Testing Of Vintage 1975 Elec. Dist. System 1

[birddogger]

Performed a walk-through of a facility to determine the condition/reliability of the electrical distribution system for a future tenant.

There are three 1000/1500kVA indoor dry-type substations, 13.8kV-277/480V substations, two of which are 29 years old. The transformer for the third SS is only 12 years old, while the switchboard and primary switch for that are both 29 years old.

The transformers, primary switches, and secondary switchboards (GE Power Break line) all appear to be in good physical condition. I do not detect any excessive humming to indicate loose windings. The transformers are quite underloaded since the prior tenant has vacated, but in a quick look at the downstream connected loads, it does not appear that any of the substations has ever operated near nameplate rating. All three subs are equipped with lightning arrestors. There is no known history of fault tripping on any of the feeders to indicate breaker wear. Antiquated but functional (and more importantly, still commericially available) GE Ground Break relays are installed on all feeders. Transformers have all been in continuous operation since prior tenant vacated, so there should be no moisture issues.

Two 1400 kW generators, both appearing to be in excellent condition (although extensive testing and maintenance log review will be recommended) are each connected to a switchboard with integral automatic transfer switches by Russ Electric. Generators and ATS’s are all also vintage 1975. Existing 5,000 gal. UG diesel tank could not be observed, will recommend checking to ensure code compliance.

For their part, GE has ensured that there should be no issues with spare parts and that from my description, it sounds like everything can stay for now. All indications are then that the gear is officially “ain’t-broke/don’t-fix”, but I want to recommend a certain level of testing to ensure reliability. The question is, to what extent should we test this equipment? I figure at a minimum we should have IR scans, a cleanliness check of the transformers, GFR testing, complete generator/ATS testing, testing of the MV switchgear, possibly vibration testing of the transformers. Does anyone have any other recommendations? Do I need to go to the extent of feeder insulation testing?

 

[Jerry123]

Only thing I would recommend is test or at least operate the low voltage circuit breakers. Thus insuring that the protective devices work and the breakers operate correctly, mechanically.

As for the low voltage feeders. This can get very time consuming. Example, from your post you mentioned transfer switches. To megger them you have to disconnect the cables from the transfer switch itself because of the sensing circuits. If the transfer switches are smaller in ampacity the easier but if you have any 1600amp TS, you see where I'm going with this. For secondary panels, first you have to find it. If it has a main breaker bonus, if not turn off all loads. Ideally there should be no ground to neutral bonds after the neutral is disconnected in the substation but in the real world there will be. Pursuing the bond could take days to find. Days=time time=money. So if you have the money its a good thing to do but I would say that this should be last of your worries.

 

[busbar]

It sounds like your serious about assessing the gear condition. You may want to get some proposals from NETA-type testing and maintenance firms.

 

[jbartos]

Suggestion: Before any hurrah testing is started, e.g. by NETA, it may be prudent to monitor strategic points for load patterns and power quality. According to monitored results, systematic testing, e.g. following NETA MTS 2001, may be started. Caution should be exercised, not to impress unnecessarily high voltages or excessive times of tests. Safety precautions should responsibly be taken since testing can become dangerous, if the neighboring old equipment is energized.

 

[PWR]

I would second busbar's recommendation to have a NETA or similar qualifed service and testing company make a proposal for evaluation. The protection features should certainly be tested. For an operating facility, the infrared scan gives you the most bang for your dollar but won't be of value on lightly loaded equipment. Much will depend on the environment that has existed. If the equipment has been kept clean, tight, dry and relatively cool it will still have a lot of life left in it.

 

[GerH]

In something similar I came across about 40% of the overcurrent trips on main LV breakers failed to trip. The breakers in question all tripped in response to manual operation. The trip coil mechanisms were seized or open circuit.

 

[jbartos]

Comment: A larger facility may require to set test priorities according to the power distribution and load configuration, e.g.