• • • RENEWABLE TECHNOLOGY • • •
Peak demand Industrial (and commercial) facilities have their power consumption levels monitored by utility suppliers several times an hour in order to work out their average energy demands. At start-up, production facilities in particular tend to draw down a large amount of energy and this can affect how utilities calculate their charges based on peak demand (the highest average demand during all the intervals in a billing cycle). The way to keep these costs down is to stagger
load cycles to mitigate demand and minimise total energy draw at any one time. To do this, it is important to ascertain what demand interval the utility uses and measure energy demand over time at the service entrance using a power quality logger. Also, it will help to identify if there are significant loads operating concurrently, using demand measurements to check readings for the individual loads. Should facilities exceed agreed contracted peak
demand levels, they can be open to significant fines from the utility companies. Therefore, preventing overspends and regulating energy costs are essential in terms of protecting income and cutting expenses.
Power factor Not all power that is generated and transported to the end user is used efficiently and it is the effective power (measured in kW) that the end user pays for. Reactive power, which is also a
part of the power transported via the infrastructure is not used and not charged to the end user, so it can be considered as waste. This means that infrastructure such as cables, switches and transformers are dimensioned to
carry the total amount of power but only part of this infrastructure is used efficiently. This total power is called apparent power (measured in kVA). The ratio of effective power over apparent power
shows how efficiently the energy is used and if this ratio is 1 then all apparent power is used and charged for – the lower this number, the less efficient usage of the apparent power is. Because energy suppliers cannot charge the end user for reactive power, a limit is stated in the contract. If this limit is exceeded, a significant fine can be incurred. The ratio of effective power over apparent power is called ‘cosine phi’ or ‘displacement power factor’ and, ideally, should never go below 0.95. As well as a fine, another negative effect of a
bad cosine phi can be overheating of the infrastructure. To avoid the problem, facilities need to install capacitor banks near heavy loads like motors with power of more than 50kW, or centrally near the main switchboard. Harmonics can also have an effect on the
power factor. If harmonics are present, compensation using capacitors on their own is not sufficient, so it is essential to use filtering to reduce the negative effect of harmonics. By tackling these six hidden energy usage
issues, facilities will be able to minimise unnecessary outlay, downtime and equipment damage while maximising productivity and efficiency. More information is available from
www.fluke.com.
electricalengineeringmagazine.co.uk
ELECTRICAL ENGINEERING • NOVEMBER 2022 37
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