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MICROMASTER

Help me: Using one MM430 for two Motors?

Thread Starter: htd21   Started: 5/22/2008 7:53 AM   Replies: 7

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  5/22/2008, 7:53 AM
htd21
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Our stupid boss decided to use 1 MM430 15kW (6SE430-2AD31-5CA0) to power simmultaneously for 2 motor (7.5kW for each of them) for 2 pumps of water chiller HVAC system. I think it is not allowed, but I could not persuade him.
Who can help me to solve the problem? Is our boss right? And Why?
Many thanks and best regards,
HTD.

P/S: Detail description drawing is in pdf file attached (To Siemens-Model.pdf)!

Attachment: To Siemens-Model.pdf  (193 Downloads)
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  5/22/2008, 10:34 AM
dchartier
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Hello htd21;
Connecting a single VFD to multiple motors is actually quite common in certain industries; it is a cheap way to obtain speed synchronisation between the motors (limited, of course). There are some conditions of course. Here is a FAQ from a non-Siemens manufacturer of VFDs, but the answers are general enough to apply to most systems:

Can more than one AC motor be operated from a single inverter?

Answer ): Yes. A VFD can operate multiple motors as long as the full load current ratings of ALL of the motors added up is less than or equal to the output current rating of the VFD. Per the NEC, multiple motor applications must have individual thermal overload protection for each motor. All of the motors connected to the output of the VFD will start and stop together, and will operate at the same speed.

Do not use contactors to start and stop individual motors

http://www.leeson.com/cgi-bin/fetchpdf.cgi?/literature/tech_info/pdf/drives_faq.pdf

Hope this helps,
Daniel Chartier
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  5/22/2008, 12:34 PM
htd21
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Thank dchartier so much. I think your answer is helpful, but I'm waiting the official response from Siemens' specialists. Thank you once again!
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  5/22/2008, 1:58 PM
tractor
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Yes you can connect two motors to a single MM430.
The VSD cannot then provide I2t protection for the motors, a thermistor in each motor would be useful for this.
The I2t must be provided by individual thermal overloads, one for each motor.
Watch out for the total cable length, the maximum for the cable will be about 60 Meters, it is easy to get a very long cable length when doing this. To get the cable length add the cable for both motors together.
Both motors will have to be started at the same time so they both benefit from the ram up time.

Good Luck..
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  5/22/2008, 3:44 PM
htd21
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Thank! It's very kind of you all.
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  5/23/2008, 5:33 AM
Tambe
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And dont do the Motor Id test.
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  5/23/2008, 10:59 AM
htd21
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I found this FAQ:
MM4: Driving more than one motor on a MICROMASTERGo to beginning

QUESTION:

Will a MICROMASTER 4 drive more than one motor?

ANSWER:

Operation with more than one motor is possible with all inverters, providing the following points are observed:

• V/f operating mode (P1300 = 0) should be used. SVC (sensor less vector control) or encoder operation is not possible under any circumstances.
• The sum of the motor currents should be less than the inverter output current.
• The stator resistance should be set to that of the total motor resistance for all the motors in parallel (P0350).
• The motor current (P0305) and power (P0307) should be set to the total value of all the motors.
• The motor protection function provided in the frequency inverter cannot be used for multi-motor operation. We recommend that a specific overload protection is provided for each motor:
  - One PTC or KTY84 + one evaluation unit 1) + one contactor per motor
  - Or connect PTCs in series + one evaluation unit 2) --> at a digital input of the frequency inverter = "External fault" (P0701…P0708 = 29).
   
  An output choke can also be used to reduce heating in the protection devices, and therefore preventing overheating and premature tripping of the devices.
• The total cable length should not exceed that recommended for the inverter.
• It is not recommended to connect or disconnect any of the motors while the inverter is running as the inrush current may cause the inverter to trip.
When the motor is disconnected high voltages may be generated which may damage the inverter.
 

 

  1) The KTY84 can be used in conjunction with 3RS104 or 3RS204 evaluation units. The PTC may be used in conjunction with 3RN1 evaluation units.
  2) It is not permissible to connect several KTY84 devices in series (nor parallel) and use these together with a 3RS104 or 3RS204 unit; the reason for this is that this would result in completely incorrect measurement results.
For PTC evaluation units, the series circuit is (limited) possible, as long as the total resistance in the measuring circuit lies below the response value of the 3RN1 unit. Normally, this is a maximum of 6 sensors in series. Additional evaluation units are required for more than 6 sensors. The units are then switched-out using the auxiliary contacts.
 
 

 

Information:

A motor manufacturer generally uses a separate sensor for each motor winding. The sensors are then already connected internally in series. There is a special version 3RN1062 for multi-motor monitoring. This permits up to 6 sensor circuits – i.e. also 3 sensor elements in series. An additional advantage is due to the fact that not only can all motors be shut down, but using LEDs, the motor whose sensor responded can be identified (i.e. the motor that is too hot). This simplifies troubleshooting.

 
Written by: A&D CST
Key words: MICROMASTER; MM4; G120; Multi-motor operation; motor protection
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  10/6/2008, 5:01 PM
JensS
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Hi,
There are a few possibilities, lets start with the motor.

How long is the summation of your cable length?
Maximum length is 300m un screent cable with output choke.
To set up the Motor data parameterise the summation of current and power, measure the resistance of all three motors.

Use v/f characteristic. Don’t use contactors, fuses or circuit breaker between inverter and motor. 

The inverter.

The dark display shows a “under voltage in the DC-link”.
May be your supply voltage is to low, a bad connection in a line cable, a broken line – fuse, a defect preecharging system.  


FAQ: http://support.automation.siemens.com/WW/view/de/14390055 

Hint :
go back to factory reset (p0010 = 30) use V/f-characteristic (P1300 = 0) set up the summation of motor current and power – and use the “Siemens Motor data”
Mit freundlichem Gruß / Best regards

Jens S
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