Ques. Is the condenser pressure ahead or behind the current and why?
Ans. It is ahead of the current. The condenser pressure, when the condenser is discharged being zero, the current enters at maximum velocity as at A in fig. 1,327, and gradually decreases to zero as the condenser pressure rises to maximum at B, this change taking place in one-quarter period. Thus the condenser pressure, which opposes the current, being at a maximum when the current begins its cycle is 90° ahead of the current, as is more clearly seen in the last quarter of the cycle (fig. 1,327).
Fig. 1,328.—Current and pressure curves, showing phase relation between the current, condenser pressure, and impressed or capacity pressure necessary to overcome the condenser pressure. The capacity pressure, since it must overcome the condenser pressure, is equal and opposite to the condenser pressure, that is, the phase difference is 180°. The condenser pressure being 90° ahead of the current, the impressed pressure is 90° behind the current.
Ques. What is the phase relation between the condenser pressure and the pressure applied to the condenser to overcome the condenser pressure?
Ans. The pressure applied to the condenser to overcome the condenser pressure, or as it is called, the capacity pressure, must be opposite to the condenser pressure, or 90° behind the current.
In circuits containing resistance and capacity, the total pressure impressed on the circuit, or impressed pressure, as it is called, is made up of two components:
1. The active pressure, or pressure necessary to overcome the resistance;
The active pressure is in phase with the current.