EEEN71372: Power System Plant, Asset Management and Condition Monitoring

Coursework 2 – OHL Design Exercise

Coursework – Overhead Line Design Exercise

1.   Structure and format/presentation of the report and marking scheme

The report should not be more than 10 pages long from Section 1 to Section 5 (see below) and discussion should be included to justify the selection of any required design coefficients and insulator properties. Overall, the discussion of the findings and conclusion are important.

The report should be divided into 5 sections following the order below:

Section 1:    “Power rating calculations” (max one page)

Section 2:    “Complete tower diagrams” for the towers designed based on the two insulator types indicating

only the tower dimensions. (max one page)

Section 3:    “Internal clearances calculations”; Justify any assumed values (when required) and use figures

(when required) to support your calculations

Section 4:    “External clearances calculations”; Justify any assumed values (when required) and use figures

(when required) to support your calculations

Section 5:    “Discussion and Conclusions”. (max one page)

How marks of the report are allocated (approximately):

Structure and overall presentation 20%

Clarity and professional quality of figures 20%   Required calculations with complete steps 20%

Discussion/Justification of any values implemented 20%

Overall discussions and outcomes from the different designs 20%

2.   Overhead Line Design

A new double circuit 66kV single Horse conductor transmission system is required to transfer energy from Manchester to Liverpool with a span length of 180m. The conductor is installed at 5ºC and 22% of its rated strength and has a maximum operating temperature of 110ºC. A U160BS insulator dish designation is used. Additional information about the conductor and the insulator used for the overhead line system are provided below.

Calculate the overhead line rating (in MVA) and the suspension tower basic dimensions required for proper operation of the overhead line system.

What will be the OHL design if the most optimum Rod composite insulator (Table 1below) is utilised? Indicate which other polymeric insulators could be used on this OHL design and explain why.

Your report should include the diagram(s) of the suspension tower indicating all the dimensions/distances required for the engineers to build the OHL. Justify any engineering decisions made in the calculation section. Any key discussion points that come from the different designs should be included in the conclusion section.

Conductor Details

Table 1 - Bare conductor details

Insulator String Details

●    Required creepage distance: 5.6m

●    Total length of fittings: 0.45m

●    Insulator dish designation properties are provided in the table below:

Table 2 - Pin and Cap, and long-rod insulator details

Cross-arm design

●    Top cross-arm design angle 11o

●    Mid cross-arm design angle 12o

●    Lower cross-arm design angle 13o

●    All cross-arms have the same length

Other Information

●    Ground clearance according to the standards

●    Shielding angle: 25o at no wind

●    Wind speed at which clearances must be maintained: 14.6 m/s

●    Maximum reduction in distance between   phase conductors (due to vertical movement resulted by the conductor galloping): 0.8 m

●    Minimum heat loss due to convection: 36.30 W/m

●     Minimum radiated heat loss: 15.40 W/m

●     Maximum solar heat gain: 11.30 W/m

Important assumptions

●    It is assumed that the tower body is rectangular and it has a width of 2.5m with the shield wire placed at the centre of the very top of the tower body.

●    The wind forces employed on the insulator and its weight can be neglected (since they are very small compared to the conductor forces).

●    The vertical movement of the conductor caused by galloping is considered only for the phase- to-phase clearances since the probability of having galloping under the maximum thermal rating of the line is negligible.