Technical Knowledge Sharing

Generator Loss-of-Excitation Protection (ANSI 40): Operating Principle, Functions and Setting Calculations

1. Overview Generator loss-of-excitation protection, also known as loss-of-field protection (ANSI 40), detects abnormal operating conditions caused by the loss or severe reduction of excitation in a synchronous generator. Following a loss of excitation, the generator may absorb reactive power from the power system and lose synchronism. Depending on the generator characteristics and system conditions, […]

2026-10-08

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Generator Reverse Power Protection (ANSI 32): Working Principle, Purpose and Setting Calculations

I. Overview Generator reverse power protection (ANSI 32R) detects active power flowing from the grid into the generator. This condition can occur when the prime mover loses sufficient mechanical input while the generator remains connected to the grid. The generator then operates as a synchronous motor, drawing active power from the grid and mechanically driving […]

2026-10-02

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Motor Differential Protection (ANSI 87M): Working Principle, Purpose and Setting Calculation

Motor differential protection (ANSI 87M) is the main protection for large high-voltage motors, used to rapidly clear internal phase-to-phase short circuits. This article explains in detail the working principle, protection functions, setting calculation methods and typical settings of 87M, helping electrical engineers quickly master the key setting points. Applicability Note: According to GB/T 50062-2008 Code […]

2026-09-30

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How to Select an Anti-Islanding Protection Relay for Solar PV Systems

As solar photovoltaic (PV) installations continue to expand worldwide, reliable grid interconnection protection has become increasingly important. Anti-islanding protection is one of the key protection requirements for grid-connected PV systems. Selecting the right anti-islanding protection relay requires more than matching a relay to the PV system voltage. Engineers should also consider the required protection functions, […]

2026-09-29

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What Does a Solar PV Grid-Tie Protection Relay Include?

A solar PV grid-tie protection relay, also referred to as a PV grid interconnection protection relay, is used to monitor operating conditions at the point of common coupling (PCC) between a photovoltaic (PV) system and the utility grid. It provides protection, control and disconnection functions in response to unintentional islanding, abnormal voltage or frequency and […]

2026-09-28

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Transformer Magnetising Inrush: Causes, Mitigation, and Differential Protection

When a transformer is energised at no load, the current drawn may temporarily rise well above its normal magnetising current. This transient current is known as magnetising inrush. It is usually a consequence of energisation and does not, by itself, indicate an internal transformer fault. Magnetising inrush can produce a substantial differential current. If the […]

2026-09-24

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Directional Overcurrent Protection Relay ANSI 67: Operating Principle, Applications and Setting Calculation

A directional overcurrent protection relay combines an overcurrent element with a directional element. Protection operates when the measured current exceeds its pickup setting, the fault is identified in the configured operating direction, and the applicable operating time has elapsed. Phase directional overcurrent protection is designated ANSI 67. Directional protection for earth faults may be designated […]

2026-09-23

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Hardwired Tripping vs. IEC 61850 GOOSE-Based Tripping: A Technical Comparison

Conclusion First Hardwired and GOOSE-based tripping should not be reduced to a simple distinction between “reliable” and “unreliable”. They have different technical characteristics, supervision capabilities and failure modes. The principal advantages of hardwired schemes are their visible circuit structure, technological maturity, readily analysable latency and ability to operate independently of the communication network. The principal […]

2026-09-22

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