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Suggested Code
of practice for connection of
Variable Frequency Drives to Surface mounted irrigation pumps.
| 1. |
Determine the
environmental requirements for the EMC levels.
| a. |
High sensitivity
area will require installation to domestic levels. |
| b. |
Standard
environment in remote area will require industrial levels. |
|
| 2. |
The variable
speed controller shall be connected to the supply in the manner described
in the manufacturers installation guide for the domestic or industrial
levels.
| a. |
Where an
input filter is specified for compliance with EMC requirements,
that filter shall be installed as close to the input of the
VFD as possible with cabling and earthing as specified by the
manufacturer. |
| b. |
Where
an output filter or ferrite ring is specified by the manufacturer
for compliance with EMC requirements, such filter shall be
installed.
Note
: Some Variable Frequency Drives require both input and output
filters fitted in order to comply with the industrial EMC
levels. Other Variable Frequency Drives only require additional
filtering to be added for compliance with domestic EMC levels |
| c. |
The
length of cable on the output or the drive shall be less than
the maximum length specified by the manufacturer.
Note
: The maximum length of screened cable may depend on the presence
of input and/or output filters |
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| 3. |
The Variable
Frequency Drive shall be connected to the motor via one or more screened
cables.
| a. |
The screen
is to be terminated to the VFD output earth or chassis via a
screened gland or clamped by a copper saddle or clamping device
as supplied/recommended by the VFD manufacturer. |
| b. |
The other
end of the screened cable shall be connected to the motor terminal
box by a screened gland or similar clamping device. |
| c. |
Where there
is an output filter, output reactors, or output isolator in
series with the output, such devices shall be mounted in the
drive enclosure with the screen terminated after these devices,
or they shal be mounted in a separate metal enclosure with the
screen glanded or clamped to the enclosure at the input and
also at the output of the enclosure. |
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| 4. |
The motor shall
be earthed to the output of the VFD and shall not be additionally
earthed back to the supply. – There shall only be one source
of earth connection to the motor.
| a. |
Where the
screened cable is an EMC cable or a four core cable, the earth
conductor shal be connected to the earth point in the VFD and
to the earth point in the motor. |
| b. |
Where a
three core neutral screened cable is used, an additional flexible
earth conductor of not less than half the cable core rating
shall be run with the main cable to further reduce the earth
impedance between the VFD and the motor. |
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| 5. |
Control cables
connected to the VFD shall be screened with the screen bonded to the
VFD chassis.
| a. |
If the
controls are mounted in a separate enclosure which does not
have an independent earth connection, then the screen shall
be bonded to the controls enclosure. |
| b. |
If the
controls are mounted in a separate enclosure which has an independent
earth connection, then the screen shall not be bonded to the
controls enclosure. |
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Suggested Code of practice for connection of
Variable Frequency Drives to Submersible irrigation pumps.
| 1. |
Determine
the environmental requirements for the EMC levels.
| a. |
High
sensitivity area will require installation to domestic levels. |
| b. |
Standard
environment in remote area will require industrial levels. |
|
| 2. |
The variable
speed controller shall be connected to the supply in the manner described
in the manufacturers installation guide for the domestic or industrial
levels.
| a. |
Where
an input filter is specified for compliance with EMC requirements,
that filter shall be installed as close to the input of the
VFD as possible with cabling and earthing as specified by the
manufacturer. |
| b. |
Where
an output filter or ferrite ring is specified by the manufacturer
for compliance with EMC requirements, such filter shall be
installed.
Note
: Some Variable Frequency Drives require both input and output
filters fitted in order to comply with the industrial EMC
levels. Other Variable Frequency Drives only require additional
filtering to be added for compliance with domestic EMC levels.
|
| c. |
The
length of cable on the output or the drive shall be less than
the maximum length specified by the manufacturer.
Note
: The maximum length of screened cable may depend on the presence
of input and/or output filters. |
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| 3. |
The Variable
Frequency Drive shall be connected to the well head terminal box via
one or more screened cables.
| a. |
The well
head terminal box shall be metal and securely bonded to the
well head structure. |
| b. |
The screen
is to be terminated to the VFD output earth or chassis via a
screened gland or clamped by a copper saddle or clamping device
as supplied/recommended by the VFD manufacturer. |
| c. |
The other
end of the screened cable shall be connected to the well head
terminal box by a screened gland or similar clamping device.
|
| d. |
Where there
is an output filter, output reactors, or output isolator in
series with the output, such devices shall be mounted in the
drive enclosure with the screen terminated after these devices,
or they shal be mounted in a separate metal enclosure with the
screen glanded or clamped to the enclosure at the input and
also at the output of the enclosure. |
| e. |
Connections
from the well head terminal box can be made by single core or
multicore cables with minimum length outside of the terminal
box and well casing. |
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| 4. |
The well head
shall be earthed to the output of the VFD and shall not be additionally
earthed back to the supply. – There shall only be one source
of earth connection to the motor.
| a. |
Where the
screened cable is an EMC cable or a four core cable, the earth
conductor shall be connected to the earth point in the VFD and
to the earth point in the motor. |
| b. |
Where a
three core neutral screened cable is used, an additional flexible
earth conductor of not less than half the cable core rating
shall be run with the main cable to further reduce the earth
impedance between the VFD and the motor. |
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| 5. |
The motor earth
shall be bonded to the well head at the well head terminal box. |
| 6. |
Control cables
connected to the VFD shall be screened with the screen bonded to the
VFD chassis.
| a. |
If the
controls are mounted in a separate enclosure which does not
have an independent earth connection, then the screen shall
be bonded to the controls enclosure. |
| b. |
If the
controls are mounted in a separate enclosure which has an independent
earth connection, then the screen shall not be bonded to the
controls enclosure. |
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See VFDs cause EMC
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