Siemens A1 User Manual
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Selecting a Drive
MICROMASTER Applications Handbook
9
3
Selecting a Drive
Often drive selection is straight forward, as a motor is already installed and the
speed range requirement is not excessive. However, when a drive system is
selected from first principles, careful consideration may avoid problems in
installation and operation, and may also save significant cost.
speed range requirement is not excessive. However, when a drive system is
selected from first principles, careful consideration may avoid problems in
installation and operation, and may also save significant cost.
3.1 Overall
Considerations
Check the Current rating of the inverter and the motor. Power rating is only a
rough guide.
rough guide.
Check that you have selected the correct operating voltage. 230 V three-phase
input MICROMASTERs will operate with single or three-phase inputs. 400 V
MICROMASTERs are for three-phase application only. Single-phase input units
can be more cost effective in some cases, but note that 230 V units will be
damaged if operated at 400 V. See section 3.2.1.
input MICROMASTERs will operate with single or three-phase inputs. 400 V
MICROMASTERs are for three-phase application only. Single-phase input units
can be more cost effective in some cases, but note that 230 V units will be
damaged if operated at 400 V. See section 3.2.1.
Check the speed range you require. Operation above normal supply frequency (50
or 60 Hz) is usually only possible at reduced power. Operation at low frequency
and high torque can cause the motor to overheat due to lack of cooling.
or 60 Hz) is usually only possible at reduced power. Operation at low frequency
and high torque can cause the motor to overheat due to lack of cooling.
Synchronous motors require de-rating, typically by 2-3 times. This is because the
power factor, and hence the current, can be very high at low frequency.
power factor, and hence the current, can be very high at low frequency.
Check overload performance. The inverter will limit current to 150 or 200% of full
current very quickly. A standard, fixed speed motor will tolerate these overloads.
current very quickly. A standard, fixed speed motor will tolerate these overloads.
Do you need to stop quickly? If so, consider using a braking resistor to absorb the
energy. A separate braking unit may be required for some VSDs. See section 0,
energy. A separate braking unit may be required for some VSDs. See section 0,
Do you need to operate with cables longer than 50m, or screened or armored
cables longer than 25m? If so, it may be necessary to de-rate, or fit a choke to
compensate for the cable capacitance.
cables longer than 25m? If so, it may be necessary to de-rate, or fit a choke to
compensate for the cable capacitance.
3.2
Supply Side Requirements
In order to achieve reliable operation, the main power supply to the inverter system
must be suited to the inverter and the anticipated power supplied. The following
points should be considered:
must be suited to the inverter and the anticipated power supplied. The following
points should be considered:
3.2.1 Supply
Tolerance
Inverters are usually designed to operate on a wide range of supply voltages. For
example:
example:
Low Voltage units
200 - 240 V ±10% i.e. 180 - 264 V
High Voltage units
380 - 480 V ±10% i.e. 342 - 528 V
Very High Voltage units 500 - 600 V ±10% i.e. 450 - 660 V
Inverters will operate over a wide supply frequency range, typically 47 - 63 Hz
However, many supplies vary outside these voltage levels. For example: