(SEM V) THEORY EXAMINATION 2023-24 ELECTRICAL STANDARDS AND ENGINEERING PRACTICES

SECTION A – Short Answers (2 × 10 = 20)

(a) What is IEC standard in electrical?

IEC (International Electrotechnical Commission) develops international standards for electrical, electronic, and related technologies — ensuring safety, performance, and compatibility across countries.

(b) Risks of not identifying or complying with electrical standards

Safety hazards – shock, fire, equipment damage.      Legal and regulatory violations.

Poor reliability and performance.                            Higher maintenance and downtime costs.

(c) IS codes applicable for electrical works

Some important Indian Standards (IS):

IS 732: Code of practice for electrical wiring installations.    IS 3043: Code of practice for earthing.

IS 2309: Protection of buildings against lightning.   IS 375: Marking and identification of conductors.

(d) Standards used for cables

IS 1554 (Part I): PVC insulated (for voltages up to 1100V).

IS 7098 (Part I–III): Cross-linked polyethylene (XLPE) insulated power cables.

IS 694: PVC insulated cables for domestic wiring.

(e) Standards for transformers

IS 2026 (Part I–IV): Power transformers – general requirements, temperature rise, dielectric tests, etc.

IS 1180 (Part I): Distribution transformers up to 2500 kVA.

(f) Standards for LV and HV switchgears

IS/IEC 60947: Low voltage switchgear and controlgear.

IS 8623: Factory-built assemblies of switchgear and controlgear for voltages up to 1000V a.c.

IS/IEC 62271: For high-voltage switchgear.

(g) What is NBC standard?

NBC – National Building Code of India.
It provides guidelines for building design, fire safety, electrical installations, and energy conservation in buildings.

(h) What are derating factors?

Derating factors are correction coefficients applied to electrical equipment ratings to account for temperature, altitude, grouping of cables, or environmental conditions to prevent overheating and failure.

(i) What is CEA regulation in electrical equipment sizing?

CEA (Central Electricity Authority) Regulations specify standards for load estimation, selection, and sizing of cables, switchgear, and transformers to ensure efficiency and safety.

(j) How do you calculate electrical load capacity?

Load (kW)=Voltage (V)×Current (A)×Power Factor1000\text{Load (kW)} = \frac{\text{Voltage (V)} \times \text{Current (A)} \times \text{Power Factor}}{1000}Load (kW)=1000Voltage (V)×Current (A)×Power Factor​

For total load, sum all individual loads considering diversity factor to avoid overdesign.

SECTION B – Descriptive Questions (Any 3 × 10 = 30)

(a) Electrical Standards Used in India

BIS (Bureau of Indian Standards) – publishes IS codes.          CEA Regulations (2010) – governs safety and performance.

IE Rules 1956 & IE Act 2003 – for electrical installations.         NEC India (National Electrical Code) – standard practices for wiring and protection.

(b) IS 7098 (Part-1):1988 – XLPE Insulated PVC Sheathed Cables

Specifies construction, insulation, and testing of cross-linked polyethylene cables.

Provides voltage grade up to 1100V.

Ensures thermal stability, chemical resistance, and mechanical protection.

(c) IS 2026-1 (2011) – Power Transformer Standards

Temperature Rise: Limits for oil and winding temperature.  Insulation Levels: Defined for each voltage class.  Dielectric Tests: Power frequency and impulse tests for insulation strength.

Short Circuit Withstand: Verifies mechanical and thermal endurance.

(d) National Electric Code (NEC) of India                 Published by BIS as IS SP 30:2011.

Purpose: Ensure safety, reliability, and uniformity in electrical installations.

Covers wiring, grounding, protection, and testing practices.

(e) CEA Regulations for Load Estimation and Equipment Sizing

Defines maximum demand and diversity factor calculations.

Guides cable sizing based on current-carrying capacity.

Specifies short-circuit ratings for switchgear.

Mandates energy efficiency and safety margins.

SECTION C – Long Questions (Any 1 from each)

3(a) Electrical Drawings & Cost Estimation

Includes single-line diagrams (SLD), wiring layouts, panel schedules, and schematic diagrams.
Cost estimation covers materials, labor, taxes, and contingencies — ensures project budgeting accuracy.

4(a) IS 3646-1 (1992) – Interior Illumination

Provides guidelines for illumination levels (lux) for various spaces.

Covers light uniformity, glare reduction, color rendering, and energy efficiency.

Example: Offices (300–500 lux), Classrooms (250 lux), Workshops (750 lux).

4(b) IS 325 (1996) – Three-Phase Induction Motors

Specifies design, testing, and performance parameters.

Covers efficiency, temperature rise, insulation class, and torque characteristics.

Ensures safety and interchangeability.

5(a) Instrument Transformers

Current Transformer (CT): Reduces high current to measurable value for meters and relays.

Potential Transformer (PT): Steps down high voltage for measurement.
Ensures isolation, accuracy, and protection for measurement circuits.

5(b) IS 8623 – LV & HV Switchgear

Specifies construction and testing of factory-built assemblies (panels, busbars, switchboards).
Covers temperature rise, dielectric strength, short-circuit withstand capacity, and IP protection levels.

6(a) Earthing vs Lightning Arrester

(Page 2 of your paper includes a note suggesting to draw both diagrams side by side.)

6(b) Hazard Classification of Electrical Equipment

Zone 0: Explosive gas present continuously.

Zone 1: Likely presence during normal operation.

Zone 2: Unlikely presence, short duration only.
Used in hazardous industries (oil & gas, chemical plants).

7(a) CEA Regulations – Sizing and Selection of Transformers

Capacity based on maximum demand and load factor.

Efficiency and losses within CEA limits.

Cooling system, short-circuit withstand, and temperature rise as per IS 2026.

7(b) CEA Regulations (2010)

Define safety, installation, and maintenance requirements.

Cover earthing, voltage levels, protection systems, and energy efficiency.

Aim to ensure safe operation and reliability in all electrical networks in India.