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News Article

07 September 2018

G59 Testing - An Overview

Utility themed banner for G59 Testing

G59 Testing Explained by T&R Test Equipment

What is G59?

G59, (currently G59 issue 3, amendment 4) is the regulation which encompasses the connection of a generator device, running in parallel (synchronised), with the National Grid. The origins of this regulation are in the Ofgem rules for Embedded Generators and it is administered as the ENA Engineering Recommendation G59, Issue 3, Amendment 4 as of July 2018. (NB this regulation is to be superseded by the upcoming G99 regulations) 

G59 is relevant for all power generation plants, including: Solar, Wind, Combined heat and power etc. G59 is relevant to any plant which generates over 16A per phase. Where the power generated is below these amounts G83 (G83/2-1) is applicable.

Why test to G59?

G59 was introduced to protect the National Grid from receiving electricity from generators in a dangerous manner. The regulation is to prevent any generator from sending the electricity onto the Grid without the knowledge and permission of the local electricity authority.

G59 - The relay’s purpose

The purpose of the relay in G59 is to prevent potentially deadly situations from occurring where a generator begins feeding electricity into a circuit which has been isolated. The relay will prevent these situations by automatically disconnecting the generator from the mains.

Numerous other aspects are considered by the DNO when assessing the potential connection of the generator to the National Grid. These will typically include:

  • Voltage Rise & Step
  • Interface Protection Capability
  • Harmonics, Distortion & Unbalance
  • Fault Level Contribution
  • Reverse Power Flow
  • Clustering of Installations
  • Planning – Local Consent & Land Rights
  • The Existing Network Suitability

G59 what tests are required?

  • Over Voltage (Stage 1 & 2)
  • Under Voltage (Stage 1 & 2)
  • Over Frequency (Stage 1 & 2)
  • Under Frequency (Stage 1 & 2)
  • Vector shift
  • ROCOF (Rate of Change of Frequency)
  • LOM (Loss of Mains)
  • Stability test

These tests are normally carried out by an independent contractor but overseen and witnessed by an engineer from the local DNO.

The G59 relay is designed to cause the connected circuit breaker to open if any of the above tests go outside of the programmed limits, for protection purposes.

T & R Test Equipment products ideal to test to G59:

Since its launch in the mid-1990’s, T&R Test Equipment’s DVS3 Test Set has been the go to instrument for anyone testing to G59 regulations.

DVS3 mk2:

T&R Test Equipment DVS3

  • 3-φ Voltage output from 1-φ supply
  • 0-133V φ-N output voltage,
  • (0-292V φ-N with optional VT box)
  • 45VA/phase maximum output
  • Variable Frequency 40-999.9Hz
  • Phase shift ±180.0°
  • Multi-function timing system
  • Ideally suited to all testing G59 schemes
  • Step change of phase and df/dt
  • Large back-lit liquid crystal display
  • Compact and lightweight
  • Automatic mains voltage selection



T & R Test Equipment have now launched their new ART3V. As with the DVS3, this is a 3-φ voltage and frequency relay tester but has a higher voltage output. 


T & R Test Equipment ART 3V

  • 3-ø Voltage output from 1-ø supply 
  • 0-450V ø-N output voltage 
  • 20VA/phase maximum output 
  • Variable Frequency 30-999.99Hz 
  • Full 360° phase shift (±180°) 
  • Multi-function timing system 
  • USB data storage 
  • Step change of phase and ROCOF 
  • Large 6.5” back-lit colour LCD 
  • Wide input supply range: 90-264V 
  • Fully Programmable test procedures 
  • Rugged case with removeable lid 
  • Weighs under 9kg 
  • Suited to testing G59/G99 schemes

 ART3V Video Icon