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443H Motor Self-Balancing Differential Protection
For motors adopting self balancing differential protection motor schemes, medium voltage motor differential protection and the self-balancing differential protection function must be properly configured; this device is applicable to the protection and monitoring of both high‑voltage and low‑voltage asynchronous motors.
Protection Configuration（ANSI）
27/46/48/49/50/51/50N/51N/51LR/59/59N/60/63/81O/81U/87M
Communication Mode
Optional: RS-485, CAN bus, Ethernet, IEC 60870-5-103 (IEC-103), IEC 61850
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Description
Overview of Motor Self-Balancing Differential Protection
- Self-balancing differential protection for motors is a relatively uncommon type of motor protection implemented by relay for motor protection.
- For motors adopting self balancing differential protection motor schemes, medium voltage motor differential protection and the self-balancing differential protection function must be properly configured; this device is applicable to the protection and monitoring of both high‑voltage and low‑voltage asynchronous motors.
Transverse Differential Protection Logic Diagram
Protection Configuration（ANSI）
- Magnetic Balanced Differential Protection 87M
- Overcurrent Stage I 50/51
- Overcurrent Stage II 50/51
- Overcurrent Stage III 50/51
- Inverse-time Overcurrent 51
- Overload Protection 49
- Stall Protection 51LR
- Negative-sequence Overcurrent Stage I 46
- Negative-sequence Overcurrent Stage II 46
- Negative-sequence Inverse-time Overcurrent 46
- Zero-sequence Overcurrent 50N/51N
- Thermal Overload Protection 49
- Long Start-up Time Protection 48
- Motor Start Blocking
- Overvoltage Protection 59
- Undervoltage Protection 27
- Zero-sequence Overvoltage 59N
- Overfrequency Protection 81O
- Underfrequency Protection 81U
- PT Circuit Break 60
- PT Voltage Loss 60
- Control Circuit Break
- System Power Loss
- Non-electrical Protection 63
Measurement and Control Functions
| Item | Parameters & Description |
|---|---|
| Bus voltage | Ua, Ub, Uc, Uab, Ubc, Uca |
| Measured current | Ia, Ic |
| Power | Active power P, Reactive power Q, Power factor COSφ |
| Frequency | f |
| Electric energy | EP+, EP-, EQ+, EQ- |
| Binary input | 21 active channels (AC/DC 220V, DC 100V, DC 48V; specify upon order) |
| Output channels | 11 protection outputs, 2 signal outputs, 1 closing position signal output, 1 device power loss output |
Other Features
| Item | Description |
|---|---|
| Communication Interfaces | 1 Ethernet port
2 RS-485 ports (the second RS-485 port is multiplexed with time synchronization port, select function via configuration) |
| Communication Protocols | Ethernet: IEC 60870-103, IEC 61850
RS-485: MODBUS RTU |
| Time Synchronization | Communication message synchronization, SNTP, IRIG-B |
Motor Protection Relay setting calculation excel
| No. | Setting Name | Setting Range | Unit | Default Value | Remarks |
|---|---|---|---|---|---|
| 1 | Motor Rated Current | 0.1–100 | A | 5 | |
| 2 | Magnetic Balance Differential Setting | 0.1–100 | A | 5 | |
| 3 | Motor Start-up Time | 0–600 | S | 5 | |
| 4 | Overcurrent Stage I Setting | 0.1–100 | A | 8 | |
| 5 | Overcurrent Stage II Setting | 0.1–100 | A | 7 | |
| 6 | Overcurrent Stage II Time Delay | 0–100 | S | 0.5 | |
| 7 | Overcurrent Stage III Setting | 0.1–100 | A | 5 | |
| 8 | Overcurrent Stage III Time Delay | 0–100 | S | 1 | |
| 9 | Inverse-time Overcurrent Setting | 0.1–100 | A | 5 | |
| 10 | Inverse-time Overcurrent Time Delay | 0–100 | S | 1 | |
| 11 | Inverse-time Overcurrent Type | 0–3 | — | 1 | 1=Normal, 2=Severe, 3=Extreme |
| 12 | Overload Setting | 0.1–100 | A | 5 | |
| 13 | Overload Time Delay | 0–100 | S | 2 | |
