Engineering reference

Standards & engineering reference

A short, practical reference to the power-quality and transformer standards we engineer to, and a glossary of the terms that come up when specifying magnetics, filters and conversion equipment. General engineering reference — the rating and configuration of any ACE unit are confirmed against your requirement on enquiry.

Standards

Standards we engineer to

IEEE-519

Recommended practice for harmonic control in power systems. Sets limits for voltage and current harmonic distortion at the Point of Common Coupling — commonly a 5% voltage-THD ceiling, with current-distortion (TDD) limits that depend on the short-circuit-to-load ratio. We size harmonic filters and multi-pulse rectifiers to help installations meet it.

IEC 61000

Electromagnetic compatibility (EMC). The 61000-3 series limits harmonic-current emissions and voltage fluctuations; 61000-4 defines testing and measurement techniques — relevant to filters, drives and power-quality equipment.

IEC 60076

Power transformers — general requirements, temperature rise, insulation levels and test procedures. Part 11 specifically covers dry-type transformers.

IEC 61869

Instrument transformers — the modern standard for current and voltage transformers (superseding IEC 60044): accuracy classes, rated burden and thermal/dynamic ratings.

Indian Standard (IS) equivalents — for example IS 2026 (power transformers) and IS 2705 (current transformers) — apply for the Indian market and are quoted on request. Standards references are for guidance; the applicable edition and limits depend on your network and application.

Glossary

Glossary of terms

Total Harmonic Distortion (THD / THDi): The ratio of the RMS of the harmonic components to the fundamental, as a percentage. THDi is current distortion; THDv is voltage distortion.
Power factor — true vs displacement: Displacement PF is the cosine of the fundamental voltage–current angle; true (total) power factor also accounts for harmonic distortion and is never higher than displacement PF on non-linear loads.
kVA vs kW: kVA is apparent power (volts × amperes); kW is real power. Their ratio is the power factor — equipment is rated in kVA because it must carry the full current regardless of phase angle.
Percentage impedance (%Z / Uk): The percentage of rated voltage needed to drive rated current through a short-circuited winding. It sets the prospective short-circuit current, voltage regulation and suitability for parallel operation.
K-factor: A rating that quantifies a transformer's ability to supply non-linear, harmonic-rich loads without overheating. A higher K-factor means greater harmonic-handling margin.
Vector group: Notation such as Dyn11 describing the winding connections (delta / star / zig-zag) and the phase displacement between primary and secondary.
Pulse number (multi-pulse): The number of DC output pulses per AC cycle in a rectifier (6, 12, 18, 24…). Higher pulse counts cancel more input-current harmonics, easing IEEE-519 compliance.
Harmonic order: An integer multiple of the fundamental frequency — the 5th harmonic is 250 Hz on a 50 Hz system. Non-linear loads draw characteristic harmonic orders.
Point of Common Coupling (PCC): The point in the supply network where an installation connects and could affect other users — the reference point for IEEE-519 harmonic limits.
Derating: Reducing a device's permissible rating for non-ideal conditions — high ambient temperature, altitude or harmonic loading — to keep internal temperatures within limits.
Detuning: Adding a series reactor to a power-factor-correction capacitor bank to shift its resonant frequency below the lowest significant harmonic, preventing harmonic amplification.

Selection

Choosing the right equipment

Passive or active harmonic filter?

Passive filters are rugged, maintenance-free and low-cost — best for steady, predictable harmonic loads with a defined compliance target. Active filters measure and inject cancelling harmonics in real time, adapt to changing or mixed loads, correct multiple orders and add power-factor correction — chosen where the load varies widely, or where guaranteed IEEE-519 compliance and future expansion matter more than first cost.

Line reactor or detuned reactor?

A line (AC) reactor limits current and attenuates harmonics on the supply side of a drive or rectifier. A detuned reactor is sized in series with a power-factor-correction capacitor bank to shift its resonant frequency below the lowest significant harmonic — use it whenever capacitors are applied on a harmonic-rich network, to prevent harmonic amplification and capacitor overload.

dV/dt filter or sine-wave filter?

A dV/dt filter slows the voltage rise and clips reflected-wave overvoltage spikes to protect motor-winding insulation on short-to-medium cable runs — low cost, low loss. A sine-wave filter produces a near-sinusoidal output for long motor cables, older motors, or wherever a clean waveform (not just spike protection) is required.

6-pulse or multi-pulse rectifier?

A 6-pulse rectifier is the simplest and lowest-cost, but draws high input-current harmonics. 12-, 18- or 24-pulse configurations with a phase-shifting transformer cancel progressively more harmonics, easing IEEE-519 compliance at the PCC with little or no added filtering — chosen for high-current process loads under strict harmonic limits.

What decides the transformer rating I need?

Primarily the load (kVA), the primary and secondary voltages, frequency and phase, plus duty cycle, cooling/enclosure and any harmonic (K-factor) or special-tap requirements. Share these and we engineer the unit to match — the nameplate rating is the rating you get.

General guidance — the right choice depends on your network and load. Send your single-line diagram and duty cycle and our engineers will recommend a configuration.

Specifying a unit?

Send us your ratings, application and the standards you need to meet — our engineers reply within one business day.

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