TECHNICAL TERMS DEFINED
- 1 kHZ Forward Transfer Impedance - LOWER IS BETTER
- Computer and similar power supply electronic loads are really AC to DC converter loads.
All AC to DC converters draw current in a single pulse during each half cycle of the 60 cycle
sine wave. This pulse of current does not resemble the 60Hz sine wave at all. If the average
(RMS) current value is 5 amps, the peak of each current pulse may be 20 amps. Also, these
current pulses have substantial frequency components in the area of 1 kHz. (The basic
repetition frequency of these pulses is still 60 Hz, but the shape of the pulse while it is
transferring energy contains the 1 kHz frequencies.) If a power conditioner is to deliver energy
to the converter it must transfer this energy from the utility company (wall socket) to the load
as efficiently as possible. Any impedence in the power conditioner at the 1 kHz frequency will
impede that transfer.
- Distortion - LOWER IS BETTER
- This is a measure of the change in the waveform introduced by the power conditioner
or UPS. Ideally, the output waveform should exactly match the input wavform, a distortion of
0%. Oneac products introduce less than 1% THD (total harmonic distortion) when measured
with a resistive load.
- Efficiency - HIGHER IS BETTER
- Energy wasted as heat or audible noise reduces efficiency from the ideal of 100%. No
electronic equipment is 100% efficient, but some can get very close. The cost of this wasted
energy can be calculated and used to justify the higher cost of a more efficient unit.
- For example, assume that energy costs 7¢/kilowatt-hour and a 10kVA unit is being
considered. At 90% efficiency, 10% or 1kVA is being wasted.
- 1kVA x .07/kilowatt-hour x 24 hours/day x 365 days/year = $613.20/year
- Increasing the efficiency to 95% will reduce the wasted energy to 5% or ½kVA.
- ½kVA x .07/kilowatt-hour x 24 hours/day x 365 days/year = $306.60/year
- Inrush and Surge Current Rating - HIGHER IS BETTER
- Electronic loads generally draw several times steady state current immediately after
they are turned on. During the 1st ½ cycle of operation, many loads require an inrush
of current up to 20 times their steady state current. A surge current is then drawn that falls
off to the steady state value during the following several cycles up to several hundred cycles,
depending on the characteristics of the load. (For example, rotating machinery such as pumps
and large disc drive motors tend to draw significant current for several seconds as the motor
comes up to speed.)
- The inrush rating specifies the peak current that can be delivered to the load during the
1st ½ cycle.
- The surge current rating specifies the maximum RMS current that can be delivered to the
load during the following 1 second (60 cycles) and 5 seconds (300 cycles).
- These current levels are available at any time during system operation. If these ratings
are exceeded, the unit's circuit breaker will turn the unit off with no adverse effects.
- Load Current Rating
- The maximum steady state RMS current that can be supplied to the load. Operation up
to this rating is both safe and reliable; oversizing is NOT required. If the unit is overloaded,
the circuit breaker will turn the unit off with no adverse effects. Drawing less than the rated
current has no effect on performance.
- Load Power Factor - WIDER RANGE IS BETTER
- Power factor is a measure of how a piece of equipment uses electrical power. A pure
resistive load has a power factor of 1.0 and will not stretch the capabilities of a power
conditioner or UPS. A power factor of .5 leading or .5 lagging can severely strain some
power conditioners or UPS systems. Oneac systems can handle a range of from .3 leading to
.3 lagging.
- Load Regulation - LOWER IS BETTER
- The average (RMS) output voltage of a power conditioner will usually change with a large
change in the load. This specification promises that the power conditioner output will change
by no more than the stated % when a resistive load suddenly changes from 10% to 100% of
the rated load.
- Load Regulation Response Time - LOWER IS BETTER
- For a power conditioner or UPS to not distort the output sine wave it must respond
rapidly to changes in the load and its response must not create any additional electrical
noise. A response time of 2 msec to a change in the load of 50% is fast enough for almost all
applications. Furthermore, the Oneac output will not overshoot or undershoot as a result of
the load change.
