Rethinking traditional fixed infrastructure
The potential for arc faults to compromise the integrity of IP and flameproof enclosures was investigated in some depth in the 1990s. The outcomes of these studies allowed a determination of arc fault behaviour and identified some unacceptable risks. Since 1990 the design of enclosures has not changed significantly, however the energy levels have increased substantially. Hence it is prudent to revisit the hazards and assess any emerging risks.
A widely utilised approach to managing fault currents is the installation of neutral earthing resistors (NERs). NERs, sometimes called Neutral Grounding Resistors, are used in an AC distribution networks to limit transient overvoltages that flow through the neutral point of a transformer or generator to a safe value during a fault event.
In order to utilise non-AS/NZS2081 compliant protection devices on an earth fault limited system, the user must ensure the key objectives of the resulting protection system are equivalent or
better than that achieved using an AS/NZS2081 compliant device.
Variable Speed Drives (VSDs) use variable frequency outputs that are produced by rectifying the supply to dc and then inverting this dc voltage back into ac using a high frequency carrier and pulse width modulation (PWM) to produce variable frequency, variable voltage supply to the motor. The consequence of introducing a dc bus into the system is that there is now a possibility of the occurrence of dc earth faults. This paper will demonstrate how a fault on the dc bus of a variable speed drive can be detected using a wideband earth leakage relay coupled with an earth leakage toroid.
Introducing the iMAC2 Supervisory Controller. Ampcontrol’s new iMAC2 Supervisory Controller extends the capabilities of the standard iMAC system, providing additional Ethernet communication and diagnostic functionality whilst maintaining compatibility with all existing iMAC installations.
The 2011 revision of AS/NZS2081 correctly recognises that system protection must be assessed in keeping with touch potential curves in AS/NZS4871:2012, but acknowledges that this curve is for 50Hz (power frequency) only. AS/NZS2081 explicitly draws attention to the fact that 50Hz curve sets are not immediately applicable in systems that contain equipment capable of generating non-50Hz components.
Transformers are highly efficient electrical devices with long life cycles. A transformer built for high efficiency and minimal upkeep will have a higher initial capital cost. But in an environment of decreased capital spending, the economic benefits of purchasing a lower first cost standard transformer compared with a high efficiency unit are worth examining.
As Ampcontrol continues to tailor our approach to transformer design and manufacture, our transformer design engineers are increasingly incorporating ester dielectric fluids, a key technical and environmental advancement occurring in the Australian transformer market.
Traditional practice is not necessarily safe. Traditional earth fault limits, earth loop impedances and protection clearance time ‘rules of thumb’ do not always result in a safe or compliant system.