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Motor differential protection 87M
Overview
The motor differential protection device adopts professional differential motor protection logic. It is an integrated protection and control unit developed for high- and low-voltage asynchronous motors, available for standalone panel installation or built-in mounting in switchgear cabinets.
Product Functions (ANSI)
87/87M/50/51/49/48/46/50N/59/59N/27/81O/81U/60
Communication Mode
Optional: RS-485, CAN bus, Ethernet, IEC 60870-5-103 (IEC-103), IEC 61850
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Description
Overview
- The motor differential protection device adopts professional differential motor protection logic. It is an integrated protection and control unit developed for high- and low-voltage asynchronous motors, available for standalone panel installation or built-in mounting in switchgear cabinets.
Product Functions (ANSI)
- Differential Instantaneous Overcurrent Protection (ANSI 87)
- Percentage Bias Differential Protection (ANSI 87M)
- Stage 1 Instantaneous Overcurrent Protection (ANSI 50)
- Stage 2 Definite Time Overcurrent Protection (ANSI 51)
- Stage 3 Definite Time Overcurrent Protection (ANSI 51)
- Inverse Time Overcurrent Protection (ANSI 51)
- Overload Protection (ANSI 49)
- Thermal Overload Protection (ANSI 49)
- Locked Rotor Protection (ANSI 48)
- Long Start-up Time Protection (ANSI 48)
- Motor Start Blocking
- Stage 1 Negative Sequence Overcurrent Protection (ANSI 46)
- Stage 2 Negative Sequence Overcurrent Protection (ANSI 46)
- Negative Sequence Inverse Time Overcurrent Protection (ANSI 46)
- Zero Sequence Overcurrent Protection (ANSI 50N / 51N)
- Overvoltage Protection (ANSI 59)
- Undervoltage Protection (ANSI 27)
- Zero Sequence Overvoltage Protection (ANSI 59N)
- Overfrequency Protection (ANSI 81O)
- Underfrequency Protection (ANSI 81U)
- PT Circuit Break Detection (ANSI 60)
- PT Voltage Loss Protection (ANSI 60)
- Control Circuit Break Alarm
- System Power Loss Alarm
- Non-electrical Protection
Principle of Motor Differential Protection
Measurement and Control Functions
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Category No. Parameter Specification Electrical Measurement Parameters 1 Bus Voltage Ua, Ub, Uc, Uab, Ubc, Uca 2 Measured Current Ia, Ic 3 Power Active Power P, Reactive Power Q, Power Factor COSφ 4 Frequency f 5 Electric Energy EP+, EP-, EQ+, EQ- Binary Input 6 Active Binary Input Channels 21 channels; input voltage options: AC/DC 220V, DC 100V, DC 48V (to be specified when ordering) Binary Output 7 Protection Output Channels 11 channels 8 Signal Output Channels 2 channels 9 Closing Position Signal Output Channel 1 channel 10 Device Power Loss Output Channel 1 channel
Communication Functions
| Item | Description |
|---|---|
| Communication Interfaces | 1 × Ethernet port
2 × RS-485 ports (the second RS-485 port shares the time synchronization port; function selectable via configuration) |
| Communication Protocols | IEC 60870-5-103, IEC 61850 (Ethernet), 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 | Differential Starting Current Setting | 0.1~100 | A | 1 | |
| 2 | Differential Instantaneous Overcurrent Setting | 0.1~100 | A | 5 | |
| 3 | Inflection Point Setting | 0.1~100 | A | 1 | |
| 4 | Percentage Bias Coefficient | 0.1~0.9 | — | 0.5 | |
| 5 | Motor Rated Current | 0.1~100 | A | 5 | |
| 6 | Motor Starting Time | 0～600 | S | 5 | |
| 7 | Stage I Overcurrent Setting | 0.1~100 | A | 8 | |
| 8 | Stage II Overcurrent Setting | 0.1~100 | A | 7 | |
| 9 | Stage II Overcurrent Time Delay | 0～100 | S | 0.5 | |
| 10 | Stage III Overcurrent Setting | 0.1~100 | A | 5 | |
| 11 | Stage III Overcurrent Time Delay | 0～100 | S | 1 | |
