Why is Harmonic Study and Analysis Important for Companies in New Zealand | Carelabs

Harmonic distortion is one of the few technical matters that can become a commercial problem with your electricity network before it becomes an engineering problem inside your plant. For a New Zealand business, the connection relationship is often what makes a study necessary.

Your distortion is not only your business

Voltage distortion on a distribution network is shared. Every customer connected to the same part of the network experiences the voltage that results from everyone's injected harmonic current flowing through the network impedance. One large distorting load degrades supply quality for its neighbours.

Because of that, the network operator has both an interest and a mechanism for managing it. The framework generally used in New Zealand and Australia for allocating harmonic emission to individual customers is AS/NZS 61000.3.6, which sets out how emission limits for distorting loads connected at MV and HV are assessed and allocated.

The principle is proportional allocation. The network has a total distortion budget that keeps supply quality acceptable, and each connected customer is allocated a share of that budget broadly in proportion to their agreed capacity relative to the capacity of the supplying network. Your permitted emission is therefore not a fixed universal number. It depends on how large you are relative to the part of the network you connect to.

Smaller equipment connected at low voltage is dealt with differently, through product-level standards such as AS/NZS 61000.3.2 for equipment drawing up to 16 A per phase, which place the obligation on the equipment rather than the site.

Why growing businesses get caught

The allocation model produces a situation that regularly surprises people. Your emission limit is tied to your agreed capacity, and your actual emission is tied to your load. Those two can move independently.

A plant that has progressively added drives while its agreed capacity stayed the same has increased emission against an unchanged allocation. Nothing was installed that anyone considered a compliance matter, and the position has moved.

Conversely, a plant seeking a capacity increase may be assessed against the framework at the point of application, sometimes for the first time in its operating life. Discovering an existing compliance problem during an application to expand is a poor moment for it, because it can delay the connection the expansion depends on.

When the question arrives

The connection relationship tends to surface harmonic questions at specific moments:

• A new connection or a capacity increase. Assessment may be required as part of the application, and the lines company may ask for a study before approving.
• Adding significant non-linear load. New drive lines, UPS capacity, induction heating or electrolysis.
• Installing distributed generation. Solar inverters are non-linear sources and also change the impedance the site presents, shifting any existing resonance.
• A query from the network operator. Where supply quality has degraded in an area, the operator may investigate and identify contributors.
• A neighbouring complaint traced back to a shared point of supply.

In each case the useful position is having measured already. A documented measurement puts you in a position to answer; its absence means the answer has to be established under time pressure.

The internal costs run alongside

The connection question tends to prompt the study, but the internal case is usually the larger one.

Transformer eddy current losses rise roughly with the square of harmonic order, so distorted load heats a transformer well beyond what its RMS loading suggests, and it may need derating — meaning capacity you have already paid for cannot be used. Triplen harmonics add rather than cancel in the neutral of a three-phase four-wire system, so neutral current can approach or exceed phase current in a conductor sized on the opposite assumption. Capacitors fail repeatedly. Motors run hot and bearings wear early. Electronic trip units and RCDs operate on a waveform that is not what their measurement assumes, producing tripping that maintenance cannot reproduce.

Each of these is typically investigated as a separate incident, which is exactly why the shared cause survives so long.

What a study settles

It establishes your measured position against the limits that apply at your point of common coupling, identifies which loads are responsible, and determines whether a planned change will cause a problem before the equipment is bought.

A material share of studies conclude the installation is within limits and the recurring fault has a different cause. That is a useful outcome, because it stops money being spent on the wrong remedy — which in practice usually means another capacitor bank, then a transformer upgrade, neither of which addresses what is actually happening.

Related reading: harmonic analysis in power systems covers how distortion behaves on New Zealand networks and how the measurement and modelling are carried out.