Steelman Industries recognizes the need for addressing harmonics in an electrical system that will soon be fitted with power factor correction capacitors. To conclusively determine whether or not a system needs filters along with the capacitors, a harmonic study must be done. The following summary of IEEE 519 1992, is a good start to understanding harmonics in an electrical system as they relate to applying power factor correction capacitors. In order to obtain the warranty (page 16), a harmonic study with the following readings must be provided to Steelman Industries at the time of order.
Harmonic Limits in Electric Power Systems
(IEEE 519 1992)
Harmonic limitations have been established by IEEE 519 1992 for the following reasons:
- To limit the damage to power factor correction capacitors and harmonic filter systems caused by excessive harmonics.
- To prevent series or parallel resonance in the electrical system.
- To keep the level of harmonics at the PCC (Point of Common Coupling) from being excessive and distorting the system voltage and damaging other equipment on the system
The PCC is defined as the electrical connecting point or interface between the utility distribution system and the customer’s electrical distribution system.
The harmonic voltage limitations set forth by IEEE 519 1992 are:
- Maximum Individual Frequency Voltage Harmonic: 3%
- Total Harmonic Distortion of the Voltage: 5%
The harmonic current limitations are defined in the following table:
Maximum Harmonic Current Distortion in Percent of IL
|120 Volt through 69KV|
|Individual Harmonic Order (Odd Harmonics)|
|ISC/IL||h < 11||11 < h < 17||17 < h < 23||23 < h < 35||35 < h||TDD|
|20 < 50||7.0||3.5||2.5||1.0||0.5||8.0|
|50 < 100||10.0||4.5||4.0||1.5||0.7||12.0|
|100 < 1000||12.0||5.5||5.0||2.0||1.0||15.0|
ISC = Maximum short-circuit current at PCC.
IL = Maximum demand load current (fundamental) at the PCC
h = Harmonic number
Even harmonics are limited to 25% of the odd harmonic limits.
TDD refers to Total Demand Distortion based on the average demand current at the fundamental frequency and measured at the PCC (Point of Common Coupling.)
* All power generation equipment is limited to these values of current distortion regardless of ISC/IL value.
Harmonic levels that exceed these recommended values should be addressed through harmonic filtering. Failure to address these harmonic issues may lead to problems on the electrical distribution system, such as those detailed above. Refer to the latest revision of IEEE 519 for more details.