Question 1
The diagram below is the schematic of a protection system for a 33/11kV double transformer
substation in which the 33kV switchboard and the 11kV switchboard are at the same location. The
protection arrangements for T2 are the same as those for T1. Define and describe the system
components, their mode of operation and where appropriate their zone limits. Indicate with reasons
those elements that need to discriminate (grade) with other elements and those which do not.
Question 1 schematic
Electricity Distribution Module 5
Version A Page 53
Question 2
In the above schematic, two Neutral Earthing Resistors are used. Would it be possible to use only
one for both transformers? If so, what are the operational or other disadvantages and how could
they be overcome?
Question 3
The diagram below is the schematic of a protection system for a 33/11kV double transformer
substation arranged as transformer feeders with no 33kV switchgear at the supplied substation.
The protection arrangements for T2 are the same as those for T1. Describe the operation of the
protection scheme and contrast and compare it with the scheme described for Question 1. Indicate
with reasons those elements that need to discriminate (grade) with other elements and those which
do not