SCADA INSTALLATION
PROVIDES FOR ISLAND-WIDE
CONTROL OF
WASTEWATER SYSTEMS

The 600 square mile Island of OAHU (HAWAII) began wastewater operations in 1901 when instrumentation and control systems were simple and basic. As wastewater capacity demands increased and effluent limits became tighter, the control systems were expanded and upgraded at regular intervals.

A major project, with focus on computer control, was undertaken recently and ended with the installation of an Island-wide Supervisory Control and Data Acquisition system (SCADA).

There are 65 wastewater pump stations, eight (8) wastewater treatment plants and four (4) preliminary treatment facilities connected to the Island-wide (SCADA) system.

In addition, two (2) storm drain pumping stations are monitored for the City and a vehicle tunnel (The Wilson Tunnel) connecting two sides of the island through the Koolau Mountains is monitored and controlled from the Central Command Center at Sand Island for the State Department of Transportation.

Weather stations have also been installed at the major wastewater treatment plants to provide additional data.

Since the Island-wide system was installed, numerous overflows of sewage into the environment have been prevented. Prior to this (SCADA) installation, an average of 20 wastewater spills were recorded each year, now the average has dropped to just 1 spill per year. One of the key control functions of the system is that it checks how often and how long the wastewater pumps run. Throughout the day, wastewater pumps run at various speeds and intervals. The system sounds an alarm if the patterns of the pump operations do not match acceptable patterns as determined from historical data.

The Island-wide (SCADA) system is a large (SCADA) system with continuous upgrade projects. The system is now in full operation and has exceeded the operational benefits originally envisioned during the design phase.

PROJECT DESIGN

The process of designing, selecting and installing the computer based (SCADA) control system was accomplished by the City and County of Honolulu Wastewater Department (now renamed the Department of Environmental Services). The specifications for the project were prepared with the goal of having a (SCADA) system that was easy to operate, expandable and flexible.

The Island-wide (SCADA) project was accomplished in four (4) phases. 64 wastewater pumping stations were completed in the first three (3) phases and 13 wastewater treatment facilities in the fourth phase, along with regional Communication Hubs that connect all the sites to a Central Command Center.

PROJECT INSTALLATION

The Island-wide (SCADA) system was installed by City Telemetering Technicians who were spending excessive time trying to keep a 30-year old decentralized telemetering system in operation. The entire installation was accomplished with no increase in work force and no additional overtime.

The first phase replaced the old telemetering system in the Honolulu metropolitan area that included WAIKIKI. Existing status and alarm points at 12 sites were connected to the new Remote Terminal Units (RTU's) then each RTU was connected to the new Central Command Center located at the Sand Island WWTP on Sand Island. Leased telephone lines were installed from each RTU to the Central Command Center at Sand Island, using a bridge circuit to decrease the telephone line costs.

The second phase replaced existing telemetering equipment and allowed additional sites to be monitored on the Windward (East) side of the island. A total of 24 RTU's were installed. A microwave communication link was also installed to connect the Communication Hub from the Windward RTU's to the Central Command Center at Sand Island.

The third phase replaced existing telemetering equipment and also allowed additional sites to be monitored on the Leeward (West) side and the Central part of the island. Twenty-four (24) RTU's were installed. Two (2) more Communication Hubs were established and connected to the Central Command Center at Sand Island via leased telephone lines.

During an upgrade expansion at the WAIANAE WWTP on the Leeward side of the island the same type of (SCADA) system was installed as a stand-alone system to monitor and control the plant equipment. That plant's SCADA system was connected to the Leeward Communication Hub.

Three (3) more stand-alone (SCADA) systems were installed at the major wastewater treatment plants at SAND ISLAND, HONOULIULI and KAILUA.

The HONOULIULI WWTP was connected to the Leeward Communication Hub, the SAND ISLAND WWTP was connected to the Metro Communication Hub, and the KAILUA WWTP was connected to the Windward Communications Hub.

RTU's were installed at the remaining six (6) smaller treatment plants, that have treatment plant operators only for the day shift, and connected to the nearest Communication Hub.

As new wastewater facilities are built, the same (SCADA) system is installed and connected to the nearest Communication Hub.

A total of 115 RTU's are presently installed that monitor and control over 8000 data points.

SCADA EQUIPMENT

TECHNICAL INFORMATION

Each RTU can monitor 128 digital inputs (DI), 128 analog inputs (AI), control 128 digital outputs (DO) and 128 analog outputs (AO).

The system is modular with input/output (I/O) cards for just DI's and DO's or for all I/O's. The majority of all wastewater pump stations require only five (5) I/O cards.

Each stand-alone (SCADA) system can support up to 256 RTU's with each RTU supporting 32 I/O cards. Each I/O card can have up to 16 physical I/O points.

The RTU's can communicate with the host computer either as individual units or connected together on a Local Area Network (LAN). The LAN method is only used at the major wastewater treatment plants since all the RTU's are in the same location.

During the design stage it was decided to use three (3) micro-computer consoles at the Central Command Center to collect data for the entire Island-wide system which would cut down on the scan time required to poll each RTU.

The island was divided into three regions;METRO (most populated), WINDWARD (east), and LEEWARD (west and central). The polling of these sites is completed under two (2) minute with the modems operating at 9600 baud.

Each RTU and all the equipment at the Central Command Center are provided with Uninterruptable Power Supplies (UPS) to maintain power and communications for up to four (4) hours for the RTU's and eight (8) hours for the Central Command Center upon total loss of power.

CENTRAL COMMAND CENTER

The three (3) micro-computers at the Central Command Center and the micro-computers at the stand-alone sites are standard desktop computers. Two (2) printers are connected to each system, one for alarm printing and the other for report printing.

The computers use a multitasking software to run five programs. One program continuously reads information from the remote sensors at the treatment plants & pump stations. One allows remote control of various equipment, one gathers and stores data for a history of operating conditions, one is the operator interface to the system, and the last program links each computer to a central server computer that allows monitoring of the (SCADA) system from remote dial-in locations.