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  1. chao_david

    Meter shows current values during CT secondary injection but zero after energization

    Thanks everyone. It seems that the no-load current is too low since we've tried to check the reading the moment the transformers were energized. We've seen around 200 Amps for the inrush current then back to zero once stabilized. It is a bit unusual since we have several BESS projects and this...
  2. chao_david

    Meter shows current values during CT secondary injection but zero after energization

    Here's the SLD for reference: Before the three pad-mounted transformers were energized, contractor performed secondary injection on T5 CT to check accuracy of meters. All results are good. After energizing the high side of the transformers, there is no reading on the meter. I was expecting...
  3. chao_david

    Why is there no existing standard for backup generator sizing?

    I'm quite shocked to find out that there are no standards that show the formula for generator sizing. Even in our local electrical code. I'm not sure why. I'm trying to set a standard for our company in sizing genset. Based on several white papers I've read and generator rentals websites, I've...
  4. chao_david

    Transformer dissolved gases decreasing through time even without degassing

    Has anyone encountered this before? This is a 333 kVA 7620/266 single phase transformer. What could be the reason for the decreasing trend? Not sure if its sampling procedure error because majority of the decreasing trend is consistent. I'm not a chemist but my guess that the gas ppm will...
  5. chao_david

    Transformer high excite at H0H3 and turns ratio at H0H3 deviates by 6% but winding resistances ok?

    Hi all. I have a 110-34.5-13.8 kV, ynyn0, NLTC, 100 MVA Toshiba power transformer (40 years old). Long story short, Buchholz relay activated. Here are the summary of results. Insulation power factor, capacitances = ok Insulation resistances and PI = ok Arresters and bushings = ok Winding...
  6. chao_david

    Islanding detection on grids with distributed energy resources

    As I'm new to this field, just wanted to say I've learned a lot from your discussions. Currently doing studies on risk assessment of unintentional islanding in a particular area. Found out that parallel operation of inverters with respect to the point of common coupling degrades unintentional...
  7. chao_david

    Islanding detection on grids with distributed energy resources

    Is there no such thing as tripping CB2 on the basis of the status of CB1? Basically, CB2 won't have a fault sensing ability on the utility side but will just "copy" the status of CB1.
  8. chao_david

    Islanding detection on grids with distributed energy resources

    There are lots of existing methods for detecting islanding conditions when the circuit breaker at the side of the utility unintentionally trips. I've seen passive methods, active, and intelligent systems that detect the islanding and trips the DG breaker within 2 seconds as required by IEEE...
  9. chao_david

    Am I correct on how voltage control works on a step voltage regulators?

    Case: 19.92 kV Line to ground voltage with a step voltage regulator If the Set Voltage setting is 120 V, and the reading on the display screen is 120 V, then the line is currently at 19.92 kV. Correct? Getting the ratio 19920/120 = 166. Does this mean that every 1 V deviation translates to 166...
  10. chao_david

    Resources and references for Partial Discharge Testing Analysis

    Hi everyone. I am looking to upgrade my knowledge in partial discharge testing. Currently, I can perform PD testing using Liona On-Line PD and b2 Off-Line VLF PD. Honestly, I can only operate the test equipment and perform data gathering. However, I cannot interpret the data, graphs, waveforms...
  11. chao_david

    Why does oil pressure drops when I increase the load on a diesel generator?

    For example, at 0% load, the oil pressure is 4.5 bar and at 100% load, the oil pressure is 3.7 bar.
  12. chao_david

    Diesel generator ancillary systems power source

    Hi. I know for sure that the electronics of a diesel generator set are powered by a DC battery source. What about the radiator fan? Is it powered by the generator itself, and therefore reducing the actual output of the generator because some of the power goes to the fan? Or is it DC powered from...
  13. chao_david

    I'm looking for standards about oil pressure range of a diesel engine generator

    I'm currently doing my research on diesel generator quality control but I can't seem to find the standard operating range of a diesel generator. Do you know any standard about that? Thanks!
  14. chao_david

    Power factor of diesel generator for a purely resistive load bank

    Follow up question. If my load bank fan connects to an external power source, does that make the power factor unity? I'm thinking that the coils from the generator somehow contributes to the inductive power factor?
  15. chao_david

    Power factor of diesel generator for a purely resistive load bank

    I'm confused with the factory test report of my 15 kVA, 60 Hz, 220 V, single phase diesel generator. This was tested using a purely resistive load bank where in the power factor is 1. The load bank used can provide maximum load of 15 kW. Since the generator has a rated 0.8 power factor, the 100%...

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