ETO ETO Exam papers 📅 Aug 2022

Exam Question

(a) With reference to voltage variation profiles caused by load changes imposed on alternating current generators when starting large motors online:

(i) Sketch a voltage dip, showing an acceptable recovery time (2)

(ii) State salient factors that cause the variation in part (a) (3)

(iii) Outline salient factors that assist recovery from the deviation shown in part (3)

(b) A three-phase induction motor is wound for four poles and is supplied from a 50 Hz system. calculate: (8)

(i) The synchronous speed

(ii) The speed of the rotor when the slip is 4 per cent

(iii) The rotor frequency when the speed of the rotor is 600 r/min

Reference Answer

(a) The regulation state that the voltage must recover within 1.5 seconds. However an acceptable recovery time would be 0.5 seconds for a brushless and 0.2 seconds or less for a compounded machine.
(ii) FOUR salient factors that cause the variation are:
Size of the Load: The larger the motor, the greater the starting current drawn, which can be up to 8 times the full load current.
Magnitude of the Load Relative to Generator Capacity: A motor nearly as large as the generator can result in a significant voltage drop during start-up.

Full answer on MeoMock — surveyor-grade reference answers for 7,000+ written exam questions.

View plans Browse library

← Browse more questions

Prepare on Android — MeoMock on Google Play