Power substations contain expensive pieces of equipment. If protection is not installed then you can watch them explode. A piece of protection also has to do with safety of personnel for instance fast trip settings, disabling breaker reclose, arc-flash settings etc.
For electrical engineers, designing the Supervisory Control and Data Acquisition system (SCADA) for an electrical substation can be a daunting task, if not confusing with the different ways you can connect various Intelligent Electronic Devices (IED’s) based on protocols each device supports. This article serves to help you understand this system so you can design one as well.
Understanding a breaker scheme is important if you plan on designing a substation. Quite often, it is overwhelming to make sense of the entire scheme at a glance. The figure below depicting a circuit breaker scheme will be used to explain various elements of the PCB’s design and its control.
The DCUB Scheme, like POTT Scheme, uses two frequencies to maintain system protection. When the system is operating under normal condition, the transceiver emits the “Guard” frequency. When a fault appears in the system, the distance relays shift the carrier to “Trip” frequency. This is where the similarities between POTT and DCUB schemes end.
POTT scheme works using the following logic:
Fault in Zone 2 AND permission-to-trip signal from remote end relay.
In the realm of protective relaying, overcurrent protection is the simplest and an essential scheme. Phase and residual protection are quite common in the industry. Phase elements should be set carefully so as to afford protection for equipment downstream of it while not limit the load current in anyway. Residual currents can be set more sensitive than phase relays since they do not limit the load current. Between these two, it is easy to forget the negative sequence protection.
