Dear All,

I have a problem when the electrical system has low voltage (about -10% of 230kV system). The norminal voltage for fans of cooling system is 400V but if the system has 210kV that make the voltage pass through fans about 310V. This event make HVDC trip so the power generation is lost. I plan to use UPS but it has to be a big one. Did anyone ever meet this problem like this? Please give me some suggestion how to keep the voltage pass through fans more than 310V; although, the main system has 210 kV. Thank you in advance.

Sincerely

Pakorn

 

Dear Pakorn,

If the fans are this critical, then a properly sized AVR (automatic voltage regulator) would help. But the difference in voltage is too high (-20% approx). That would need a rather big sized AVR.

Thanks

Tomy

 

A voltage stabilizer or ferroresonant transformer might help. You might also investigate why a -10% drop in line voltage gives a -20%+ drop in fan voltage.

Regards

cww

 

The sub probably has a staion-battery. Why not use an UPS or change fan motors to DC?

Regards,
Phil Corso, PE
Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}

 

You may want to consier a isolation transformer which would provide some regulation of the secondary voltage during sg or brown out condition, the problem there is tha ttypically these devices will not provided much sag support as the primary dips to -10%, of course if you were to size it for a heaveir load, you will gain some added benefit, contact SOLA for some input and you may wanto search the internet for isolation transformers or voltage regulating transformers. UPS solution is too expensive and too large of a unit to provide a reasonalble solution. DC fans are not a bad idea, but now you need a dedicated power supply to converet your 400+ secondary voltage (fan voltage) to a suitable DC voltage.

The trade offs are basically cost vs performance and how quickly you need a solution.

Technical Consultants
303-883-8538
[email protected]

 

if I were you, I will concentrate on the bigger picture, the dip in voltage (230kV). I have worked at an HVDC facility in the past. Try to eliminate the problem by adding capacitor banks to the electrical system (either rectifier or inverter end) whenever the voltage dips. Alternatively, for a cheaper soln, you can control the firing angle of the thyristors as well to control the power factor and bring up the voltage (or bring down in case of light loads downstream).

As far as the fan stuff goes, many ppl have already suggested great ideas like moving to dc fan motors etc.
hope that helps
Rahul

 

Pakorn: this is in reply to your problem and a comment on the last message.
Rahul,
I think you hit on the head, why is the voltage coming into the substation dipping -10 or -20%, that is a real problem and could be causing more serious problems. One thing for sure, get with the utility provider and have them take a look at the incoming power transformers and other connections, another thing to possibly consider is retapping the stepdown transformer for a slightly higher voltage output, ie..480 vs 460, if your fans are truly not providing enough airflow as the voltage drops, you may even consider a cap. bank on the ourput of the stepdown transformer, that would help some, - unfortunately, without real specifics and some hard data or even seeing what is going one, it is hard to provide a quick fix to this problem. Anything you do is going to take some time and a little money and assistance from a outside source (utility provider). Get a power monitor on the primary and secondary voltage taps, that will tell you a lot and then you can proceed with a solution which best fits the problem.
Case in point, I installed a remote SCADA unit at a light pole, the power company let us tap their power at the pole. After 3 weeks and some electrical storms, they lost a phase and neutral (supposedly or according to them), we spent weeks doing power monitoring and such, and finally checked the wiring at the light pole - we found that they had not bonded the ground wire, there was no neutral wire and in fact there was a dead phase, IT took them 6 months to fix the problem (big power companies do not repsond quickly just because a mile of street lights are out.), we did finally get everything fixed and would up putting in a disconnect, a step down transformer (isolation type), had to provide our own neutral and did get the ground bonding issue resolved.

The point is, don't go this alone, get some power generation guys to help out, they have the tools and knowledge to deal with the higher voltage issues and probably have seen this at least once or twice.

Good luck, but keep mind, look at the bigger picture here, find the root cause and your problem will be solved, don't do a band-aid fix, the band-aid will fail and you will be back to smacking your head on the pavement.


Matt,

By the way, if you need some power generation input, I have a contact with a major power generator, let me know OK.

Matt
[email protected]