Seimens VFD issue

ascot01

Lifetime Supporting Member
Join Date
Jul 2007
Location
Magnolia, TX
Posts
81
Apologies in advance for the long-winded problem.

I have two 30 kW Seimens SED2 VFD running two identical 480VAC 3P 30HP motors driving fans which pull a suction on a piping system.

One of the motors shut down and we discovered smoke coming from the VFD, phase-C fuse in the disco blown and the 3-phase branch-circuit breaker tripped and the 3-phase breaker feeding that panel tripped as well.

We sent the VFD to a repair center and they said the power supply in the VFD had burned up.

The motor leads were not shorted phase-phase nor phase-ground.

We bought a new replacement VFD while the first one was being repaired and entered the drive and motor parameters, exactly matching the other good VFD.

The start signal from the SLC 5/03 digital output starts the VFD OK.

For the VFD frequency (speed) control, analog input 1 is dipswitch-selected for 4-20 mA and the firmware parameter for speed control source is also selected as analog input 1, 4-20 mA, just like the other identical working VFD.

The parameter for minimum frequency is set at 20hz and max frequency is set at 60Hz. All parameters on both the old (working) VFD and the new VFD match.

The 34 VDC 4-20mA speed control circuit starts at terminal 17 (DIN 6) on the VFD and routes through a vacuum gage and back to terminal 3 (AIN1) at the VFD.

Problem: As the motor ramps up it holds at 20Hz and won't go any higher.

If we change the parameter for minimum frequency from 20Hz to 60Hz, the motor will ramp up to 60Hz.

With the motor off and the min frequency parameter still set to 60 Hz, we disconnected the wire at analog input 1 and put a Fluke 867B DVM in series, set for DC milliamps. It reads 4 mA when the motor starts and as the vacuum increases, the current increases up to 18mA at max vacuum, like normal. The SLC 5/03 does not play any part in VFD speed control.

If the 4-20mA current is functioning, why doesn't the VFD ramp the motor up any higher than 20Hz when the minimum frequency parameter in the VFD is set to 20Hz and the max set at 60Hz?

I wanted to ask you guys first before going through an adventure with Seimens tech support.

The size of the VFD manuals exceeds the forum upload limit, sorry.

Thankyou for any help.
 
This sounds like an external PID control system to control vacuum and the error detector needs its output inverted.

jraef will be your best resource on this as it is Siemens.
 

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