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fx-in
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Join Date: Apr 2008
Posts: 4

DBR in VVF Drive

04/09/2008 1:05 AM

Dear Friends,

Dynamic braking Resistor(DBR) at VVF drive helps motor braking or stops shaft rotation. I heard it is suppressing the generated power to ground when motor stopped from running state.

My Application is Hoist operation of 30 tons. when at down operation even I give stop command the Hoist goes down when the VVF Drive without DBR. How it stops or Hold the Shaft rotation?

Kindly make me to know about this control.

Thanks and Regards,

Francis
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nirav soni
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Join Date: Jan 2008
Location: Gujarat
Posts: 13
#1

Re: DBR in VVF Drive

04/09/2008 2:10 AM

As i know about this matter,

During the stop command the reverce voltage is fed to the motor. This produces the reverce torque to the motor rotor and this reverce voltage is taken from Drive it self which is actually a D.C voltage but it is inverted to A.C before it is fed to the motor.

U can understand this matter better with the help of drive's manual.
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JRaef
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#2

Re: DBR in VVF Drive

04/09/2008 10:31 AM

DB is NOT suitable for a hoisting application on a VFD all by itself. Hoists are VERY SPECIALIZED applications that take EXPERIENCED engineers to set up and control properly.

YOU CAN KILL SOMEONE by not knowing all the subtle issues involved.

Please hire a professional with experience and who knows the proper technology required to apply a VFD to a hoist. This is NOT something you can solve with tips from a website.

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CrossFire
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#3
In reply to #2

Re: DBR in VVF Drive

04/09/2008 11:13 PM

Please take JRaef's advise on this.
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dkwarner
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#4
In reply to #3

Re: DBR in VVF Drive

04/09/2008 11:28 PM

I second that! (Meaning I strongly agree)

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Andy Germany
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#8
In reply to #4

Re: DBR in VVF Drive

04/10/2008 6:02 PM

I "Thirdly" that which means I agree even more strongly than you do!!!

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Shawn33
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#5

Re: DBR in VVF Drive

04/10/2008 5:55 AM

Francis,

DBR's are useful in overhauling load situations. When a VFD is trying to stop or slow a load whether it be spinning or linear travel that load will cause the motor to act as a generator which dumps voltage back into the VFD. This causes the bus voltage of the VFD to rise. What dynamic braking does is puts a chopper transistor across the bus with a resistor in series. It senses the voltage on the bus and when it goes above a fixed threshold will start to turn on and off disappating power in the resistor. This acts as a load for the motor (generator in the overhauling condition) to work against so it causes the motor to slow faster aas it is now doing work in "heating" up the braking resistor. Without the DBR the bus voltage rises and may cause the VFD to trip out on "Overbus Voltage" to protect itself. DBR's are not useful in holding a stationary load stationary.

Shawn
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Kyoto
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#9
In reply to #5

Re: DBR in VVF Drive

04/14/2008 9:44 AM

Absolutely correct in that DBs cannot stop a motor, but is used to slow it down. You must have motor armature current in motion cutting the magnetic field to generate a voltage to pump back into the DB resistors and power source.

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fx-in
Participant

Join Date: Apr 2008
Posts: 4
#10
In reply to #5

Re: DBR in VVF Drive

04/15/2008 4:49 AM

Dear Shawn,

Your explaination is just fantastic. I understood DBR suppress the generated voltage by means of heat energy. As other friends said Thruster Brake hold when VFD in offline for effective Braking.

Really The name "Dynamic Braking Resistor" confused me.

Thanks to all.

Francis
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mfiedler56
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Join Date: May 2007
Posts: 22
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#6

Re: DBR in VVF Drive

04/10/2008 9:52 AM

If you are designing a hoist then follow JRaef's advice.

If you are troubleshooting an existing hoist, there is most likely a mechanical brake that is slipping. You said there are no DBR's which makes sense because as Shawn33 said they absorb the power of a spinning motor but do nothing to hold a stationary motor.

Since it has a VFD there should be a short deceleration period before the mechanical brake engages. The brake will engage with no power to it and disengage when energized.

There may be a brake relay in the electrical panel that energizes the brake. These brake relays take a beating and need to be replaced occasionally. If there is one, check this first. If the contacts are fused closed it will be holding the brake open.
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suresh sharma
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Join Date: Dec 2007
Location: Mumbai, India
Posts: 1983
Good Answers: 25
#7

Re: DBR in VVF Drive

04/10/2008 12:03 PM

I am from Hoist and crane industry for 33 years. You should have selected Elctro Hyraulic Thrustor Brake for smooth stoppage and starting of the hoist. If you need more details on this please contact me.

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Users who posted comments:

Andy Germany (1); CrossFire (1); dkwarner (1); fx-in (1); JRaef (1); Kyoto (1); mfiedler56 (1); nirav soni (1); Shawn33 (1); suresh sharma (1)

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