Water treatment plants are part of any community’s critical infrastructure. Residents expect water to be available every time they turn the tap, even during local utility power outages. A large regional water treatment plant near the shores of Lake Michigan wanted to ensure that water would continue flowing to more than 200,000 residents even if the electric utility failed, so it installed a standby power system to prevent service interruptions. Going a step further, the standby system also helps the water treatment plant save money on its electric bills by generating its own lower-cost power during the electric utility’s summer peak demand periods. Coincidentally, that’s when lawn watering and other summertime activities push water demand to as much as 80 million gallons per day.
The standby power system the water treatment plant chose included two PowerCommand 2.7 MW diesel generator sets from Cummins Power Generation Inc. for a total capacity of 5.4 MW. In addition to the standby generators, the water treatment plant had two separate utility feeds brought in from different substations for additional reliability. As water demand and the plant’s electrical loads grow over time, there is room to add two more generator sets. Cummins Bridgeway, the local distributor for Cummins Power Generation in Michigan, supplied the power system.
According to the plant’s maintenance supervisor, the generators provide dependable standby power for continuous flow of water to the community’s customers. “Basically, we’re using the generators as an uninterruptible power source so that if we have a power outage–or have our power curtailed by the utility for load-shedding during the summer peak–we can run these two generators and supply enough power to keep the water flowing,” says the maintenance supervisor. In the plant’s rate agreement with the local utility, it receives an incentive for allowing the utility to interrupt electrical service and help reduce the utility’s peak demand. This saves the facility about 15 percent off its electric bills–or about $150,000 to $300,000 per year.
Power System’s Dual Role
There are two circumstances in which the generators need to produce power for the plant. One is when both utility feeds fail due to a widespread power outage. The other is when the utility asks the plant to remove all or part of its load from the grid during days with high peak demand.
Michigan water plant keeps taps flowing and lowers costs with 5.4 MW standby power system from Cummins Power Generation
In the case of a utility outage, the generators are programmed to start after a 10-minute delay. This allows time for the pump valves to close before the pumps are restarted. During the 10-minute switchover, water storage tanks throughout the distribution system prevent any noticeable decrease in water flow to consumers.
Whenever power to the plant is to be interrupted because of summer peak demand, the electric utility calls the plant 24 hours in advance. During any given summer, the power curtailments during peak demand periods may happen only six or seven times, but they occur during the lawn-watering season when water demand is the highest. However, the generators have enough power capacity to operate the plant even when the demand for water is high.
Under the rate agreement with the utility, the plant also is required to limit the amount of power it consumes between the hours of 11:00 a.m. and 7:00 p.m., Monday through Friday. If the plant needs more power during that timeframe, it had the ability to generate power in parallel with the utility and just shed some of the plant’s load.
Transfer System Avoids Breaks in Power
When the utility requests the plant to switch to self-generated power, the plant starts the generator sets and makes the transition using a paralleling load transfer system. This style of transfer equipment parallels the generator and the utility together for a brief period during the transition, and then gradually ramps the load onto the generators and off the utility. The process is reversed when the utility notifies the plant that they can resume the use of utility power. This system reduces stress on components and avoids a break in power flow when the plant is transitioning from generator to utility power and back again.
Northeast Power Grid Outage Tests System
Sometimes, power disturbances from far away also can affect the local power supply. The Northeast power blackout of August 2003 occurred shortly after the standby power system was installed. When the massive outage occurred, the standby power system’s master control detected anomalies in the local utility’s line voltage and automatically started the generator sets and disconnected from the grid. While the power was out all over the region for up to a week, the water treatment plant was able to supply water continuously using its standby system.
Since the Cummins Power Generation standby power system was installed, it has not only kept the water flowing to more than 200,000 customers during utility outages, it has helped reduce the plant’s electric bills and the cost of water.