POWER METERING, MONITORING AND CONTROL

Applying an Energy Management System in a Large Automotive Assembly Plant

An energy management network system has been applied at the Ford automotive assembly plant in Richmond Virginia, to provide electrical and cost information relating to electrical power use in the plant. The system monitors signals from the main incoming power supply utility meters and also reads data from thirty seven meters installed on selected feeders in the plant's internal substations.

The metering information, collected by the system, is presented to the user both in real time and historically, via existing workstations connected to the plant's LAN.

The system provides real time load profile data for operations staff and automatic report generation of historical cost data for billing analysis and cost allocation. The system is in use with Virginia Power's utility rate schedules, which include both real time pricing and time-of-use tariffs, and automatically obtains and downloads Virginia Power's energy cost/hour data via modem.

System Architecture
The system architecture is shown in Figure 1. It can be seen that there is a remote terminal unit (RTU) in the main substation for monitoring the utility metering pulses and other RTU's located throughout the plant for collecting data from local power meters. These RTU's are connected to the data acquisition computer via an existing plant-wide Ethernet highway. The data acquisition computer is located together with a file server in the plant's computer equipment room. These computers are interconnected by a local serial connection.

The file server also connects to the plant's main LAN, allowing users throughout the plant to access metering data.

Main Substation RTU
The RTU in the main substation consists of a wall mounted cabinet containing OPTO22 digital equipment and associated power supplies. One digital I/O chassis with a B1 brain board is provided. The digital boards are equipped with optically isolated input modules operating at 24v dc. These modules are connected to the utility kWh duplicating relay contacts.

The B1 brain board is connected by an RS422/232 converter and TCP/IP serial converter to the plant's existing Ethernet highway. Communication between the main substation RTU and the data acquisition computer is via this highway.

Main Substation Power Metering
The two incoming lines are metered using kWh and kVARh metering signals obtained from duplicating relays installed on the utility power meters. The pulses are routed from the duplicating relays to the RTU using twisted and shielded pair instrument cable. The utility also provides a duplicate timing signal indicating the end of a billing window interval.

Figure 2 shows the main substation RTU power metering panel arrangement.

Local Substation RTU's
The RTU's installed in each of the seven local substations consist of a wall mounted cabinet containing an EFX processor, OPTO22 digital I/O equipment and associated power supplies.

The EFX processor is a microprocessor unit designed to provide high speed local data polling of the 3710 power meters and storing the data in its own registers. By continuously locally polling a group of up to 16 meters, the overall response time to remote computer requests for data is greatly improved.

The EFX also services a 32 point OPTO22 I/O board supplied in each RTU location which is ready to accept optically isolated G4 series input modules operating at 24v dc. These modules will be connected to future gas, water and air metering signals.

Each RTU EFX processor is connected to the plant's Ethernet data highway by an RS232 -- Ethernet converter, each with a unique IP address. The converter is connected on one side to one of the EFX RS232 ports and on the other side to the Ethernet highway using a 10 BaseT connection.

Computer equipment
The network system supplied for this project consists of two computers located in a single cabinet in the plant's main computer room. These computers are:
- A data acquisition computer which accesses the metering information through the plant's Ethernet highway. This computer is connected to the NT workstation through a serial link.
- An NT workstation computer which stores all data and contains all the executable files.
The computers and all auxiliary equipment in the cabinet are supplied with power from the computer room's UPS.

System Operation
The EFX microprocessor equipment in each RTU independently collects metering data from each metered point and stores the data locally. The data acquisition computer requests this metering data from each RTU unit every minute using the plant's Ethernet communication lines. The protocol used is TCP/IP. Using the received information, the computer forecasts the electrical load on each of the metered points and displays to the operators in both graphical and tabular form.

At the end of each 15 minute period, as determined by a timing pulse generated by a master clock in the main substation RTU, the NT workstation computer writes the accumulated energy and demand data to its hard disk. This 15 minute data read resets all RTU EFX energy registers to zero and a new 15 minute period commences.

During the 15 min writing of data to the NT workstation hard disk, the system computes and updates all peak data, coincident data, costs and energy files.

Instantaneous power, voltage, current and power factor readings are also available to authorized users on the plant's LAN. Direct access to any of the plant's 3710 power meters is provided through a menu driven display screen.

System Software
The software used in the Assembly plant is ECAMNet. This software is for network use and provides plant-wide Windows access to the E2MS real time and historical data through the network connection. The software allows the user to configure the system to group metered loads into cost centers. Figure 3 shows the addressing. The software features both time of use rates (TOU) and real time pricing. The software is modular in construction and includes the following key components:
(a) Communication programs: RTU and 3710 communications
(b) Prediction program: predicts plant loads to end of billing window
(c) Filing routines: saves data to disk every 15 minutes
(d) Alarm module: monitors communications
(e) Optional demand control program: produces alarms on high demand
(f) Operator interface programs: allow users to analyze data
(g) Report generation: produces reports to customer formats
(h) Price downloading: automatic downloading of utility price information

Operator interface
The operator can view the data, both in real time and historically, through a menu system. Password protection is provided so that access to restricted areas is only allowed to authorized users. Key menu items are:
- tables for each cost center showing predicted loads
- meter data on a per meter basis
- single line graphics showing equipment status
- graphical data of cost center demand predictions
- alarm data and alarm status
- cost allocation
- real time demand control

Historical Data selections
- Display of load factors showing cost center efficiencies
- Daily/monthly load summaries showing demand/energy
- Coincident demand and energy data
- Max feeder and cost center daily/monthly loading
- Lowest feeder and cost center daily/monthly loading
- Daily load v time plots for feeders and cost centres
- Power factor analysis
- kWh v time plots for feeders and cost centres

System Experience
The system went into service in 1998 and has provided the plant with useful information relating to the electrical system operation and energy use. There have been several updates to the system reporting software, to allow accounting to access daily and monthly cost information for making cost comparisons with the utility bills.

The system metering data for the whole plant has been consistently accurate when compared to the utility bills.

The system is used by accounting, engineering and electrical maintenance.

By using the meters' direct read features it is possible to examine electrical conditions existing throughout the plant, directly from the computer terminals. Phase balancing and feeder loading can easily be verified and the status of monitored circuit control devices immediately seen.

The following summarizes the features of the system:
(a) Permits the utility bill to be verified. Bill verification is complex because the method used to bill the user uses variable rate costs and baseline information.
(b) Provides cost center information by automatically splitting the costs allowing for true cost allocation by tracking the cost center's contribution to demand and its use of energy above and below the baseline.
(c) Produces output signals when demand is higher than preset target allowing demand to be reduced before utility metering registers the new higher value.
(d) Produces Output signals when kWh cost is greater than preset target.
(e) Provides user selectable direct access to 3710 meter registers for electrical data.
(f) Allows gas and water signals to be wired into the system.