| 12 | Inverse Time Overcurrent Setting | 0.1~100 | A | 5 | |
| 13 | Inverse Time Overcurrent Delay | 0～100 | S | 1 | |
| 14 | Inverse Time Overcurrent Type | 0~3 | — | 1 | 1=Normal, 2=Very, 3=Extreme |
| 15 | Overload Setting | 0.1~100 | A | 5 | |
| 16 | Overload Time Delay | 0～100 | S | 2 | |
| 17 | Overload Protection Type | 0~2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 18 | Locked Rotor Protection Setting | 0.1~100 | A | 2 | |
| 19 | Locked Rotor Protection Delay | 0～100 | S | 1 | |
| 20 | Negative Sequence Stage I Overcurrent Setting | 0.1~100 | A | 2 | |
| 21 | Negative Sequence Stage I Overcurrent Delay | 0～100 | S | 1 | |
| 22 | Negative Sequence Stage II Overcurrent Setting | 0.1~100 | A | 1 | |
| 23 | Negative Sequence Stage II Overcurrent Delay | 0～100 | S | 2 | |
| 24 | Negative Sequence Stage II Protection 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 Protection Type | 0~2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 28 | Negative Sequence Current 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 | Overheating Alarm Level | 10%~100% | — | 80% | |
| 32 | Long Starting Time Setting | 0.1～100 | A | 5 | |
| 33 | Long Starting Time Enable Duration | 0～100 | S | 3 | |
| 34 | Start Interval Time Setting | 0～100 | min | 10 | |
| 35 | Undervoltage Block Starting 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 Protection Type | 0~2 | — | 1 | 0=Disabled, 1=Trip, 2=Alarm |
| 43 | Overfrequency Setting | 35～60 | Hz | 49 | |
| 44 | Overfrequency Time Delay | 0～100 | S | 0.5 | |
| 45 | Underfrequency Protection Setting | 35.0～65 | Hz | 51 | |
| 46 | Underfrequency Time Delay | 0～100 | S | 0.5 | |
| 47 | Undervoltage 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 Delay | 0～100 | S | 0.1 | |
| 54 | High Temperature Trip 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 |
Outline and Installation Dimensions
FAQ
Q：What types of motors require differential protection?
A:motor differential protection scheme
Motors of 2000 kW and above shall be equipped with differential protection. For motors below 2000 kW, differential protection is required if instantaneous current protection lacks sufficient sensitivity.
High-voltage motors for critical special applications (such as mine main drives and main ventilation) must be fitted with differential protection to ensure safe, reliable operation and avoid major losses and incidents.
Critical six-lead motors below 2000 kW shall also use differential protection as main protection for internal short circuits, when instantaneous protection cannot meet sensitivity requirements.
Q：What is the CT wiring configuration for motor differential protection?
For standard motors, the polarity end of CT (T/P marked terminal) must face the busbar or transformer side to ensure correct secondary current direction.
In motor differential protection CT connection, the wiring of differential protection of motor shall strictly follow A-A, B-B and C-C phase matching.
For units adopting motor differential protection self balancing, it is required to configure motor differential protection core balance CT and zero-sequence balance CT; please refer to the official wiring diagram for specific connection methods.
Q: ANSI code for motor differential protection?
A: ANSI standard code is 87M.
Q: What is motor differential protection?
A: It is a primary internal fault protection for medium and large motors. It compares the inlet and outlet currents of motor stator windings. Under normal operation or external faults, the two currents are balanced with nearly zero differential current. When internal faults occur, current balance is disrupted, the differential current rises rapidly, and the protection trips to isolate the faulty motor.
