I was quite free this period of time so I am trying to achieve one post a day, because it seems that the website is a bit empty. I was doing a lot of coordination works relating to transformer room design recently, so today I will be talking about the design criteria and considerations of transformer room. First, let me explain the utility supply of Hong Kong. In Hong Kong, there are three major territories: New Territories, Kowloon, and Hong Kong Island. China Light and Power Group (CLP) provides power to mainly the New Territories and Kowloon Area. On the other hand, Hong Kong Electric (HKE) provides power to the Hong Kong Island area. These two utility companies have different transformer room designs. As I only worked on projects for New Territories and Kowloon areas, I will only talk about the transformer room designs for CLP Group.
So, first question to the topic will be: What is a Transformer Room? Transformer room is basically the core of electrical distribution within a building, it stores the transformers. Without transformer, you won’t have power distribution to each floor of the building. The idea of the transformer is to step up / step down a voltage. In Hong Kong, CLP deliver 11 kV cables through underground cable ducts towards the building’s transformer room. Then, the transformers inside of the transformer room will step down the 11 kV voltage to a 380V three phase voltage. The 380V main voltage cables will then deliver electricity towards the low voltage switchgears in the low voltage switchrooms. The switchgear will then distribute the main cables into different sub-main risers towards different electrical loads of the building. The switchgear will also have control and protection ability, meaning that it can switch the electrical loads on/off, and can trip the electrical loads in case of a fault.
The next question will be: How to plan a transformer room? The first step is to determine the amount of electrical loads within the building. Information such as equipment schedules should be obtained from different trades (Mechanical Ventilation, Fire Services, Plumbing & Drainage Services) so that the total amount of electrical load can be determined. This can allow you to figure out the amount and rating of the transformers. Usually, consultants will then do their electrical loading estimations, and have a brief picture on the amount of transformers they need from CLP. However, in order to obtain these amount of transformers, a formal transformer room submission to CLP is required. This will require the consultant to fill in Load Estimation Sheet provided by CLP (See picture below):
This load estimation sheet is different from the electrical load estimation done by the consultants, as the unit loading specified in the table shall follow the ADMD Figures (After Diversity Maximum Demand Figures) provided by CLP. This figure usually is larger than the actual loading. Also, it is worth to mentioned that all the fire services load shall not be entered in this estimation sheet. Therefore, the total loading might be reduced due to the omission of fire services load. Hence, you will need to adjust the loading figures to match with your total load profile. CLP will only check the total amount of loading to approve the requested amount of transformers. On the side note, CLP has recently issued a new standard, stating that if the total amount of transformer capacity is over 20 MVA, a 132 kV substation shall be provided to them (Link in page end). Therefore, do pay attention if you are managing large scale projects in Hong Kong.
Once you know the amount of transformers, the last part will be to coordinate with architects/structural engineers on the framing and layout arrangement of the transformer rooms. CLP’s COP 101 is the one and only standard to follow for the layout and framing arrangement of the transformer room. However, there do have some important points that are worth to be explained. As the post is too lengthy, this topic will be divided into two parts and the points will be discussed in the next part. If you would like to know more about the requirements of the transformer room (such as headroom requirements, double slab requirements, fan requirements, transformer room equipment requirements…etc), you can refer to the links provided below. The drawings version provide the typical arrangements of the transformer room layouts. The text version provides the guidelines to plan the transformer rooms.
COP 101 Version 15 document (text) Jun 2020: https://www.clp.com.hk/en/customer-service-site/open-and-close-account-site/cop-101-distribution-substation-design-site/Documents/Cop101%20version%2015%20black%20letters.pdf
CLP 132 kV Substation High Load Density Development: https://www.clp.com.hk/en/customer-service-site/open-and-close-account-site/cop-101-distribution-substation-design-site/Documents/High%20Load%20Density%20Development%20typical%20132kV%20drawings.pdf