To Protect and Serve: The Modern Micro-Processor Relay
The modern micro-processor relay is a complex device, incorporating functions that can not only be utilized for protection but also for operation of equipment.
Because of this, the design, start-up and commissioning processes need to address the dual functionality of this device, as it typically follows separate paths for protection versus operation.
At the beginning of a project, an engineer will generate the protection settings for all equipment on site. These settings will then be implemented and tested by an InterNational Electric Testing Association (NETA) firm. Following this, the commissioning authority will verify that the protection settings have been properly set and tested. The protection engineer will then perform a final verification that the devices have been set as intended. Operational characteristics of the protection devices are not addressed during this process.
On the same project, the switchgear manufacturer will design the connections and relay logic necessary to operate its equipment. The connections will be completed by an electrical contractor, and the manufacturer will then perform a series of startup activities to confirm the correct installation and operation of the equipment. Following completion of start-up, the commissioning authority will perform testing to verify that the operation is correct per the designed sequence of operation and document that all necessary start-up documentation has been completed. As a final verification, an integrated systems test will be performed to verify that the switchgear operates with the additional equipment that it is connected to. This process does not address the protection characteristics of the relays.
As illustrated above, the challenge of duality of the modern relay can easily cause problems if not addressed. An example of one such project involved the installation of a methane-powered generator in a waste-water treatment plant to use the waste methane as a power source. In this case, the switchgear was rudimentary, with a breaker feeding a transformer and a generator breaker. An SEL 751A was used to protect the transformer feed, and an SEL700G was used to protect the generator. Due to the simple system, there was no PLC to control the switchgear; instead the control functions were implemented from the relay logic in the 751A and the 700G with inputs from the generator controller. This is a cost-effective method, as the relay already has the capability for programing free logic and connecting it to inputs and outputs
The issue arose with implementation. The protection engineer created settings for the relay, but for the protection only. The NETA company tested these settings, but the inputs and outputs were not yet programmed due to the generator manufacturer’s concern over liability, so the equipment could not be confirmed to be fully functional through this process. This prompted delays to the process while roles and responsibilities were re-defined to address the relay setting scope overlap between multiple vendors.
The lesson learned is that the modern relay adds additional complexities to the design, start-up and commissioning processes, and it is important to be aware of and prepared for potential issues or scope gaps to ensure that projects stay on track. Specifications and contracts need to clearly define scope, so that each vendor is aware of what needs to be performed. Regular communication is a necessity between all parties so a process for integration is maintained. There needs to be an agreed-upon method of tracking revisions to relay programming, and NETA testing of the relay needs to be scheduled only after all changes and revisions are complete, prior to vendor start-up
The modern relay has a great capability to protect and serve, but only by incorporating both functions into each step of the project-delivery process.