DieselElectricMan
Marine/Ocean
- Oct 24, 2006
- 2
I have been researching this subject and to date have come up with no real definitive answers or solutions. I have been reading the site for some time and thought this might be the place to start.
I am looking after a marine plant consisting of two 670kva alternators and two 1600kva alternators, all driven by diesel prime movers, the larger being Caterpillar and the smaller MTU engines. The main consumer is a 3MW motor drive frequency converter, six pulse to the network with 4 branches of 5th Harmonic filters connected dependent on output of the main drives. Bus network is 690V. This is a new installation and intially it appeared to function ok, but it has recently shown a few serious faults.
Basically, when the main drive is engaged, the harmonic filter is engaged to the network, and whilst running the larger gensets with the main frequency drive there is no apparent problems. However, as the load is increased and a smaller generator is paralleled, active load sharing will take place and then appears to stop at say 50% of the running engine. After 30 seconds or so this will then trip off line, the DEIF PPU control for the generator gives the alarm for 'reverse reactive power'(var import). This fault occurs regardless of engine combination, but always when the smaller sets are joining a larger set or sets. There is no problems connecting the smaller engines if the load on the motor drive is reduced below 30%. It appears from my limited experience that the affect of the harmonic filter is to draw the smaller sets into a 'leading power factor' scenario, and hence the trip is real and not nuisance as the designers insist.
The DEIF unit is controlling Reactive load sharing, the proposal is to disconnect this feature. It is apparent that this problem disappears when the Harmonic filters are switched off, i.e syncrohnising and sharing is not a problem at any load, and no trips occur in any configuration.
My question is does anyone have any experience of this in similar installation, and is this a design issue as it has 'technically' never been proven to work in this installation to date. I have long said that the Harmonic filter should have been installed to protect low end consumers (in the 440v network) rather than on the main 690v distribution, as it appears on the surface that the smaller sets are unable to cope with the reactive power generated when the Harmonic filters are on line, despite the fact that this is under the generators load reactance curve.
Many thanks.
I am looking after a marine plant consisting of two 670kva alternators and two 1600kva alternators, all driven by diesel prime movers, the larger being Caterpillar and the smaller MTU engines. The main consumer is a 3MW motor drive frequency converter, six pulse to the network with 4 branches of 5th Harmonic filters connected dependent on output of the main drives. Bus network is 690V. This is a new installation and intially it appeared to function ok, but it has recently shown a few serious faults.
Basically, when the main drive is engaged, the harmonic filter is engaged to the network, and whilst running the larger gensets with the main frequency drive there is no apparent problems. However, as the load is increased and a smaller generator is paralleled, active load sharing will take place and then appears to stop at say 50% of the running engine. After 30 seconds or so this will then trip off line, the DEIF PPU control for the generator gives the alarm for 'reverse reactive power'(var import). This fault occurs regardless of engine combination, but always when the smaller sets are joining a larger set or sets. There is no problems connecting the smaller engines if the load on the motor drive is reduced below 30%. It appears from my limited experience that the affect of the harmonic filter is to draw the smaller sets into a 'leading power factor' scenario, and hence the trip is real and not nuisance as the designers insist.
The DEIF unit is controlling Reactive load sharing, the proposal is to disconnect this feature. It is apparent that this problem disappears when the Harmonic filters are switched off, i.e syncrohnising and sharing is not a problem at any load, and no trips occur in any configuration.
My question is does anyone have any experience of this in similar installation, and is this a design issue as it has 'technically' never been proven to work in this installation to date. I have long said that the Harmonic filter should have been installed to protect low end consumers (in the 440v network) rather than on the main 690v distribution, as it appears on the surface that the smaller sets are unable to cope with the reactive power generated when the Harmonic filters are on line, despite the fact that this is under the generators load reactance curve.
Many thanks.
