MA7200 PLUS Operating Manual
TECO – Westinghouse Motor Company Cn-35 - Cn-38 Parameter Details
Cn-35
Speed Search Detection Level
(0 – 200%)
Cn-36
Speed Search Time (0.1 – 25.5s)
Cn-37
Min. Baseblock Time (0.5 – 5.0s)
Cn-38
Speed Search V/F Curve (10 – 100%)
The speed search function will search the speed (frequency) of a coasting motor starting with the frequency
command or maximum frequency. Using this frequency value the motor will be restarted from this point providing
a smooth recovery. This is effective in situations such as switching from a commercial power supply to an
inverter without tripping.
The timing of speed search function as shown in Fig. 9.2.2.9 below.
Fig. 9.2.2.9 Speed Search Timing Chart
The speed search command can be set through one of the multi-function contact input terminals
-
using
parameters Sn-25 - Sn-28.
If Sn-25 - Sn-28= 21: Speed search is performed from the Max. output frequency and motor is coasting freely.
If Sn-25 - Sn-28= 22: Speed search starts from the frequency command when the speed search command is
enabled.
After the inverter output is blocked, the user should input the speed search command and then enable the run
operation. The inverter will begin to search the motor speed after the min. baseblock time set by parameter Cn-37.
In speed search operation, if the inverter output current is less than Cn-35, the inverter will take the output
frequency as the real frequency at that time. Using the values of real frequency, the inverter will accelerate or
decelerate to the set frequency according to the acceleration or deceleration time.
While the speed search command is being performed, the user can slightly decrease the setting of the V/F curve
(Cn-38) in order to prevent the OC protection function from being enabled. Normally, the V/F curve need not be
changed. (As below)
The speed search operating V/F curve = Cn-38 x (normal operating V/F curve )
Notes
: 1- The speed search operation will be disabled if the speed search command is enacted from the Max.
frequency and the setting frequency. (I.e., Sn-25=20, Sn-26=21 and multi-function input terminals
,
is used at the same time).
2- The FWD/REV command must be performed after or at the same time the speed search
command is enabled. A typical operation sequence is shown below.
3- When the speed search and DC injection braking are enabled, the Min. baseblock time (Cn-37) must
be set long enough to allow for the motor’s residual voltage to decrease. If an overcurrent is detected
when starting a speed search and DC injection braking is active, increase the setting of Cn-37 to
prevent a fault from occurring. As a result, the Cn-37 setting cannot be set too small.