Directional Overcurrent Protection Function Test
I. Pre-test Instructions
Directional overcurrent protection adds power-direction discrimination to the overcurrent protection logic: the protection will operate only when the fault occurs in the protection's forward direction and the current exceeds the set value; for faults in the reverse direction, the protection will not reliably operate regardless of how high the current is.
test objective:
1. Verify the setting value of the operating current for directional overcurrent protection;
2. Verify the operating delay of the time-delay section;
3. Verify the operating time of the reverse-time interval;
4. Verify the power-direction blocking logic: the forward-direction fault protection shall operate, while the reverse-direction fault shall be reliably rejected;
5. Verify the device event logs and confirm that start and trip events have been correctly recorded.
Example of setpoint definition for this test:
1. Section I overcurrent setpoint: 1 A
2. Overcurrent for a duration of 0.1s
3 Low-voltage trip threshold: 70 V
4 Negative sequence voltage trip threshold: 7 V
5. Overcurrent Section I energized via directionality
6. Overcurrent Section I: de-energize via voltage
7. Section I of Overcurrent Protection: Activated
II. Pre Preparation
1. Device-side parameter settings
1) Enter all protection setpoints for this section;
2) Install the corresponding soft protection busbar in the protected section;
3) Control settings: Overcurrent Section I via direction = energized; overcurrent Section I via voltage = de-energized; overcurrent protection Section I = energized.
Only when the set value, soft pressure plate, and control word are all properly configured will the protection functions be fully activated.
2. Secondary wiring
1) Current output of the tester: IA, IB, and IC are connected to devices Ia, Ib, and Ic; IA′, IB′, and IC′ are connected to devices Ia′, Ib′, and Ic′;
2) Tester voltage outputs: UA, UB, UC, and Un shall be connected to the device terminals Ua, Ub, Uc, and Un, respectively;
3) Connect the device's protection trip output contacts to the input terminals of the test instrument for capturing the trip status change and timing.
⚠️Key reminder: Directional protection must be applied with three-phase voltage, with line voltage greater than 15 V; the voltage serves as the basis for power-direction determination and must not be set to zero.
III. Experimental Items and Operating Procedures
Operating Condition 1: Time-limited – forward direction; verify the operating current threshold
Phase relationship condition: the phase voltage leads the phase current, satisfying 0° <Arg(Uph/Iph) <120°; in this case, Ua∠0° and Ia∠‑30° are adopted.
1. Apply balanced three-phase voltage:
Ua=57.74V∠0°
Ub=57.74V∠‑120°
Uc=57.74V∠120°
2. When the initial amplitude of the three-phase current is less than the overcurrent setting value of 1 A, the protection does not trip or operate.
3. Keep the voltage phase unchanged and slowly increase the amplitude of the three-phase currents in synchronization until the protection trips; record the measured operating current and compare it with the set value of 1 A to verify the error.
Operating Condition 2: Time limit – forward direction; 120% setpoint verification actuation time delay
1. Maintain the voltage at the above three-phase balanced level;
2. Step output current: the amplitude is set at 120%; 1 × 1.2 = 1.2 A; condition for phase to remain in the positive direction:
Analog excitation:
Ua=57.74V∠0°
Ub=57.74V∠‑120°
Uc=57.74V∠120°
Ia=1.2A∠‑30°
Ib=1.2A∠‑150°
Ic=1.2A∠90°
3. The tester begins timing and captures the change in position of the trip contacts;
4. Record the measured action time and compare it with the set time of 0.1s.
Requirements for phase-separation verification:
First, complete the three-phase test as a whole; then, separately apply forward-direction fault currents to phases A, B, and C individually, while setting the currents in the other two phases to zero; record the operating values for each phase separately to identify any abnormalities in the single-phase data acquisition circuit.
Operating Condition 3: Reverse Time-Interval Verification (200% setpoint)
1. The three-phase balanced voltage remains constant;
2. Step input current with an amplitude set at 200% (i.e., 2 A) and a phase maintained in the positive direction;
Analog excitation:
Ua=57.74V∠0°
Ub=57.74V∠‑120°
Uc=57.74V∠120°
Ia=2A∠‑30°
Ib=2A∠‑150°
Ic=2A∠90°
3. The tester shall time the process and record the actual action time;
4. Compare the measured time with the theoretically calculated time derived from the reciprocal time formula for verification.
Operating Condition 4: Reverse-direction fault verification (directional interlock verification; critically important)
The current phase is shifted by a total of 180°, simulating a reverse fault; the current magnitude remains at 1.2 A (greater than the operating setpoint).
Incentive settings:
Ua=57.74V∠0°
Ub=57.74V∠‑120°
Uc=57.74V∠120°
Ia=1.2A∠150°
Ib=1.2A∠30°
Ic=1.2A∠‑90°
✅Decision criterion: The current has exceeded the operating setpoint, but the fault is in the opposite direction; therefore, the protection must reliably remain inactive and must not trip.
Operating Condition 5: Cycle verification for all other flow passages
Complete the entire procedure for operating conditions I–IV in sequence, and perform all verification tests for the remaining flow passages in directions II, III, and the others:
• Measure the operating current during slow rise in the forward direction
• Forward-direction step test duration delay
• Reverse time-limit verification (if applicable)
• Reverse-direction interlock verification
IV. Trial Completion Verification
Stop all outputs of the tester; enter the device's [Event Recording] menu and verify each item one by one:
✅Ensure complete preservation of protected startup events;
✅Ensure the complete preservation of protection trip events;
Verify the faulty phase, current, and operating time within the event, ensuring consistency with the conditions of each test conducted this time.
✅ Summary of the complete testing procedure
Setpoint configuration + soft-limiting plate + control word → wiring (voltage and current + trip input)
→① Slowly increase the current in the forward direction to verify the actuation threshold
→② Apply a 120% step in the forward direction and delay the verification time limit; perform phase-by-phase individual verification
→③ 200% set-value verification reverse time limit
→④ Reverse-direction high current: verify that the directional lockout prevents operation
→⑤ Repeat the full set for the remaining protection sections
→⑥ Verify the device event log
