Page 273 - Fluid Power Engineering

240 Chapter Eleven

Loading on WTST is considerably more cyclical than tradi-

tional transformers. The thermal cycling caused by varying
load can cause damage to insulation and to internal and ex-
ternal connectors.
Imperfect sinusoidal waveform because of power electronics

converters cause additional loading. If high-frequency filters
are not used, then electrostatic shielding may be required to
prevent transfer of harmonic frequencies to the higher voltage
side.
Ability to withstand low-voltage ride-through (LVRT) re-

quires that transformer be able to handle full short-circuit
current for at least 0.625 s. During such a transient period,
the transformer experiences high mechanical forces.

Wind-Plant Interconnection and Transmission Study
Wind farms that deliver power into the utility grid are required to
submit to an interconnection study that is performed, in most coun-
tries, either by the local utility or a regional transmission organization
(RTO) or a regulatory agency. The description of the various studies
and agreements in this section is specific to the United States, although
most countries have similar processes. Furthermore, the intent of this
section is not to be comprehensive, since there are variations to the
process from one country to another and within a country from one
region to another.
An interconnection agreement only provides the right to connect
tothetransmissionline;itdoesnotprovidetherighttotransmitpower.
A separate transmission agreement is required. Interconnection and
transmission agreements do not guarantee that a utility will buy the
energy; a power purchase agreement is required with a buyer to sell
the energy produced in the wind farm. The interconnection study, as
practiced in the United States, is separated into two types:

Large generator interconnection request (LGIR) for 20 MW or

more
Small generator interconnection request (SGIR) for less than

20 MW with a request for energy resource service

LGIR is a three-step process. Although the following process is
specific to United States, most other countries have a variation to the
following process: 18,19,22

Feasibility study: The primary purpose is to check if the system

can accept power injection at the interconnect point chosen
by the wind farm developer, and to provide high-level cost