| 14 | Overload Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 15 | Stall Protection Setting | 0.1–100 | A | 2 | |
| 16 | Stall Protection Time Delay | 0–100 | S | 1 | |
| 17 | Negative-sequence Overcurrent Stage I Setting | 0.1–100 | A | 2 | |
| 18 | Negative-sequence Overcurrent Stage I Time Delay | 0–100 | S | 1 | |
| 19 | Negative-sequence Overcurrent Stage II Setting | 0.1–100 | A | 1 | |
| 20 | Negative-sequence Overcurrent Stage II Time Delay | 0–100 | S | 2 | |
| 21 | Negative-sequence Overcurrent Stage II Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 22 | Negative-sequence Overcurrent Stage II Setting | 0.1–100 | A | 1 | |
| 23 | Negative-sequence Overcurrent Stage II Time Delay | 0–100 | S | 2 | |
| 24 | Negative-sequence Overcurrent Stage II Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 25 | Zero-sequence Overcurrent Setting | 0.1–100 | A | 2 | |
| 26 | Zero-sequence Overcurrent Time Delay | 0–100 | S | 2 | |
| 27 | Zero-sequence Overcurrent Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 28 | Negative-sequence Thermal Coefficient | 2–10 | — | 6 | Default: 6 |
| 29 | Thermal Time Constant | 0.01–100 | min | 5 | |
| 30 | Heat Dissipation Time Constant | 1–5 | Times | 5 | Normally 1~5 times of thermal time constant |
| 31 | Thermal Overload Alarm Level | 10%–100% | % | 80 | |
| 32 | Long Start-up Time Setting | 0.1–100 | A | 5 | |
| 33 | Long Start-up Time Enable Duration | 0–100 | S | 3 | |
| 34 | Start Interval Time Setting | 0–100 | min | 10 | |
| 35 | Low Voltage Block Start Setting | 1–400 | V | 70 | |
| 36 | Overvoltage Setting | 1–600 | V | 120 | |
| 37 | Overvoltage Time Delay | 0–100 | S | 0.5 | |
| 38 | Undervoltage Setting | 1–400 | V | 80 | |
| 39 | Undervoltage Time Delay | 0–100 | S | 1 | |
| 40 | Zero-sequence Overvoltage Setting | 1–400 | V | 30 | |
| 41 | Zero-sequence Overvoltage Time Delay | 0–100 | S | 0.5 | |
| 42 | Zero-sequence Overvoltage Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 43 | Underfrequency Protection Setting | 35–60 | Hz | 49 | |
| 44 | Underfrequency Protection Time Delay | 0–100 | S | 0.5 | |
| 45 | Overfrequency Protection Setting | 35.0–65 | Hz | 51 | |
| 46 | Overfrequency Protection Time Delay | 0–100 | S | 0.5 | |
| 47 | Low Voltage Block Frequency Setting | 1–400 | V | 20 | |
| 48 | Slip Block Frequency Setting | 1–30 | Hz/S | 3 | |
| 49 | PT Circuit Break Time Delay | 0–100 | S | 5 | |
| 50 | PT Voltage Loss Time Delay | 0–100 | S | 5 | |
| 51 | Control Circuit Break Time Delay | 0–100 | S | 10 | |
| 52 | System Power Loss Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 53 | High Temperature Alarm Time Delay | 0–100 | S | 0.1 | |
| 54 | High Temperature Trip Time Delay | 0–100 | S | 0.1 | |
| 55 | Non-electrical Protection 1 Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 56 | Non-electrical Protection 1 Time Delay | 0–100 | S | 0.1 | |
| 57 | Non-electrical Protection 2 Type | 0–2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 58 | Non-electrical Protection 2 Time Delay | 0–100 | S | 0.1 |
Motor Differential Protection diagram
Outline and Installation Dimensions
FAQ
Q：What tests must be performed on motor differential protection devices before they are officially put into service?
A:Before putting digital motor protection relays into service, multiple tests such as accuracy verification, functional inspection and motor differential protection stability test must be carried out; only after meeting specification requirements can the relay motor protection systems be officially commissioned.
Q: Advantage vs conventional longitudinal differential?
A: Only 3 single-window CTs needed instead of 6 separate CTs; less wiring, lower installation cost, higher ground-fault detecting sensitivity.
Q: What is motor self-balancing differential protection?
