Does anyone have any advice on this.

I have been involved in commissioning some VSD drives on a ship. They are being used to control the starting and stopping of hydraulic power-packs and we have had loads of problems.

The layout is 2x75kw 1 x 90kW and 1 x 120kw drives connected to 3x230kW generators.

The generators are Hawker Siddley 415V sets built around 1979.
On initial start up with two generators connected starting any drive resulted in the busbar volts rising to 475V where we stopped the drive.

To get round this I reduced the VSD carrier frequency to .7kHz and this problem seemed to have sorted. Now the drives start up ok, but when loaded generators trip off line on reverse power. We are fairly sure the VSD's are not the problem and it's noise on the current waveform causing the reverse power relays to trip. Reverse power on these sets is by electronic means. There is a current shunt in one of the phases and compares the signal from this with phase voltage. The resultant lagging or leading dictates weather the set is generating or motoring.

The solution is to put by-pass contactors around the VSD's but this is not curing the problem.

Anyone any ideas?
Al

 

Al... it is quite clear that the Generating Units are "swamped" by the (large?) non-linear VFD- load. As a starter answer the following questions:

1) What are the Nameplate ratings of the generators, i.e., kVA (or kW) and pf capacity?

2) Are all generators and their AVRs suppied by the same mfg?

4) What are the prime-movers: steam-turbine, combustion-engine, other?

5) What is the combined VFD load in output Hp or kW?

6) Does one generator seem to be more "tolerant" to its particular load?

Regards, Phil Corso

 

Al... one more question:

7) Are the 3x230kW generators synchronized on one bus, or are there 3 busses, coupled together thru inter-tie cables?

Phil

 

> 1) What are the Nameplate ratings of the generators, i.e., kVA (or kW) and pf capacity?

Information on them is a bit sketchy. Back in UK now but will try and find out.

> 2) Are all generators and their AVRs supplied by the same mfg?

Yes Hawker Siddley

> 4) What are the prime-movers: steam-turbine, combustion-engine, other?

Diesels

> 5) What is the combined VFD load in output Hp or kW?

Could only try one at a time the smallest load is 75kW with the same effect.

> 6) Does one generator seem to be more "tolerant" to its particular load?

Seems random although with one gen set we ran the small drives individually OK. We had a 60kW base load on there.

Many thanks
Allan

 

> 7) Are the 3x230kW generators synchronized on one bus, or are there 3 busses, coupled together thru inter-tie cables?

Hi again Phil
The cables from the sets came to the middle of the switch board and switched on to a common bus bar. The supplies for the VSDs are tapped off using single core cable crammed into the back of the switch board. It's all very tight and they haven't included for Circuit breaker protection. All very worrying.

Cheers
Al

 

Al...

I'm trying to develop a qualitative and not a quantitative anaysis, which leads me to ask the following question:

Although the facility is about 33 years old, were they ever tested at the load for which they were originally designed?

Phil Corso

 

Hi Phil,

Probably once upon a time. I doubt they have had more than basic maintenance carried out. They have had a few AVR changes in the past.
The ship has changed hands 3 times since it was built and the gen sets are original.

I don't know the reason why they had all this installed power available in the first place. The ship must have had a different function way back as for the last few years it has been used for fuel bunkering.

The rating plates have been hidden under several layers of paint over the years.

We are looking at by-pass contactors to drop out the VSD at full speed.

Cheers
Allan

 

Al, it is very difficult to provide exact solutions. However, because of the non-linearity of the load and because individual correction is costly, following are several ideas:

1) Arrange for testing of the system to uncover hidden flaws or weakness!

2) Include in your amelioration strategy, the addition of 'Harmonic Suppresion' reactors/filters to each of the generator feeds to the bus, rather than one for each of the drives!

3) Rather than bypass VFDs just eliminate them where they’re not warranted!

4) Look at beefing-up Gen-set inertia, although if 90kW is the largest load, there should not be a starting problem!

5) Contact Gen-set/AVR specialist(s)!

Sorry, I could not be more helpful Phil