Test: Heating, cooling and mounting of thyristors - Electrical Engineering (EE) MCQ

The correct answer is 200.

• National Highways Authority of India (NHAI) has inked initial pacts with 200 technical institutes to encourage them for voluntary adoption of highway stretches for research etc.
• So far, 18 IITs, 27 NITs and 207 other reputed engineering colleges have consented for the MoU.
• Out of over 250 institutes which have consented for the MoU, 200 have become signatories.

Concept

Here,

P_av = Average rate of heat generated at a thyristor Junction

Q_JC = thermal resistance between the junction temperature T_J and case temperature T_C

Q_CS = thermal resistance between the case temperature T_C and sink temperature

Q_SA = thermal resistance between the sink temperature T_S and ambient temperature T_A

 
Where Q_JA = Q_JC + Q_CS + Q_SA

Calculations:

T_A = 25°C

I_J = 50°C

P_av = 25 watt

 ∴ % change in thermal resistance

Thus total average power loss in the thyristor – sink combination is 203.70 W. with improved coaling

Thyristor rating is proportional to the square root of average power loss

∴ Percentage Increase in thyristor rating

From the above equivalent circuit

T_J = T_s + P_av (θ_JC + θ_CS)

Thyristor rating is proportional to the square root of average power loss

% increase in thyristor rating

 x 100 = 4.08%

Pilot SCR is an SCR which is fired which activates the firing circuit and fires the main SCR.