DC Relay and Trip Coil Testing
Direct-current relays and coils are the part of a protection scheme that does the physical work: the trip coil opens the breaker, the close coil closes it, the DC relay blocks or permits a function, and the contactor changes state. All of them are tested with the same basic method: apply a variable DC source, read the contact and time the change. The limits are set by the DC range of the source.
What can be tested
| Test object | What to measure | Method |
|---|---|---|
| DC auxiliary relay | Pickup voltage, dropout voltage, return coefficient, operating time | Voltage ramp up and down with a binary input on the contact |
| DC contactor | Pickup and dropout, contact timing, chatter | Voltage ramp and step with contact timing |
| Trip and close coils | Operating current, operating time, minimum operating voltage | DC source with current and voltage recorded; binary input on the breaker auxiliary contact |
| DC under/overvoltage relay | Pickup and dropout thresholds, time delay | Voltage ramp or step at the relay terminals |
| DC time relay | Delay accuracy | Step the coil voltage and time the contact change |
| Interposing relays and lockout relays | Pickup, dropout, manual reset, target | Voltage step and contact timing |
The DC range and what it covers
| Output | VAE-430 | VAE-660 |
|---|---|---|
| DC current | 3 × ±10 A | 6 × ±10 A |
| DC voltage | 3 × ±160 V | 6 × ±160 V |
| DC accuracy | ≤ 0.5 % | ≤ 0.5 % |
| DC power | 3 × 120 VA at 10 A; 3 × 70 VA at 160 V | 6 × 70 VA at 10 A; 6 × 70 VA at 160 V |
| Auxiliary DC supply | 110 / 220 V, max 1.5 A, fixed | 110 / 220 V, max 1.5 A, fixed |
The programmable DC output covers 24 V, 48 V and 110 V control systems with margin. It does not reach 220 V DC coils. The fixed 110/220 V auxiliary supply can power a relay or a small load, but it is not adjustable, so it cannot be used to find a 220 V coil’s pickup or dropout. For 220 V DC coils, use the station battery with a variable series resistance or a dedicated adjustable DC source, and record the method.
Pickup, dropout and return coefficient
The standard sequence for a DC relay is a slow ramp up to pickup, a hold, then a slow ramp down to dropout. The return coefficient is the dropout value divided by the pickup value. The test set records both transitions through a binary input, so the values come from the same time base. For a trip coil, the important values are the minimum operating voltage, the current at that voltage and the time from energisation to the breaker auxiliary contact change.
Coil current and burden
The DC output records voltage and current, so the coil resistance can be derived at the operating point. That is useful for detecting a coil that is out of tolerance or a circuit with unexpected series resistance. It is not a substitute for a winding resistance measurement at a defined temperature; the coil is a load, not a test specimen with a temperature correction.
What the test set does not do
| Item | Why |
|---|---|
| 220 V DC coils | Programmable DC output stops at ±160 V |
| DC ground fault relays with a bridge circuit | Some schemes need a dedicated bridge or injection unit; check the scheme manual |
| Breaker mechanical characteristics | Travel, velocity and bounce need a breaker analyser |
| Contact resistance | Requires a micro-ohmmeter |
| 1500 V DC traction equipment | The DC output is a control-level source, not a traction power source |
| Coil insulation and withstand | Requires an insulation tester |
Frequently asked questions
Can the VAE-430 test a 110 V DC trip coil?
Yes. The programmable DC source reaches ±160 V and ±10 A, with 0.5 % accuracy. The binary input records the auxiliary contact and the operating time.
Can it test a 220 V DC coil?
Not from the programmable output. The fixed 110/220 V auxiliary supply is not adjustable. Use the station battery with a variable resistance or a dedicated adjustable source, and document the method.
Does it measure coil resistance?
It records coil voltage and current at the operating point, so resistance can be derived. That is a functional value at the test temperature, not a temperature-corrected winding resistance.
How accurate is the timing?
The VAE-430 records binary events with 0.1 ms resolution; the VAE-660 with ±1 ms. Both are sufficient for DC relay and coil operating times.
Can it test the breaker as well?
It can time the trip and close commands through the breaker auxiliary contacts. Mechanical travel, velocity and contact resistance need a breaker analyser and a micro-ohmmeter.