# What is the difference between zero leading and zero lagging?

The armature reaction of an alternator will be completely magnetising when load power factor is

A unity
B zero lagging
D 0.8 lagging


As per my understanding if angle =90 then only magnetizing will be maximum. So by this load power factor cos90 =0 But I am confused about the lagging and leading power factor in this ? How will I decide if its leading of lagging power factor ?

• I'm voting to close this question as off-topic because it's homework and there is no clear attempt at answering or thoughts about what could be the correct answer. Oct 15, 2015 at 17:55
• @Andyaka actually II have logged with my mobile so difficult to type.I have edited the question now Oct 15, 2015 at 18:00

Zero power factor means that the load connected to the alternator is either purely capacitive (zero leading) or purely reactive (zero lagging), therefore, there's no KWatt (real power) consumed by the load.

As you know, the armature mmf (Fa) depends on the armature current (Ia). when the load is purely resistive, (Fa) is 90 electrical degrees behind the field mmf (Ff).

When the load is purely capacitive (zero leading pf), (Ia) advances by 90 degrees, thus (Fa) is in phase with the field mmf (Ff) and in this case it helps in increasing the resultant mmf (Fr). That's why we say it is magnetizing.

• I think you mean "purely inductive". Both capacitors and inductors are reactive. Jun 15, 2016 at 17:04
• Oh yes, sorry, it was a typo
– Abdu
Jun 15, 2016 at 23:07