The Role of Distributed Generation in Power Quality and Reliability

Figure A.1
Sinusoidal Waveform of Alternating Current
When there are disturbances in the power system as will be defined in the next section, this ideal
waveform becomes distorted or the voltage and current get out of phase with each other. When
these distortions exceed certain levels, equipment outages or damage may result. The
Information Technology Industry has published a curve that defines the region in which
electronic equipment can operate. 7 The ITI Curve is shown in Figure A.2. The curve shows that
electronic equipment have steady state voltage tolerances of 90-110% of nominal voltage.
Equipment can operate normally with an 80-110% voltage excursion of less than 10 seconds, 70-
120% for less than half a second. Systems can operate normally with a complete loss of voltage
lasting for only one or two cycles. Equipment can tolerate surges of 200% or more in voltage
that last 1 millisecond or less, though such extremely short duration effects are not typical of
power system disturbances.
The nature of power disturbances that cause power characteristics to fall outside this normal
operation zone and the associated protection equipment that can be used to protect customers
from their effects are described in the next section.
7 ITI (CBEMA) Application Note, Information Technology Industry Website http://www.itic.org/technical/iticurv.pdf
Appendix A A2 The Role of DG in Power Reliability