Circuit Master and IEEE-519 Recommendations

The design of the Circuit Master, when properly sized and installed, meets the recommendations of IEEE 519-1992, Sections 10 and 11, and those most commonly referenced in Table 10.3.

The IEEE Std 519-1992 (IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems) is often referenced, but not often well understood. The scope of IEEE-519-1993 clearly states to establish GOALS for the design of electrical systems that contain linear and non-linear loads. It defines the interface between the source and the load as the ‘point of common coupling’ (PCC). It has sections on the problems caused by harmonic currents and voltages, calculation examples, application examples, and the harmonic currents caused by different types of power converters and non-linear loads.

The primary use for IEEE 519, though, is to reference the recommended limits on harmonic currents and voltages in a power system. Section 10 titled “Recommended Practices for Individual Consumers” and Section 11 “Recommended Practices for Utilities” are particularly relevant. Table 10.3 is the most commonly cited (and applicable) table, and is reproduced below:

Current Distortion Table

The titles of these sections of IEEE 519 point out an interesting characteristic that is often overlooked. That is, the standard (or recommended practice) was written to apply to the utility to consumer interface (emphasis added). That interface point (usually where there the revenue meter is installed), is the strict definition of the ‘point of common coupling,’ or PCC. The original purpose of IEEE 519 was to set limits on the harmonic currents a user could inject into the power system, and also set limits on the voltage distortion a power provider could have on the power delivered to a customer. The assumption in IEEE-519 is, if all the users limit their harmonic current injection, the system voltage distortion will be within the accepted limits.

Meeting the requirements defined within IEEE-519 does not mean crossing every t and dotting every i without applying common sense. It is very common to move the PCC from the interface with the power supplier to the point at which a non-linear (harmonic producing) load is connected to a supply bus in the user’s facility. In this circumstance, the issue is no longer the total harmonic current coming from the entire plant, but the harmonic current produced by the non-linear load (like a drive system). In this case, the assumption is by limiting the total harmonic distortion coming from the non-linear load then the overall harmonic distortion at the PCC is also limited. For this to be true, every branch circuit with harmonic distortion must be treated.

Section 11 limits voltage distortion to 5% on systems with voltages less than 69 kV. Again, this applies to the voltage at the PCC, which makes it a responsibility of the utility to deliver relatively clean power. However, this can be applied within a plant to keep each supply bus acceptably clean. Calculation procedure of the voltage total harmonic distortion (THD) is more clear-cut, as a nominal voltage exists for each bus. Moreover, notice there is no intended coordination of the current TDD limits and the voltage distortion limits, as the current limits apply to the user and the voltage limits apply to the supplier. However, when IEEE 519 is applied to the current distortion on a supply bus in a plant, it is almost certain the voltage distortion limits will not be exceeded.

With this understanding, the harmonic filtering and the power factor correction capabilities of the Circuit Master, when properly sized and installed, meet or exceed the limits recommended by IEEE-519-1992, Table 10.3.

Installation on a branch circuit, with distortion on other branch circuits, and the distortion also appears at the utility PCC (meter) does not meet the intent of IEEE-519. In that case, Circuit Master distributors cannot guarantee the installation of Circuit Master on ONLY the branch circuit will meet the IEEE-519 recommendations at the PCC.

Daniel T. Jones, PE
Chief Engineer, RCSI, LLC
Registered Professional Engineer
MD 10992

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