Question

A single-phase energy meter of the induction type is rated 230-V; 10-A, 50- Hz and has a meter constant of 600 rev/kWh when correctly adjusted. If ‘quadrature’ adjustment is slightly ***** so that the lag is 85, calculate the percentage error at full-load 0.8 p.f. lag.

Answer 1

Td depends among other factors, on sin α where α is the angle between the two alternating fluxes.

∴ Td ∝ sin α

If the voltage flux-lagging adjustment is ***** so that the phase angle between the voltage flux and the voltage is less than 90 (instead of being exactly 90) the error is introduced.

Now cos φ = 0.8, φ = cos−1 (0.8) = 3652′

∴ α = 85 − 3652′ = 488′

where it should be = 90 − 3652′ = 538′

∴ error = (sin538 + sin488)/sin538 x 100 = 7%