The ACRWC Wastewater Treatment Plant (WWTP) located in Strathcona County, north of Sherwood Park, Alberta, receives and treats the sanitary flows from our 13 member communities surrounding the City of Edmonton.
The ACRWC’s Fort Saskatchewan Pump Station is on the west bank of North Saskatchewan River, across which is the City of Fort Saskatchewan. The pump station is collecting wastewater from the Town of Bon Accord, the Town of Gibbons, and the City of Fort Saskatchewan and then transfers the wastewater to the ACRWC WWTP.
The pump station is currently equipped with four 261 HP sewage pumps. SEP-1 and SEP-4 are powered by 4160V bus. SEP-2 is a combination electric and engine driven pump. SEP-3 is an engine driven pump powered by diesel only.
The Pump Station has two electrical distribution systems: 4160 V switchgear and 600 V generator. The 600 V Siemens MCC is currently divided into an emergency bus and a non-emergency bus. The nonemergency bus is exclusively powered from the 4160 V switchgear.
A 600V generator is used to power the low voltage loads such as lighting, grinders, HVAC, sump pumps etc. during utility power failures. The generator is original to the 1985 construction of the station and it does not provide emergency power to the four sewage pumps.
The engines used to drive the pumps SEP-2 and SEP-3 are not adequate enough for long term use and are expensive to maintain. If the Pump Station loses power on the 4160V bus, only SEP-2 and SEP-3 can be operated through diesel engines for wastewater conveyance, with reduced total pumping capacity that is not adequate to pump out the wet weather flow during heavy rainfall events. The two pumps currently require seal water and the engines that drive the pumps require cooling water.
Because SEP-2 is equipped with both an electrical motor and a backup diesel motor, only one driver is allowed to run at a time. When a running contact is received from the electric motor (11-XI-A-SEP2), the diesel engine cannot be started. When a running contact is received from the diesel engine (11-XI-B-SEP2), the electric motor cannot be started.
To support the engines, a fuel system consists of a day tank in the utility room and it is equipped with a guided wave radar level transmitter (11-LIT-603). The tank system is in bad condition as well and needs to be replaced.
If the Pump Station loses power on the 4160V bus, the emergency generator 11-GEN-601 will automatically start; this is indicated by the transfer switch position (11-ZIO-914; Level 2 Alarm) and the generator running status (11-XI-904; Level 3 Alarm). When these signals are received, the PLC will automatically designate SEP2 engine as the follow1 pump and SEP3 as the follow2 pump. If the level in the wet well rises to the follow1 start level set point, then SEP2 will automatically start via PLC control; if the level continues to rise to the follow2 start level set point, then SEP3 will automatically start.
The emergency generator 11-GEN-904 provides the PLC with a running status (11-XI-904; Level 3 Alarm) and a fault signal (11-XA-904; Level 2 Alarm). There is no direct PLC control over the generator.
The 600V generator has been operated for 35 years and is approaching its mean time to failure. ACRWC is considering replace the existing one with a 4160 V generator to provide emergency power to the sewage pumps. The size of the generator will be able to power all four pumps and all existing 600V equipment. Accordingly, the engine driven pumps will be changed to electrical motor drive to eliminate the diesel engines and their auxiliary gears.
The consultant needs to review the 600V system and recommend the scope of replacing the 600V MCC or part of it if necessary. The FSPS HVAC was upgraded in 2016 to 2017. This project added a new section of 600V MCC (11-MCC-03) to the existing 600V MCC. No need to replace 11-MCC-03 if the rest of the 600V MCC needs to be upgraded. The consultant also needs to consider the scope of replacing the 4160 switchgear and MCC, incorporating a transfer switch that allows it to be powered by a generator.
