Power Consumer Energy Metering Concepts
Domain 2: Power Consumer Energy Metering Concepts
This domain checks whether you understand what a consumer meter measures, how primary values relate to meter-registered values, and why multipliers, accuracy class and sealing matter.
Core rules
- A watt-hour meter integrates active power over time; reactive energy may be registered in kvarh and apparent energy in kVAh.
- The meter constant, imp/kWh, defines pulses per unit and is used in testing and electronic registration.
- Accuracy class 1 means error within ±1% under specified conditions; class 2 means ±2%; static meters are covered by IS 13779.
- CT ratio and PT ratio convert secondary meter energy to primary energy: primary energy = meter energy × CT ratio × PT ratio.
- Sealing protects the register and terminal cover; breaking a seal invalidates verification.
Worked example
A CT-operated meter has a 200/5 CT, so the CT ratio is 40. The register advances by 15 kWh. Primary energy = 15 × 40 = 600 kWh. If a PT of 11,000/110 V is also used, its ratio is 100, so primary energy = 600 × 100 = 60,000 kWh. Reasoning: the meter sees secondary quantities; both ratios must be applied once.
Traps that cost marks
- Applying a CT ratio to a direct-connected meter.
- Applying the CT ratio twice.
- Ignoring the PT ratio on high-voltage metering.
- Reading kVAh as if it were kWh.
- Treating accuracy class as a load rating rather than an error limit.