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However quite often these renewable energy projects require connection to an existing transmission line somewhere between the utility substations and so connection options must be considered carefully.

Tee Connection

The Teed connection is arguably the most simplest connection simply tapping on to the existing transmission line at some point between the two existing substations.

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Tees are therefore generally not a main stream option.

Three CB In-Out Connection

This arrangement involves three Circuit Breakers (and associated plant) in a "Y" type arrangement. 
This is achieved typically at two of the existing poles/towers in the line where they are re-diverted in and out of the new substation.

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However the problem with this arrangement is that it relies on all three circuit breakers being in service.  Any one CB out of service will disrupt the normal operation of the three substations.

Three CB Mesh Connection

A simple re-arrangement of the three Circuit Breakers used in the In-Out arrangement produces a small three Circuit Breaker mesh - sometimes drawn as a triangle with a CB on each side of the triangle.

In this mesh arrangement, we only need any two of the three Circuit Breakers to be closed for full operation between all three substations.  This allows for maintenance on the circuit breakers plant without disruption to the ability to generate power to the grid.

Key