IESL Part II Electrical case studies

IESL Part II Electrical · Put your knowledge to work in context.

The IESL Part II Electrical examination sits inside the professional pathway of the Institution of Engineers, Sri Lanka - the body incorporated in 1968 by Parliament Act No.17 and described on its own site as "the largest engineers' organization in Sri Lanka with over 25,000 members." IESL awards credentials such as Chartered Engineer – CEng (SL) and AMIE (SL) that enable a person to practise as a licensed engineer in the country, and it is the sole credentialing authority for engineering degrees offered in Sri Lanka, including under the Washington Accord. This page is an independent study resource for candidates working toward the Electrical, Electronics & Telecommunication Engineering discipline, which is one of the institution's sectional committees; the same committee opens registrations for each session, so the technical scope tracks that committee's field. The IESL Part II Electrical case studies are 5 cases and about 5,128 words.

Harmonic-rich office riser: parallel neutrals and a capacitor bank in resonance

An eight-storey office building is fed at 400 V, 50 Hz, TN-S from a 1,000 kVA, 11/0.4 kV transformer through a 630 A air circuit breaker. The main riser is two parallel runs of 4×185 mm² copper XLPE/SWA cable, 45 m long, on a perforated tray shared with three other loaded cables.

1,035 words, about 5 min 2

Standby generator on a UPS load: rating, ATS neutral and earth fault protection

A telecommunications hub has a 400/230 V, 50 Hz standby diesel generator rated 100 kVA / 80 kW at 0.8 pf; the alternator has X″d = 12% and its rating assumes a 40 °C ambient. The load is a 30 kVA double-conversion UPS with a six-pulse rectifier (input displacement factor 0.82, THDi 32% at full load), 15 kW of AHU motors including one 11 kW direct-on-line unit, and 5 kW of lighting, giving 45 kW steady demand.

1,053 words, about 5 min 3

18 GHz microwave link: link budget versus rain margin and Fresnel clearance

A utility is designing a 12 km point-to-point microwave link between two hilltop sites to carry 155 Mbit/s. The chosen 18 GHz radio delivers +23 dBm at the antenna port; each end uses a 0.6 m dish with 38 dBi gain, 2.5 dB of feeder and connector loss, and a receiver threshold of −78 dBm for the planned 16-QAM modulation.

853 words, about 4 min 4

4–20 mA loop with a Zener barrier: voltage budget, IS limits and an earth-loop offset

A two-wire gauge pressure transmitter (range 0–16 bar, 4–20 mA, minimum terminal voltage 12 V at 20 mA, maximum permissible loop resistance 600 Ω) is connected to a PLC analogue input card with a 250 Ω shunt. The signal passes through a Zener barrier whose series resistance is 300 Ω.

1,139 words, about 6 min 5

Direct-on-line start of a 1,250 kW motor on a 6.6 kV bus with a 10% dip limit

A 6.6 kV, 50 Hz plant is fed from an 11/6.6 kV, 5 MVA transformer of 7.5% impedance; the 11 kV bus has a utility fault level of 250 MVA. A new 1,250 kW, 6.6 kV, four-pole motor driving a centrifugal pump is to be started direct-on-line.

1,048 words, about 5 min