Design Decisions
Reasons for Mechanical Design Choices:
1.) Contact Layout:
a. Options
i. Linear
ii. Circular
b. Decision: Circular
c. Reasons for choice
i. Easier to control change time
ii. Able to employ Geneva Mechanism
2.) Resistive and Reactive Bridging
a. Options
i. Reactor or Inductor
ii. Resistor
b. Decision: Resistive Bridging of contacts during change
c. Reasons
i. Much Easier to make and calculate needed resistance than reactance
ii. Can just buy a resistor
iii. Simpler to add to contact arms
d. Cons
i. More Power lost due to heat
3.) Phases in or out of plane from each other
a. Options
i. 3 Rings for each phase parallel to each other but out of plane
ii. All Three Phases in one larger plane
b. Decision: One Larger Plane with stipulation
i. If Schweitzer Needs To be able to go from 0-1 only
ii. Need three separate planes if you need movement ability from 0-1 and 0-10
c. Reasons
i. We can machine slightly larger parts with a lesser tolerance. (easier)
ii. We must meet the specifications of the client (stipulation)
4.) Attaching Wiring to Contacts
a. Options
i. Solder
ii. Set Screws
iii. Plugs
b. Decision: Set Screws
c. Reasons
i. Solid Unmoving connection when in use
ii. Still easy to change and adjust
5.) Contact Force Direction
a. Options
i. In Plane ⇒
ii. Out of Plane ↓
b. Decision: In Plane
c. Reasons
i. Net force on shaft is 0 at 120 degrees apart
ii. No Moment on the arm
iii. Compression springs are easier to model than cantilever springs
6.) Geneva Gear should have 11 slots to give an exact angle output after the driver has turned a full revolution.
a. It gives precise control and the ability to have fast motion controlled when in conjunction with a spring/wheel configuration.
7.) Materials
a. Casing of Gear Box:
i. Plexi Glass or Some other Translucent material to see the workings
ii. Non Conductive
b. Handle for Tap Changer:
i. Rubber
ii. Non Conductive, Avoid Getting Shocked
c. Tap Changer Components
i. Aluminum:
1. Shafts, Arms, and Supports
ii. Copper:
1. Contacts and Electrical Components
iii. Silicon or Some Other Non Conductive Material
1. needs to be cheap and easy to machine
2. contacts sit in it, smooth for less friction when tap changing
8.) Dimensions
a. Stem first from size and spacing of contacts
b. Radius to be found from 1 or 3 planes of contacts
c. Using 50ms as the changing time, calculate average rotational velocity of tap change and tangential velocity
d. Use averages to find moment or torque to achieve this
e. Find a spring that will give that force and needed torque on the driving wheel when stretched for first half of rotation. Also using deflections
f. Make Contacts concave in the radius so the arm can be more easily brought to rest centered on the contact.
g. Pick easiest sizing for all other components that do not need exact or related sizing