Energy Efficient Utilization

Motors consume the bulk of industrial electricity, so a few percent efficiency improvement yields large lifetime savings. Life-cycle cost compares the higher purchase price of an efficient motor against the present worth of its lower running losses.

Variable-frequency drives (VFDs) on fans and pumps exploit the cube law (power ∝ speed³): a small speed reduction gives a large energy saving compared with throttling. The BEE star label guides appliance selection in India.

Relation 1 —

Write this relation with symbols exactly as in Art & Science of Utilisation of Electrical Energy — H. Partab before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

Write this relation with symbols exactly as in Art & Science of Utilisation of Electrical Energy — H. Partab before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

Write this relation with symbols exactly as in Art & Science of Utilisation of Electrical Energy — H. Partab before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Annual energy loss cost = loss power × operating hours × tariff. Summing the discounted losses over the motor’s life and adding the purchase price gives the life-cycle cost; the option with the lowest total is chosen even if its first cost is higher.

Demand-side management shifts flexible loads away from peak periods, reducing the maximum-demand charge and easing the grid; time-of-day tariffs incentivise this.

Non-linear loads (drives, rectifiers) inject harmonics that increase transformer and cable losses and can require de-rating; filters or higher pulse-number converters mitigate them.

State assumptions explicitly before using any relation for energy efficient utilization — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In Electrical Utilization viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in Electrical Utilization papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to energy efficient utilization.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Energy Efficient Utilization appears in industry and railways. In Indian electrical curricula this topic is tested because it connects theory to traction, illumination, and heating.

GATE and semester exams often combine energy efficient utilization with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use energy efficient utilization?" — answer with a lab, mini-project, or plant visit example if possible.

• Comparing only purchase price, ignoring lifetime energy cost
• Forgetting the cube law when estimating VFD savings on pumps/fans
• Neglecting harmonic losses from non-linear loads
• Using rated efficiency at part load (efficiency drops at light loading)

Before attempting energy efficient utilization problems, confirm you can:

1. IE3/IE4 high-efficiency motors; VFD for variable loads
2. Star rating for appliances (BEE India labels)
3. Harmonic distortion from non-linear loads increases losses

Revise the solved examples in Art & Science of Utilisation of Electrical Energy — H. Partab and one previous-year GATE or university paper for this unit.