As efforts to make the low-carbon economy a reality gather pace, the smart grid has ushered in great new opportunities for energy efficiency. Crucial to energy efficiency on the demand-driven, decentralised smart grid is the ability to monitor and measure. Which is where voltage transformers (VTs) come in. What exactly do they do, though?
Also called potential transformers, they’re used in power metering applications. They have three main functions.
First, they step down high line voltages to safe, low ones – from 20,000V to, say, 100V – so that electronic monitoring and metering devices can be connected directly. Second, they produce measurements with very low error margins. Their third function is to isolate line voltages from the supply voltage to protect operators and metering instruments.
Those functions sound critical, don’t they? Yet distribution network operators (DNOs) have widely considered VTs a weak point.
Why were voltage transformers a weak point?
Because, in air-insulated traditional switchboards, they are over-sensitive to operating environmental conditions, like pollution and temperature swings. So they need MV fuses – not to protect the VTs, of course, but to isolate them from the rest of the switchboard by breaking a fault current and stop it from spreading .
However, adding fuses makes cubicles bulky. And as the rise in demand for energy-efficiency and in the use of multiple renewable energy sources requires more voltage measuring points – i.e. more VTs – the only solution is more and bigger substations at a time when space is at a premium. Not to mention, that fuses, being air-insulated, are also sensitive to the operating environment.
In short, some DNOs have been reluctant to increase their use of VTs.
Voltage transformers without a fuse changes the picture
I’m pleased to say, however, that VTs are now being considered in a new light as essential to monitoring, measuring and meeting the demands of the smart grid.
Recent improvements in the production process – from design to manufacturing – have improved their quality. Even more significantly, perhaps, shielded solid insulation technologies have supplanted fuses and drastically reduced their footprint.
2SIS use earthed shields to block electrical field lines and it is built into the insulating medium. The VTs are totally insensitive to the operating environmental conditions, which makes them safe, rugged, more reliable, and longer-lived. And, crucially, much smaller because they’re “fuse-free”.
Recent improvements herald even smaller, “low-power” VTs
Where once DNOs were loathe to use VTs because the addition of fuses had such an impact on cubicle footprints, they are now choosing to use fuse-free VTs which have shrunk cubicles by 10% to 20%.
Indeed, I believe that if developments of the past two to three years run to their logical conclusion, there will soon be “low-power” voltage transformers that electronics will eventually make even smaller. That will open new vistas for the once disregarded voltage transformer.
Where there was maybe a single set of VTs in a substation, there may now be 10 sets of “low-power” VTs, bringing with them a huge increase in monitoring and measuring points – without having to build new cubicles.
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