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  • Users: bspace123
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  1. 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...
  2. 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...
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  10. 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...
  11. bspace123

    High impedance bus differential - CT Saturation Calculation

    Hello I am looking at the manual for a MFAC34 high impedance bus differential relay. In the manual it states the following: "The minimum setting voltage to ensure stability is VS = IF (RCT + 2RL) N The relay plug setting voltage VR must be set to the nearest tap above VS. The minimum CT knee...
  12. bspace123

    Unbalanced wye transformer

    Hello In a wye secondary transformer with the star point connected to ground, if phases are unbalanced the star point remains at ground potential. Does a current flow into to ground if phases are unbalanced? If so, how can it if it has no return path to the transformer itself?
  13. bspace123

    HV/LV distribution earthing

    Hi all, I'm trying to understand earthing requirements in a high/low voltage (6.6kV/0.4kV) installation. Can someone please clarify/confirm my understanding is correct based on some research I've done: - For all high voltage equipment "conductive parts" (e.g. motor frames or terminal boxes)...
  14. bspace123

    CT Saturation - asymmetrical faults

    Hello We have completed a fault study to identify symmetrical fault levels of 50kA RMS and asymmetrical peak fault levels of 100kA according to IEC60909 using SKM. CT's proposed by the supplier are 2000A/1A 10P40. This implies CT's will not saturate for the RMS symmetrical fault current (i.e...

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