A quick summary and review of 10 previous blogs
We’re now at 11 weeks into this series of blogs. I thank you for reading, and I appreciate your comments and questions. This might be a good time to pause a bit to review and summarize what we’ve said so far in the 10 preceding blogs. Those blogs have been generally historical background for the real topic coming soon–to “Cut the Copper” in modern data centers. Here’s a summary of our past discussions:
- In the earliest days of the electrical industry in the United States, good old mineral oil-filled distribution transformers proved to be very reliable devices, except when they blew up in a big ball of orange flames and black smoke. In order to be safely installed indoors, they had to be placed only inside fireproof vaults.
- The development of Askarel fluids in the 1930s allowed distribution transformers to be moved indoors, physically closer to the secondary loads, without risk of fire. The liquid was essentially nonflammable, and the transformers could be installed almost anywhere inside a facility, without worries about fire safety.
- During the World War II years, the overall national supply of copper became very tight, and most of the copper that could be produced was rationed to the construction of war machinery and munitions. This forced electrical engineers to become more creative in their power systems designs for facilities of all types, and the “loadcenter unit substation” concept was refined, caught on, and was very widely adopted. With intelligent system designs, the total tonnage of copper required for a distribution system could be reduced by about 80% from previous typical designs.
- From the beginning of World War II into the mid-1970s, tens of thousands of Askarel-filled distribution transformers were produced and installed inside plants of all types in the U.S., arranged in “Loadcenter Unit Substation” configurations. One of the key chemical ingredients in the Askarel fluid was a compound known as polychlorinated biphenyls (PCBs).
- In the early 1970s, the U.S Environmental Protection Agency was formed by Congress, and soon began to study the harmful effects of PCBs on humans when PCBs entered into the food chain. In 1979, the EPA concluded that PCBs were a very dangerous substance that caused genetic problems in humans, and issued a formal ban on all production of PCBs in the U.S.
- Transformer manufacturers experimented with other liquids as substitutes for Askarel–but all of those liquids had serious drawbacks that prevented widespread adoption. None of the new liquids worked nearly as well as the Askarel they were intended to replace.
- Open-ventilated dry-type transformers soon became quite popular, and worked very well in loadcenter unit substations until medium-voltage vacuum breakers became popular in the early 1980s, and were widely applied in all types of electrical distribution systems.
- The unique fault-interruption characteristics of vacuum circuit breakers highlighted a weakness in dry-type transformers, that hadn’t really been seen before with liquid transformers. When switching the primary windings of a distribution transformer, the load current and magnetizing current that had been flowing through windings dropped to “zero” nearly instantaneously, and the energy trapped inside immediately displayed itself as a huge transient voltage across the winding terminals.
- This phenomenon has caused many catastrophic failures of medium voltage dry-type transformers applied inside facilities of all types. Dry-types installed in data centers have been particularly vulnerable to this mode of failure, for a variety of reasons that have been discussed in recent blogs, and will be discussed further in upcoming blogs.
Coming next week will be a little more history: “The early 2000s: The amazing boom of data center construction.”
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