FACTORS

CAUSING INSTABILITY OF WIND POWER

As

due to nonlinear and delicate in nature of these loads are majorly pretentious

by the power worth problematic .There are dual sorts of turbines namely fixed

speed and variable speed turbine, in fixed speed turbine variation in haste offer

to large voltage changing on network where as in variable speed wind turbine’s

situation, where we use power electronic devices, in this can we need to take

into attention about harmonic distortion.

A: Voltage

Variations

On the native level, voltage variances are the core issue related

with wind power. This can be the limiting factor on the quantity of wind power

which can be installed. In ordinary operational condition the impact of attaching

a wind farm on the gird voltage is directly related to the short circuit power

level.

The short circuit power level at a specified point in the

electrical system indicates the strength of a system. If the voltage at a

distant point is represented by Us which is a constant voltage and the short

circuit power level (commonly represented by SSC )is demarcated as Us2 / Zk where Zk represents total impedance between

the points concerned. The system voltage at the supposed inestimable busbar and

the voltage at the Point of Common Coupling (PCC)

are Us and Ug, correspondingly. The output power and reactive power of the

generation entity are Pg and Qg, which corresponds to a current Ig. It is clear

that the variations in the produced power will cause variations in the voltage

at PCC. If the impedance Zk is

small then the voltage deviations will be small. Similarly, if Zk is large, then the voltage deviations

will be large .

B: Steady-state voltage

Operation of airstream turbines may disturb the

voltage in the concomitant network. If essential, the suitable methods should

be taken guarantee that the wind turbine installation does not fetch the amount

of the voltage outside the compulsory restrictions. It is suggested that

load-flow analyses be accompanied to evaluate this effect.

Several

wind turbines are fortified with induction generators which ingest reactive

power. At no load the reactive power intake is around 35-40% of the rated active

power, and rises around 60% at rated

power. Reactive power is one of the main reasons of voltage uncertainty in the system

due to the associated voltage drops in the transmission lines, reactive current

also subsidizes to system losses.

C: Voltage Fluctuation

Rise

and fall in the system voltage may be the source of observable light flicker

depending on the amount and frequency of the variation. This kind of disorder

is called voltage flicker.

The flicker extent is based on the

measurements of three sudden phase voltages and currents shadowed by means of “flicker algorithm” to compute the Pst and

Plt. where Pst is the short term flicker severity factor and computed over 10

minutes, and the long term flicker severity factor Plt is distinct for two hour

periods. The flicker calculations can also be accompanied with simulation

procedure.

Turbulences

just noticeable are supposed to have a flicker severity factor of Pst = 1 The

flicker emanations, Pst and Plt may also be predictable with the coefficient plus

factors, cf(?k, va ) and kf(?k) attained from the measurements, which are generally given by

wind turbine manufacturers.

It

is suggested that Plt?0.50 in 10-20 kV networks and Plt?0.35 in 50-60 kV

networks are considered satisfactory. However, unlike utilities may have different

flicker emission limits.

D: Harmonics

Harmonic disorders are a phenomenon associated by means of

the disturbance of the fundamental sine wave and are shaped by

non-linearity of electrical apparatus. Harmonics causes rise in currents, power

losses and probable disparaging over-heating in the instrument. Harmonics may as well increase difficulties in

communiqué circuits.

Entire harmonic distortion, or THD can be related to either current harmonics or

voltage harmonics and it is distinct as the fraction of total harmonics to the

amount at fundamental frequency multiplies by 100%

THDv = (V2^2+V3^2+V4^2+…. + Vn^2) ^. 5 * 100%

V1

THDI = (I2^2+I3^2+I4^2+…. + In^2) ^ .5 * 100%

I1

The Pulse

Width Modulation (PWM)

switching frequency, with a characteristic switching

frequency of a few thousand Hz, alternates the harmonics to upper

frequencies where the harmonics can be simply

detached by smaller filters. Popular general harmonic standards can be encountered

by means of contemporary wind turbines.