A: It is an optimized algorithm for medium and large motors. It automatically calibrates and balances amplitude and phase deviations between motor terminal CT and neutral-point CT, compensating unbalanced current from CT errors and inconsistent parameters. It achieves high-precision differential fault judgment without manual secondary loop adjustment.
Q: What is its core working principle?
A: The protection collects real-time current from motor terminal and neutral side. Under normal operation and external faults, the algorithm compensates CT inherent deviations to offset steady-state unbalanced current and keep differential current near zero. When internal faults (turn-to-turn, phase-to-phase, grounding) occur, the fault-induced current deviation cannot be balanced, triggering rapid trip action to isolate the faulty motor.
Q: How does it differ from traditional motor differential protection?
A: Core differences are as follows:
1. Balancing Mode: Traditional scheme relies on manual CT ratio matching and external balancing resistors; the self-balancing scheme adopts automatic software algorithm balancing with no auxiliary equipment or manual adjustment.
2. Error Adaptability: Traditional protection is sensitive to CT parameter deviations and prone to maloperation; this scheme adapts to minor CT errors and on-site wiring deviations.
3. Protection Performance: Traditional protection uses high thresholds to avoid maloperation, leading to low sensitivity to minor faults; this scheme minimizes steady-state unbalanced current, supports lower thresholds and accurately detects slight internal faults.
Q: What motors is it applicable to?
A: Suitable for medium and large high-voltage motors requiring high protection reliability:
1. 3kV/6kV/10kV industrial high-voltage AC motors in power, chemical, metallurgical and mining industries;
2. Variable-frequency motors with complex current waveforms and CT sampling deviations;
3. Key motors with strict anti-maloperation requirements;
4. Motor loops with unmatched terminal and neutral-point CTs.
Q: Can it completely avoid maloperation?
A: It greatly reduces maloperations caused by steady-state unbalanced current, but cannot eliminate all abnormal risks. Maloperation may still occur under severe CT saturation, secondary circuit open circuit, wrong wiring and extreme external faults. It is usually equipped with locking logic to enhance anti-interference capability.
Q: Does it require complicated commissioning?
A: Commissioning is much simpler than traditional schemes:
1. No CT ratio calculation, matching or balancing resistor adjustment;
2. The device completes self-calibration and balance learning automatically under no-load or light-load conditions;
3. Only routine function and fault simulation tests are required, shortening on-site commissioning time.
Q: What faults can it protect against?
A: It covers all major stator winding internal faults:
1. Phase-to-phase short circuit;
2. Turn-to-turn short circuit (hardly detected by traditional protection);
3. Single-phase grounding short circuit;
4. Insulation breakdown and winding short-circuit faults.
Q: What are common on-site problems and solutions?
A: Typical abnormal issues and countermeasures:
1. Persistent small differential current: Caused by CT sampling deviation and harmonic interference; Solved by re-calibrating self-balance and enabling device harmonic filtering.
2. Starting-period maloperation: Caused by CT saturation under large starting current; Solved by optimizing start locking threshold and transient compensation algorithm.
3. Refusal of minor faults: Caused by overhigh action threshold; Solved by properly lowering the threshold on the premise of operational stability.
Q: Its coordination with other motor protections?
A: It acts as the main protection for motor internal short circuits. It coordinates with overload and negative-sequence overcurrent protection for abnormal operating condition monitoring, and matches zero-sequence protection for grounding fault protection, serving as the primary trip protection for sudden internal short-circuit faults.
Q: What are its engineering advantages?
A: 1. Low cost: No need for high-precision matched CTs or external resistors, reducing equipment and wiring costs;
2. High stability: Adapts to on-site CT errors and load fluctuations, avoiding frequent maloperation and refusal;
3. Low O&M workload: Free of manual balancing adjustment, suitable for long-term unattended operation;
4. High sensitivity: Detects early minor winding faults effectively, reducing motor burnout and equipment failure losses.
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xiao zhang –
Self-balancing (magnetic balance) differential relay (ANSI 87M) is the primary internal fault protection for medium & high voltage critical motors ≥3kV/200kW. Each phase adopts single toroidal window CT: motor line-side lead and neutral-side lead pass oppositely through one same CT core, flux counteracts under normal load, no secondary output. Instant trip for stator phase short, winding ground & inter-turn fault with ultrahigh sensitivity, simpler wiring vs conventional split CT longitudinal differential.
Jack –
Time-stamped fault records help pinpoint root causes accurately.