The standards DIN VDE0105-100 and EN50110-1 clearly state that a GIS system must be measured with ground on both sides. The problem, which is particularly relevant for GIS, is the very low ground resistance resulting from the encapsulation of the entire switchgear in a metal housing. Often, the ground and case resistance may be lower than the main contact resistance. This makes it difficult to carry out a condition assessment of the switchgear using standard measuring equipment.

For testing GIS systems grounded on both sides, the Dynamic Timing method cannot be used in the same manner as used with AIS testing grounded on both sides. It is not possible to measure the correct switching time of the circuit breaker integrated in the GIS.

The components installed in GIS like current transformers, cause measurement delays. Depending on the switching sequence, the result will contain correspondingly faster switching times when tripping or slower switching times when closing.

KoCoS uses the “GIS Timing” method to measure correct switching times. For this measuring method, the GIS must have at least one insulated ground lead to the outside. Again, PROMET resistance meters are used which generate current outputs of up to 600 A depending on the version. The resistance measuring devices are controlled by ACTAS. The resistance measuring devices are only used as current sources and not as actual measuring instruments.

In order to obtain measured values, in addition to the resistance meters and ACTAS, current sensors specifically developed for KoCoS are used. They are flexible rogowski coils which can be attached to the insulated ground. The current curves measured during the switching operation on the insulated ground can be used to determine the switching times for opening and closing during the various switching sequences of the circuit breaker.