Low- and medium-voltage distribution networks carry the power that keeps plants, mines, municipalities, and solar farms running. When protection is not designed or coordinated correctly, a single fault on one feeder can trip whole panels, take down backup systems, or expose people and equipment to serious risk.
South African networks face extra pressure. Ageing municipal reticulation, long rural line lengths, poor power quality, growing solar capacity and frequent grid disturbances all push feeder and earth leakage protection to the limit. Traditional protection, designed for simple grid-only operation, now has to cope with VFDs, inverters, harmonics, and hybrid supplies.
This Q&A guide explains how to approach electrical distribution protection across:
- Utilities and municipal substations
- Mining reticulation and MCCs
- Solar and renewable plants
- Industrial feeders and backup power systems
It is written for distribution engineers, project and design teams, MCC specialists, solar EPCs, and maintenance electricians who require safe operation, selective tripping and stable uptime. The values mentioned here are indicative. All settings must be confirmed on site with CT checks, OEM data, and commissioning procedures.
You can learn more about relay behaviour and application in the NewFeed Relay Deep Dive, see how GA, GA+ and GA MS0 compare on the Product Comparison Page, or explore the full Electrical Distribution Industry overview. If you want to relay suggestions for the current range and mounting, use the Relay Selector tool.
What are the essential types of protection required in low and medium-voltage electrical distribution?
Distribution protection is usually built from a set of core functions that work together. Missing one or applying it incorrectly often leads to nuisance trips or undetected faults.
Core protection types
Feeder protection
Protects cables, busbars and downstream loads against phase-to-phase and phase-to-earth faults.
- Instantaneous and time delayed overcurrent
- Short circuit protection
- Directional elements were needed
Recommended NewElec relays: KG and KH PQM Relays, NewFeed
Earth leakage protection
Detects insulation breakdown and dangerous residual currents that return through earth rather than the intended path.
- Essential in mining, municipal networks, industrial MCCs and pump stations
- Needs careful coordination on long lines and with VSD and VFD feeds
Recommended NewElec relays: GA, GA+
Thermal and overload protection
Prevents long-term heating damage to cables, transformers and motors.
- Time current characteristics aligned with the insulation class
- Integrated into motor protection relays and feeder devices
Phase imbalance and single phasing protection
Addresses unbalanced voltage and current, common on rural feeders and stressed networks.
- Detects missing phases and serious imbalance
- Limits negative sequence heating in motors
Power quality monitoring
Modern networks need visibility of:
- Harmonics and waveform distortion
- Repeated voltage dips and swells
- Frequency drift, especially on hybrid or islanded systems
Recommended NewElec relay for PQM (Power Quality Monitoring): KG Relay, KH Relay and NewFeed
Engineering implication
Distribution protection design is not just about picking a breaker size. It is about choosing the right relay family, ensuring correct CT sizing and wiring, and combining feeder, earth leakage, thermal and PQ supervision into a coordinated scheme.
What makes feeder protection different in utility, municipal, mining and renewable applications?
The basic protection principles stay the same, but the environment changes the stress on the network and the behaviour of faults.
Utility and municipal networks
- Long rural lines raise line impedance and reduce fault currents.
- Reclosers and sectionalising practices affect coordination.
- Old infrastructure creates voltage dips and PQ problems.
Feeder relays must:
- Operate reliably at lower fault levels
- Coordinate with upstream primary protection and downstream EL devices
- Tolerate frequent PQ disturbances
Mining distribution
- MV and LV feeders to crushers, conveyors and pumps often run hundreds of metres.
- Cable capacitance increases earth leakage.
- VSDs and soft starters introduce high-frequency components.
Feeder relays and EL devices must:
- Handle high leakage without nuisance tripping
- Coordinate with motor relays and MCC zoning
- Provide good event logging for fault tracing
Solar and renewable networks
- Inverters change fault levels and fault duration.
- Reverse power flow can occur when export exceeds load.
- Harmonics and PQ events are more frequent.
Feeder protection must:
- Recognise power flow direction where required
- Monitor voltage, frequency and harmonics
- Support grid code and utility interconnection requirements
Backup and hybrid systems
- Generator, UPS and grid tie configurations change network impedance.
- Automatic transfer switches create transients.
- Frequency can drift under load.
Relays such as KG/KH Relays and NewFeed help stabilise these supplies by supervising voltage, frequency and PQ while providing feeder and EL protection.
