Power Quality
A harmonic distortion survey at the point of common coupling (PCC) is a measurement campaign that captures the voltage and current harmonic content at the electrical interface where an entire facility connects to the utility or the system that serves it. IEEE 519-2022 sets its limits at that point for the whole installation: they apply to the installation's contribution as seen from the PCC, not to any one drive, rectifier or other piece of equipment inside the facility, and readings taken inside the facility are not compared with them. The form records voltage distortion (total harmonic distortion and the largest individual harmonic, line-to-neutral) and current distortion (total demand distortion, the largest order in each order band, the even orders 2, 4 and 6, and any dc offset), along with interharmonics and other informative measurements that are recorded but never graded. Readings are entered at three percentile statistics - the weekly 95th, the weekly 99th (current only) and the daily 99th - so acceptance is graded at each statistic rather than on a single spot reading.
A supply system and every customer on it share the same voltage at the PCC; an installation that injects too much harmonic current distorts that voltage for everyone on the same segment of the system. IEEE 519-2022 answers this with limits set at the PCC: voltage distortion is held below the voltage limits for the PCC voltage, and the installation's current distortion, expressed as total demand distortion (TDD) in percent of the maximum demand load current, is held below the current limits selected by the PCC voltage and the short-circuit ratio Isc/IL. The standard describes these values as design guidance that is not binding in every case; this form grades them as written and names IEEE as the source of every graded value. A survey before a major load change, after a rectifier or drive retrofit, or as part of a power-quality investigation shows whether the installation sits within those limits or whether mitigation - a harmonic filter, retuning of a capacitor bank, or a rearrangement of nonlinear loads - is needed, and the recommended mitigation is recorded on the form.
Acceptance: a baseline survey is run before a new rectifier, variable-frequency drive or other known harmonic-producing load is placed in service, or when a facility with substantial nonlinear loads has its first power-quality survey; a rectifier acceptance record can link this survey's result instead of re-entering it. Maintenance: the survey is repeated on the interval the facility's power-quality program assigns, after a process change that adds nonlinear loads, or when nuisance tripping or overheating points to harmonic distortion. The observation period is set by the statistics IEEE 519-2022 uses: the weekly percentiles need a full seven-day period and the daily 99th percentile needs a full day, so a survey of at least one week is needed for a complete record. A shorter survey is recorded with a review issue and the record is indeterminate, and a spot reading is informational only. Where the survey runs longer than one period, the highest value among the complete periods is entered.
The analyzer is connected at the PCC itself; a reading taken anywhere else is recorded but cannot be graded. The form asks for an analyzer that meets IEC 61000-4-30 Class A and the harmonic measurement method of IEC 61000-4-7, measuring to at least harmonic order 50, with a 12-cycle window at 60 Hz or a 10-cycle window at 50 Hz, aggregation at 3 s and 10 min, and percentiles taken by linear interpolation. The analyzer make, model, serial number and calibration date are recorded, together with the observation start and end dates and times (optionally with UTC offsets, so a daylight-saving change cannot add or remove an hour); the observation period is computed from them. Before the readings are graded the form settles applicability: whether DER or inverter-based resources are present at the installation and, if so, whether combined rated generation reaches 10 percent of annual average load demand, in which case the current limits come from IEEE 1547 or IEEE 2800 and the current rows are not graded here. The PCC nominal line-to-line voltage, the maximum short-circuit current Isc from the short-circuit study or utility data, and the maximum demand load current IL (the average of the monthly maximum demand over the last 12 months, the months available, or the projected first-year demand of a new installation) are entered in amperes and the form computes Isc/IL, which selects the current table and row. The weekly 95th and 99th percentiles come from the 10 min values over the week and the daily 99th from the 3 s values over each day; the resulting readings are entered as percent of rated voltage for the voltage rows and percent of IL for the current rows, and the form computes each limit and margin.
Identification: facility, PCC designation, serving utility or system owner, service transformer rating and voltage, the nonlinear loads served, the largest converter pulse number and the survey date. Applicability: whether the measurement point is the PCC, whether DER or IBR is present, combined site rated generation and annual average load demand with the records they come from, and whether the installation is a power generation facility with no other applicable standard. PCC data: nominal line-to-line voltage, Isc with its source document and revision, IL with its basis, and the computed Isc/IL. Instrument and window: analyzer identity and calibration date, Class A conformity, highest order measured, measurement window, aggregation, observation start and end, and the computed observation period. Voltage distortion: the measurement connection (line-to-neutral or line-to-line), any HVDC terminal allowance with its basis, voltage THD and the largest individual voltage harmonic with its order, at the weekly 95th and daily 99th percentiles. Current distortion: TDD, the largest order in each band and the largest of even orders 2, 4 and 6, each at the weekly 95th, weekly 99th and daily 99th; any Table 5 claim with the readings for the claimed orders; dc offset in the ac current; the largest interharmonic current and its frequency. Informative measurements (TIF, I-T product, notch depth and area) are recorded when taken, never graded. The engineer's notes, recommended mitigation, ambient conditions, test equipment, comments and deficiencies complete the record.
Voltage is graded whatever the generation status: line-to-neutral readings in percent of rated voltage must be below the IEEE 519-2022 voltage limit for the PCC voltage at the weekly 95th percentile and below 1.5 times it at the daily 99th; a reading equal to the limit fails, and line-to-line readings are recorded only and raise a review issue. Above 161 kV an HVDC terminal allowance may be claimed only when both the cause and its attenuation are shown. Current is graded only when the Figure 1 decision keeps the current limits in this standard, which is the case with no DER or IBR at the installation, or with combined rated generation below 10 percent of annual average load demand; otherwise the current limits come from IEEE 1547 or IEEE 2800, the current rows show no limit and only the voltage rows are graded. Where they apply, TDD in percent of IL must be below the table value selected by the PCC voltage and Isc/IL at the weekly 95th, below 1.5 times it at the weekly 99th and below 2.0 times it at the daily 99th; the largest order in each band is held to the same factors against its band value, and even orders 2, 4 and 6 to half the first-band value. A power generation facility with no other applicable standard is held to the first row regardless of Isc/IL. A Table 5 claim earns a higher individual-order multiplier only when every claimed group is recorded below its 25 percent value; TDD is never multiplied. Any dc offset found at the PCC fails. Interharmonics, telephone influence factor, I-T product and notching are never graded. Grading also depends on prerequisites: a reading at the PCC, a Class A analyzer measuring to order 50, an observation period long enough for the statistic, a determinable current row and every in-scope reading entered; a missing item leaves the record indeterminate with a review issue rather than a pass. The limit values themselves are in IEEE 519-2022 and are not reproduced on this page.
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