Electronics & Scientific Guide, Measuring & Testing

Best Protection Relay Testing Procedures

For the monitoring of power grids, digital line protection relays are used which switch off or switch over broken lines or transformers. How can you quickly and safely check these relays for their function?

Networks are being monitored more and more precisely – monitoring is supposed to be simpler and safer. With the test plug-in system Fame, the power grid center achieves a high level of flexibility with increased safety and increased ease of use. The unique advantage over previous solutions is that even during the test, the protection function is retained.

For more than 80 years, the EAM Group has provided safe and reliable energy to approximately 1.4 million people in central Germany. The subsidiary Energieetz Mitte operates the approximately 50,000 km of electricity and natural gas networks as well as 71 substations.

Test procedure enables safe operation

A prerequisite for the safe and reliable service of the power grid is the rapid detection of a fault. For this, it is essential to monitor different measurands such as current and voltage continually. Digital network protection relays are used to control the measured variables – they handle the switching off and switching of defective cables or transformers. If a line protection relay detects a fault on a supply line, the breaker of this line receives a trip signal and the line is switched off.

The mains protection relays are regularly tested for their proper function as part of a projective test. To make this test simple and safe, the EAM traditionally uses a plug-in contacting variant. After establishing the connection, the transducers are first short-circuited via a rotary switch and then the signal “Circuit breaker off” is interrupted.

Only after this step can you start the actual function test. Since only one protective device is typically installed in the medium voltage, all protection functions are missing for the period of the test.

Consequently, if a fault occurs in the network during the test, the protective device can not react – with potentially far-reaching consequences. This can lead to network interruptions or even the destruction of system components.

Phoenix Contact has developed the Fame plug-in test system to make protection testing easier and safer. This system connects a large number of necessary contacts in a single plug-in with the tester. There is no need to operate a switch – all switching operations are positively guided by plugging in the test plug. The connector specifies the order of contacts, disconnections and short circuits of the transducer and thus always correct.

Simplified and error-free protection test

In contrast to operating a switch, there is 100 percent contact overlap at all times. By using prefabricated test plugs, the safety can be increased even more. Permanently connected test leads, which are equipped with a system plug of the tester, make the individual connection of the test leads superfluous. This eliminates another source of error and, also, the protection test becomes faster.

A standardized test plug connector makes it possible to test various tests – such as independent maximum current time protection (DCT) or distance protection – with a single plug. Additional accessories such as a color-coded single-pole service test plug supplement the test system. With the single-pole connector, individual measurements or the separation of the off-signal to the high-voltage switch can be carried out by the protection device.

Protection function is retained during testing

“An important reason to switch to Fame is the rapidly increasing complexity of the systems, which inevitably leads to more complex protection tests,” explains Markus Hose, who is responsible for the protection testing in the substations at Energieetz Mitte.

The test switches selected at that time are no longer up-to-date. With contacts for only three currents and three voltages, as well as an off signal, they no longer fulfill today’s technical requirements. “In contrast, with a once constructed Fame plug, the entire system or all protection systems are tested” – so pants. He, therefore, intends to equip all new systems with fame.

Likewise, the test with Fame can be done safely and easily in systems that cannot be unlocked. During the test, a reserve protection device can be ground in with the test plug. Thus, the network protection is maintained during the protection test. This particular feature for consistent network security is also used when a protection device fails. Then an employee grinds an interim protection device over the Fame plug easily and quickly.

Simple replacement without protection technician

If a protection device fails or causes faults, a service technician who does not need to be a trained protection engineer can replace the protection device outside of regular working hours via the fame connector. This will quickly fix an error and minimize network disturbance. The next day a protection engineer can then replace the defective device without affecting the network.

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