Tariff and Power Factor Improvement

A low, lagging power factor means the same real power draws more current and kVA, raising I²R losses and the utility’s kVA-based demand charge. Shunt capacitors supply the lagging reactive power locally, reducing the kVAr drawn from the supply.

The capacitor bank rating to improve from an initial angle φ₁ to a target φ₂ (at the same real power P) is Q_c = P(tanφ₁ − tanφ₂). Tariffs often penalise pf below 0.9.

(improvement from φ₁ to φ₂)

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 —

(improvement from φ₁ to φ₂)

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.

After correction the new kVA = P/cosφ₂ is lower, so the maximum-demand charge falls; the payback of the capacitor bank is the annual saving in demand and energy-loss charges.

Place capacitors close to the inductive load to relieve the whole feeder, or at the substation for bulk correction. Automatic switched banks track the varying load to avoid over-compensation.

Over-correction produces a leading power factor, which can raise voltage and is also penalised; the target is usually just below unity (e.g. 0.95–0.98).

State assumptions explicitly before using any relation for tariff and power factor improvement — 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 tariff and power factor improvement.
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.

Tariff and Power Factor Improvement 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 tariff and power factor improvement with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use tariff and power factor improvement?" — answer with a lab, mini-project, or plant visit example if possible.

• Using cosφ instead of tanφ in the capacitor kVAr formula
• Forgetting real power P stays constant during correction (only reactive changes)
• Over-correcting into a leading power factor
• Confusing kVA (apparent) with kW (real) demand

Before attempting tariff and power factor improvement problems, confirm you can:

1. Most utilities bill on kVA demand — low pf increases cost
2. Capacitors at load vs at substation
3. Avoid over-compensation leading pf

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.