Q: What faults can motor differential protection detect?
A: It detects stator internal faults: phase-to-phase short circuit, turn-to-turn short circuit and single-phase grounding short circuit (low-resistance grounding system). It cannot detect motor overload, open phase, rotor faults or mechanical failures such as bearing damage and rotor stalling.
Q: Why is it the main protection of motors?
A: It features fast response, high sensitivity and no blind protection zone. It can cut off motor internal faults within milliseconds to prevent winding burnout and motor damage, which cannot be replaced by overcurrent or overload protection.
Q4: What is its core working logic?
A: The core is two-terminal current balance comparison. CTs are installed at the motor line side and neutral side. The protection device collects real-time three-phase currents from both ends, calculates differential current and braking current, and trips when the differential current exceeds the setting threshold under valid braking conditions.
Q5: Difference between motor and transformer differential protection?
A: ① Motor differential has simple logic without voltage ratio and phase angle conversion; transformer differential needs phase and ratio correction. ② Motor differential only protects stator windings; transformer differential covers primary and secondary winding faults. ③ Motor differential has lower setting value and higher sensitivity for minor turn-to-turn faults.
Q6: Why adopt double-ended CT configuration?
A: Double-ended CTs fully collect the inlet and outlet currents of stator windings to form a valid differential comparison loop. Single-ended CTs cannot reflect internal winding faults, causing protection failure.
Q7: Key setting parameters?
A: ① Differential start current: minimum threshold for protection operation;
② Braking coefficient: prevents maloperation caused by unbalanced current during motor start-up and external faults;
③ Time delay: generally 0s for instantaneous tripping.
Q8: Why is braking characteristic required?
A: Motor starting current is 5-8 times rated current, which causes CT saturation and unbalanced three-phase current, generating false differential current. The braking function raises the operation threshold with load current, effectively avoiding protection maloperation during start-up and external faults.
Q9: Does it work during motor startup?
A: Yes. It operates throughout startup and normal operation. The braking characteristic is specially designed for startup transient conditions to ensure no maloperation during startup and reliable tripping for internal faults.
Q10: Common causes of protection maloperation?
A: ① CT abnormalities: saturation, wrong wiring, reversed polarity, inconsistent ratio; ② Three-phase load unbalance; ③ Secondary circuit interference; ④ unreasonable parameter settings; ⑤ Transient current impact from external short circuits.
Q11: Inspection steps for accidental tripping?
A: ① Check for actual motor faults (burning smell, winding damage); ② Verify CT polarity and secondary circuit integrity; ③ Check three-phase current balance; ④ Confirm protection parameter settings; ⑤ Exclude transient interference and external fault impact.
Q12: Causes of protection refusal to operate?
A: ① Excessively large differential start current (insensitive to minor faults); ② Severe CT saturation leading to current sampling error; ③ CT secondary circuit open circuit; ④ Tiny fault current from slight winding insulation damage.
Q13: Applicable motor scope?
A: It is configured for medium/high-voltage motors above 2MW and key motors with high operational reliability requirements. Low-power low-voltage motors adopt overcurrent protection instead.
Q14: Coordination with overcurrent protection?
A: Differential protection is the instant primary protection for motor internal faults. Overcurrent protection acts as thedelayed backup protection, covering external faults and replacing differential protection when it refuses to operate.
Q15: Can it protect single-phase grounding faults?
A: It works for low-resistance grounding systems with large grounding fault current. For high-resistance grounding systems, the grounding current is too small to trigger differential protection, requiring dedicated grounding protection.
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xiao zhang –
This motor differential relay (ANSI 87M) serves as main protection for medium-high voltage motors. It compares currents from motor terminal and neutral CTs, features high sensitivity against stator short-circuit and earth faults, with CT broken blocking to avoid misoperation. Multiple communication options are available for industrial and power station projects worldwide.
Jack –
Low burden on CTs and PTs — doesn’t affect measurement accuracy.