The need for efficient voltage control is particularly important for remote mining sites, but also for sites where frequent island-operation may be necessary.
Frequently these sites have stand-by or permanent motor generator sets.
Depending on the type of loading the generator will be rated appropriately for standby, limited time, prime, or continuous running with the latter applying to island sites, far removed from the main grids.
Almost invariably island grids are not stiff giving rise to voltage as well as frequency instability.
It is therefore sensible to segregate loads, connecting those requiring voltage stability to environmentally-suitable local voltage regulators, such as the TSi VRx series.
This can be a much more economical solution than oversizing local generation facilities in order to obtain local network stability.
Isolated generators, when compared to the grid power distribution systems in terms of frequency stability, impedance, power quality, voltage regulation, or transient response have inferior characteristics.
As a point of comparison, a typical 500 kVA distribution 11 kV/415 V transformer will have leakage reactance of perhaps as high as three or four per cent.
A typical 500 kVA generator will have a sub-transient reactance of ten per cent or more - it can be as high as 18 per cent.
For this reason generators are often oversized with respect to the connected load in order to mitigate the instability that would occur when generator and load are closely matched.
Many loads such as control gear and generally IT systems do not respond well to frequency changes.
Equipment relying on phase-locked loop (PLL) means for example, only work within a vary narrow range of frequencies, PLLs also respond badly to fast slew rates - and all this poses a problem for more modestly rated generators.
Sharp load variations can cause wild gyration of the voltage and frequency parameters.
So-called power walk-in features when available can ameliorate the situation although depending on load impedance characteristics, for example a passive filter, the generator might initially see a large capacitor causing leading VARs.
The Automatic voltage regulator (AVR) is likely in those instances to reduce excitation current - again leading to instability.
For the above reasons, the reticulation for a mining site should be planned so as to employ generation assets that are for economy reasons reasonably matched to loads capable of tolerating a large degree of variation in voltage, and even frequency.
For other loads such as process control, communication and IT, effective voltage regulation should be installed, such as the new VRx precision voltage regulerators from TSi Power Corporation.
They are designed for outdoor use and suit applications including control apparatus, microwave relaying stations, remote telemetry, etc.
The VRx voltage regulators are packaged in IP65 (NEMA 44) housing making them wash down and corrosion resistant and thus well suited to challenging environments.
They withstand stressing environmental conditions including ambient temperatures ranging from -20°C to + 50°C, humidity to 90%, and altitudes to 3300 metres.
The voltage regulators employ IGBT-based PWM-converter-inverters and buck-boost transformer to provide very low distortion precision-regulated voltage with less than 3 per cent variation.
An automatic bypass provides assurance that in the unlikely event of equipment failure, voltage for mission critical applications can still being supplied.
The VRx voltage regulators are equipped with coordinated voltage surge protection in accordance with IEC 61312.
In addition a noise filter is provided for the regulated output.
The VRx voltage regulators are available in ratings of 10 kVA, 15 kVA, and 20 kVA.
*Subodh Bhatia is from Westek Electronics.