In 1924, the Protection Relays were electromechanical and Self-powered. Their sole function consisted of protecting the electrical systems that they were associated with (by tripping a disconnecting element in the event of a short-circuit or a ground fault).
Thanks to the development of electronics and specifically microprocessors, the so-called digital or numerical protection relays were presented for the very first time during 1969.
The new relays, as an addition to the protection monitoring and the event and oscillography recording functions, included an HMI (Human Machine Interface) that was featured with an LCD screen, a keyboard and reached some degree of the logic configuration of the multiple inputs and outputs of the device. Thus, this change in the technology/performance led to a change of its name, what was formerly called protection device was now called protection and control device.
But this new generation of protection devices needed auxiliary energy to power the electronic components, and it was necessary to provide them with different power sources (24Vdc / 48Vdc / 110Vdc / 125Vdc / 220Vdc /…) depending on the facility, the country, the customer…
Given that the protection and control devices already had microprocessors, the natural next step was to include communication functions in the relays. The devices began to incorporate two types of communication ways through different protocols: communication with the control devices and communication with the protection staff.
The control devices that work together with the protection relays request them information about the status of the device, the status of the protection functions themselves, and the current and voltage measurements that are captured by the protection relays. Then they send commands to control the cut-off and reconnection devices monitored by the protection. To standardize communications and allow interoperability among devices and manufacturers, different protocol standards were developed: DNP 3.0 (in America) and IEC60870-5- (in Europe). The standardization of the physical environment was less successful. Each manufacturer/customer decided on a different physical connection: RS485 twisted pair, Fiber Optic Glass (FOC), Fiber Optic Plastic (FOP), various field buses (Profibus, CAN, …).
The protection staff also wished to communicate with the protection relays to download the protection settings and to extract the reports and logs. For this type of communication, there was no standardization, and each manufacturer used a different protocol, a proprietary protocol in the majority of the cases. The most used physical connection was the RS232 and it became a standard indeed. There were two ways of working of the protection staff: either they approached the facility where the protection relay was located and then they connected locally with a laptop or they connected with the protection relay by the phone line through a modem to communicate with it remotely at a later time.
With the ICTs booming (the internet) communication devices had greater significance, in which physical channels of communication through Ethernet and USB are becoming standards. Regarding the standardization of communication protocols, some efforts were made to develop regulations to standardize and to unify the protocols among all devices, whether they were for protection, control, or communication purposes. The IEC 61850 standard is the result of this effort.
Not all the protection relays have followed this evolution and some of them remained self-powered, even as digital relays.
Digital self-powered relays have faced other challenges:
- Capability to turn on and to be operational in the shortest possible time, considering that in case of absence of current in the system, the relay is off and after the tripping and the current cutting sequence it turns off again.
- It must be able to work with very low currents. If there is an electrical power failure and the current is not enough to maintain the relay turned on, it will never detect the electrical problem.
- Operation with very low currents: its power consumption must be very low and therefore its processing capacity is very limited. Consequently, the performance offered by the self-powered relays does not reach the performance of the relays with auxiliary power.
Nowadays, there are manufacturers of self-powered relays such as Fanox that have managed to deploy auxiliary-powered relay features in the self-powered relays with very low starting currents and very short operating times:
- HMI with LCD screen and keyboard.
- Signaling LED in the non-volatile memory.
- Different protocols for the Serial communication: Modbus, DNP3, and IEC60870-5-103
- Multiple protection functions.
- Different setting groups.
- Registration of information, events log, load profiles, and even oscillography records in the COMTRADE format.
Oscillography records are one of our latest successes and not all our competitors have achieved it:
Why are there few self-powered relays with oscillography registers?
Manufacturers of Self-powered Relays have to overcome two challenges:
- As the energy available at low currents is limited, the CPUs’ processing capacity is very low, making it extremely difficult to implement oscillography registers.
- In a self-powered relay, the size of the oscillography registers is variable depending on the trip time. After a trip, the relay opens the breaker and the current that allows the self-powered relay to be working disappears. For that reason, it is necessary to close the oscillography register before the relay turns off.
What are the next challenges that self-powered relays must overcome?
- Implementation of directional protection functions: ANSI 67N and 67.
- Implementation of Ethernet communications with the DNP3, IEC60870-5-104, and IEC61850 protocols.