The Audrey Emerton Building was opened in 2005 and as a result is reasonably well fitted out with energy efficient electrical equipment.
The site operates primarily five days a week, with limited activity at evenings and weekends.
The site would normally run at around 200kVA and have a maximum demand of approximately 300kVA. The over night base load was typically 35kVA. Onsite voltages averaged 242.5 and peaked at 246.5V (Phase to Neutral).
The building is fed by a single 1000kVA transformer.
Before installation, we conducted a survey of loads at the facility, listing their size, type, duty cycle and time of operation. This enabled us to understand the patterns of electricity use at the facility to accurately size the voltage control equipment. In addition, the incoming electricity supply was logged for one week to gather detailed information on the incoming electricity supply and assess aspects of power quality such as power factor and harmonics at the facility.
We decided to set the initial output voltage to 222V as there are control transformers in the lifts that would need to be reset before the voltage could be reduced below 222V. At this target voltage, the load survey indicated savings of 9.5% could be achieved.
Installation was more complex than usual as there was little available space in the switchroom. To overcome this, we installed the single-phase version of the voltage regulators, which allowed us to distribute the regulation equipment in different parts of the switch room. We chose the PSR 10 Regulator (specified at 384 kVA and 576 Amps per phase) as it has the capacity to control the voltage below 220V after the lift transformers have been reset. A bypass switch gives the hospital full control over their electricity supply and allows the voltage regulator to be taken off-line for inspection and maintenance if required. An additional MCCB sized to the Regulator was placed in front of it to give additional protection.
Preparations took three days and final connections were made during a two-hour period early on a Friday evening to cause minimum disruption to hospital activities.
• Cost savings: £9,298 (Year 1)
• Project Net Present Value: £134,418 (at a 5.65% discount rate)
• Internal Rate of Return: 29%
• Payback time: 45 months
• Electricity savings: 8.6%
• Improved power quality
• CO2 emissions reduction: 57 tonnes (Year 1)
For a time after installation, for observation purposes, output was set to 225V. During this time, electricity use was reduced by 8.6%.
After three months the voltage was dropped further to 222V, giving an incoming voltage of 220V (P-N) at the furthest point on site. Early indications are that electricity use has been reduced by 10.1%.
At this time a further test was conducted to determine how well the regulator was controlling the voltage. For one week after the voltage was set to 222V, the incoming electricity supply was logged and analysed. The data clearly show that the voltage was controlled to within ±0.5% of the 222V target.
Over the initial period with the voltage set at a target 225V, electricity use was reduced by 8.6%. After the voltage was reduced to 222V, electricity use was reduced by 10.1%. With a steady incoming voltage, electrical equipment will operate in a more benign electrical environment, thereby reducing maintenance requirements and extending the life of electrical equipment.
The voltage will be reduced to 218V when the lift motors are reset, at which point savings should be in excess of 12%.
Diagram 1: Profile of the voltage entering the Audrey Emerton Building before and after voltage optimisation