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  1. GroovyGuy

    Neutral Grounding Resistor IEC

    Hi Tim, I am pretty sure that 230V hi-resistance ngrs are used on 400/230V 3P4W systems in the iec world. Regards, GG "I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
  2. GroovyGuy

    Gas Insulated MV Switchgear Low Gas

    Angga, To be on the conservative side of this issue. I would say that it is not safe to keep this gear energized. Having said that, are you absolutely convinced that you so have a low-pressure event occuring (and not just say a faulty pressure-switch}? If I recall correctly MV SF6 switchgear...
  3. GroovyGuy

    Sealed-Tank Design vs Conservator-Tank Design in 20MVA power transformer, pros & cons

    Howdy everyone, I have a question or two. I currently have a project where I am out for tender for a couple of 20mva (CSA C-88) 55C ONAN 69kv delta - 13.8kv wye step-down transformers. I have asked for pricing for both a sealed-tank design and a conservator-tank type design. The pricing that I...
  4. GroovyGuy

    Generator and PLC

    Howdy Emad, Need some additional info; What is the size (in hp) of the VFDs? What is the voltage rating of the gen-set? What is attempting to start when you hear the "severe" sound from the generator? Where does the "severe" sound come from (ie the engine or the generator?) GG "I have not...
  5. GroovyGuy

    Low Resistance Ground (LRG) on 480V System

    Nope, never seen a LRG applied to a 480Vac system. What size of resistor are they proposing (ie 400A)? Is this (400A) resistor to be continuously rated or short time (ie 30s)? I think it would make more sense to install a 5A (ie HRG) continuously-rated resistor. GG "I have not failed. I've...
  6. GroovyGuy

    Generator and Alternator kW and KVA Confusion

    Hey Bill, Let's not loose site of the fact that diesel gen-sets can have up to three power ratings, including; Standby Prime Continuous Would a 2MW standby unit not be rated 1.6MW continuous (ie 80% of standby rating)? 18.2MW (ie 91% of standby rating) seems a tad high to me. Regards, GG "I...
  7. GroovyGuy

    480 VAC VFD Power - Do I need an Enclosure & Disconnect?

    hi paul, in reply to your query above; Q1) Am I required to have a disconnect switch for the incoming power circuit (480 VAC)? Or is it allowable to simply land the incoming power circuit at finger safe fuse holders, relying on the fuses as the means by which someone would remove power from the...
  8. GroovyGuy

    Motor Schematics (Large Motors above 4MW)

    Howdy Ashdgee, Scotty is correct, you will be using CBs to start (22MV-36MW) motors (and not contactors). More importantly, how will these motors be started (ie Direct-on-line, reduced voltage, ASD)? Regards, GG "I have not failed. I've just found 10,000 ways that won't work." Thomas Alva...
  9. GroovyGuy

    Heat dissipation in IP 67 Enclosure

    Hoffman has an app available from their website which allows you to design wrt heat loss from an enclosure. (per jraef's comment above.) "I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
  10. GroovyGuy

    Ground fault on a Delta System

    You betcha Curious; The zero-sequence CT is always installed on the 'neutral point' of the zig-zag transformer. (ie in series with the ground resistor). GG "I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
  11. GroovyGuy

    Automatic Source Transfer Scheme with Switchboard?

    Howdy Curious Electron, I agree with JG above. (ie what are the voltages and current involved here?). GG ps I have always preferred to use a actual ATS in these cases (ie a ASCO 7000 series type of AT switch for LV applications). Obviously for MV ATS applications you will need to use modified...
  12. GroovyGuy

    Metal Clad Switchgear

    Howdy Curious Electron, I think what you are describing above is commonly referred to as a bifurcated feeder. Yes , you can do this. But keep in mind that you will almost certainly require two (2) sets of CTs and two (2) protective relays. GG ps What are the loads that these two feeders will...
  13. GroovyGuy

    Medium Voltage switchgear Cable connection

    Howdy 144X, I believe what you are looking for is called metal-enclosed switchgear (as opposed to metal-clad switchgear). In metal-clad switchgear the load connections are always contained within a separate compartment. Are you considering a circuit-breaker type of device or a...
  14. GroovyGuy

    Ground fault protection for HVAC

    Hi Steve, Correct me if I have it wrong but NEC 210.63 requires you to install a 15A or 20A, 125V receptacle outlet within 25 ft of heating, air conditioning, and refrigeration equipment. The only exception to this rule is that you need not install GFCI protection for fixed electric snow melting...
  15. GroovyGuy

    Difference between Star-Delta and Reactor Starting Method

    Howdy Arshad, Have you considered RVSS (reduced-voltage solid-state) type of starter, as opposed to reactor or wye-delta type of starter. RVSS starters are very common these days for variable-torque type of loads (such as a centrifugal pump). I am sure that that the installed cost of a RVSS...
  16. GroovyGuy

    Power Factor Correction Design

    Howdy Ashdgee, I don't believe that you will have any issues with PF correction with the bulk of your load consisting of ASDs. Check with you ASD OEM, but I believe that the input PF of a 6-pulse type of ASD is near unity. However, you will need to consider the harmonics of your system. I can...
  17. GroovyGuy

    Ground fault protection for HVAC

    Howdy rajendrarohra1978, I have never encountered a specific requirement for GF protection on HVAC equipment. Having said that, what is your distribution voltage and do you have a high-resistance grounded (HRG) neutral? [ie as opposed to a solidly grounded neutral or a ungrounded (ie delta)...
  18. GroovyGuy

    Taming a transformer's inrush.

    Howdy Keith, I recently had the same issue, but with transformers rated up to 12.5MVA, all with a 25kV primary. We had to do something to reduce the % voltage-drop at the PoCC with the Utility, and hence not impact other customers on the same 25kV distribution feeders. What we ended up doing...
  19. GroovyGuy

    UPS explanation

    Ho Mohd, Yes, it is possible to provide a DC & AC UPS from the same set of equipment. This is assuming of course on the voltage of the DC UPS; it needs to be the same potential as the battery voltage (ie 125Vdc). With this type of system, the rectifier & battery serve the same function for...
  20. GroovyGuy

    Is it safe to install a 24-pulse AFD next to a 1 MVAR capacitor for a 3.5 MW motor?

    hi DvHz Do you have a simple one-line diagram of what you are trying to accomplish? Is the vfd required only for starting the motor? What is the nature of the load? (ie variable or constant torque?) GG "I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison...

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