Protection in Power Systems aims to identify and isolate areas of the electrical network during a fault, so asto avoid dangerous situations for persons, irreparable damage to equipment and reduce the impact on the remaining healthy system.
The elements that consist a protection system are the following:
- Circuit breakers
- Current and voltage transformers
- Protection relays
- Communication infrastructure
- DC supply systems
Especially the protection relays are very important for detecting and restoring faults, as they are the "brain" of protecting schemes and they control the status of the breakers as the result of an internal measurement or comparison function.
The penetration of Distributed Generation (DG) and renewable energy sources in distribution networks can lead to failure of existing protection, as the direction of power flow and short circuit currents ceases to be unique since the contribution of DGs in faults could be significant. In order to study new protection problems arising, a laboratory adaptive protection system is being developed at NTUA as shown in the picture below.
In the given implementation, the electrical networks are designed and studied in the real-time digital simulator (RTDS). Through analog and digital signals the RTDS is connected to external devices, like the protection relay SEL-311B. The relay is programmed to protect a feeder of the electrical network and receive voltage and current signals from the RTDS. It also controls the status of the simulated breaker in the RTDS while its condition is fed back to the relay.
The adaptive protection algorithm is implemented in SIMATIC S7-300 PLC (Programmable LogicController). Specifically, the SIMATIC S7-300 receives the status of the simulated breaker (event table) from the RTDS and decides which setting group should be active. Also, the SIMATIC S7-300 transmits digital signals in the SEL-311B (hardware relay) and the simulated relays to switch to the appropriate setting group.