Dears,

I have Sinamics S120 drive system consists of:

• Control unit: CU320-2DP
• Active line module: 16KW 6SL3100-0BE21-6AB0
• Double motor module: 9.7KW 6SL3120-2TE21-8AAx
• Double motor module: 9.7KW 6SL3120-2TE21-8AAx

At random times (especially when stopping the motors very fast) I get the following alarm messages:

• 30045 Power unit: Supply undervoltage
• 30003 Power unit: DC link undervoltage

I tried to increase the delay time for undervoltage fault message p3492 to 3 seconds but it did not work.

I measured the input voltage to the drive and found that it is stable.

I attached 2 screenshots:

1. Supply unit fault history
2. Voltage related parameters

What should I do?

Hello,

Can you please specify connected motor Kw load.

ALM capacity is 16 KW. 

DMM capacity is 2*18 Amps = 2 nos = 72 Amps. So total connected load on ALM = 43.2 KW. Compare this with total motor connected power load.

Are you stopping all motors at same time? If yes, suggest you to stop motor one by one & check if fault triggers. What I suspect is when you are trying to stop motor in fastest time, DC bus power is not sufficient ( 16 KW, depends upon input supply voltage level & individual load on motor) & drops below under voltage threshold value which in turns triggers alarm.

You may try by increasing ramp down time or sequence of motor stopping.

Hope this helps.

I have only 2 motors each connected to one of the motor modules:

1. 7.6 A rms: ramp down time, 0.7 sec. OFF3, 0 sec
2. 11 A rms: ramp down time, 1 sec. OFF3, 1 sec

So total used capacity is 18.6 A which is around 9.5 KW

Yes, I stop both motors in the same time according to the above mentioned OFF3 times.

Do I understand that when both motors stops rapidly, the DC bus voltage goes down below the under voltage threshold? I don't completely understand, so I would appreciated explaining your proposed solution.

Thanks 

Hello,

The best way I can suggest you is, with STARTER software, use trace mode & check/monitor DC bus voltage while setting trace condition as alarm/fault triggered. This way you can find out exact DC bus voltage & how much it drops & when.