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Yaskawa VFD tripping during ISLANDING

We have commissioned a 220 KW variable frequency drive (VFD) of Yaskawa F7 MODEL at a customer in XYZ State.

They have a 12 MW power plant are having Turbines & one steam boiler. For controlling of speed of FD fan you have used 220 KW, F7 model L&T Yaskawa VFD.
(Speeds are varied by their DLS system or by remote Up & Down push buttons)

Earlier they were using for 220 KW soft starter for driving FD fan. On 25th Feb 2013, they have connected 220 KW VFD to achieve power saving.
The power plant is paralleled with state XYZ Electric Board) grid. & they are exporting/Importing power to/from State grid.
Normally this arrangement is working fine without any problems since long period.

They have arrangement to "Island" the power plant from state grid, if there is any disturbance in state grid. This "Islanding" take place within 30 to 50 million seconds.

Recently they had some problem in XYZ State grid. & there was voltage fluctuation in the grid due to some problem in State grid.

The "Islanding" system worked & islanded itself from grid.

In this "islanding period" of 30 to 50 milli seconds, the 220 KW VFD tripped & FD fan tripped immediately. This all caused major chaos/problem in the 12 MW power grid.

Restarting of VFD & bringing back the system to "Normal" was time consuming & created chaos.

This also resulted in waste of time of power generation & coupled with loss in revenue

As per them, when they were using Softstarter this problem never came up.& "Islanding" was smooth. It is to be noted that "RUN" command to VFD is given through DLS system , which has got a battery backup. Hence It is to be noted that during this "Islanding" period "RUN command is still" Active"

In short THEY DO NOT WANT VFD TO TRIP IN THIS CRUCIAL PERIOD OF "ISLANDING ' WHICH IS ABOUT 30 TO 50 MILLI SECONDS".
Considering the very basis of islanding period of 30-50 milliseconds, we had discussions with experts & want to summaries solution as follows

Make
1)L2-01=1
2) L2-02=0.5

This will ensure smooth change over during islanding period.
It is also to be noted that any "Time gap more than 0.50 milliseconds" will make safety parameters of VFD to operate & will trip off VFD.
Pl also note that these parameters can not be changed while your VFD is in "RUNNING"

Another Issue is that Start of DRIVE is through CONTACTOR, bypassing is possible..
- - - -> by: VFDs.org
Most VFDs have an auto restart during power or voltage fluctuation & several of these allow for the restart into a spinning load, such as in this case. It's been a while since I worked with a Yaskawa, but they are a good variable frequency drive and should offer these parameter adjustments. Check the parameter list & you should find them.
- - - -> by: Jeff
I observed the same in ABB 600 & 800 VFDs also. Drives will be tripping on Undervoltage or Overcurrent faults in this case. It is due to the DC Bus Supply.
- - - -> by: Lakum
While Islanding, the problem is the generator does not know it has been islanded and assumes it is still feeding power into a large grid. The unbalance between generation and load will either cause frequency to increase (generation > connected load) or decrease.
By L2-01 (Momentary Power Loss Detection Selection) =1 and L2-02 (Time for Power Loss Ride Through; selection between 0.0 to 25.5 Sec), you can activate the feature and duration, in case of power failure.
However for frequency changes or fluctuations in supply to drives, I feel you need to widen input frequency fluctuation parameter to the variable frequency drives to attack the problem.
- - - -> by: Debi
Grid frequency fluctuation can be one reason which triggers Islanding What exactly happened here? The information should be available on your recorders Also what was the parameter displayed on the Yaskawa F7 after the drive tripped?
Yaskawa F7 VFD can tolerate an supply input frequency fluctuation of _+ 5% Thats not adjustable ( the analog input frequency reference is) The downloadable Yaskawa F7 VFD manual shows how.
If the cause of trip was momentary power loss, then the settings as suggested by DP should be adequate
Re bypass through contactor the question is not clear Its possible to bypass the VFD with a DOL contactor start either manually or through auto but that needs to be built before hand and requires a panel with hardware
The input contactor to the inverter is however required if the power supply is to be controlled through a remote on off circuit.

I think I understood the contactor by pass question. It might be possible that the input contactor drops during the occurence of the event which might render the power ride through function of the variable frequency drive inoperable. It is possible to get delayed drop out contactors or better to get a contactor with 24V dc coil fed by a separate 24V dc control supply from a battery which should be available in the plant.
- - - -> by: Aswin

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