Beckwith M-3430 Generator Protection Relay

50/27- Unintentional Energizing Protection

Prevent the generator from accidentally closing and exciting during shutdown, which may cause damage to the asynchronous start-up of the unit. This function combines overcurrent and undervoltage criteria to ensure rapid locking and tripping under abnormal operating conditions.

59N/27TN -100% stator grounding protection

By using a combination criterion of detecting the third harmonic voltage (59N) at the machine end and the third harmonic undervoltage (27TN) at the neutral point, a 100% grounding protection for the stator winding is achieved, covering the fault area near the neutral point that cannot be detected by traditional fundamental zero sequence voltage protection. This protection requires an external third harmonic filter and appropriate PT configuration.

2.3 Voltage and Frequency Protection

27- Undervoltage/Overvoltage protection

RMS undervoltage (27): Two stage setting, adjustable from 5-200V per stage, with a delay of 1-8160 cycles. Supports two measurement modes: RMS (full waveform) and DFT (fundamental wave), with the former having higher accuracy over a wide frequency range.

Third harmonic undervoltage (27TN): used for neutral point third harmonic monitoring, set to 0.3-20.0V.

Overvoltage protection (59): prevents insulation damage caused by abnormal voltage rise of the generator.

81- Over/Underfrequency protection

Four independent frequency protection settings, each segment can be set as overclocking or underflocking. The frequency setting range depends on the rated frequency (50Hz or 60Hz model), with a delay of 5-65500 cycles. Suitable for scenarios such as generator low-frequency operation protection and system frequency abnormal disconnection.

2.4 Circuit Breaker and System Abnormal Protection

50BF - Breaker Failure Protection

When the generator circuit breaker fails to disconnect normally after the tripping command is issued, the delay action will trigger the adjacent circuit breaker to trip or issue a malfunction alarm. This function ensures reliable fault removal and prevents the fault from expanding.

60FL-VT fuse breakage detection and locking

By comparing the balance and negative sequence components of the three-phase voltage, detect the melting or disconnection of the secondary circuit fuse of the voltage transformer. Once VT disconnection is detected, the relevant voltage protection functions (such as 21, 27, 59, 81, etc.) can be programmed to be locked to prevent misoperation.

Precautions for key parameter tuning

3.1 V/Hz protection setting

The setting of overexcitation protection should be based on the weaker V/Hz tolerance of the generator and step-up transformer. Typical setting: timed starting value of 105%~110%, delay of 5-10 seconds; The inverse time limit curve should be matched with the excitation limit curve provided by the manufacturer. Special attention should be paid to the fact that low-frequency operation may cause an increase in V/Hz value during the start-up and shutdown process of the unit.

3.2 demagnetization protection setting

The M-O circle setting for demagnetization protection needs to be calculated based on the synchronous reactance (Xd) and transient reactance (Xd ') of the generator. Usually, the first zone (alarm) is set for reactive power reverse detection, and the second zone (trip) covers the demagnetization stability limit. It should be coordinated with the low excitation limit of the excitation system to prevent conflicts between protection and regulators.

3.3 100% stator grounding protection

The distribution of the third harmonic voltage changes with the load of the generator, so the 59N/27TN protection usually requires two-stage setting: the third harmonic overvoltage at the machine end (under light load) and the third harmonic undervoltage at the neutral point (under heavy load). The "OR" logic of both achieves full coverage. Before operation, the amplitude of the third harmonic under different loads should be measured to determine a reliable operating threshold.

3.4 Reverse power protection

The reverse power protection setting of a steam turbine generator is usually -0.5% to -2% of the rated power, with a delay of 0.5 to 2 seconds (to prevent misoperation). Gas turbines and diesel generators can be tuned for lower sensitivity and longer delay due to allowing for brief reverse power.

Additional functions and data management

4.1 Oscillograph Recorder

The M-3430 has built-in recording function and can store 170 cycles of data. Users can configure it into 1-4 partitions. The sampling rate is 16 times the rated frequency (800Hz for 50Hz system, 960Hz for 60Hz system). The trigger source can come from specified state inputs, trip outputs, or serial communication. The recorded data can be downloaded and analyzed offline through IPScom software (M-3801D IPSplot optional) ™  Plus software).

4.2 Target Storage and Event Recording

32 target storage records include: functional components that have been activated, functional components that have been activated but not yet activated, input/output contact status, timestamp, timer status, phase current and zero sequence current at the time of tripping. Each target has a millisecond level time scale, which facilitates fault timing analysis.