A commutation notch is a disturbance of the voltage wave that lasts less than half a cycle and starts with polarity opposite to the wave. Annex C of IEEE 519-2022 recommends depth limits (10, 20 and 50 %) and area limits (16,400, 22,800 and 36,500 V·µs at 480 V) for low-voltage systems, depending on the type of system.
Short answer
A commutation notch is a disturbance of the voltage wave that lasts less than half a cycle and starts with polarity opposite to that of the wave, so that it subtracts from it. It is described with two numbers: the depth and the area. Annex C of IEEE 519-2022 (informative) recommends limits for low-voltage systems: depth of 10 %, 20 % or 50 % and area of 16,400, 22,800 or 36,500 V·µs, depending on the type of system.
What a notch is
Clause 3.1 defines the notch as a switching (or other) disturbance of the normal voltage waveform, lasting less than 0.5 cycles, that initially has polarity opposite to the wave. For that reason it subtracts from the normal wave in terms of the peak value of the disturbance. It includes complete loss of voltage for up to 0.5 cycles.
The standard’s definitions to describe it:
- Notch depth: the average depth of the line voltage notch relative to the sine wave.
- Notch area: the area of the line voltage notch. It is the product of the depth, in volts, and the notch width, measured in microseconds.
Figure C.1 of the standard defines the two quantities on the wave: the depth percentage is d/V × 100, with d the depth and V the peak value of the nominal voltage, and the area AN is the product of the width t, in microseconds, and the depth d, in volts.
Where they come from
The definition speaks of a “switching (or other)” disturbance, so Annex C does not tie it to a specific piece of equipment. Clause 1 cites static power converters, rectifiers and drives among the common sources of harmonic currents. Notches are evaluated on the voltage waveform, not with the percentages per harmonic order of the tables in clause 5.
The recommended limits of Table C.1
Annex C.1 recommends limiting the line-to-line voltage notch depth at the PCC as a percentage of the nominal peak voltage. The table gives three columns, according to the type of system:
| Special applications | General system | Dedicated system | |
|---|---|---|---|
| Notch depth | 10 % | 20 % | 50 % |
| Notch area (V·µs) | 16,400 | 22,800 | 36,500 |
The table notes define the terms:
- Special applications: include hospitals and airports.
- Dedicated system: one that supplies exclusively a single user or a specific load.
- Area values: given in volt-microseconds, at rated voltage and current, and developed for 480 V systems.
How to scale the area to other voltages
The Table C.1 area values are for 480 V. To apply them to other voltages they must be multiplied by V/480, with V the system voltage.
An illustrative example, with a voltage of 240 V (half of 480 V, so the factor is 0.5):
| Type of system | Area at 480 V | Area scaled to 240 V |
|---|---|---|
| Special applications | 16,400 V·µs | 8,200 V·µs |
| General system | 22,800 V·µs | 11,400 V·µs |
| Dedicated system | 36,500 V·µs | 18,250 V·µs |
The depth, on the other hand, is already a percentage and is not scaled.
How it is verified
Annex C indicates two paths:
- Direct measurement of the voltage wave with an oscilloscope or a power quality monitor with that capability, where the depth and the area are read according to Figure C.1.
- Simulation, when measuring is not possible. Detailed simulations with advanced models of the supply system and the loads can give approximate waveforms that are used in place of the oscilloscope measurements.
How the instrument is connected and which settings to use depends on each installation, and is not part of what the standard defines.
For a project, the logical sequence is to identify the type of system (special applications, general or dedicated), scale the area to the nominal voltage with the V/480 factor, and compare the measured or simulated depth and area with the two values of the corresponding column. It is advisable to meet both criteria: the table gives one depth limit and one area limit for each type of system.
How they relate to the rest of the standard
The Table C.1 limits are a criterion separate from those of Tables 1 to 4: they are expressed in depth and area, not in percent per harmonic order, and Annex C does not associate them with the percentiles of clause 4.4. A facility with drives or rectifiers may need to check both. The origin of the distortion in this equipment is explained in VFD Harmonics: Effects and Solutions, and electromagnetic compatibility in EMC and Shielding for Variable Frequency Drives.
Notches are a different effect from the harmonics of Table 1 (IEEE 519-2022 Voltage Harmonic Limits at the PCC). In a drive with a six-pulse rectifier they appear together with the current harmonics, and how to raise the limits for those is explained in IEEE 519 Limit Multipliers for Pulse Count and Filters.
We help with your case
At Tiza Group we carry out power quality studies, in Colombia, or elsewhere on request: if your plant has hospitals, airports or sensitive processes supplied near rectifiers and drives, we assess the notches together with the harmonics and define the measures if needed.
Related guides
- IEEE 519 Limit Multipliers for Pulse Count and Filters
- VFD Harmonics: Effects and Solutions
- IEEE 519-2022 Voltage Harmonic Limits at the PCC
- EMC and Shielding for Variable Frequency Drives
- IEEE 519 Harmonic Limits: Key Concepts, PCC and TDD
References
- IEEE Std 519-2022, IEEE Standard for Harmonic Control in Electric Power Systems: clause 3.1 (definitions of notch, depth and area); informative Annex C, C.1, Table C.1 and Figure C.1.
Frequently asked questions
What is the difference between the depth and the area of a notch?
The depth is how far the voltage dips relative to the sine wave, expressed as a percentage of the nominal peak voltage. The area is the product of the depth, in volts, and the notch width, in microseconds, and is expressed in volt-microseconds.
Are the area values valid for any voltage?
The Table C.1 values were developed for 480 V systems. For other voltages, the standard says to multiply them by V/480.
How are the notch limits verified?
Annex C states that they are recommended limits for low voltage, where the area is easily measured with an oscilloscope or a power quality monitor with oscilloscope function. If it cannot be measured directly, detailed simulations of the system and the loads can give approximate waveforms.