with backup motors are equipped with protective inlet grilles to protect
the fan impeller (blades) from being damaged by the remains of a torn belt
(of the main motor).
Figure 1
42
REMAK Control Systems for Backed-Up Air-
Handling Units
The backup fan section is always equipped with two dP air flow sen-
sors. One sensor is assigned to the main fan motor while the other is
for the backup fan motor. Information on a main motor failure from
the assigned sensor is sent, as a warning signal, to the control unit
terminals. These terminals must be used for a visual or an acoustic
alarm situated in a suitable location to inform the operating staff
that the backup mode has been activated. This failure is not signalled
in the control unit. As soon as the main failure has been registered,
the backup motor is started and the air-handling unit OPERATION will
continue in the backup mode without interruption and without need
for the operator's intervention.
This mode will last until the main fan motor failure is rectified; the unit must
be switched off (i.e. reset sequence must be carried out). The main motor
restart (e.g. after cooling down) is disabled; the main motor can only be
restarted after the air-handling unit has been switched off and checked, the
failure rectified, and restart of the unit carried out. Direct transition from the
backup mode to the basic mode is not possible. If air pressure is reduced or
lost because of belt breakage or motor failure (overheating, thermo-contact
opening) during the backup mode, the air-handling unit will be switched to
STOP mode, which will be signalled acoustically as well as
trol unit in a standard way, respectively using optional external outputs of
failure signalling (other than those used for the backup mode signalling). If
the drive has been switched to the backup motor (backup mode), it is neces-
sary to check the fan's built-in assembly, including its drive, rectify the main
drive failure, and if necessary replace damaged parts, and restart the unit (in
the basic mode); when doing so, remember to observe all safety measures.
The backup motor is intended only for temporary operation if the main motor
fails (this feature can differ depending on the M & C system).
Warning:
When connecting the fan section with a backup motor, it is necessary to be
careful and strictly observe the M & C project requirements. It is especially
necessary to pay attention to the wiring! If a service switch is used, it must
be of the duplex type for safety reasons, i.e. it must enable both motors to
be switched off at the same time.
1) The backup motor concept does not provide regular alternation of motors as
far as the equivalent number of operating hours is concerned. Moreover, due to
the backup design (without a clutch) both motors always turn. Backup reliability
is ensured by idle turning of the backup motor during the basic operation mode
and extended belt length of the backup motor (reduced wear). Of course, regular
maintenance must be preformed (belts, bearings). When performing regular or
occasional servicing, it is advisable to replace both belts; respectively, if the broken
main motor is being replaced, use the backup motor to replace the main motor and
a new one to replace the backup motor. The broken main motor must be replaced
as soon as possible and the air-handling unit must be recovered in basic operation
mode with the backup function available.
by the con-
visually