What is earth leakage protection in distribution networks and why do nuisance trips occur?
Earth leakage protection detects residual currents that flow through earth instead of returning along the neutral or phase conductors. In distribution networks, several factors increase leakage without a real fault.
Why nuisance trips happen
- Long cable runs increase capacitance to earth, which generates steady leakage.
- VSD and VFD feeds produce high-frequency leakage currents and common-mode noise.
- Multiple downstream loads share an upstream EL device, and their leakage adds together.
- Poor power quality distorts waveforms, which basic EL relays may misinterpret.
- Incorrect relay choice leads to very low trip thresholds that are unsuitable for long or VSD-driven feeders.
Practical example: A municipal feeder that supplies a pump station 200 metres away may show more than 150 to 250 mA of healthy leakage when all drives and motors are running. A 30 mA or 100 mA EL relay on that feeder will almost certainly nuisance trip.
How does the NewFeed Relay support solar, renewable and grid interconnection requirements?
The NewFeed Relay is designed as a feeder and motor protection relay for modern LV and MV networks that include renewables and hybrid supplies.
Key features for solar and renewables
- Voltage, current, thermal and earth fault protection
- Harmonic monitoring up to the 37th harmonic
- Positive, negative and zero sequence supervision
- Frequency and voltage protection suited to grid codes
Application examples
Solar farm feeder
- NewFeed monitors the inverter side voltage and current.
- Detects overcurrent, reverse power flow and PQ deviations.
- Supports safe disconnection during grid disturbances.
A hybrid plant with a generator and solar
- NewFeed supervises switching between the grid, generator and solar.
- Supports stable changeover at the ATS or breaker.
- Logs PQ events to help engineers diagnose flicker and nuisance trips.
Engineering implication: instead of adding separate PQ meters, standalone EL devices and simple overcurrent, NewFeed integrates these in one relay, making it easier to commission and maintain.
What relays are Eskom-approved and what does the approval process mean?
Eskom approval gives utilities and municipalities confidence that a relay type has passed technical evaluation and field testing under local conditions.
NewElec relays used in Eskom applications include:
-
- 320 Series Relays
- NewCode Relay
- NewCode Dual Ethernet Relays
- KD Series Relay
- KE Series Relay
This approval typically confirms:
- Compliance with protection and performance specifications
- Robust operation on PQ disturbed networks
- Suitability for South African distribution practices
- Availability of local support and spares
Engineering note: using Eskom-approved devices in municipal or industrial networks simplifies specification, purchasing and long-term maintenance.
Newelec 320M
Newelec SDR1 Stall unit only
Newelec KD & KE
How do the KG/KH Relays and NewFeed relays differ, and when should each be used?
Both KGK and NewFeed are feeder relays, but they target slightly different environments.
KG and KH PQM Relays
- Suited to grid level and municipal feeders
- Focuses on robust overcurrent and earth fault protection
- Ideal where PQ monitoring is important, but renewable penetration is low
NewFeed Relay
- Phase Negative Sequence functions for solar and hybrid systems
- Provides harmonic analysis and detailed event logging
- Ideal for feeders supplying inverters, VFDs and mixed industrial loads
Rule of thumb
- Choose KG and KH PQM Relays for traditional grid and municipal feeders with limited inverter content.
- Choose NewFeed where solar, VFDs, UPS systems, and hybrid supplies are common.
How do NewElec relays maintain long-term reliability, 20 to 30 years in service?
Many NewElec relays remain in service for two to three decades. This long life comes from:
- Conservative design with safety margins
- Components chosen for harsh environments
- Noise-immune inputs for PQ-stressed networks
- Stable firmware and protection algorithms
- Local manufacturing and support, which simplifies repairs and spares
Example: the 320 Series has been installed in South African plants since the 1980’s and still operates reliably in many MCCs.
What are the most common causes of protection failure in distribution systems?
Failures rarely come from the relay alone. They usually result from design or commissioning issues.
Typical causes
- Incorrect CT ratios, polarities or wiring
- Breakers and relays are not time-graded correctly
- Default settings left unchanged after installation
- No PQ monitoring, so harmonics and dips go undiagnosed
- Loose connections on CT circuits or earth bars
- Using devices not suitable for VFD-rich feeders
For a deeper look at common mistakes on motor circuits, see the blog The 10 Pitfalls That Cause Nuisance Trips and Downtime in Mining Motor Protection. Many of the same issues apply to distribution feeders.
