There is a need to test C37.94 Circuits and Relays to ensure correct operation and performance of these critical protection elements

When testing C37.94 Protection Circuits and Relays there are several different tests that can be performed to help ensure correct operation and performance. Some of these tests can be performed on the C37.94 communication circuits that connect the protection relays to ensure the circuits are operating within certain operational parameters, others can be performed on the protection relays themselves to ensure the relays function as expected under simulated network conditions.

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C37.94 tests normally focus on physical transmission properties such as frequency, optical power, Jitter/Wander, and impairments in the transmission path. One of the most important tests that can be performed with C37.94 circuits and relays however is testing delay, the delay inherent in the C37.94 protection circuits, and the performance and operation of relays when encountering communications delay, especially differential delay.

The Albedo Telecom xGenius and Zeus products can perform delay measurements including differential delay measurements on C37.94 circuits and can also simulate C37.94 symmetrical and asymmetrical delays allowing for testing of C37.94 enabled devices such as protection relays.

When testing C37.94 devices such as relays out-of-service, having the ability to connect relays through a ‘pseudo’ network connection and being able to apply different network conditions/impairments can prove invaluable. C37.94 relays would normally recover their clocking from the C37.94 interface of a mux connected to the network.

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If users wish to test relays in a back-to-back configuration however, the relays will often not function as they are unable to recover network clock from each other and the C37.94 communications signals will suffer from slip or other impairments due to the clock signals not being synchronised. Using the Albedo xGenius or Zeus in through mode relays can be connected to each other, with the tester providing the network clock to each device allowing the relays to synchronise and communicate with each other.

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Once connected, it is possible to assess C37.94 device operation under different network conditions by simulating typical network impairments. The most important of these is network delay, differential protection relay misoperation can occur when either network delays are too large or there is excessive delay asymmetry. In through mode xGenius and Zeus can simulate symmetrical and asymmetrical delays allowing users to test relay operation under different network conditions.

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Through mode can also be used when connected to the utility network and in-service testing of C37.94 relays is required. In this scenario xGenius/Zeus would be connected between the C37.94 Relay and Mux/Router. In normal operation no impairment/delay would be applied to the C37.94 signal, but if a user wanted to test the operation of the relay if a network event occurred such as a path switch in the backbone, a symmetrical or asymmetrical delay could be introduced in the circuit.

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As well as simulating a C37.94 circuit and introducing network delays, xGenius/Zeus can measure the one-way-delay and asymmetry on C37.94 circuits, ensuring the overall path delay and asymmetry is within acceptable limits. Equipped with the GPS /Glonass module and a unit at each end of the circuit, xGenius/Zeus can automatically measure the Forward and Return path delay and provide an asymmetry measurement.

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Using the standard event logger function built into xGenius/Zeus users can log all the delay measurements such as Forward & Return Path and Asymmetry over time providing a graphical view which can be invaluable when testing delay performance over time, especially as Utilities transition their core networks from SDH to packet based MPLS networks.

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