A dc A-h meter is rated for 15 A, 250V. The meter constant is 14.4 A-sec/rev. The meter constant at rated voltage may be expressed as

The voltage-flux adjustment of a certain $$1$$-phase $$220$$ $$V$$ induction watt-hour meter is altered so that the phase angle between the applied voltage and the flux due to it $${85^0}$$ (instead of $${90^0}$$). The errors introduced in the reading of this meter when the current is $$5$$ $$A$$ at power factors of unity and $$0.5$$ lagging are respectively

A wattmeter reads $$400$$ $$W$$ when its current coil is connected in the $$R$$ phase and its pressure coil is connected between this phase and the neutral of a symmetrical $$3$$-phase system supplying a balanced star connected $$0.8$$ $$p.f.$$ inductive load. The phase sequence is $$RYB.$$ What will be the reading of this wattmeter if its pressure coil alone is reconnected between the $$B$$ and $$Y$$ phases, all other connections remaining as before?

The two wattmeter method is used to measure active power on a three phase, three wire system. If the phase voltage is unbalanced, then the power reading is