Three Phase Load Balancing - It Can Be a Moving Target

Conventional industrial three phase systems have traditionally been balanced by physically reconfiguring loads at the switchboards. However, this is not always effective – especially if the site load profile changes during the day.

The challenge is usually associated with single phase loads which change according to the operation of the premises as the day progresses.

One such sector where load balancing can present challenges is the supermarket store.  It’s energy consumption is highly variable depending on the time of the day.  For example, whilst most are sleeping, the bakery department swings into life at 4:00AM , with its mix of single and three phase equipment in full use.

As the day progresses, the other departments begin to come on line – it’s now 6:00AM and the instore café is also being set up for the day ahead - also using single phase and three phase equipment ranging from espresso coffee machines, heated food cabinets to small refrigerated displays etc.

The lighting load profile in the various behind the scenes store rooms will also be changing  e.g. the grocery, fresh produce, butchery departments is switched on or off depending on the time of the day to suit loading in and loading out of stock.

It’s now 7:00AM and the doors are opened, the main store lighting is switched on and the store is ready to trade through to midnight.  However, as the afternoon approaches the bakery department is winding down and setting up in preparation for yet another early start – and another day of the ever changing load rollercoaster ….

The Power Electronics inverter based Static Var Generator (SVG) not only accurately manages and compensates for Power Factor to maintain a desired setpoint e.g. 0.99 Cos phi; it also has the ability to automatically balance the power system to ensure balanced loading on the site supply transformer, thus resulting in optimum transformer efficiency, and to keep neutral conductor loading to a minimum.

To further complicate matters, many of the single phase loads are now “non-linear” loads, meaning that they are not purely resistive or inductive loads and incorporate power supplies e.g. LED light drivers, electronic ballasts, computer switch mode power supplies, UPS units, air conditioner inverters  etc.

These non-linear single phase loads generate neutral harmonics that may result in neutral conductors overheating, power supplies failing, and electronic equipment mal-performing.

The Advanced Static Var Generator (ASVG) is ideal for applications where high proportions of non-linear three phase and single phase loads are present and accurate power factor compensation is required.  Both the SVG and ASVG units are being used across the New Zealand supermarket sector.

Features of the ASVG include;

  • Sub-cycle and accurate Power Factor control
  • Current Balancing
  • Harmonic mitigation (to the 11th harmonic)

Below is an actual screen shot of a supermarket installation comprising 2 x 100kVAr SVG Units i.e. this is one half of the system;

screen shot of a supermarket installation comprising 2 x 100kVAr SVG Units

For more information, get in touch with us.