I need to design a 300KVA substation on a H structure for a course but can't find info about measures anywhere
Help pliz
Answer:
300 kVA is far too small to be considered a utility substation. Is an H structure mandetory, or can you use a single pole structure cluster mount? Please update your question with the following information:
a) Primary Voltage
b) Secondary Voltage
c) One 3-phase transformer or three 1-phase transformers?
d) Available fault current (or assume a maximum value)
e) Is secondary over-current protection required?
---- Thanks for updating your question -----
Weights: A single phase 100 kVA transformer weighs around 1000 lbs. A three-phase 300 kVA transformer weighs around 3800 lbs.
Vertical Clearance: Wood poles are typically set in the ground “10% plus 2 feet”. This means a 45’ pole will be 6.5’ in the ground. The typical spacing from the top of the pole to the neutral connection for a 3-phase transformation is 13.5’. You will also need approximately 15’ to 20’ of ground clearance for the secondary wires. This dimension will vary depending on the accessibility. (i.e. pedestrians, driveway, accessible to trucks, crossing roads, etc.)
For a single pole installation, the cluster-mount rack is installed so the top mounting hole is 8.5’ from the top of the pole. A 45’ class 2 pole is more than sufficient for the vertical pole loading. If you can get by with a 40’ pole, only a class 3 is needed.
Spacing: Here are some common dimensions from the top of the pole.
The top crossarm that attaches the 13.2 kV primary is typically 5” down from the top of the pole. A second “device arm” is used to mount the cutouts (fuses). This arm needs to be positioned so the open fuse tube does not interfere with the bushings of the transformer. This arm is typically 33” below the crossarm. The top of the platform is generally at least 10.5” below the device arm. This 10.5’ dimension is often adjusted to take up the “extra” pole height after ground clearance is met. The construction crew who builds the installation likes the extra space between the platform and the device arm.
Fuses: This transformer bank will typically be fused with a 25 amp K-speed fuse link.
Connections: The three 1-phase transformers are most often connected wye on the HV side, and delta on the LV side. They "could" be wired delta on the HV side, but that is less common.
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Good Luck.
300 kVA hardly qualifies as a substation.
If you need to lay out the distances for the various equipment, why not just go looking around town. It would help if you had datasheets for the actual equipment, but if you don't, perhaps there is something else nearby you can look at.
First, what voltages? At 300 kVA, this would probably be MV primary (in the very wide range of 4 kV to 38 kV). Start with that. Look for some comparable installations.
Will this 300 kVA "substation" be padmounted or pole mounted? Indoor or Outdoor?
Will fuses on the primary be sufficient? (Probably so...)
What will the secondary voltage be? What type of load will it serve? How long is the circuit from transformer terminals to load switchgear (breaker panel)?
Basically, don't worry about detailed measurements until you've asked and answered all the bigger questions. By defining the voltages and application, many other details fall into place as a matter of course.
Good luck!
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