The LMS project comprises three main components: the LMS computer, the communication system and the CADs.
* LMS Computer. The LMS computer has a dedicated desktop PC using Microsoft Windows-for-Work-groups as the operating system. The LMS software that must operate on a Pentium PC with Windows also can be linked with the energy management system. Based on the required load control strategy, the host computer will broadcast addressing and control information via the communication system to various CADs. When there is an address match of the decoded message, the CAD implements the message. The LMS master station, located in the LDC, programs the CADs remotely using the customer's data imported from SCECO-WEST's IT department. * Communication System. The paging system (168.68 MHz) consists of four sites within the boundaries of Jeddah-one at the LDC and three at strategic locations that are selected following a propagation survey to ensure coverage of the entire city.
Each site is equipped with a simulcast digital radio transmitter. The communication link between LDC and each DTR is established via the existing twisted pair telecommunication cables. The paging system is a typical simulcast system suitable for frequency shift keying format CADs. The remote transmitter control (RTC) regulates the radio transmitters relaying the broadcast instructions to the transmitters. Four digital transmitters transmit radio signals to CADs at the specified time. The performance of each radio transmitter depends on the power output, antenna height and level of signal required by the receiver. The system design and sensitivity level of the CADs consider areas within the city where signal strength is low. Therefore, the paging system is able to control a large number of CADs located in 90 percent of Jeddah. Figure 3 shows a schematic diagram of the communication network. * Customer Alert Devices. The CAD is a very-high-frequency radio receiver for indoor use that plugs into a conventional 105-V/240-V ac, 60-Hz power source. This unit was jointly developed by SCECO-WEST and Scientific Atlanta USA, Norcross, Georgia, U.S.
The CAD is a flush-mounted self-supporting unit containing three light emitting diodes (LEDs), which provide status information and a buzzer.
The LEDs that have an illumination level visible to a customer at a 20-ft (6-m) distance are programmed as follows: * A green LED is illuminated continuously, indicating "normal mode" when load control is not in operation. * A yellow LED is illuminated when CAD receives a "test on" message and remains illuminated until a "test off" message is received. Utility field staff use this LED during installation because it verifies that the signal strength is sufficient for correct operation. * A red LED is illuminated during load control. On the transition from non-control to control periods, the buzzer sounds with a 1-Hz bleep for 30 sec. On the transition from control to urgency, a second level, the red LED flashes and the buzzer sounds a 2-Hz bleep for 30 sec. This condition continues until the load-control period expires or until another command from the LMS master station terminates it. On transition from control to non-control periods, the buzzer sounds with a 0.5-Hz bleep for 10 sec.
The audible alarm attracts the customer's attention at the beginning and end of each load control period. Its volume is loud enough to be heard at a reasonable distance within the average-size property.