Fairford Electronics QFE Series, Manual

Page: 34 / 194

Electrical Installation
QFE
page 2-10
FD8413 issue03_F
2.4.2 Multiple Motor Starting & Stopping
The QFE is capable of starting parallel-connected motors simultaneously provided each
motor has similar characteristics and load. For such configurations the unit rating should be
at least the sum of the current ratings of all the motors.
Alternatively, the QFE can start and stop motors sequentially using bypass contactors under
the control of the programmable relay set as a 'Top of Ramp' relay. The dual setting feature
allows for the control of motors with different start-up requirements. Details on multiple
motor applications can obtained via your supplier.
2.4.3 External Motor Protection Relay
The rating for a motor protection relay should be as for Direct-on-Line (DOL) starting, and if
it is an electronic relay, then the user should confirm it's suitability for use with a soft-starter.
If the motor load is high-inertia (extended start time) then a longer trip time may be required.
2.4.4 Motor Reversing
The diagram in figure 2.4.6 shows a typical motor reversing circuit using two contactors, K1
and K2, to interchange two phases of the 3-phase supply connections.
For this application the soft stop must be set to zero.
It is also recommended that: -
A period of 150 - 350 ms elapses between the FORWARD and REVERSE commands
If the reversing rate is high, the QFE current rating may need to be increased compared to
the operational current of the motor. Refer to sections 2.10.3 & 2.10.4 and also the Overcurrent
trip curves shown in section 2.10.5.
The current limit and the overload must be set with more consideration to the “reverse”
function rather than the “start” as the motor will initially be “plug braked” then be stationary
for a moment and finally undergo a normal soft start.
2.4.5 Connection of an External Current Transformer
When using a bypass contactor with the QFE, it is possible to connect an external current
transformer (CT) to the internally mounted electronic control card. This allows more of the
control functions of the unit to be used than would normally be available when the unit is
bypassed. The current display is also still active. The CT used must be of the same
specification as the original item fitted to the unit and the internal CT must be shorted out
(preferred option) or removed. For further details, consult your supplier.