Voltage immunity & SEMI F47 disputes.

§1Scope of work

A voltage sag is a brief reduction in RMS voltage between 10% and 90% of nominal, lasting 0.5 cycles to one minute, per IEEE 1159 §4.4. Sags are produced by faults on the utility’s transmission or distribution system (a tree contact on a 138 kV line two counties over can produce a 30% sag across an entire utility’s 23 kV network for the 80-millisecond fault-clearing duration), by motor starting on the customer’s premises (a 250 HP motor starting across-the-line can produce a 15% sag at the supply transformer secondary for two to three seconds), or by transformer inrush following utility-side breaker reclosing.

R-05 work begins with the customer’s process upset log — what equipment tripped, when, and what fault code was logged. The trip events are correlated against the on-site PQ analyzer’s sag log, against the utility’s SCADA records (obtained via subpoena or by cooperative agreement with the utility’s power-quality engineer), and against Vaisala NLDN stroke data where lightning is on the table.

The firm has filed 41 R-05 matters since 2014. The most common finding — about 55% of the docket — is that the sag events were utility-side and that the customer’s process equipment was non-compliant with SEMI F47 or with the ITIC curve. In those matters the engineering question shifts from utility responsibility to in-plant immunity hardening (ride-through inverters, sag compensators, controls with voltage tolerance built in).

§2Sag sources catalogued

• S1 · Utility transmission fault. A fault on the bulk transmission system (typically 138 kV or higher) cleared by the transmission protection in 3–6 cycles. Affects a wide area; the same sag event is logged by many customers on the same utility within a 50-mile radius.
• S2 · Utility distribution fault. A fault on a parallel distribution feeder cleared by the substation breaker in 5–30 cycles. Affects customers on the same substation bus.
• S3 · Distribution feeder reclosing. Multiple sag events at 2–10 second intervals as the utility’s recloser cycles to clear a fault. Distinctive multi-event signature.
• S4 · In-plant motor start. A 1–3 second sag at the supply transformer secondary as a large motor starts across-the-line. Localized to the customer’s premises; not seen by neighbors.
• S5 · Transformer inrush. A 100–500 ms sag following utility-side breaker reclosing onto an unloaded transformer. Characteristic asymmetric current signature.
• S6 · Lightning-induced. Sub-cycle to 3-cycle sag coincident with a documented NLDN stroke within 5 km of the supply feeder. Cross-referenced under R-07.

§3Measurement & classification

The measurement methodology is identical in instrumentation to R-04 (Class A under IEC 61000-4-30) but configured for transient capture rather than steady-state aggregation. The Hioki PQ3198 is set to half-cycle RMS recording with a 15% sag threshold; events are captured to the instrument’s internal memory for retrieval at the end of the survey period. The survey period is typically 30 to 90 days, longer than R-04 because sag events are less common than steady-state distortion and a representative sample requires a longer window.

Each captured event is classified by sag source per §2 above. Classification uses (a) the event’s duration and depth (which constrains source category), (b) the simultaneous capture or absence of capture at sister analyzers at neighboring customers if available, (c) the utility’s SCADA event log, (d) the customer’s motor-start log, and (e) NLDN stroke data. Events that cannot be unambiguously classified are reported as inconclusive; we are explicit about that in every finding.

§4Deliverable & fee

The R-05 deliverable is a sealed PE report with: scope; survey period; instrumentation; event log (classified per §2); SEMI F47 / ITIC compliance map; finding on the source of the disputed events; recommendations on in-plant mitigation where applicable. Fee band $8,500 to $28,000.

§5References