What it is and when you need it
Secondary injection of relays means applying to the relay, from a test set, the currents and voltages that the CTs and VTs would deliver during a fault or an abnormal condition, and measuring whether it picks up, how long it takes to trip and which signals it issues. It is the way to confirm that the relay does what its settings say before entrusting it with a substation or a plant.
It is done at these moments:
- Commissioning of new relays or new panels, in substations and in industry.
- Settings changes, from a new coordination study or from changes in the network.
- Periodic maintenance, according to each company’s plan.
- After an incorrect operation, to find out whether the cause lies in the relay, in the settings or elsewhere.
We test line, feeder, transformer, busbar and generator relays, and recloser controls, in medium, high and extra-high voltage. It is part of our protection testing.
What is included
We test each enabled function against the approved settings table:
- Distance (21) Reach of each zone on the impedance characteristic, zone times, directionality and power swing logic when enabled.
- Phase and ground overcurrent (50/51, 50N/51N) Pickup, inverse-time curve at several multiples of the setting current, and the instantaneous element. Our guide on phase and ground overcurrent protection explains each element.
- Directional overcurrent (67, 67N) Boundary of the operating zone, characteristic angle and polarizing method. See the guide on directional ground overcurrent.
- Differential (87T, 87B, 87L) Operating and restraint characteristic, vector group and ratio compensation, and second and fifth harmonic blocking where applicable.
- Frequency (81) Under- and overfrequency thresholds, rate of change of frequency (81R) and undervoltage blocking.
- Logic and outputs Reclosing (79), breaker failure (50BF), trip contacts, signaling and GOOSE messages when the relay is on IEC 61850.
How we work
- Settings review. We read the relay settings with the manufacturer’s software and compare them with the approved table. Any difference is clarified before testing.
- Test preparation. We build the test files in Omicron Test Universe with the modules for each function: overcurrent, distance, differential, ramps and state sequences.
- Relay isolation. We open the test blocks to separate the relay from the CTs, VTs and trip circuits, with the CT secondaries shorted on the primary equipment side.
- Injection. With the Omicron CMC 356 we inject the quantities of each case and record pickups and trips through binary inputs. We test points along the characteristic and the boundaries where the relay must change its decision.
- Records. We download the relay’s events and waveform records to confirm that the signaling and records match what was injected.
- Restoration. We close the test blocks and verify that the relay measures the real values again.
Protection setting criteria for 50/51, 21 and 87 explain where the tested values come from.
Standards and criteria
The result of each point is compared with the theoretical value calculated from the setting and with the tolerance declared by the relay manufacturer for that function. The IEC 60255 series defines how those tolerances are specified and verified: IEC 60255-151 for overcurrent, IEC 60255-121 for distance, IEC 60255-187-1 for differential and IEC 60255-181 for frequency. Inverse-time curves follow IEC 60255-151 or IEEE C37.112, depending on what the setting uses. IEEE C37.2 defines the function numbering.
A failed point is not declared bad without repeating it and checking the connection, the setting read and the configuration of the test file. We also check that the test represents the real condition: in a transformer differential, for example, the vector group compensation in the file must match that of the relay, or the result tells you nothing useful. When a relay fails a function repeatedly, we report it with the exact case so that you can decide with the manufacturer or the person responsible for the study.
What you receive
- A report per relay with the result of each function: expected value, measured value, tolerance and result.
- The settings read from the device and their comparison with the approved table.
- Test Universe test files, to repeat the test in the future.
- Events and waveform records of each trip.
- Comments on settings, logic or wiring worth reviewing with the person responsible for the study.
Why Tiza Group
- One responsible engineer from start to finish, who reads the settings, runs the tests and writes the report.
- Experience in substations and industry, in medium, high and extra-high voltage.
- Relays from the main brands: Siemens, Schneider Electric, SEL, ABB, GE, Fanox, NOJA Power and Efacec.
- Remote configuration capability: if the test shows a setting to correct, we can load it with your approval.
We do field work in Colombia, or elsewhere on request. Tell us about your project.