Page 260 - Fluid Power Engineering

Deploying W i nd T urbines in Grid 227

1. Wind farm with multiple turbines connected to feeders. Each
turbine with switch gear and transformer is connected to a
switch and then to the feeder. The switch is used to disconnect
a single turbine before any work is done on it.
2. The two feeders collect energy from turbines and put it on
a common bar. This is then stepped up to the grid voltage
using a transformer. This transformer must be rated to step-
up the entire power output of the wind farm. The bus-bar and
transformer are separated by a circuit breaker.
3. A utility-grade meter is installed to measure the amount of
energy that is delivered to the grid.
4. The last item is a circuit breaker that monitors grid voltage,
current, frequency, phase difference, and other parameters.
Depending on the data and the processing logic programmed
into the IED, the circuit breaker connects/disconnects the
wind farm from the grid.

Transmission and Distribution
Wind turbines are connected to three types of electricity networks:
Transmission, distribution, and directly to the delivery point. The
distinction between the three is based on the line voltage (see Table
11-1 for voltage and power-carrying capacity). The current-carrying
capacity depends on the size of the conductor. The table contains
sample current capacity of conductors. The power is carried in three
conductors, one for each phase. There is usually a fourth smaller con-
ductor, which is the neutral conductor. The power carrying capacity
of three-phase AC is:

√
P = 3Vi (11-1)

The other factors that influence power-carrying capacity include re-
active power, sagging of power line, and temperature.
The primary limitation on the capacity of a transmission line is the
thermal capability of the line. Thermal capability is determined by:

Electricity Network Voltage Current, amps Power
Transmission 110–750 kV ∼500–1000 60–1300 MW
Distribution 11–69 kV ∼500 10–60 MW
Secondary 400–11 kV 5–200 0.8 kW–3.6 MW

TABLE 11-1 Guide to the Amount of Power Carried in the Three Types of Power
Networks