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G99 mains protection – are you ready?

The world of mains protection is changing. G99 mains protection will replace the current G59-3.4 in April 2019.

What is G99?

G99-1 was announced in July 2018 and comes into effect from 27th April 2019:
G99-1 July 2018 Requirements for the connection of generation equipment in parallel with public distribution networks on or after 27 April 2019

Equipment that is compliant with G99 can be connected in advance of 27th April, as it will also comply with the pre-existing G59-3.4 requirements.

After the 27th April 2019, you will be unable to connect using equipment that is compliant with G59-3.4 only.

Compliant G59-3.4 and G99 mains protection relays from ComAp

The ComAp's MainsPro and InteliPro mains protection relays are DNO compliant to both the G59-3.4 and G99-1 non-type tested standard. Installing these relays will help to future proof your sites against these upcoming changes in requirements.


Type tested vs non-type tested equipment

There is a difference between type tested and non-type tested equipment. According to the ENA’s G99 document, type tested equipment is defined as:

A product which has been tested to ensure that the design meets the relevant requirements of G99 and that all similar products supplied will be constructed to the same standard and will have the same performance.

Type tested equipment includes inverters (the device that converts Direct Current to nominal frequency Alternating Current).

ComAp’s MainsPro and InteliPro are classified as non-type tested equipment. The MainsPro and InteliPro mains protection relays no longer use Vector Shift as a form of Loss of Mains protection as per the latest update to G59-3.4 recommendation. Because the functionality of the ROCOF cannot be tested, the relays will remain as non-type tested equipment.

It is important to remember that non-type tested equipment can still be G99 mains protection compliant.

If a piece of equipment has not been listed on the ENA’s ‘type-tested’ preferred supplier list, it has not been recognised as ‘type-tested’ by the ENA and cannot be used as such.

‘Non-type’ tested equipment works the same way. The ENA will supply a preferred supplier list for ‘non-type’ tested equipment. Both the MainsPro and InteliPro feature on this list.

Retrospective upgrades

It is still unclear on what the official recommendations will be for retrospective upgrades. Until very recently (August 17th 2018), the subject was still under public consultation. This has now been closed, so an announcement is likely to be released soon. It is not clear if there will be additional funding available to complete these mandatory upgrades.

Why is G99 mains protection important?

The power generation landscape has seen a dramatic change over recent years. Instead of relying on a relatively small number of high-capacity power stations, we are turning towards a much larger number of low-capacity generators. Wind farmsphoto-voltaic (PV) solar sites and hydro-electric plants are replacing coal and oil power stations. In 2017, renewable sources generated 30% of the UK’s energy.

When talking about generators on power generating sites, we are referring to synchronous generators.

A synchronous generator is known as such because the frequency of the voltage is directly proportional to the RPM.

In the case of asynchronous generating units, the output frequency is regulated by the power system to which the generator is attached.

The output frequency of a synchronous generator can be more easily regulated to remain at a constant value. They are also often more efficient. This is because they can easily be accommodated to load power factor variables.

The rapid expansion of lower-capacity generators can cause the grid to become less stable and this risks damaging both the generator and the grid. Systems that run ‘parallel-to-mains’ must include a relay to decouple the generator from the grid if a problem arises with either.


European Requirements for Generators Code Types A – D

The European Requirements for Generators (RfG) Code was recently introduced to bring a coherent set of requirements into the power generation market.

There are now 4 types of power generating modules and they are classified by their registered capacity and connection voltage. The types are:

  • Type A: From 0.8 kW to < 1 MW and connected at < 110 kV.
  • Type B: From 1 MW to < 10 MW and connected at < 110 kV.
  • Type C: From 10 MW to < 50 MW and connected at < 110 kV.
  • Type D: ≥ 50 MW or connected at ≥ 110 kV.

Please note that Type D generators fall under another ENA requirement – G100. This is mainly applicable to Distribution Network Operators (DNOs).

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