FEATURE SURGE & CIRCUIT PROTECTION
Rectifier failure in emerging markets – a thing of the past?
M
any emerging markets are plagued by bad AC (alternating current)
power, due to unstable power grids, faulty grid stabilisation equipment and old or poorly maintained gensets. This is fundamentally different from the power issues typically observed in more developed markets, so it is hardly surprising when power conversion electronics designed for developed markets fail when they are used in their emerging counterparts. So what is the solution? The first step is to identify the most commonly recurring causes of component or system failures due to bad power in emerging markets. These can be grouped into the following disturbance categories, all of which need to be addressed by equipment vendors in order for power conversion electronics to be able to perform consistently over an extended lifetime.
DISTURBANCE AREA A Disturbance Area A includes voltage spikes of 2μs or less. These typically result from on/off switching of large loads at some distance from the rectifier. Common examples of such loads are pumps and air-conditioning systems. This type of disturbance can also come from lightning surges causing voltage spikes on incoming power lines.
The eSite is a hybrid power system specifically developed for outdoor use in emerging markets
It is important to take a
be caused, for example, by induction between closely routed aerial power lines, or accidental direct contact between the power lines feeding the re ctifier. Such direct contact can be due to wind, or as a result of power line tampering.
holistic view of the types of power and to plan for them with components developed for use in emerging markets ”
DISTURBANCE AREA C This area includes voltage spikes and inrush currents up to 1ms. Electromechanical voltage stabilisers, with motor driven autotransformers using collector rails, can cause
disturbances during rotational movement. Voltage stabilisers are commonly used in emerging markets.
DISTURBANCE AREA B Disturbance Area B includes voltage spikes of up to 100 μSeconds. These can
DISTURBANCE AREA D Disturbance Area D includes voltage spikes up to 10ms. Accelerated aging in extreme outdoor conditions can cause faults in genset magnetising control circuits and spikes of up to 500V.
DISTURBANCE AREA BEYOND D Slow voltage swells and sags, lasting tens of seconds to minutes, often result from improper generator RPM/speed control, or severe AC grid load imbalance in remote locations. Such imbalances can occur when voltage drops in long under- dimensioned cables, which is often caused by grid voltage variation from voltage stabilisers during connection, disconnection and other faults. These power issues are not new phenomena. On the contrary, they have been well known for decades. However, current regulatory requirements only concern themselves with a very narrow region in Disturbance Area A, while offering no guidelines at all relating to Disturbance Areas B, C and D. This leaves a lot of room for non-recoverable rectifier failures from many commonly experienced and entirely predictable AC disturbances. In a world where solutions to overcome these issues are entirely feasible, this is totally unacceptable. It is clear that power conversion
electronics designed for indoor applications in developed markets, are wholly inadequate for emerging markets. Therefore, to deliver on the promise of long product life in emerging markets, it is important to take a holistic view of the types of bad power discussed above and to plan for them with electronics components developed, from the ground up, for use in emerging markets. It is time for suppliers to take these problems seriously.
Flexenclosure
www.flexenclosure.co.uk
8 MAY 2017 | ELECTRICAL ENGINEERING
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