G10/G59 Protection

Why is G10/G59 Protection Needed?

The main reason for the G59 recommendations is to regulate generator applications, so that no generators are connected to the grid without the specific knowledge and permission of the local electricity authority. The principle reason for this is to prevent the embedded generator from sending electricity out onto the National Grid in a dangerous manner.

For example, let’s say that a cable out in the street has been broken. Along comes the electricity network operator to repair it. They go to the nearest substation and isolate the cable to make it safe to work on. However, in a nearby building is an embedded generator, which suddenly starts up and begins feeding electricity down the other end of the broken cable, making it live. The repair crew would have no knowledge of this, and so would be placed in a potentially fatal situation.

The G59 relay protective device prevents this situation by automatically disconnecting the embedded generator from the mains.

There are a number of other aspects that will be considered by the DNO (District Network Authority) when asked to approve the connection of a power generation source to the National Grid. These include:-

What does the G10/G59 Device actually Do?

A G59 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), 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.