Wind Energy 5-7

what are the electrical components in power generation?

generators; power electronic converters

what are the electrical components in interconnection and distribution?

power cables; switch gear; circuit breakers; transformers; power quality

what are the electrical components in control?

sensors; controller; yaw or pitch motors; solenoids

what are the electrical components in site monitoring?

data measurement & recording; data analysis

what are the electrical components in storage?

batteries; rectifiers; inverters

what are the electrical components in lighting protection?

grounding; lightning rods; safe paths

what are the electrical components in end loads?

lighting; heating; motors

what are the different types of power transformers?

dry, oil-cooling

what are the benefits and disadvantages of each type of power transformer?

dry: smaller, low maintenance, more expensive, located inside WT

oil-cooling: larger, oil-changing maintenance, cheaper, located outside

what are the types of electric generators for large wind turbines?

induction generator; synchronous generator

what are the types of induction generators?

doubly-fed induction generator; squirrel cage induction generator

what are the types of synchronous generator?

wound rotor generators; permanent magnet generators

what are the main electrical components for an induction generator (squirrel cage) based WECS?

turbine rotor; gearbox; induction generator; soft-starter; capacitor bank; transformer; grid

what are the model equations for a steady-state equivalent electric circuit diagram (SCIG)

V1 = R1 x I1 + j x X1 x I1 + j x Xm x (I1 + I2)

0 = R2/s x I2 + j x X2 x I2 + j x Xm x (I1 + I2)

performance slip equation

s = Pcu2 / Pdelta

(Pcu2 = rotor losses; Pdelta = air-gap power)

how is the internal mechanical torque related to the electromagnetic torque?

Tmi = Tem

internal mechanical torque equation

Tmi = Pmi / Om

electromagnetic torque equation

Tem = Pdelta / O1

how is the mechanical torque developed in an induction machine?

the ratio between the internal mechanical power and the mechanical speed

approximated expression for mechanical torque

Tmi ~ (P_p x 3 x R₂ x V²) / [(s x w) x ((R₁ + R₂/s)² + (X₁+X₂)² )]

synchronous speed equation (rad/s)

O1 = w1/P_p

synchronous speed in rpm

n1 = 60*f1 / P_p

rotor mechanical speed equation (rad/s)

wm = P_p x Om

slip equation

s = O1 -Om/ O1 or s = w1 - wm /w1 or s = n1 - nm / n1

what is the relationship between synchronous and mechanical speed

Om = O1 x (1-s)

generated active power equation

P1 = 3x V1 x I1 x cos(beta1)

stator losses equations

Pl1 = Pcu1 + Pfe1

Pcu1 = 3x R1x I1²

Pfe = 3xV1² / Rfe

internal mechanical power equation

Pmi = -3x R2 x (1-s)/s x I2²

rotor losses equation

Pl2 = Pcu2 +Pfe2;

Pcu2 = 3 x R2 x I2² ;

Pfe2 ~0

air-gap power equation

Pdelta = P1 + Pl1 = Pmi - Pcu2 = Pmi/(1-s) = - Pcu2/s

what is the torque-speed characteristic in motor mode?

Pmi > 0; driving torque (Tmi) and mechanical rotational speed (Om) with same sign

what is the torque-speed characteristic in generator mode?

Pmi < 0; driving torque (Tmi) and mechanical rotational speed (Om) with opposite sign

what is the purpose of the capacitor bank?

supplies reactive power to the induction generators

how is reactive power drawn from the grid minimized?

mechanically switched capacitor banks (used in fixed-speed or limited variable-speed wind turbines, Types I and II)

what are transient overvoltages?

extreme switching events that stress the capacitors due to the wind’s highly and continuously variable nature

what is used to limit the current inrush during start-up?

soft-starter

how does a soft-starter work?

operates as an AV voltage controller, increasing the voltage gradually, by controlling the angles of the SCR devices; function is to reduce the inrush current, limiting disturbance to the grid

what is the equation for the supplied stator voltage of a steady-state equivalent circuit?

Vs - Rs x Is = j x ws x Psi

what is the equation of the supplied rotor voltage of a steady-state equivalent circuit?

Vr - Rr x Ir = j x s x ws x Psi

what is the equation for the stator Psi?

Psi = Lm (Is + Ir) + Lsigma x Is

what is the equation for the rotor Psi?

Psi = Lm (Is+Ir) + Lsigma x Ir

what is supersynchronous mode?

wm > ws —> wr < 0 —→ s <0

what is subsynchronous mode?

wm < ws —> wr > 0 —→ s > 0

mechanical power equations (neglecting the cupper power losses in the stator and rotor)

Pm = Ps + Pr; Pm = (1-s)Ps; Pm = Tem x wm/rho

what happens to power