transformer loading
transformer loading
(OP)
We have a unit substation in our manufacturing facility. The transformer section is a 5oo Kva 4.16Kv to 480/277v. It is connected to an 800 amp main breaker which feeds a large panelboard. The low votage amp rating of the transformer is 602 amps. the unit is about 5 years old and installed in a clean environment which is climate controlled year round. It has a Siemens panelview meter on it that reads 450 amps. We want to add another piece of machinery onto this sub that is 140 amps total bringing this sub to almost max.However the air conditioning load on this sub is starting to drop due to colder weather so the sub will drop about 25% in the next few weeks. So this sub will be maxed out about 4 months out of the year when the Ac load is on then will drop off. The load is on this sub 24/7 and it is supervised. It looks like there are provisions to mount a exhaust fan in the transformer section but I am not sure if it is common practice to overdrive a transformer a little bit and put a fan on it. Thanks for any input






RE: transformer loading
It is common and standard practice to increase the capacity of a trasformer by 25% to 40% (typically 33%) by use of forced fan cooling. The unit windings needs to be fitted with temperature sensors to automatically control the fan. Check with the mfrs.
Not recommended, but if you know what you are doing and by keeping a watch on the temerature rise of the transformer, you can set up external cooling by fans. The idea is to disspate the heat generated in the tranformer so that the winding temperature does not exceed the rating of its insulation.
RE: transformer loading
RE: transformer loading
………the unit is about 5 years old and installed in a clean environment which is climate controlled year round
The actual equivalent transformer capacity varies with the ambient temperature. For instance, if the ambient temperature is 20oC (68 oF), the transformer rated for 500 kVA at 30 oC is able to be continually loaded up to 500x110% = 550 kVA according with ANSI Std C57 (see enclose figure below).
This means that the ampacity available at 480 V side is 661A. If the unit is suitable to accomodate fan coolers, it is possible to add extra capacity as described in the previous post.
It is good idea to double check the protective devices setting and rating to make sure they can handle the additional load.
RE: transformer loading
RE: transformer loading
RE: transformer loading
jcraft, no, you can't monitor the transformer with an IR scanner, the hot spot of interest in buried deep within one of the cores.
RE: transformer loading
I agree with you, it depends what the tranformer nameplate indicates. It it says temperature "rise" then what you say is true.
However tranformers are specified with insulation "class" and there are insulation classes other than 220 (185 dec C I beleive for 115 deg rise). The insulation "class" indicates maximum temperature permitted at any spot.
185 is for smaller units dont know where the break is.
RE: transformer loading