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Recent content by TS Liew

  1. TS Liew

    Publish IEC 61850 Sample Values - Merging Unit

    Dear friends, I am working on a project to produce a merging unit to publish sampled value for IEC 61850 protocol. I have been looking around for a suitable device like the NovTech IoT Octopus & the Analog Device AD7616 board. Is there a good SV publishing software stack +hardware that's...
  2. TS Liew

    Open delta transformer with delta connected load

    Dear friends, I am curious about the subject above. Many literature discusses the power requirement of open delta transformer power requirement in the form where the load is star connected. In this case, the load current naturally has a phase shift of 30 deg. Thus causing a power factor of...
  3. TS Liew

    Zero sequence current & impedance for an all delta network

    Thank you guys for the valuable info. They have been really helpful. TS Liew (Electrical testing, Commissioning, Power system studies)
  4. TS Liew

    Zero sequence current & impedance for an all delta network

    Hi Guys, thank you for your valuable input. Assuming negligible capacitance. If the delta network experience a solid low resistance (Zn) fault to ground. Do you recon the fault current from line to ground to be Vfault/Zn? Based on the zero seq equivalent network for delta we see that the zero...
  5. TS Liew

    Zero sequence current & impedance for an all delta network

    Dear friends, If a delta generator/network (without neutral) experience a solid line to earth fault. What will the fault current be? How can it be calculated/simulated? TS Liew (Electrical testing, Commissioning, Power system studies)
  6. TS Liew

    Realistic max earth fault current for transformer

    Also with regards to David's proposal of %Z(o)=0.85 %Z(+), this is for core type transformer right? As for limb type, we can safely assume %Z(o)=%Z(+)=%Z(-) if only %Z(+) is given right? TS Liew (Electrical testing, Commissioning, Power system studies)
  7. TS Liew

    Realistic max earth fault current for transformer

    Thank you guys for your reply, David for your take on the steady state condition of fault, Waross for your take on the transient condition of the fault. Please correct me if I am wrong and show the right path. I believe the off-set @ 2.828 time ASCC is approached at really really high X/R ratio...
  8. TS Liew

    Power Transformer name plate with weird %Z naming

    Dear friends, I've recently come across a power transformer with a very interesting way of putting its %impedance, especially the tertiary winding. The attached nameplate does not show the tertiary winding power rating but the %Z=243.9% (tap 10) meaning the voltage has to be 2.439 P.U rated...
  9. TS Liew

    Realistic max earth fault current for transformer

    Dear friends, For calculation of max fault current of 3 phase transformer. The usual method of using the % positive seq Z & the rated MVA is common. How should I calculate the max single phase to ground fault current? Say I have a 220KV/6.9KV, 70MVA, 12% zero seq Z assume +,-,0 seq Z to be the...
  10. TS Liew

    CT dimensioning factor definition

    Hi Scottf, thanks for your sharing, Let's say a CT has a Ktf=10, what does it mean? If I were to perform a test on such a CT, How do I measure the Ktf of the CT? If the CT is good, should the Ktf be <10 or >10. Some literature define Ktd as Ktf with duty cycle, as such Ktd is derived from Ktf...
  11. TS Liew

    CT dimensioning factor definition

    Hi buddies, I hope you guys can help me understand the definition of current transformer transient dimensionning factor Ktf. It has been defined as the ratio of theoretical max flux over the max instantaneous flux of the ac component. I find this definition more confusing that the term itself...
  12. TS Liew

    DC offset during fault in capacitive circuit

    Hi fellas, thank you for the posts you have put up. I now understand that with the cap bank in the network, with the L, R & C switching in and out, this would cause significant transient to the network at high frequencies depending on f=1/√LC. What if in a situation where the cap bank is already...
  13. TS Liew

    Why Transformer zero sequence impedance differ from (+)&amp;(-) sequence impedance

    Thank you fellas for your valuable posts. I totally get it now. The transformer zero sequence impedance test circuit shows exactly the point you mentioned in your posts. I now understand why the (0) seq test uses a single phase current injecting into all 3 branches of the transformer, forcing...
  14. TS Liew

    Why Transformer zero sequence impedance differ from (+)&amp;(-) sequence impedance

    Most instances during fault analysis, I assume the transformer zero seq impedance = given positive sequence impedance in the transformer manual, but sometimes actual zero sequence impedance is quite different from the given (+) seq impedance. Hope to get some conceptual explanation as to why the...
  15. TS Liew

    Coupling coefficient of non idea transformer

    Hi Fellas, many literature proposed to accept that the coupling coefficient of both side of the transformer to be the same. As such deriving the expression of mutual inductance M=K√L1L2. Base on the picture, what if Φ11≠Φ22 then K1≠K2 then M should be M=√K1K2L1L2 but I have not come across...
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