SECTION
NON-LINEAR LOAD ISOLATION
®
TRANSFORMERS
ACME ELECTRIC
•
MILWAUKEE, WI
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800.334.5214
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acmetransformer.com
42
1. Linear loads
Loads where the current waveform conforms to the waveform
of the applied voltage. Or loads where a change in current
is directly proportional to a change in applied voltage. For
example:
• Resistance heating
• Incandescent lighting
• Water heater
2. Non-linear loads
Loads where the current waveform does not conform to the
waveform of the applied voltage. Or loads where a change in
current is not proportional to a change in applied voltage.
Examples are:
• Computer power supplies
• Motor drives
• Fluorescent lighting
Non-linear loads produce non-sinusoidal current or voltage
waveforms.
3. Sinusoidal current or voltage
This term refers to a periodic waveform that can be expressed
as the sine of a linear function of time.
4. Non-linear currents or voltages
A waveform of current or voltage which cannot be expressed
as the sine of a linear function of time. A non-linear load would
result in a non-sinusoidal current or voltage.
5. Harmonic
A sinusoidal waveform with a frequency that is an integral
multiple of the fundamental 60 Hz frequency.
60 Hz
Fundamental
120 Hz
2nd Harmonic
180 Hz
3rd Harmonic
240 Hz
4th Harmonic
etc.
Current waveforms from non-linear loads appear distorted
because the non-linear waveform is the result of adding
harmonic components to the fundamental current.
6. Triplen harmonics
Odd multiples of the 3rd harmonic
(3rd, 9th, 15th, 21st, etc.).
7. Harmonic distortion
Non-linear distortion of a system
characterized by the appearance in the output of harmonic
currents (voltages) when the input is sinusoidal.
8. Voltage harmonic distortion (VHD)
Voltage harmonic distortion is distortion caused by harmonic
currents flowing through the system impedance. The utility
power system has relatively low system impedance, and the
VHD is very low. But, VHD on the distribution power system
can be significant due to its relatively high system impedance.
9. Total harmonic distortion (THD)
The square root of the sum of the squares of all harmonic
currents present in the load excluding the 60 Hz fundamental.
It is usually expressed as a percent of the fundamental.
10. Root mean squared current
(or voltage) RMS
1:
The vector sum of the fundamental current and the total
harmonic distortion.
2:
Square root of the sum of the squared value of the
fundamental current and the squared value of the total
harmonic distortion.
11. Eddy currents
Currents flowing in a conducting material in the presence of a
time varying magnetic field. These currents are in addition to
the current drawn by the load.
12. Eddy current losses
Power dissipated due to eddy currents. Includes eddy current
losses in the core, windings, case and associated hardware of
a transformer.
13. Stray losses
A term used to express the difference
between the measured alternating current losses on a
transformer and the direct current (DC) losses (I
2
R). Stray
losses include eddy losses. Stray losses are usually
expressed as a percent of the direct current (DC) losses.
14. Per unit value
1:
Percent value divided by 100.
2:
The ratio of two components of a system.
15. Harmonic spectrum “K” factor
The sum of the product of each harmonic current squared
and that harmonic number squared for all harmonics from
the fundamental (60 Hz) to the highest harmonic of any
measurable consequence. When the “K” factor is multiplied
by the stray losses of the transformer, the answer represents
the losses in the transformer caused by harmonic currents.
When these losses are added to the I
2
R losses of the
transformer, the total load losses are known. The “K” factor for
a linear load without harmonics is one (1).
