1. Overview and Objectives An 11 kV / 0.4 kV substation is an important part of the power distribution infrastructure serving industrial facilities, commercial buildings, and public facilities. Its primary functions are to receive power, step down the voltage, and distribute electricity. Power is supplied from the upstream 11 kV network and transformed to 0.4 […]

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 […]

1. Internal Arc Fault: A Rapidly Developing and Destructive Fault Internal arc faults in MV/LV switchgear are among the most destructive fault types in power distribution systems. When insulation breaks down or a sustained arc forms between conductors, intense light radiation, high temperature and pressure effects are produced within an extremely short time. As the […]

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 […]

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, […]

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 […]

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 […]

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.

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 […]

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. […]