DNOs G99 Compliance Testing Acutest Test Equipment

In the last 20 years the world has seen a massive change in the way power is generated.  Historically within the UK, power was generated by a few large power generation stations, the power was then exported onto the National Grid and transported throughout the country.  When exporting to the grid, we have always ensured synchronisation using relays to ensure the grid remained stable (checking voltage and frequency).

This task was easier to plan on one hand as there was less generation sites - but each individual site would have had a bigger impact on grid stability!  To keep the grid to capacity there where standby/quick to manoeuvre Power Stations as well as companies with generators who could be called upon to top up the supply.  When top up generators started to be utilised, a need was identified to control them.... and the G59 Standard was introduced!

We at T & R were one of the first companies to produce a dedicated Relay Test Set to test to this standard - DVS3 was born.  The DVS3 followed the structure of the G59 Standard, helping Testing Engineers conduct commissioning and acceptance tests and thus the DVS3 became one of the sought-after products in respect of this testing regime.

These schemes typically exported to the grid at a HV level (11KV) and that is why the DVS3 generated a 0-130V output to test the relays set for 11KV.  Over the years this has changed, many small-scale generation projects have been commissioned which export at 230V.  To adapt to this a small transformer, plus a kit, was introduced to the DVS3 to up the available test voltage.


Greener Carbon Neutral Generation

In recent years there has been a move to greener carbon neutral generation: Solar PV, Wind, Hydro, Tidal, Geothermal and Biomass.

These generation methods tend to be on a smaller scale compared to the older Power Stations, with locations not necessarily convenient for existing cabling resource. This has led to an update: G59 → G99 (April 2019).

G99 reflects the changes in the regulation, not just the actual testing and commissioning but whole process. Changes were made to reflect the changes within microgeneration including the availability of infrastructure.  All in the effort to maintain grid stability.

The UK now has less in terms of large-scale generation; the gap has been filled with these renewable small-scale projects, and we also need to factor in the changes taking place in respect of electric recharging vehicles (EVSE).  The culmination of this puts a strain upon the grid and its stability with a greater need for local small-scale generation as well as battery facilities to keep the grid stable.



How T&R Test Equipment Always Adapts

The G99 regulation is meant to keep the availability and quality of the grid where it needs to be.

T&R Group are committed to the future and to the various companies all working toward assisting Power Engineers. We introduced a replacement to the DVS3 and launched the ART3V.

This unit is smaller and lighter with a higher voltage output (0-450v). It still follows the G99 steps to testing and commissioning, directly addressing a need presented by the Commissioning Engineers. 

T & R Test Equipment ART3V Infographic


Another product being utilised by offshore wind farms is the Z-OVR, this unit is a device which measures cable impedance.  Offshore windfarms have cabling coming from each wind turbine to an offshore connection point, then to the shore via an umbilical cable.  The protection utilised here is Impedance Relays.  The measurement of the cabling impedance therefore is crucial to the protection - A perfect solution comes in the form of the Z-OVR Cable Impedance Test System


G99, G98 Which Regulation Do I Follow?

Depending upon the size of the generation project there is one of two standards to follow:

  • Smaller projects, less than 16A per phase - G98 (formerly G83)
  • Larger projects, greater than 16A per phase - G99 (formerly G59)

As part of a piece of European Legislation (the Third Energy Package), a Network Code called Requirements for Generators (RfG) was written.  A legally binding containing technical and operational requirements for generation connecting to networks.  G98 and G99 were written to incorporate these new requirements into the existing requirements within Great Britain.  The standards apply not only to generation but to storage projects also. The electric car market is growing quickly - we will therefore witness a considerable rise in storage projects going forward.

G99 is the regulation surrounding the connection of any form of generator device to run ‘in parallel’ or ‘synchronised’ with the mains electrical utility grid (National Grid).  The regulation has its roots in Ofgem rules, it is administered by the Energy Networks Association (ENA).

Engineering Recommendation G99 "Recommendations for the connection of generating plant to the Distribution System of Licensed Distribution Network Operators – Amendment 1”.


How Does the Process Start?

The process starts with an application to your Distribution Network Operator (DNO) - the company that owns and operates the power lines and infrastructure which connects the network to your property.  On agreement the project is built but before being allowed to become part of the grid supply it must be commissioned and tested in line with the G99 Standard.


Power Generation Source  → National Grid

Upon connection approval the DNO also considers:

  1. Voltage Rise and Step
  2. Interface Protection Capability
  3. Harmonics, Distortion and Unbalance
  4. Fault Level Contribution
  5. Reverse Power Flow
  6. Clustering of Installations - overloading one area and leaving others untouched
  7. Planning Consent and Land Rights
  8. Existing Network Suitability


G99 Relay Test

The key aspect to the acceptance test is the G99 relay itself, a G99 compliant Mains Protection Relay is an electronic monitoring device which looks at the quality and stability of the mains electricity.  It is programmed to certain fixed parameters dictated by the DNO, these typically include voltage, frequency, ROCOF (rate of change of frequency), phase angle and so on.  Should any of these areas go outside the programmed limits, then the relay will cause a protective device such as an MCCB or other type of circuit breaker to open, thereby instantly disconnecting the generator from the grid for protection and peace of mind.

T&R Group recognise the importance of providing the right product for the right job. We work closely and in collaboration with our customers to provide a product which meets their specific requirements - This is imperative to the survival of our company.

In addition to our comprehensive portfolio including Transformer Rectifiers for both Traction and Industrial applications, Voltage Stabilisers, Voltage Regulators and Earthing/Auxiliary Transformers, T&R are pleased to announce our new range of Low Loss Transformers compliant with the Eco Design Directive (EU) No 548/2014 Tier 1 and Tier 2.

The combined T&R Group product portfolio provides an excellent platform for all types of businesses worldwide including excellent range of electrical testing equipment helping make electrical engineering in the 21st century easier.