Earth Leakage Protection for VSD’s

Earth Leakage Protection for VSD’s

In the past, if an earth fault relay was designed for use with or near a VSD, it typically meant utilising a fixed-frequency filtering algorithm centred near the fundamental frequency, i.e 50Hz. The ‘noise’ and harmonics created by a VSD meant that the output frequency would not always be fixed at 50 or 60 Hz, and any faults outside of that may go unnoticed until the system has already sustained significant damage.

Uniquely suited to Earth Fault Monitoring of Variable Frequency Drives, the Littelfuse EL731 series is a new and sensitive Earth Leakage Technology – the first of its kind to offer complete coverage of all frequencies from 0(DC) to 6,000Hz, including DC earth leakage typical for VSD applications.

This technology uses TWO current transformers (CT’s) to monitor either end of the frequency range which helps overcome unwanted trips due to noise or harmonics. This is a common occurrence in older Earth Leakage Relays which use one CT.

The significant benefit of using two current transformers is that independent trip and alarm levels can be set for each CT.

1. CT1 will detect from DC & (0Hz) – 90Hz AC

2. CT2 will detect from 20Hz – 6,000Hz, but is configurable for various ranges

How the Littelfuse EL731 Relay Protects Variable Frequency Drives

Overcoming Unwanted Trips

Two independent trip levels allow the user to adjust CT2 to account for noise or harmonics while keeping CT1 trip level at lower setting.

This means that if a fault occurs at 50/60Hz, CT1 can respond at the lower setting, but if the fault is in the higher frequencies, then CT2 can respond but at a higher trip level. 

Achieve Compliance and Low-Level Earth Fault Protection

High Resistance grounded systems have many advantages, but the increasing use of VSD’s can make it difficult to monitor for ground faults and other problems. The Littelfuse EL731 relays are a new generation level of protection and go a long way towards eliminating these problems, leading to a safer and more reliable electrical system.

Features & Benefits

  • Adjustable pickup (30-5,000 mA)
  • Wide frequency protection (including DC)
  • 32-char OLED display
  • Local LED indication
  • CT-Loop monitoring
  • Analogue Output (4-20mA)
  • Adjustable time delay
  • Alarm and trip settings
  • Temperature-sensor input
  • Output contacts
  • Network communication
  • Harmonic filtering
  • Microprocessor based
  • Universal power supply

How can Fuseco help you?

We supply a range of Earth Leakage & Earth Fault relays to protect your equipment, protect your people, and reduce your downtime. Our engineers are experts in their fields and can help you to select the right product for your needs. Contact Fuseco today to see how we can help.

We're here to help

Talk to an expert today.
Our friendly team of highly trained specialists will quickly assist you.

Get a quote technical support 1300 387 326

We promise to respond within 4 business hours (AEST).

Or you will receive $100 off your next purchase. Read how it works.

Top FAQs

A protection relay is a device that receives inputs typically from current transformers CT’s (but can be other sources) and then compares these inputs to set levels. If these inputs exceed the set levels a protection relay can then provide that information via display or indication, feed that information to other electronic control devices or it can be connected to a circuit breaker to isolate power.

Yes, currently Fuseco can offer both earth leakage and NER relays that are compliant to AS2081:2011. The relay manufacturer (Littelfuse) is also currently in the final stages of development for an AS2081:2011 compliant continuity relay that we expect to release in the near term.

An arc fault is a type of electrical fault that results from the breakdown of an insulating medium between two conductors where the energy is enough to sustain an arc across the insulator (often air) and can cause extreme amounts of light (arc flash), immense heat upwards of 19,000 degrees, and a resulting explosive pressure wave (arc blast). By using a relay that has optical sensors we can detect the flash of light the emanates from an Arc Flash and within 1 msec send a signal to a breaker to interrupt power. Because of the immense energy being released by an Arc Flash reaction time is critical. It can be seen on the graph that with a relay reaction time of only 1 msec (+ circuit breaker reaction time) we can interrupt power before the Arc Flash can result in critical damage.

An arc-flash happens when electric current flows through an air gap between conductors. There are several ways this can happen but the most common occurrence is when conductor insulation is worn or broken down.

The most important aspects of arc-flash relays are:

  • reaction time
  • trip reliability
  • ease of installation
  • sensor flexibility
  • software
  • sensor design
  • avoidance of nuisance tripping
  • scalability

To gain a deeper understanding of which features to consider when selecting an arc-flash relay please refer to the downloadable application guides.

Arc-flash relays are a necessary component in an electrical cabinet because they reduce the amount of incident energy in the system. While an arc-flash relay cannot prevent an arc flash from happening, it will protect critical assets and workers’ safety by reducing the severity of the flash. An arc-flash relay is an integral part of an arc-flash protection scheme that can minimize damage, and save money, time, and lives.

Three phase power systems are most often solidly earthed, however by using a Neutral Earthing Resistor (NER) a power system can be resistance earthed. This is done so that if an earth fault were to occur the amount of fault current will be limited by the NER resistance. One potential problem with a resistance earthed system is; what happens if the NER goes open circuit due to damage? If this were to happen the power system has now changed from a resistance earthed system to a system with no earth reference (floating). Now the NER is no longer restricting the amount of fault current and other devices that rely on an earth reference in order to operate, cannot do so. By using a NER monitoring relay the resistance and integrity of a NER can be continually monitored to detect for any variance in the NER resistance or integrity.

An earth fault can occur as a result of inadvertent contact between and energized conductor and earth or equipment frame. There can also be earth leakage from a system without “inadvertent contact”. This type of fault can be called capacitive earth leakage and it is caused by a capacitive effect between a high power conductor and earth. Small amount of earth leakage current can occur as a result of this capacitive effect. Whether it is smaller amounts current from capacitive earth leakage or larger amounts of current from direct inadvertent contact an earth leakage relay can detect this fault current. In all electrical circuits, current returns to its source. An earth fault relay can use a zero sequence CT to monitor phase current to ensure that all current coming from the source returns on those same conductors or it can monitor current in the connection between transformer neutral and earth. By either method the earth leakage relay detect any lost current to earth.

Hi Tim, just wanted to thank you and the Fuseco team for your help. You've managed to help us solve some nagging issues here and the Littelfuse SE-330AU relay installation has saved us a lot of time. Thanks!

Mark Sherman

PGS Silver, Queensland

Just wanted to send a note of thanks to you guys. When it comes to relays, your advice & service is high level & appreciated. Cheers.

Jesse Marshall

Newcrest WA

The Littelfuse SE-701 & the CT's are functioning well. Thanks guys, really appreciate your help. Good to work with people you can rely on.

Cliff Peligro

Alpha Coal, Queensland

Technical Support

Our experts are all pre-eminent leaders in electrical products who provide excellent support in their areas of expertise.

Technical support

Talk to an expert

Our friendly team are highly trained product experts who really enjoy helping customers find what they need.

1300 387 326

call 1300 387 326

Enquire by email

We promise to respond within 4 business hours (AEST) or you will receive $100 off your next purchase.

Enquire now