Doble Testing?
- Thread starter khixxx
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zog
Senior Member
- Location
- Charlotte, NC
There is not really such thing, just slang. It refers to a Power Factor/Dissapation Factor test done on mostly transformers but also motors and MV cables. Doble makes the most commonly used test equipment for these tests. Hence the name Doble test.
Just like a Megger test, which is really an Insulation Resistance test, but Megger is the most common brand name equipment.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Doble test could also refer ( slang ) to a timing test for a breaker with a shunt trip. Doble made early equipment for this also. It measured the time from the moment the trip signal was initiated until the contacts opened.
rcwilson
Senior Member
- Location
- Redmond, WA
Another name is insulation power factor test.
Doble equipment puts a 2.5 kV or 10 kV AC signal on the transformer or other test specimen, then carefully measures signals proportional to the watts and VA. From that you can calculate, or read directly on the fancier instruments, the power factor of the current flowing into the insulation. A perfect insulation only has capacitive current flowing, power factor zero. Wet, dirty or degraded insulation will have resistive leakage current, raising the power factor. 1% or lower is good, but like megger readings a lot is relative.
A true Doble test sequence makes several measurements, similar to the megger readings on a transformer: Hi & Lo to gnd, Lo to Hi & gnd, Hi to Lo & Gnd plus others with guard inputs. A lot of care is needed to get accurate readings and to accurately adjust for temperature and other factors. Doble supplied a data base of readings for all the transformers tested with their equipment. That gave the customer something to compare his readings too on a unit of a similar size, type and manufacture.
Doble equipment puts a 2.5 kV or 10 kV AC signal on the transformer or other test specimen, then carefully measures signals proportional to the watts and VA. From that you can calculate, or read directly on the fancier instruments, the power factor of the current flowing into the insulation. A perfect insulation only has capacitive current flowing, power factor zero. Wet, dirty or degraded insulation will have resistive leakage current, raising the power factor. 1% or lower is good, but like megger readings a lot is relative.
A true Doble test sequence makes several measurements, similar to the megger readings on a transformer: Hi & Lo to gnd, Lo to Hi & gnd, Hi to Lo & Gnd plus others with guard inputs. A lot of care is needed to get accurate readings and to accurately adjust for temperature and other factors. Doble supplied a data base of readings for all the transformers tested with their equipment. That gave the customer something to compare his readings too on a unit of a similar size, type and manufacture.
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