Power Trend Management System

Detailed Description

This document describes the high-level purpose and functionality of a generic power trend management system.

The PTM system is a networked monitoring and control system aimed at reducing peak power demands at the main power panel. It is not the intention of this system to reduce or restrict the energy usage. User-adjustable parameters allow maximum cost reduction while maintaining “business as usual.”

Network Architecture

The load monitor devices (IED) are multi-dropped throughout the plant. They connect to a PLC that does all the data scanning and controlling functions. The PC Host provides the management functions such as sending alarms, data historian, report generation, and power trend graphs.

Failure Modes:

The PLC can function without the host. If the host PC is down for extended periods host will have gaps in history data. The IEDs can function without the PLC. If the PLC is down for an extended period, the IEDs will continue to function in a reduced capacity. Load protection will continue. PLC and IED failures are reported by the host to whoever is responsible for attending to the system. This can be done via pager service or Internet e-mail at an extra cost.

Main Functions

• Provide a means by which facilities management can define and set a reasonable limit to the peak power demand.
• Prevent peak power draw from exceeding the defined demand limit by delaying for a very short period (in seconds) the activation of certain loads.
• Prevent peak power draw from exceeding the defined demand limit by keeping certain large loads powered on constantly as opposed to cycling them off and on.
• Allow the load to be energised if the imposed delays exceed reasonable time limits. In other words, do not interfere with business as usual, but do report unavoidable excursions in peak demand.
• Advise facilities management of gradual increases in power usage due to changes in regular business activity.
• Provide facilities management with software tools that help pinpoint repetitive activities or events that are major contributors to setting demand peaks. In other words, “shine a light” on certain work areas that are causing excursions in peak demand.
• Advise facilities management if and when any of the load equipment’s normal operational parameters are being exceeded as a result of abnormal circuit conditions or decreases in efficiency of the loads being monitored.

Secondary Benefits

• Demand Power is calculated and stored for reconciling against the utility company’s invoice.
• Total energy draw is calculated and stored for reconciling against the utility company’s invoice.
• Loads are monitored for abnormalities in their electrical characteristics. Each electronic load monitor (IED) protects the loads from most electrical faults.
• The system can sense gradual wear and tear for each load over long periods (worn out ball bearings, bad connections). A load trend report shall give management a chance to schedule corrective actions for during off hours. When there is enough data to predict an imminent load failure, an alarm is generated by the host PC. The alarm report will indicate the estimated time to failure.
• Daily and weekly trends show when and where peaks are being set.
• The overall power draw for the facilities can be monitored and trended over long periods. This tool can be used to predict when electrical panel upgrades will be necessary. Same-period data can be viewed from year to year for comparative analysis.
• The real-time operating voltage and current for each load can be viewed at the load monitor device. This facilitates maintenance of the load and its power branch.

System Maintenance Requirements

The heart of the system consists of a PC and a programmable logic controller (PLC). The PC can be stopped or shut down without interrupting the power trend management functions. This is because they are provided by the PLC. The PLC can be stopped without interrupting the load protection and data gathering functions of each load monitor (IED).

An CD-RW drive can be used for periodic storage of history data from all the load branches and the main power panel. A person must be assigned to the task of loading and unloading the backup discs.

There is no special requirement for technical training and expertise. When a look-ahead report is needed, the user can refer to concise report generating and printing procedures in the user manual. All HMI functions will be documented in this way. The manual will be on-line in the system PC. Example pictures will be used to guide the users through each procedure.

If load monitors need to be relocated or added due to future facilities expansions, customer support is available. Some system reconfiguration will be required. The PC and the network are sized from the start to handle at least 30% expansion without changes to hardware, except for the additional load monitor devices and their associated wiring.

Site Requirements

• A normal office environment is required for locating the system PC.
• Network cabling:
• A bridging device will be located near the bulk of the load monitors. Shielded twisted pair cable will be needed to connect all the load monitor devices with the controller PLC and host PC.
• The load monitors will be wall-mounted near each load contactor. A clamp-like current monitor device is placed around each AC conductor and screwed to the nearest vertical surface.
• The IED requires a normal 120 volt AC outlet within 6 feet of where they will be mounted. Power is supplied via a CSA approved 24 VDC power adapter.
• Loads that only need to be monitored do not need to require a contactor. If it becomes desirable to intervene in the operation of that load, a contactor will have to be added by a licensed journeyman. The existing load monitor and the network system will require some changes to their operating configuration.
• The main power panel will require a main line load monitor, connected just after the utility meters. This is where the total facilities electrical load will be monitored.
  Number of load monitor IEDs = 1 + number of individual branch load IEDs

End of Document