Handbook of Electrical Installation Practice - BeKnowledge

* Standby earth fault.
Table 22.1 gives a general guide as to the protection suitable for different transformer
ratings, although it should be noted that modern relays such as Duobias M
allow economical protection over the complete range.
Duobias M system
Although Duobias protection, using transductor type relays described above, is used
throughout the world in great numbers, advances in technology have allowed the
development of a microprocessor version known as Duobias M (Figs 22.17 and
22.18). This protection incorporates within software two restricted earth-fault elements,
models of interposing CTs for almost every primary transformer configuration
and inherent phase angle change compensation. The algorithms also include
operation and indication for additional inputs such as Buchholz and winding temperature
protection, and the data storage and fault recording is included.This development
allows an extremely economic but very comprehensive system to be applied
to a full range of power transformers.
ROTATING PLANT
Table 22.1 Transformer protection.
Protective Systems 623
The operation of rotating machines can be affected by faults within or by external
disturbances on the network. The protection of a machine must therefore be
designed to be highly discriminative to react efficiently on internal faults and external
disturbances.
The number and type of protective relays applied to a machine is a function of
the machine characteristics such as size, driving device, single of parallel operation,