An adjustable speed motor that does not trip ground‐fault‐interrupters (GFI’s)
Presented by DynaMotors, Inc.
2012 Motors, Drives and Automation Conference
1
An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• Inverters that drive induction motors, brushless dc motors and
switched reluctance motors can produce ground fault currents
that cause GFI to trip
2012 Motors, Drives and Automation Conference
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Typical 1 and 3 Phase Input PWM Motor Drive Inverters
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• Inverters that drive induction motors, brushless dc motors and
switched reluctance motors can produce ground fault currents
that cause GFI to trip
• Cabling between drive inverters and motors can conduct
common-mode energy to the motor stator windings which will
generate ground currents.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
2012 Motors, Drives and Automation Conference
5
An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• Inverters that drive induction motors, brushless dc motors and
switched reluctance motors can produce ground fault currents
that cause GFI to trip
• Cabling between drive inverters and motors can conduct
common-mode energy to the motor stator windings which will
generate ground currents.
• An example of the ground current produced by a typical PWM
motor drive with a 230Vac output and a 10kHz carrier
frequency follows here:
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• The ground currents generated in the example are about 1.3
Amperes peak with a duration of 1 uSec resulting in an
average current over a half cycle of one phase of about 26
mAmps. Adding the ground current from the other two phases
will increase the current.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• The ground currents generated in the example are about 1.3
Amperes peak with a duration of 1 uSec resulting in an
average current over a half cycle of one phase of about 26
mAmps. Adding the ground current from the other two phases
will increase the current.
• The ground currents exceed the Class A GFI device tripping
specification of 4 to 6 mAmps. Even the Class B GFI trip
current specification of 20 mAmps is exceeded.
2012 Motors, Drives and Automation Conference
9
An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• The ground currents generated in the example are about 1.3
Amperes peak with a duration of 1 uSec resulting in an
average current over a half cycle of one phase of about 26
mAmps. Adding the ground current from the other two phases
will increase the current.
• The ground currents exceed the Class A GFI device tripping
specification of 4 to 6 mAmps. Even the Class B GFI trip
current specification of 20 mAmps is exceeded.
• The conclusion is that this drive and motor will trip a GFI.
2012 Motors, Drives and Automation Conference
10
An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Background
• The ground currents generated in the example are about 1.3
Amperes peak with a duration of 1 uSec resulting in an
average current over a half cycle of one phase of about 26
mAmps. Adding the ground current from the other two phases
will increase the current.
• The ground currents exceed the Class A GFI device tripping
specification of 4 to 6 mAmps. Even the Class B GFI trip
current specification of 20 mAmps is exceeded.
• The conclusion is that this drive and motor will trip a GFI.
• Tests of typical commercial PWM drives and motors were
conducted to determine if this conclusion is justified.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
• There are several ways to eliminate the generation of ground
currents. One way is to use VFDs that have linear sine wave
outputs – this is a rather inefficient solution but will work.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
• There are several ways to eliminate the generation of ground
currents. One way is to use VFDs that have linear sine wave
outputs – this is a rather inefficient solution but will work.
• Another solution is to use a brushless repulsion motor.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
• There are several ways to eliminate the generation of ground
currents. One way is to use VFDs that have linear sine wave
outputs – this is a rather inefficient solution but will work.
• Another solution is to use a brushless repulsion motor.
• The brushless repulsion motor is a variable speed motor that
uses a stator winding that is connected directly to the ac mains,
this implies that there is no fast rising, high frequency voltages
being applied to the stator coils.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
• There are several ways to eliminate the generation of ground
currents. One way is to use VFDs that have linear sine wave
outputs – this is a rather inefficient solution but will work.
• Another solution is to use a brushless repulsion motor.
• The brushless repulsion motor is a variable speed motor that
uses a stator winding that is connected directly to the ac mains,
this implies that there is no fast rising, high frequency voltages
being applied to the stator coils.
• The brushless repulsion motor is also constructed with the
control devices built into the motor frame.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Construction of a Brushless Repulsion Motor
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Simplified image of a Brushless Repulsion Motor
Armature coil is open
Armature coil is shorted
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Flux pattern in 4‐pole Brushless Repulsion Motor
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
View of FET switches and heat sink
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Armature PC board‐view of photo sensors
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
View of control board and IR emitters
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
View of motor interior
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Conclusions
• The adjustable speed brushless repulsion motor eliminates the
need for high frequency PWM drive inverters that produce
radiated and conducted energy and high frequency commonmode currents.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Conclusions
• The adjustable speed brushless repulsion motor eliminates the
need for high frequency PWM drive inverters that produce
radiated and conducted energy and high frequency commonmode currents.
• The problem of common-mode currents is eliminated because
all the power switching is done in a closed space on the
armature.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Conclusions
• The adjustable speed brushless repulsion motor eliminates the
need for high frequency PWM drive inverters that produce
radiated and conducted energy and high frequency commonmode currents.
• The problem of common-mode currents is eliminated because
all the switching is done in a closed space on the armature.
• The filtering requirement for the input power line is reduced.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
Conclusions
• The adjustable speed brushless repulsion motor eliminates
the need for high frequency PWM drive inverters that
produce radiated and conducted energy and high frequency
common-mode currents.
• The problem of common-mode currents is eliminated
because all the switching is done in a closed space on the
armature.
• The filtering requirement for the input power line is
reduced.
• No filtering is needed for the space between the controller
and the armature.
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
• Patents
Dynamotor™ technology is protected by the US patents
listed below.
5,424,625 ‐ Brushless Repulsion Motor
5,491,398 ‐ Brushless Repulsion Motor
5,686,805 ‐ Brushless Repulsion Motor
5,936,374 ‐ Brushless Repulsion Motor
6,049,187 ‐ Speed Control for Brushless Repulsion Motor
6,108,488 ‐ Speed Control for Brushless Repulsion Motor
6,321,032 ‐ Brushless Repulsion Motor
2012 Motors, Drives and Automation Conference
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An adjustable speed motor that does not trip ground‐
fault‐interrupters (GFI’s)
•
References
– Michigan Municipal Workers Compensation Fund •
Ground Fault Circuit Interrupters‐9‐D‐1
– 2D2C Electrical Safety and Energy
•
Ground Fault Circuit Interrupter (GFCI)
– G,Skibinski, D,Dahl, K.Pierce, R.Freed and DGilbert/,”Installation Considerations for Multi‐Motor AC Drives and Filters Used in Metal Industry Applications” 0‐7803‐4943‐
1/98 1998 IEEE
– J.Erdman, R.J.Kerkman,D.Schlegel and G.Skinbinski,”Effect of PWM Inverters on AC Motor Bearing Currents and Shaft Voltages”, Allen Bradley Drives Div.,IEEE APEC Conference Dallas, TX March, 1995
– D.Busse, J.Erdman, R.J.Kerkman,D.Schlegel and G.Skinbinski,”System Electrical Parameters and Their Effects on Bearing Currents”, Allen Bradley Drives Div., IEEE APEC Conference San Jose, CA March, 1996
– OSHA,”29 CFR 1926.404(b)(1)(ii), Ground‐fault circuit interrupters”
2012 Motors, Drives and Automation Conference
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