Relay 59G Earth Fault Protection

VT & SP (Voltage Transformer and Surge Protection) is two in one equipment. This voltage transformer is connected to relay 59G and for metering.

Relay 59G could be active from 3 phase Generator Transformer neutral over voltage alarm. This neutral over voltage problem could be from one phase, for example phase w.

In the transformer world, 3 phase of R S T could be change U V W. In primary winding side usually use capital word like U V W and at secondary winding use u v w.

If Relay 59G neutral over voltage got active, the problem could on fuse that broken, or the VT (voltage Transformer) Problem, or actual one of three phase got problem.

But lets learn first about the tranformer symbol that make us confusing.


There are only 4 possible transformer combination:
Delta to Delta - use: industrial applications
Delta to Wye - use : most common; commercial and industrial
Wye to Delta - use : high voltage transmissions
Wye to Wye - use : rare, don't use causes harmonics and balancing problems.

For transformer 525kV/22.8kV (high voltage transmission) as a top picture use Wye to Delta (YD11 code will explanation on below). If one phase got problem, the transformer still can be use for emergency by connection Open Delta (V connection)like picture below this.

Picture below is table of Transformer connection, like o'clock numer position. In primary winding that phase V always on 0 o'clock or 12 o'clock. And for secondary winding, phase v is following the code number.

For example Dy11 is transformer which has Delta connection at primary winding and wye connection at secondary winding with phase v at 11 o'clock position. The connection configuration is like on the table.