Energy-Efficient Power Supply

Regarding energy efficency in wastewater treatment, not exclusively the plant equipment's energy consumption should be optimzed.

The following power supply components should also be taken into consideration:

   

   

Idle Power

Idle Power

Idle Power Compensation

  • Changing electro-magnetic fields in motors generate idle power. The higher their ratio of idle to real power, the smaller is their cos φ power factor.
  • Transmission of idle power burdens power grids and increases their losses; it may be charged by utilities.
  • Idle power compensators can keep cos φ above 0.9 so that over 90 % of apparent power is real power.
  • Power distribution loss and cable heating are reduced, e.g. by 40 % if cos φ is reduced from 0.7 to 0.9.

Transformers

Transformers

  • Plants are usually supplied with medium-voltage power (10 kV) that is transformed down to low-voltage power (400 V) within the plant.
  • Transformers are sized to maximum simultaneous apparent power consumption. By load management their size and loss can be reduced.
  • Total transformer loss is the sum of no-load loss and short-circuit loss.
  • No-load loss is usually 0.1 – 0.2 % of a transformer’s nominal power Pnom.
  • Short-circuit loss rises proportional to the square of the utilization factor n and is around 1 % • n² • Pnom.
  • Transformers with reduced no-load losses are usually economical.
  • Over-sized transformers are often economical because they have higher no-load loss, but considerably lower short-circuit loss.

Supply Contracts

Supply Contracts

Power Supply Contracts

  • Usage price usually differs between high- and low-tariff periods.
  • Demand price depends on peak power supply within a period; maximum demand must often be declared in advance and if exceeded, a penalty applies.
  • Idle power is often charged if a certain minimum cos φ (e.g. 0.9) is not maintained.
  • Continuous usage rebates may apply for high ratios of average to peak supply.
  • Consumers in deregulated power markets can negotiate with various suppliers and choose the best offer.
  • In some countries, power utilities have to pay statutory minimum prices for power fed into their net.

Load and Energy Management

Load and Energy Management

  • Shifts power demand from high to low tariff periods,
  • Equalizes power consumption and reduces peak demand,
  • Generates power by co-generation, e.g. from digester or natural gas,
  • Uses emergency power generators to cut peak power demand,
  • Anticipates short and medium term power demand and takes corrective actions.