Q 1: What are Constant Torque &
Variable Torque applications?
Q 2: What is
High Torque & Standard Torque selection?
Q 3: What are the applications on
which Energy Saving can be achieved?
Q4 : Can an AC Drive straightaway
replace DC Drive?
Q 5 Can AC Drive replace a
Q 6 Can an imported m/c designed
for 60Hz supply be fed through an AC Drive?
Q 7 Are there any precautions to be
taken if output cable length is more?
Q 8 What is RFI / EMI?
Harmonics different than RFI?
Q 10 Can a slip ring induction
motor be connected to an AC Drive?
Q 11 What is max safe frequency at
which an ordinary motor can be run?
Q 12 While testing a drive with a
small motor, why torque is not sufficient at
Q 13 What is skip frequency?
Q 14 What precautions are to be
taken to operate two or more motors in parallel
on one drive?
Q 15 When should auto tuning be
Q 16 What is Slip Compensation?
Q 17 What is flying start /
catching a spinning load?
Q 18 What is Power loss ride
Q 19 What is close loop operation?
1: What are Constant Torque & Variable Torque
A : Application
like Conveyors, roller tables, grinder etc. etc.
are Constant Torque
and Centrifugal Pumps & fans are Variable Torque
Q 2: What is High Torque &
Standard Torque selection?
A : High Torque
& Constant Torque are one and the same thing and
& Variable Torque are one and the same thing.
3: What are the applications on which Energy
Saving can be achieved?
A : Energy
saving can be achieved on Variable Torque
: Can an AC Drive straightaway replace DC Drive?
A : No.
Starting torque requirement of the load has to
be matched with deliverable
torque with AC
Drive. As a thumb rule one rating higher motor &
Drive should be
5 Can AC Drive replace a gear-box?
A : No.
Gear-box is not only a speed reducer but a
torque multiplier as well. (P=NT).
For example :
If output speed is 1/5th of the input speed,
otput torque shall be 5
times the input
6 Can an imported m/c designed for 60Hz supply
be fed through an AC Drive?
A : Yes only
for single motor load. But No for Non-motor
loads because output wave
shape is a
chopped DC and not AC. No for multi motor m/c as
switching on &
off the motor on a operative system with
contactors at the output
sizing the AC Drive so that it is capable of
handling the starting current
(5-6 times) of
the incoming motor.
7 Are there any precautions to be taken if
output cable length is more?
A : Yes, if
cable length is more than 100 m, installation of
an output choke is strongly
is advisable to keep the output choke close to
motor as for as
than putting it in the drive panel. Pls. Note
that output choke sizing
should not be
equal to input choke sizing. Refer ATV66 motor
choke selection table
8 What is RFI / EMI?
A : RFI is
Radio Frequency Interference and EMI is Electro
the range of 150 KHz to 20 MHz is called Radio
Q9 Are Harmonics different
A : Yes. Low
frequencies of 150 Hz to 10KHz range (in
multiples of the base frequency)
Harmonics.Frequecies ranging from 150KHz to
20MHz are called RFI.
10 Can a slip ring induction motor be connected
to an AC Drive?
A : Yes. But
take care of torque requirement of the load.
11 What is max safe frequency at which an
ordinary motor can be run?
A : Please
check with the motor manufacturer.
12 While testing a drive with a small motor, why
torque is not sufficient at lower
A : Auto-tuning
can improve the torque performance to some
shall give excellent performance.
13 What is skip frequency?
A : Every
mechanical system has a natural resonance
frequency at which a lot of
comes into picture. Bypassing that particular
frequency (speed) is known
frequency. Some systems may have more than one
14 What precautions are to be taken to operate
two or more motors in parallel
A : a)Drive
selection should be such that Nominal output
current of drive should be 10-
than arithmatic sum of nominal currents of
motors to be connected in
is to allow circulating currents.
external thermal O/L relay must be incorporated
at output for each
to their ratings.
15 When should auto tuning be used?
A : Auto tuning
can be very helpful in improving torque
generated at lower speeds when
the motor used
is non-standard or does not confirm to IEC
using special motors e.g. Textle duty motor can
also be avoided by
16 What is Slip Compensation?
working on DOL starter, on-load speed of the
motor is lower than no-load
speed. For some
applications, this speed drop may not be
acceptable. This drop
compensated with the help of Slip compensation
17 What is flying start / catching a spinning
applications require that drive picks up an
already rotating load to desired
start / catching a spinning load parameter
allows the drive to determine
the speed &
direction of a rotating motor and begins its
ramp output at that speed.
18 What is Power loss ride through?
A : The ability
to keep on working while short power
interruption is called power loss ride
feature. The duration of Power loss ride through
for ATV28 is 300ms and
that of ATV58
is 500ms. This an outcome of DC link capacitor
19 What is close loop operation?
A : Some
applications demand high speed accuracy. Speed
accuracy can be improved
by using a
Pulse Generator or Tacho Generator for actual
speed feed back. This is
loop operation. ATV58 can accept PG/TG feed back
with the help of
a suitable I/O