How do relays support grid stability in high renewable penetration sites?
As the share of solar and other renewables increases, distribution relays play an important role in keeping the network stable.
Relays such as NewFeed and KG/KH Relays help by:
- Monitoring and logging frequency swings
- Detecting under- and overvoltage conditions that stress inverters
- Assisting with anti-islanding requirements
- Managing reconnection after dips and outages
- Providing PQ data that planners and operators can use to improve design
On hybrid feeders, this information helps engineers decide where to add filters, change settings or adjust inverter behaviour so that nuisance trips are reduced, and compliance is maintained.
Can NewElec relays interface with SCADA, PLCs and digital substations?
Yes. NewElec relays are built to integrate with common control and monitoring systems used in South Africa.
Typical options include:
- Serial or Ethernet-based communication ports
- Support for standard protocols used in utility and industrial SCADA
- Remote access to measurements, status, events and fault records
- Trip and alarm signalling to PLC-based control systems
This makes it easier to build digital dashboards, alarm lists and maintenance views that show the health of feeders and MCCs in real time.
Applied Engineering Scenarios
How should distribution protection be designed for backup power, generator, UPS and hybrid systems?
Backup and hybrid systems create non-standard fault conditions, so protection must be set with care.
Design points to consider
- Generator and UPS short circuit levels are often lower than grid fault levels.
- Frequency can deviate during load acceptance and rejection.
- Voltage dips and transients occur at changeover points.
- Earthing arrangements may differ from the grid supply.
Practical steps:
- Use KG Relay/KH Relay or NewFeed to supervise voltage and frequency on generator and hybrid feeders.
- Use GA+ where VFDs and long cables are present on backup supplies.
- Time grade EL and overcurrent settings between grid and generator modes where required.
- Test changeovers under load during commissioning and record relay behaviour.
What documentation, wiring diagrams and commissioning guides does NewElec provide?
NewElec supports engineers and technicians with:
- Product manuals and quick reference guides
- Wiring diagrams for DOL and Star-Delta connections among others
- Application notes for solar, mining and municipal networks
- Case studies that show settings and field performance
- Training material and commissioning support on request
These resources can be downloaded from the relevant product pages and from the Resources and Downloads area. A consolidated Electrical Distribution Protection Guide, Q&A Edition, can also be offered as a PDF for plant and project teams.
Frequently Asked Questions Recap
Does every feeder need both feeder and earth leakage protection?
Most critical feeders benefit from both. At minimum, apply feeder overcurrent, short circuit and EL on circuits with high safety or production impact.
Can NewElec relays be added to older panels without a full MCC replacement?
Yes. Many devices are available in retrofit-friendly formats, which allows targeted upgrades on priority feeders first, then phased rollout to the rest of the plant.
What role does power quality monitoring play in distribution protection?
PQ data explains many nuisance trips and helps engineers design better networks. Devices such as KG and KH Relays as well as NewFeed provide this insight without separate meters on free Front-End Software and via Mobile App.
Who can assist with setting and coordination?
NewElec’s engineering team and local partners can support coordination studies, setting reviews and training for plant teams and system integrators.
How long have NewElec been around
NewElec has been operating for more than 30 years.
They were established in the early 1990s, and their relay families like the 320 Series, GA Series, and later GA+, GM0, KG/KH and NewFeed have all been developed and refined over that time.
This is why their documentation consistently refers to “30+ years of field reliability” in South African industrial, mining, water and utility networks.
Why Choose NewElec?
- Feature-Rich Products – Our relays come equipped with advanced functionalities, including real-time event recording and seamless integration with various communication protocols. These features provide comprehensive protection and control, setting NewElec apart from competitors.
- Long-Term Durability – Designed for a lifespan of 20 to 30 years, NewElec’s products offer long-term reliability and reduced maintenance costs. This durability ensures a solid return on investment and uninterrupted operations.
- Exceptional Support – Our dedicated team provides ongoing guidance and assistance, from initial consultation to post-implementation support. We work closely with clients to tailor solutions that meet their specific needs, ensuring a seamless integration process and optimal performance.
Don’t wait for a shutdown or system failure to upgrade. Why Wait to Automate™ is your practical, scalable, and affordable path to intelligent motor protection and automation. Contact us today to learn how easy it is to bring your MCC into the digital age.
