OMICRON Magazine

and new infeed approximates zero or moves into this range. Suppose this type of connection is not possible. In that case, the MBT system will make the connection when the residual motor voltage has dropped to a particular value or a specific amount of time has elapsed. The logic integrated into the MBT system determines the best method during these circumstances. The asynchronous motor model integrated with RelaySimTest enables realistic simulations. An initial MBT stability test is conducted by simulating start-up behavior. The motor start-up and the associated under-voltage must not initiate a transfer during this period. In other testing scenarios, the switch-off behavior or motor-inertia is simulated, as well as the circuit breaker, infeed, motor, and load components interplay. The software then calculates the currents and voltages for regular operation and fault cases. This allows both transfer methods to be tested and the integrated logic to determine the method that should be used. During regular operation, it is possible to close the circuit breaker from the new infeed before the circuit breaker from the old infeed is opened. However, this “hot” transfer cannot be used during a fault. When a fault occurs, the MBT system will initiate an open transfer for this specific reason. This means it opens the circuit breaker from the old infeed before closing the circuit breaker from the new infeed so that both circuit breakers remain open momentarily. RelaySimTest simulates both “hot” and open transfers. In the RelaySimTest grid editor, the primary system is replicated first. Figure 2 shows a typical industry topology with a coupling circuit breaker that can switch from one infeed to another with the infeed circuit breakers. In addition to testing the behavior of the MBT system during transfer, the entire protection system can also be tested. This includes all protection relays in the system, such as the motor protection relay and the infeed relays. This makes it possible to verify whether or not the motor protection remains stable during the transfer. In addition to testing the transfer’s behavior, the entire motor protection can be tested, for example, by triggering a fault in the motor supply line or the motor terminals. The same test documents as those used in the laboratory can also be used for commissioning in the field. Further models integrated with RelaySimTest enable testing for feeder protection, busbar protection, line protection or transformer protection, and recloser systems. Version 4.1 can perform all these simulations, and a free download is available on: A software license and an OMICRON test set are required for outputting test values. «In addition to testing the behavior of the MBT system during transfer, the entire protection system can also be tested.» Figure 2: Example showing industrial motor bus with double infeeds and coupling circuit breaker Y y6 M Y y6 M M M MBT 26