Captech has Launched the Only NER Monitor Compliant to AS/NZS 2081May 20th, 2019 Filed under Power Factor Correction
The earthing system plays an important role in an electrical network. For network operators and end users, avoiding damage to equipment and providing a safe operating environment for personnel and continuity of supply are major drivers behind implementing reliable fault mitigation schemes.
A widely utilised approach to managing fault currents is the installation of neutral earthing resistors (NERs). NERs, or neutral grounding resistors, are used in AC distribution networks to limit transient over voltages that flow through the neutral point of a transformer or generator to a safe value during a fault event.
Generally connected between ground and neutral of transformers, NERs reduce the fault currents to a maximum pre-determined value that avoids a network shutdown and damage to equipment, yet allows sufficient flow of fault current to activate protection devices to locate and clear the fault.
The standard AS/NZS 2081:2011 was the first standard to include the requirements for NER integrity protection devices. NER monitors monitor the integrity of the current limiting device (NER). If there is a substantial increase or decrease in the resistance of the NER, the power to the primary of the transformer is required to be disconnected.
NER monitors are required by AS/NZS 2081 section 8 therefore to monitor the integrity and value of the NER where the increase in impedance shall be no more than 100% or the decrease in value of more than 50% from the nominal value of the NER. The maximum operating time of no more than 10 seconds is required of the monitor.
The Bender NGRM700 monitors monitor earth leakage and voltage on the neutral via a CT and uses ‘sensing resistors/coupling devices’ for various voltages up to 25kV. It is the only monitor that is AS/NZS 2081 compliant.
The NGRM700 is capable of detecting DC earth leakage and phase monitoring, tripping on RMS/fundamental component signal or harmonics and monitoring when the circuit is de-energised.
This makes the NGRM700 a first choice for the Australian market as there is no current product that has the same capabilities and that meets all of the requirements of AS/NZS 2081.