Snowed In 1500 KVA Dry Type Transformer
What happens when you ship a 1500 kva dry type power transformer in the winter, up North, without properly tarping it? It gets 86’d. Send it back. We don’t want it. Besides the snow and ice, there will be dirt, small debris, and very sad faces. Pictures do not do justice to the amount of snow and dirt on the windings. It can be a chore securing a dry type power transformer for shipment, what we call “Bagging it,” but it has to be done. Hidden openings in the tarping on the bottom are usually the culprit. Driving in the rain can be even worse if there is any opening in the tarp. When this happens there’s a lot of discussion about cleaning the transformer and drying it; Procedures; Warranties; Who’s going to pay for the shipping; and, of course, who is going to pay for a new transformer because the customer sure does not want to accept a brand new but wet and dirty 1500 kva, 13,200 volt to 480/277 volt transformer. It’s deficient. That’s all they know. Any suggestion the warranty protects the customer’s interest is met with open anger. A warranty is only for 2 ½ to 5% of the expected life of the transformer. And the cost of taking out an old unit and installing a new transformer can be horribly expensive. A large dry type power transformer is sometimes buried deep within a building’s structure. Sometimes the building has expanded around the transformer substation. We have seen many projects where the cost of the replacement transformer was less than the cost of the installation. Think of the cost of not properly securing the transformer from rain, snow and road dirt as being $1,500.00 per minute of the time it would have taken to do it right. Fortunately this does not happen very often.
Transformer Blocking Shows Its Age
MIDWEST’s Engineering Department has a shelf with miscellaneous parts that we use for training. One of the items is a very simple 2” X 2” X 5” porcelain block. This is from a 1000 kva, 13,200 volt primary to 480/277 volt secondary, dry type power transformer. The transformer was one of seven new transformers installed in the 1960s at a customer’s commercial facility. MIDWEST’s service included cleaning and inspecting the transformers. They ranged in size from 500 kva 120/208 to 2000 kva 480/277 volts. The transformers were very clean from service by many companies over the years. All the test results were good. Previous maintenance notes classified all the transformers as “Excellent condition for continued service.” This facility handled critical data processing and the “results of failure” would include lose of power to data processing equipment. MIDWEST’s physical inspection revealed the winding blocking for one of the transformers was loose. Much of the upper blocking was so loose it could be removed. The porcelain block in our training room was taken from one of the 1000 kva dry transformers after it was replaced two years later. But based solely on the test results and a cursory visual inspection, the transformers looked great. The only problems were defective fans. But a focused inspection, TBLR in our jargon, a “top to bottom, left to right” hard focused inspection revealed very brittle insulation and loose blocking that could not be secured. The transformers ‘might’ have lasted another 20 years, but not reliably and this owner wanted reliability. So based on the physical condition, not the test results, the customer initiated a 5 year plan to replace the transformers and some of the associated secondary switchgear. This is another example of the value of experience when servicing power transformers, old, used, new, GE General Electric, Siemens, or Cutler Hammer, it doesn’t make a difference.
