Low Voltage

[maen]

Does anyone else have experience of the Nation Grid three phase system dropping down to 380v and even 370v. This make generating to the grid very difficult.

 

[sjt01]

Does anyone else have experience of the Nation Grid three phase system dropping down to 380v and even 370v. This make generating to the grid very difficult.

Legal requirement phase to neutral must be above 218 volts at the metering point. If it is below this, complain to your DNO, keep records of the complaint, and keep complaining until they fix it.

 

[Fowler VF]

yes. used to be a major problem to us. kept complaining and put on data logger to prove it to the grid operator and that they were outside the legal requirements. Much better now. Was always a problem at weekends, most of the big 3 phase users switched off and only single phase use happening? Issue was always one phase much lower than the rest. Only so far that you can adjust the G90 settings!

 

[sjt01]

yes. used to be a major problem to us. kept complaining and put on data logger to prove it to the grid operator and that they were outside the legal requirements. Much better now. Was always a problem at weekends, most of the big 3 phase users switched off and only single phase use happening? Issue was always one phase much lower than the rest. Only so far that you can adjust the G90 settings!

At least you can access the G99 settings. On our G59 relay the settings are set and sealed under a DNO witness test, or by someone certified by the DNO.

 

[Fowler VF]

How come you are still on G59? I thought we all had to change to G99. In fact the G99 parameters are actually quite a bit wider than the old G59. Our old G59 was programable as well; but as you say the DNO checked it. We had our own copy of the software and could tweak it once the DNO had gone; when we had the G99 installed it turned out that the settings on that were pretty much the same as we had got to on the G59! To be clear, the only reason we had to tweak the settings was to accommodate the DNO's own failure to maintain the proper grid parameters, otherwise we would drop out all the time. Only so far you can safely go with the settings, not because they mess up the grid but they mess up your own generator in trying to match a poor grid, e.g. matching low voltage on one phase causes excess current on that phase from your generator.

 

[maen]

Will the DNO compensate for lack of export revenue when a power cut takes place?

Also the same during Low Voltage and unable to connect?

 

[Fowler VF]

No. and No. They will deny and deny. The most they will do is adjust the tappings on a transformer. But this is a mixed blessing since you might then be over voltage at times.

 

[sjt01]

How come you are still on G59? I thought we all had to change to G99. In fact the G99 parameters are actually quite a bit wider than the old G59. Our old G59 was programable as well; but as you say the DNO checked it. We had our own copy of the software and could tweak it once the DNO had gone; when we had the G99 installed it turned out that the settings on that were pretty much the same as we had got to on the G59! To be clear, the only reason we had to tweak the settings was to accommodate the DNO's own failure to maintain the proper grid parameters, otherwise we would drop out all the time. Only so far you can safely go with the settings, not because they mess up the grid but they mess up your own generator in trying to match a poor grid, e.g. matching low voltage on one phase causes excess current on that phase from your generator.

We had to update to a new G59 relay, replacing Vector Shift with ROCOF, and relaxing some parameters.

Description of originally installed loss of mains and overfrequency protection: 1 x OLD DEIF GPU2 relay had two stage over frequency 51.5 Hz at 90 secs, 52.0 Hz for 0.5 secs as well as vector shift set at 6 degrees. ​

Description of work undertaken to make the change A new ComAp Mainspro relay was installed, as the old GPU2 could be not be firmware updated to enable ROCOF. Vector shift disabled and ROCOF enabled at 1 Hz/s with 0.5 second time delay. The G59 voltage and frequency G59/3 programmed with the over frequency stage one disabled. System was injection tested to prove the full G59/3 system trips and well as its stability inline with G59/3 amendment 7. The DEIF PLC also had the vector shift disabled and the ROCOF set to 5Hzs without a time delay (max setting)​

Description of the interface protection post the change being completed ROCOF set in the ComAp Mainspro relay ROCOF enabled at 1 Hz/s with 0.5 second time delay.​