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  • Users: skm
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  1. skm

    Short Circuit Rating of Cable

    We are required to design a 11kV system for a rated fault current of 25kA for 1 sec. Based on this requirement the minimum cross section of XLPE insulated Cu cable to be used comes out as 185 sqmm. The actual current required for feeder is 40A. Now my question: The permissible short circuit...
  2. skm

    Cable Outer Sheath Material

    I have one requirement for using HFFR PE outersheath for XLPE insulated cable. I guess HFFR means Halogen Free Flame Retardent. Can anyone suggest me a cable manufacturer who supplies this. My efforts at google.com could not fetch any useful result. Thanks in advance. Good day gives you...
  3. skm

    Impedance Voltage

    I don't think there are any advanrages of having higher %Z. At the first place when you have selected the impedance as 12.25%, I presume it must be based on the short circuit requirement and the voltage regulation required for the purpose. Further for a given X/R, this will also mean increase in...
  4. skm

    Lighting Transformer

    Is it necessary to employ a lighting transformer to feed the lighting distibution board from a 3P4W (TPN) source? I understand that lighting transformer is used for reducing the fault level on the lighting DBs so that MCBs (typicall 9kA) can be used. This reduction in the rated fault level of...
  5. skm

    Measurement of Head Loss Across Trash Rack

    JEB66 Didn't get you. Do you meas use of differential transmitter across screen or other wise? Any way let me explain. This intake tower is surrounded by water all around so the upstream head for all screen is same. Similary on the downstream of screen is the well which is again common for...
  6. skm

    TRANSFORMER CLEARANCE FROM VAULT ROOM WALLS

    I guess there are no exposed live parts in the transformer. In that case in ths part of world (India), we provide at least 750mm around the transformer for the purpose of ease of access. This is as per the recommendation of one of authorities (TAC). Good day gives you happiness, Bad days give...
  7. skm

    Measurement of Head Loss Across Trash Rack

    Can any one one help me with a tricky issue of head loss measurement in an intake water station well with multilevel intake opening with trachracks. This intake station has 4 intakes at different levels and are provided with trashrack to prevent debris from entering th intake well. Water is...
  8. skm

    Protecting long distance transmission line through Pilot wire

    jghrist : HORM 4 is the relay used for pilot wire protection and it mainly marketed in this part of world (India)by erstwhile Alstom-T&D. As for its applicatiuon is concerend I remember using this relay for pilot wire protection application of 33kV overhead line + cable with a total route...
  9. skm

    Droop vs Isoch Control

    i would put it as below: Droop Mode: It is the mode of operation in which the machine will react to the load variation by changing its speed. It is utilised when multiple machine run in parallel so that load is shared between the machines. For this sharing to be equal the machine need to have...
  10. skm

    Derating of Electrical Equipment

    dpc, can you let me know which GE book you are referring to? One method to arrive at the voltage derating is given in IEC60071-2 which is e^(m*H/8160), where H is the altitude above MSL and m is factor which depends on whether we are calculating the factor for LI, SI or PF withstand voltage. I...
  11. skm

    Electrical Cable - Acceptablity of PVC for Sub zero temperature

    We need to install cable at a project site where the temperature goes 30 degrees below zero during winter. Is it OK to use PVC as the insulation and outer sheath material. As per my information PVC can be used upto -5 deg C and bcomes hard and brittle at lower temperature. Is it OK to go with...
  12. skm

    Derating of Electrical Equipment

    I understand we need to derate electrical equipment rating when installed at higher altitude due to reduction in the density of air. What is the standard derating factor used for various equipment? How are the clearance and the crrepage get affected by this altitude and to what extent?
  13. skm

    Regulating Real Power

    Hi, I have an interesting scenario which I would like to discuss / share with you all. Our client is having a cement plant (peak demand of 20MW) which is presently being fed from the utility grid sunstation “A” through a tapping. They are planning to put up a power plant of 42MW at about 2-3...
  14. skm

    Effect of connected burden on CT performance

    We have specified CTs with 40VA rated burden for both metering as well as protection cores, whereas the connected load is less than 10VA. My question is whether this will have any adverse effect on the connected relays / meters? Any precaution to be taken while specifying ISF / ALF? Regards, SKM
  15. skm

    Choice of Vector Group for a 6.6/0.415kV Auxiliary Transformer

    I have used Dzn0 transformer of 2MVA & 1 MVA as this gives the most optimal solution for application where one requires zero shift between the primary and secondary and also provides the possibility of neutral earthing on lV side. These transformer are used for supplying station aux loads and...
  16. skm

    NGR / NGT Sizing

    Can anyone help me with the guidelines for sizing the Neutral Grounding Resistor(NER) or Neutral Grounding Transformer (NET). Bye
  17. skm

    De-energizing an Electrical System under load

    Absolutely no danger involved as long as the disconnectin equipment is rated for opening under rated load condition. If the disconnectiong equipment used is breaker you can simply take the feeder off. In case of disconnector / isolator please check its rating w.r.t. on load and off load...
  18. skm

    Transformer feeder protection

    For a transformer feeder, is earth fault protection required if differential protection has already been applied. If yes,any tips on how the relay cordiantion is done?
  19. skm

    Cable Sizing - Derating factor

    While calculating the derating factor we need to have the total no. of cables for finding group factor. Now to have the total no. of cables we need to have the derating factor. Please let me know how to proceed and which one shall be selected first. Thanx
  20. skm

    Feedback on Restart Module and Auto Start Delay Module

    Can anyone help me with their past experience on the usage of Restart Module or Auto Start Delay Module being manufactured by M/s Holech. What should be the duration of the starting pulse for a motor operated from Distributed Control System/ Safe Gauarding System with ASDM fitted in its module?

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