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Recent content by matwong

  1. matwong

    Single phase tripping

    In a delta-wye 33/11kV system, what will be the imbalance current detected by the 11kV substation relay in the event one of the downstream protective device operated on single-pole tripping ? Say the load current is 60A, is the relay seeing 40A (i.e.{60+60}/3) when one phase is out, and 20A...
  2. matwong

    EHV tower base - lighting

    Is there any product in the market that can produce lighting at the tower base which is using the induced emf or capacitive type energy from the energized EHV lines? I was thinking why we can't utilize the free power from EHV lines (not direct tapping) to light up tower base and install some...
  3. matwong

    Power Coaxial Cable

    Dear All, Does anyone of you come across the application of LV coaxial cable in power distribution network ? The idea is to prevent energy losses due to tampering cases. How feasible & practical is this idea ? Which cable manufacturer has produced this kind of cable & use in which utility ...
  4. matwong

    Overbuild distribution circuits

    We normally installed so-called "broken wire guard" for these kind of circumstances. It is just something like a bracket (made of hot-dipped galvanised material) installed on the cross-arm beneath every phase of the HV conductors and were grounded(or earthed). It can be installed on the pole...
  5. matwong

    Cross-Bonding Specifics

    The sheath voltage on the section (3 + 3)will shoot up if neither x-bonding or grounding is being applied between the major section. Extraction from Electric Cable Handbook for reference : http://i11.tinypic.com/34t69g2.jpg
  6. matwong

    5kv bus bar question

    Dear kvar, Over here, we are referring to BS159 where the minimum clearance between phases in air for 3.3kV & 6.6kV are 2" and 3.5" respectively. Sorry, no reference on 5kV for you.
  7. matwong

    Cross-Bonding Specifics

    Dear FEinTX, Based on my understanding on IEEE575, I would agree with you. It will fall under Clause 5.6.5: Continuous Cross Bonding where you have to transpose cable & X-bonding the sheath instead of applying st-thru splice. However, under Clause 5.6.3: Sectionalized Cross Bonding, you may...
  8. matwong

    When is cross-bonding needed?

    Some basic info on the following link. http://www.energynetworks.org/cables/cable_bonding.asp Further info may refer to IEEE 575 : Application Guide for sheath bonding on single core cable & calculation of induced voltage & sheath current.
  9. matwong

    ELCB problem

    I'll suspect the leakage current from neutral to ground. Firstly, you may check all cables of your electric appliances, eg. kettle, fridge, heater, oven etc whether there is any damage. Next, you may check on all the connection at the sockets or appliances end to confirm the condition is still...
  10. matwong

    ELCB too sensitive

    This is one of the common question I always encountered but without any firm answer. There is always a particular house among a row of link-houses which ELCB operates whenever there is thunderstorm weather (whereas the rest of the houses are intact). All the houses having the same rating of...
  11. matwong

    parallel feeders

    What I suspect is the connection problem at your terminals of transfer switch or MCCB. I presume the cable carries the highest current is connected directly to the terminals of the equipment (and the same applied to other phases), whereas the other cables are either cascaded or connected to the...
  12. matwong

    Low voltage over top of high voltage

    Another reason i can think of is that higher voltage system can withstand higher impulse voltage especially from lightning. With the proposed construction, your equipment might be more susceptible to transient interference and moreover directed to your equipment which is undesirable.
  13. matwong

    Joslyn breaker

    What is your specification of the breaker ? Does the present one comply with it ? I don't really understand when you say that one phase of the breaker is not 'openned' and closing of the other 2 phases caused explosion ?? Isn't that is more hazardous when one of the phases is live when it...
  14. matwong

    CircuitBreaker

    It is a bit confusing when lack of information (as we only refer to the drawing). Once we get into the other site, i.e "http://www.gwelec.com/product_vault/vault_vi.cfm" then we just realise the manufacturer actually meant vacuum interrupter for circuit breaker which say "The vacuum...
  15. matwong

    Relay test equipment

    Not very sure of your requirement but programma testing set seem to be quite popular in our region. Worth for study. http://www.cuthbertsonlaird.co.uk/datasheets/programma/Programma_Protective_Relays.htm
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