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  • Users: mgtrp
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  1. mgtrp

    Protection CT Location for Small Generators

    I'm looking for opinions on the location of protection CTs for small medium-voltage generators (800-1200 kW) that do not use differential (just overcurrent). Some people prefer them to be mounted on the neutral end of the generator winding, so that they can measure the generator contribution to...
  2. mgtrp

    Need for Transformer Instantaneous Overcurrent

    I work for a utility that is reviewing its standard protection package for substation transformers at the moment. At present, we provide each transformer with redundant differential relays from the same blue-box manufacturer. In each relay, we set timed overcurrent elements to back up the...
  3. mgtrp

    Cable Sizing for Generator-Connected Excitation Transformer

    I'm looking for guidance on sizing of cables between the generator terminals and its associated excitation transformer. I'm specifically concerned with short-circuit withstand, as the fault currents at the generator terminals can be quite high in comparison to the size of the cable that would...
  4. mgtrp

    Generator Diode Failures

    We had a diesel generator blow a pair of diodes in the rotating rectifier during synchronising (both failed open circuit). The generator is a 4.16 kV/3 MVA unit with brushless PMG excitation. The immediate cause of the failures seems to be that the generator breaker closed onto its bus with...
  5. mgtrp

    Field Ground Protection Power Supply

    Typically protection devices are sourced from the station DC power source, but I note that a lot of older-style field ground monitors (e.g., ABB/Westinghouse 64F, Basler BE1-64F, GE 3S7932YA122) require a 120 or 240V AC power source. I've seen this addressed in two ways - either to use a supply...
  6. mgtrp

    Writing Transformer Ratio

    I recall that somewhere in the IEEE standards collection, there is a note on the correct way to write the transformer voltage and ratio, e.g. 13800-600/347V vs 13800/600V vs 13800:600V, etc. I have been looking through them this morning trying to find this, but haven't managed to yet - does...
  7. mgtrp

    Overhead Distribution Lines - Neutral Conductor and Grounding

    Hi all, After moving to Canada 6 years ago, I have been walking for a small utility that predominantly works with generation and transmission but also dabbles in small amounts of distribution. One significant difference between Canada and my native country is that the medium-voltage...
  8. mgtrp

    Ground Fault Current Contributions

    Hi all, I'm in the process of preparing settings for a transmission line protection relay, and as part of this am simulating faults in various locations using our load flow/fault calculation software (ETAP). With reference to the simplified network diagram in the attachment, the operation of...
  9. mgtrp

    Flexitest Switches Induced Currents

    Hi, The utility that I work for often uses ABB Flexitest switches for isolating CT and VT circuits from protection relays. I have observed in some relays that even with the CT shorting switches opened (but the circuit still live - i.e., current passing through the shorted CT's), there is still...
  10. mgtrp

    Change in Transformer Inrush

    We are having issues with one of our step-up transformers tripping on inrush almost every time we energise it. The transformer is 3/5 MVA and is a star-connected autotransformer with delta tertiary. It is a step-up between a four generators and the grid, and has been in-service and...
  11. mgtrp

    Synchronising at Transmission Level

    Hi all, I was curious as to what various utilities were doing as standard practice for synchronising in transmission systems. At our older substations, we would typically have a single synchroniser with relays switching in the appropriate VT's and close coils. SCADA would issue a brief pulse...
  12. mgtrp

    Primary Injection Testing - Regional Differences

    I am relatively new to North America, but have noticed a difference in approach to the importance of protection systems as compared to my home country - highlighted recently, when during commissioning of a generator, on-site staff decided to get rid of those pesky differential trips by turning...
  13. mgtrp

    Recloser Curve Equation

    Does anyone have an equation that approximates the old Cooper recloser curve 142? Thanks.
  14. mgtrp

    Abandoned Power Stations

    Passed of as art, but still some interesting photos of abandoned power stations and substations: http://www.darkroastedblend.com/2009/02/epic-abandoned-substations-and-power.html http://www.darkroastedblend.com/2009/09/battersea-and-other-abandoned-power.html And also on the same website...
  15. mgtrp

    Megawatt Transducer Calibration

    Hi, We are trying to check the calibration of a MW transducer and display gauge. The meter is configured for 2 CT inputs and 3 voltage inputs. Unfortunately, the technicians test gear isn't too happy creating the wye-connected B-phase-grounded system that the transducer is expecting to see...
  16. mgtrp

    Generator - Transformer Connections

    I have a somewhat unusual case of having several 2MVA generators that although star-connected, cannot have the neutral point earthed due to their unconventional construction. The generators will feed into a common step-up transformer, with no loads (other than static excitation) fed directly...

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