WTT Electrical Systems & Power Generation 3

Question 1

Which standard governs the testing and certification of electrical equipment used in potentially explosive atmospheres in wind turbine nacelles?

Accepted Answer

ATEX / IECEx (IEC 60079 series)

Answer

ATEX (EU) and IECEx (international), based on the IEC 60079 series, govern equipment used in explosive atmospheres such as areas near hydraulic oil mist or battery rooms.

Question 2

What is the function of a varistor (MOV) installed across the terminals of a wind turbine's electrical panel?

Accepted Answer

To absorb transient overvoltages and protect downstream components

Answer

Metal oxide varistors clamp transient overvoltages (lightning, switching surges) by conducting heavily once a threshold voltage is exceeded, protecting connected equipment.

Question 3

A technician measures 480 V line-to-line on a three-phase system. What is the approximate line-to-neutral voltage?

Accepted Answer

277 V

Answer

Line-to-neutral voltage equals line-to-line voltage divided by √3 (1.732), so 480 ÷ 1.732 ≈ 277 V.

Question 4

What is the primary reason wind turbines use IGBT-based converters rather than SCR (thyristor) converters for variable-speed operation?

Accepted Answer

IGBTs can be turned both ON and OFF by gate signal, enabling PWM for sinusoidal output

Answer

IGBTs are fully controllable (turn-on and turn-off), allowing PWM control for low-harmonic sinusoidal output; SCRs are only turn-on controllable and require natural or forced commutation.

Question 5

In a Type 4 (full-converter) wind turbine, what component decouples the generator frequency from the grid frequency?

Accepted Answer

The full-scale power converter (back-to-back converter)

Answer

The back-to-back full-scale converter rectifies generator AC to DC, then inverts to grid-frequency AC, completely decoupling generator and grid frequencies.

(WTT) Wind Turbine Technician Certification Practice Test

(WTT) Wind Turbine Technician Certification Practice Test

WTT Electrical Systems & Power Generation 3