Traditional end to end testing worked by pinging the PTT Tx channel and measuring the response from the IED. However, there are some major downsides to this approach. The time constraints of this point to point pinging method mean that reliable and repeated testing of the auto reclose functionality is impossible. End to end relay testing was developed to combat this issue and provide a more comprehensive testing method.
A fault on a transmission line can be detected simultaneously using end to end testing. This is achieved by using multiple test sets at a range of locations to simulate a fault. Global timing reference (GPS) was implemented to synchronize the end to end testing. GPS testing works by calculating relevant test points within the power system so that it can test the response of the protection scheme. These specific test points are chosen from specific settings from the protection relays.
There are several steps to simulate a fault. An initial test is first carried out to ensure the tele-protection media is operational and the test set-up is connected correctly. This is achieved by causing a fault in zone 1, if successful, this causes the circuit breakers to trip and reclose in zone 1.
A commissioning engineer at station A would detect a fault in zone 1 within the overreaching zone, a fault would also be detected in zone 1 at station B. The permissive signals are received by the relays. The relays at station B should trip and close zone 1 time.
Whereas the relays at station A should also trip and close zone 1, but at an accelerated time which is approximately equal to zone 1 time with the addition of the tele-protection propagation delay.
This is then repeated for other positions, where station B would detect a fault in the overreaching zone.
A further test will be performed to study the security of the system. To do this, a reverse fault is simulated on relays A and a forward fault on relays B within the overreaching zone. If this test is successful, relay A will detect a PRR Rx signal from relay B which signals relay A to not accelerate the zone timers. In doing this, relay B would trip and reclose, causing the relay to trip but not to reclose.
System based end-to-end testing uses fault voltages and current levels independently to the relay settings. This allows the commissioning engineer to visualize a more accurate representation of what will occur under a real fault. Source impedances and impedance data are studied using this method, showing the behavior of the protection system. This approach allows for easier testing of advanced functions, these include a failure in auto reclose cycle, mutual coupling on parallel lines, and power swings.
Our end to end relay testing provides a more reliable and comprehensive option for testing that relies on actual system parameters as opposed to idealized values. Get in touch today to learn more about our Electrical Relay Protection Services and how they could benefit you and your business.