Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Search results for query: *

  1. bspace123

    Roof truss installation

    I agree, they are useless. What’s even more annoying is the manufacturer species an alternative “engineered solution”, called a “fast fix” screw. Link: https://pryda.com.au/for-builders/pryda-fastfix/ Of course they sell this for triple the price of a batten (bugle) screw, which I find hard...
  2. bspace123

    Roof truss installation

    Apologies here is the link again https://www.mitek.com.au/wp-content/uploads/2021/06/MiTek-Guide-for-Roof-Truss-Installation.pdf The bracket shown in the previous post is the correct one. I’m not concerned about the truss shaking, the trusses are braced with hoop iron, speed brace, roof...
  3. bspace123

    Roof truss installation

    Hello I have just installed roof trusses which are designed to hold a metal roof. The installation manual from the truss manufacturer states to secure internal non load bearing walls using L Brackets, where the bracket is attached to the wall top plate and to the truss bottom chord. The manual...
  4. bspace123

    Parallel synchronous generators and power output regulation

    Hello I am trying to understand fundamentally how generators operated in parallel with a solar PV facility are able to regulate their power output. I understand the concept of synchronous generation. Basically, for a stand-alone synchronous generator, the rotor induces a voltage into the...
  5. bspace123

    Wye-Wye Transformer and grounding

    I’m also still puzzled by the floating neutral on the primary leading to no earth fault current in the secondary. If we have a Wye connected motor with no neutral connected and we increase voltage on one of the phases, the increased current will flow back through the other two phases? There’s...
  6. bspace123

    Wye-Wye Transformer and grounding

    Makes perfect sense, thanks!
  7. bspace123

    Wye-Wye Transformer and grounding

    Hi All I have been reading for hours and still confused about the grounding concepts for wye-wye transformers. 1. Say we have a wye-wye transfrormer and the primary side neutral is not connected to ground but the secondary side neutral is connected to ground, if we have a phase-ground fault on...
  8. bspace123

    Ik” and Ip iec60909

    Hi With fault analysis using iec60909 Ik” is used to determine the thermal withstand of switchboards, cables etc. But Ik” does not consider the dc offset present for asymmetrical faults. So if Ik” is calculated as say 20kA, but the fault is asymmetrical with peak of 60kA, does this not imply...
  9. bspace123

    Motor contributions to earth faults

    But where is the fault path? The second transformer is now acting as a step up transformer to what is generated current from the motors. There is no ground fault current path back to the delta side?
  10. bspace123

    Motor contributions to earth faults

    Consider a delta/Wye 66kv/22kv transformer supplying a bus then from the bus a feeder supplying another delta/eye 22kv/6.6kv transformer. From this second transformer a bunch of DOL motors are powered. The delta sides of the transformers are not earthed. The Wye sides are at their star points...
  11. bspace123

    SKM powertools - fault contribution

    Balanced 3 phase fault
  12. bspace123

    SKM powertools - fault contribution

    Hello all I have a model setup in SKM with a bus which has a single incomer and supplies a bunch of DOL motors. Attached to the bus are also some generators. When I simulate a fault at the bus and open all the feeders, the fault leave at the bus is 3kA which is showing as being supplied purely...
  13. bspace123

    Line differential relays - phase shift

    Thanks for the response CT’s are both wired in star and appear correct on the schematics. If they were transposed wouldn’t we see either 120 or 180 deg phase shift? I’m not sure how you would wire them differently to get 60 and 30deg. I guess the next step is to physically verify them by...
  14. bspace123

    Line differential relays - phase shift

    Hello We have two line differential relays on two parallel cables supplying a 6.6kv switchboard. The diff relays are linked by fiber communication. The cable run lengths are 100m and 200m. The switchboard supplies a bunch of DOL started 1Mw motors. Whenever we start one of the motors, the...
  15. bspace123

    High voltages seen on CT's

    Thank you for all the responses! Turns out it was a poor earthing connection on the STAR point causing capacitive voltages to build up and discharge.
  16. bspace123

    High voltages seen on CT's

    Thank you for the responses. I thought the same initially, there may be an open circuit somewhere in the CT circuit, but there is not, as when you short either CT out, the high voltages dissappear off the relay. We have also measured continuity throughout the circuit and all is fine. If there...
  17. bspace123

    High voltages seen on CT's

    Hello We have a 6.6kV switchboard drawing ~100A as per this single line diagram: Link The switchboard has two sets of current transformers connected opposite in parallel, acting as a differential scheme. When current flows into and out of the board, the currents cancel and the protection relay...
  18. bspace123

    Secondary injection tester going into overload

    Hello I am currently trying to test a protection relay per the attached schematic. Basically, the relay has two sets of CT's connected together in parallel with the relay, which are mounted on different feeder cables. The idea is that when feeder A is reading xx Amps and feeder B is reading yy...
  19. bspace123

    High impedance bus differential - CT Saturation Calculation

    Thanks for the responses. You're right, the manual is inconsistent and in my opinion wrong. The safety factor for the relay pickup is what you define as security factor. I used 1.5 instead of 1.6. The safety factor used for CT knee point was just arbitrary, to ensure the CT will not...
  20. bspace123

    Battery consumption calculation

    Hello I have a device which consumes 83uA during idle, but once every 2 hours it consumes 247mA for 12s during transmission of a signal. The device is powered by a 6600mAh LiPo battery. I am trying to calculate how long the battery will last and have used the following formula: % Of hour...

Part and Inventory Search

Back
Top