Remote Monitoring of Smart SPDs

Remote Monitoring of Smart SPDs

SPDs can be installed in electrical rooms and distant locations where there is not necessarily maintenance staff. This creates a need for monitoring from a remote location. There are several methods in use for observing an SPD at a distance. Manufacturers offer a choice of remote monitoring approaches, raising the questions of pros and cons depending on the application needs. The following paragraphs provide a brief description of possible approaches, summarized in Table bellow.

A. Direct Connection 

By far the most common type of connection, this is usually achieved by connection to the Form Crelay. The amount of information is limited and is often only the status of the unit, operating or not.Some models have been able to transmit the information on each phase and send three separate signals to a remote station in the same building. The manufacturer that supplied the SPD can also supply this circuit. Then the optoisolator connection discussed above can be utilized by connecting to a dedicated product intended to supply remote information. However, the amount of information that can be sent is limited and the distance is generally limited to the same building as the SPD.

B. Addressable Relay

A sophisticated building automation system might not be able to directly connect to a Form C relay.To connect to building automation system, an addressable relay can be used. This is a device that can be addressed on a network and can read the status of a Form C relay. This allows the Form C relay on the SPD to be seen anywhere on the network. With the presence of wide area networks, this allows the status of the SPD to be determined anywhere in the world. However, the amount of information transmitted is very limited in this application.

C. Network Connectivity

For the most complete monitoring of the information that the SPD can provide, a network connection is required. Such connections generally fall into three categories: local connections such as RS232/RS485, industrial control systems such as Modbus, and local area networks such as Ethernet.For the most part, the differences in these networks are not important. The differences are in the implementations of the connected hardware and software. The presence of a network connection allows information to be transmitted anywhere it is needed. Modbus would likely be preferred in industrial settings while Ethernet connections would be more common elsewhere.RS232 and RS485 will require a product-specific computer program to properly transfer the information in the SPD to the computer system that is eventually involved. Modbus and similar protocols require a driver specific to the SPD and the protocol. Finally, an Ethernet enabled SPD can be designed to use TCP/IP and connect directly to a computer by using a Web browser such as Netscape Navigator or Internet Explorer. The information is written into the SPD as a Web page that can be downloaded as needed without need for additional software on the host computer.The above approaches provide a method of getting the information the SPD has collected into the user’s ‘hands’. However, only the last approach, using an imbedded Web page, allows for seamless computer upgrades and software upgrades. Since the viewing software is now effectively part of the operating system, the new computer will always have the required software without the need to separately install the SPD software. Computers are changed every two to three years in a business environment and often upgraded even more frequently. This situation creates a problem, as the SPD software might not work on the new computer or with the upgraded software. The other benefit of the Ethernet connected version is the ability to update the firmware by downloading a new image into the SPD if there are ever any issues that need to be resolved in the future.