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  1. 3I0

    PT Ferroresonance vs Modern SEL relay

    I have encountered two different installations with Yg-Yg PTs and no damping resistance connected to the secondary that went into ferroresonance while they were running ungrounded on the high side (normally they were connected to high impedance grounded systems) and a transient occurred to start...
  2. 3I0

    Exothermic welds VS Clamps Connections

    Can't speak to the Netherlands but in Canada I have seen a lot of IEEE 837 qualified compression style connections (Burndy Hyground) used underground in industrial/mining facilities - where for example they might be designed with a 25 year life expectancy and there is some cost/time savings to...
  3. 3I0

    High Resistance Grounding (HRG) on 4.16kV System

    Commonly medium voltage grounding resistors are not sized for continuous operation, at least in the vast majority of the industrial facilities I have worked in. In the typical industrial distribution substation I have seen, fault selectivity is accomplished on high resistance grounded systems...
  4. 3I0

    Groundfault detection query for a mine site

    Not familiar with IEC standards but in Canada we have CSA M421 as an electrical standard for mines. Based on what I have seen in hardrock mining here it is typical for underground LV distribution that in addition to high resistance grounding at the source transformer and overcurrent protection...
  5. 3I0

    Estimating Split Factor using Annex C in IEEE 80

    It is my understanding that when using the Annex C tables "distribution lines" are for lines with a multigrounded neutral conductor, whereas "transmission lines" are those with a shield wire - the main differences being the assumptions used for the conductor impedance, spacing between grounds...
  6. 3I0

    Transformer Differential Protection trip Fault

    Never used a Sepam 2000, but I have seen similar happen where the relay was programmed with the wrong transformer winding vector group. If the event records don't turn up anything too suspicious, that's where I'd look first.
  7. 3I0

    soil resistivity measurement and interpertation

    I agree with MKFPE - have any geotechnical boreholes been drilled/test pits dug in the area/etc for design of the overall project? I have found this type of data can help interpret soil resistivity measurements for grounding design, if available. For what it's worth, your apparent resistivity...
  8. 3I0

    Insulating gravel vs coarse subgrade gravel

    The only way to actually know is to measure the resistivity of the material, preferably taking into consideration the effects of moisture content/temperature. Another consideration is making sure it is installed in such a way to prevent vegetation growth. IEEE 80 provides guidelines on how to...
  9. 3I0

    F60 Form A Voltage monitoring Contact Voltage

    The voltage monitoring circuit acts as a high impedance in parallel with the output contact, provided it is wired in-circuit (I believe there are options for 'Voltage Monitoring w/ Optional Current' and 'Current Monitoring w/ Optional Voltage' which require jumpers). Testing them requires a...
  10. 3I0

    Grounding

    It wouldn't be purely a parallel connection as that would imply your equivalent distribution line grounding impedance approaches zero with the more shunt connections to ground, which isn't the case in reality. The line would form a series-parallel impedance network, with shunt impedances to...
  11. 3I0

    Gounding of an industrial facility

    The design of a ground grid is based, essentially, on how much current returns back to its source through the earth under fault conditions. Often times (but not always...) primary faults are the basis for the entire design.
  12. 3I0

    Transformer Differential Protection - CT Saturation

    CT saturation calculations should be carried out, and the CT's should be sized appropriately for the application. Just because there is an internal fault does not necessarily mean the CT's will saturate, either fully or partially. There are also degrees of saturation from either transient DC...
  13. 3I0

    Ground fault

    Breakers are tripped in high resistance grounding systems if the resistor is not rated for continuous current (i.e. 10 second resistor rating is seen on most medium voltage systems here). There may also be code requirements that outline under what conditions you can leave the system energized...
  14. 3I0

    Excitation Transformer Sizing

    The power rating of an excitation transformer is based on the steady state power requirements, plus derating factors for the high harmonic load. The static excitation systems I have been exposed to have a 6-pulse front end on them, so present a lot of 5th/7th/etc harmonics. The voltage rating...
  15. 3I0

    Newton-Rafson load flow for synchronous condenser bus

    For simple modelling it will be a PV bus initially. If you are given reactive power capability limits on it though, and it exceeds the limits after converging, it will have to turn into a PQ bus with Q at the positive/negative limit.
  16. 3I0

    Transformer Differential Protection CT Accuracy Class Mismatch

    That depends entirely on the fault current levels and X/R ratios of the system the CT's are connected to. One potential issue is if only one set of the CT's saturates for a through-fault and the relay calculates a differential current above the pickup threshold, then you have a risk of nuisance...
  17. 3I0

    Standalone NGR monitor vs 50/51G relay functions

    Typically another benefit of using a resistor monitoring relay like a Startco SE-330 is that if it's used in conjunction with a sensing resistor (part # ER-5KV) it monitors the continuity of the neutral-ground connection through the resistor. I believe the sensing resistor is also used to derive...
  18. 3I0

    CT wiring - Can a #10AWG wire come loose from a standard terminal block over time?

    Typical installations here would use good quality ring (not fork) connectors and screw-down shorting terminal blocks. The only exception to this I have seen are designs that are built to older Ontario Hydro standards where screw connection terminal blocks are used on bare wire with two clamping...

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