Blog

An on-load tap changing transformer corrects voltage while the unit stays live, and the tap position table is where its regulation range is stated. This article walks through a nine-position ±4×2.5% table line by line, explains why currents appear only in the rated row, separates on-load from off-circuit tapping, and lists what to put on the enquiry so the quoted range matches the network.

An intelligent universal circuit breaker is usually ordered from a short specification: a current rating, a voltage, and a breaking capacity. Those three numbers are necessary and not sufficient. This article explains why the frame size is a mechanical platform rather than the current the breaker will run at, what Icu, Ics and Icw each measure and which one governs the design, how the trip unit grade changes what the breaker can protect, and which operating conditions — ambient temperature, altitude, protection degree, installation category and mounting tilt — belong on the enquiry rather than in the maintenance procedure.

Adding a second transformer beside an existing one looks like the cheapest route to more capacity. It often is, but only when four conditions line up exactly: turns ratio and tap position, vector group, impedance voltage and phase sequence. Where they do not, the result is not reduced capacity but circulating current flowing between the units before any load is connected, heat that appears with no explanation, and protective devices that operate without a fault. This article sets out each condition, what happens when one of them is not satisfied, and a five-step check for a proposed pairing that can be carried out before energisation.

A transformer feeding a plant full of variable frequency drives can run dangerously hot while a clamp meter reads less than its rated current. Harmonic currents are the reason a transformer k-factor exists as a separate specification. This article explains why non-linear loads heat a transformer more than their current suggests - eddy current losses rise roughly with the square of frequency, so the extra heat appears in the windings while the fundamental current stays below the kVA rating - what a K-factor rating does and does not guarantee, why neutral conductors need separate attention under triplen harmonics, and how to size for harmonic currents using measured total harmonic distortion, a load profile, a matched K-factor and a derating factor for the real plant room.

A unit ordered for a coastal plant and the same unit installed at 2,500 m are not the same machine in service, even when the nameplate reads identically. Air density falls with height, and thinner air does two jobs less well: it carries heat away from the windings, and it insulates. This article explains what physically changes at height - cooling capacity and dielectric strength - how the altitude correction factor is applied, either by reducing the permissible temperature rise or by raising the insulation requirement, and what should be confirmed on the enquiry: the real site elevation, the reference conditions behind the quoted rating, whether the kVA figure is the sea-level or the corrected value, and the ventilation design at the corrected load.

Transformer selection is usually treated as a single question: what kVA rating do I need? The parameters that cause the most expensive mistakes rarely appear on a quotation. This article explains how ambient temperature and site altitude change the rating a transformer can actually deliver, how the load profile of the plant - continuous versus cyclic duty, future load growth, harmonic content and the cost of oversizing - decides where to sit below the kVA ceiling, and which electrical checks should be completed before the order is placed: vector group, impedance voltage, tap range, insulation class and the written confirmation of derating. Getting these right at the enquiry stage costs one line; correcting them afterwards costs a transformer.