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ausphil Thanks for your input. At last someone got it. The phenomenon is the issue. I, like you, have been involved at the high end (>>138kV). Much of the SF6 filled buses and breakers and isolating switches at these levels have built in grounding and isolating switches. Sometimes with TV or...

burnt2x Your getting close to the point. from1910.296(n) "General." For the employee to work lines or equipment as deenergized, the lines or equipment shall be deenergized under the provisions of paragraph (m) of this section and shall be grounded as specified in paragraphs (n)(3) through (n)(9)...

Thank you for your opinions. I was really looking for some helpful experience. Note that OSHA and most industrial safety procedures don't require grounding LOAD circuits whenr the entire switchgear lineup has been deenergized, cleared, tagged, and locked out. If you have done some HV DC...

An electrician got a minor shock from a 4 kV EPR insulated cable after the cable was deenergized for 45 minutes. While the fellow wasn't hurt the safety folks are interested in establishing a procedure that will prevent this. Initially grounding the cable appears to have been done by momentary...

We have a 15000 hp induction motor that has experienced a coil insulation breakdown due to system lightning surges. Can the coil be isolated from the phase winding and permit the motor to operate on a temporary basis? Any experience doing this would be appreciated. I expect there would be an...

Gents, The project that started this thread is a small cogen installation in a plastic fabrication plant. Two 2000 kVA gas engine driven units supplement utility power. It was built without the generator breakers. The question arose during a transfer of ownership. One engineer stated it was...

Your right about inspectors many of those I met didn't understand what an interrupting rating was on a molded case breaker. Previous NEC editions provided room for a professional engineer to make design decisions. Now the committees try to provide pre-engineered packages. We can at least be...

ScottyUK, Your practice is pretty much universal for the big units. jbartos, This system is a small generator (2MW) connected directly to the transformer. The transformer is a wye at 4.16kV and delta at 13.8kV. Both the wye point of the generator and the wye point of the transformer are...

uno, If you use U/L labled molded case breakers check out what the interrupting rating really means. The U/L test method calls for about 10 feet of wire on the load side of the breaker during the test. The wire used will be the maximum size permitted for the breaker size. On the smaller breakers...

rmw, Your right about the safety and lockout tagout, but the presence of a generator breaker really doesn't improve safety. Most units avoid generator breakers between the machine and the step-up xfmr because the price is high. The last unit I commissioned in NJ was 250MW and a generator breaker...

I think I found the answer to the need for a generator breaker. Art. 705.21 DISCONNECTING MEANS, EQUIPMENT on page 2001 of the 2002 NEC HANDBOOK describes the exact case I was investigating. If the generator and transformer are designed to operate as a "unit" no disconnecting means is required...

Having just finished investigating the destruction of a 21MVA bank operating at 27kV it is apparent caps are very sensitive to overvoltage. The stated max voltage for continuous duty is 110%, but no responsible vendor will sell a design rated to operate at the level. IEEE Standard 18 has a table...

As a former member of the API 500 /505 committee I can tell you these standards are based on keeping the oil business safe. The NEC has adopted these standards in 70A and other documents. If the Auhority Having Jurisdiction feels a particular site needs a hazardous classification, then the NEC...

Anyone know of any reliability surveys that include dry power transformers in the 500kva to 2500 kva range. Specifically, the mean time to failure or life expectancy. Looking for 4160 to 13.8kV types

Thank you for the responses. The NEC is pretty quiet re generator installations. Re transformers, the NEC states nothing about step-up transformers. The table in the protection section 450.3(A) table doesn't require "secondary" protection for a "supervised location". The code is very vague on...

Is there a Code or other reason to require a generator breaker between the generator and the step-up transformer. No auxiliaries are supplied at the generator voltage (4160 v). This is for a small (4MW) cogeneraton installation. A breaker is on the high voltage side. The stepup transformer is...

nass1 I have recently obtained budgeary quotes from ABB, and Alstom. Both site experience on their web sites. Utilities have numerous units in service. PSE&g has two right in northern NJ. They are old technology. Utilities usually get them with same input and output voltage levels to...

The fault current through the replacement transformer will change inversely with the Z% of the transformer. The Z% is generally based on the voltage ratio and is reported on the kVA base of the transformer. That said, usually a lower kVA xfmr will reduce the fault current, while a higher kVA...

This phase shifting transformer will be connected from a 230kV utility and supply power to a 13.8kV load bus. Other conventiional transformers are now connected to the same 230 kV utility. The PST will essentially be in parallel with these conventional transformers. The PST is needed to control...

Any experience with specifying a large (50MVA) phase shifting transformer. What computer tool or model was used to develop the phase angle shift requirements? Who was asked to bid?