GE 269Plus Instruction Manual page 199

E ASYMMETRICAL STARTING CURRENT
APPENDIX EE ASYMMETRICAL STARTING CURRENT
It is commonly known that current lags voltage by 90° when a voltage is applied to a purely inductive load. As
can be seen from the figure below, if the AC voltage is applied at a peak, the current will rise from 0 A to its
peak, 90° later in time. It may also be seen that during the time voltage completes a positive or negative half-
cycle, current has made the transition from one peak to another.
Thus, as shown below, if voltage is applied at a zero crossing, current will make the transition from minimum
peak to maximum peak. Current of course, cannot instantaneously be at its minimum value, it must begin at
zero.
Thus it rises from zero to a value that is equal to 2 times the peak value (2 × I
Figure E–2: APPLYING VOLTAGE AT A ZERO CROSSING ON AN INDUCTIVE LOAD
Depending on when the voltage is applied, the RMS current may vary by as much as 1.73 times.
where I
is current when voltage is applied at a maximum, or the symmetrical current.
RMS
GE Power Management
Courtesy of NationalSwitchgear.com
Figure E–1: VOLTAGE & CURRENT ON AN INDUCTIVE LOAD
I
DC
RMSasymm
2
⇒ (
I
RMSasymm
⇒
I 3 I
RMSasymm
269Plus Motor Management Relay
2 2 2 2
2 I I
AC
RMS RMS
2
2 2 2
)
2 I I 3 I
RMS RMS RMS
RMS
DESCRIPTION
E.1 DESCRIPTION
).
max
E
E-
1