Rail and Metro Relay Testing

Railway traction power has two electrical families and they behave differently. AC traction uses 25 kV at 50 or 60 Hz, or 15 kV at 16.7 Hz, with distance, overcurrent, earth-fault and auto-reclosing schemes on the feeder side. DC traction uses 750 V or 1500 V with high-speed DC breakers, DC overcurrent and frame-leakage protection. A secondary-injection test set covers the relay side of both; the DC family has a hard voltage limit that has to be stated before the quotation, not after.

What is tested in the AC traction family

Test object	Functions	Injection	Recommended
Traction feeder protection	Distance zones, overcurrent, earth fault, directional	Three V and three I with phase control; impedance sweep	VAE-430 or VAE-660
Auto-reclosing scheme	Reclaim time, single-shot and multi-shot logic, synch-check	Status sequence and binary I/O, two voltage sets for sync-check	VAE-660 for two sources
Transformer feeder and TSS differential	87T, 50/51, 51N	Six currents for 87T	VAE-660
AT and sectioning protection	Overcurrent, earth fault, interlocking	Three V and three I, status I/O	VAE-430 or VAE-660
16.7 Hz schemes	Distance and overcurrent at the railway frequency	Frequency set below 20 Hz from the PC software	VAE-430 or VAE-660 in PC mode

The 16.7 Hz constraint

The VAE-430 has two frequency modes. In PC mode it covers 0–1000 Hz. In local mode it covers 20–300 Hz. A 16.7 Hz test therefore has to run from the PC software; the front panel cannot set the frequency. The VAE-660 covers 0–1000 Hz without that restriction. The frequency accuracy at 16.7 Hz is well inside the relay’s own setting resolution on both models, but the test plan should state which mode was used.

A second constraint is physical. Railway protection at 16.7 Hz is sometimes verified with real load or with a low-frequency source that can drive the actual CT/PT burden. The test set proves the relay and the scheme logic; the real-load validation is a separate commissioning step.

What is tested in the DC traction family

Test object	Functions	Injection	Limitation
DC feeder protection relay	DC overcurrent, undervoltage, rate-of-rise where applicable	DC voltage and current within ±160 V and ±10 A	Control-level source, not a 1500 V traction source
DC relay and contactor	Pickup, dropout, operating time	DC source and binary timing	220 V DC coils need a separate source
Frame leakage protection	Leakage current threshold and alarm	Low-level DC or AC injection at the relay input	Scheme-specific; check the relay manual
DCCB protection and high-speed trip	Overcurrent, di/dt and Delta-I elements	Not reproducible with a control-level source	Requires a high-current test set or the manufacturer’s test equipment
Stray current and rail potential monitoring	Monitoring functions	Not a protection relay test	Separate monitoring system

The DC boundary

The VAE series is a secondary-injection source. Its DC output is ±160 V and ±10 A, which is a control-level output: enough for DC relays, coils at 24/48/110 V and relay measurement inputs, not enough for a 750 V or 1500 V DC feeder. A 1500 V DC breaker test needs a high-current DC test set that can produce the fault current and the di/dt the protection is designed to see. If a tender asks for DCCB primary testing, the VAE is the wrong instrument and the answer should say so.

Model choice

Requirement	VAE-430	VAE-660
Feeder distance and overcurrent	Yes	Yes
Auto-reclosing with two voltage sources	Limited: four voltage channels	Yes: six voltage channels
TSS transformer differential 87T	No: three current channels	Yes: six current channels
16.7 Hz in PC mode	Yes	Yes
DC relay and control-level DC tests	Yes	Yes
DC 750/1500 V primary or DCCB di/dt	No	No

What the test set does not do

It does not inject traction primary current or voltage.
It does not test the DCCB high-speed trip, di/dt or Delta-I elements.
It does not reproduce the non-linear impedance of a 2 × 25 kV AT system; the relay is tested with the impedance values and the scheme logic, not with the traction network.
It does not test IEC 61850 GOOSE or Sampled Values used in some digital traction substations.
It does not replace the real-load validation required by some railway authorities at 16.7 Hz.

Frequently asked questions

Can the VAE-430 test 16.7 Hz railway protection?

Yes, in PC mode, which covers 0–1000 Hz. The local mode starts at 20 Hz, so the front panel cannot be used at 16.7 Hz.

Can it test a 1500 V DC breaker?

No. The DC output is ±160 V and ±10 A. DC feeder relays and control-level DC relays can be tested; the DCCB primary and high-speed trip tests need a high-current DC test set.

Can it test the auto-reclosing scheme?

Yes. The VAE-430 covers the logic and timing; the VAE-660 adds a second three-phase voltage source for synch-check and two-end schemes.

Does it support the 25 kV feeder distance protection?

It tests the relay at the secondary side with the VT and CT ratios applied. The primary impedance is a calculation, not an injection.

Can it test digital traction substations with IEC 61850?

No. The VAE series is an analog secondary-injection test set. Digital process-bus testing needs a dedicated IEC 61850 test set.