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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Automatic Bus Transfer vs High-Speed Bus Transfer: Differences, Principles and Selection
Automatic bus transfer devices and high-speed bus transfer devices both transfer loads from a normal power source to an alternative source when the normal source fails or becomes abnormal. However, they differ significantly in their operating objectives, transfer criteria, operating speed, synchronism supervision and typical applications. In simple terms: An automatic bus transfer device restores […]
2026-09-20
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Motor Phase-Loss Protection Relay: Operating Principle, Functions and Setting Calculations
Motor phase loss, also known as open-phase operation or single phasing, occurs when one phase of a three-phase power supply or one phase current is interrupted. A three-phase motor may fail to start if phase loss is present before starting. If phase loss occurs while the motor is running, the motor may continue to rotate, […]
2026-09-20
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How to Select Substation DC Power Supply System Panel Capacity and Charger Modules
This guide explains how to size a substation DC power supply system panel, covering nominal DC voltage selection, load classification, backup duration, battery capacity calculation, momentary-load verification and N+1 charger module configuration.
2026-09-19
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Transformer Buchholz Relay: Operating Principle, Functions and Setting Calculations
A Buchholz relay is a gas and liquid actuated relay used to protect conservator-type liquid-immersed transformers and reactors. It is installed in the pipe connecting the transformer main tank to the conservator. In accordance with IEC terminology, a Buchholz relay is intended to detect: Gas release from the protected equipment; Liquid surge from the main […]
2026-09-13
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Transformer Overcurrent Protection Relays: Operating Principle and ANSI 50/51 Setting Calculations
Transformer overcurrent protection relays continuously monitor transformer currents through current transformers (CTs). When the measured current exceeds the configured pickup setting and the relevant operating conditions are satisfied, the relay sends a trip command to the circuit-breaker to clear the fault. For small and medium-sized distribution transformers, overcurrent protection may serve as the main protection. […]
2026-09-13
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