GE BUS1000, Instructions Manual

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4. APPLICATION
4-2 BUS1000 Busbar Protection GEK-98514B
4.1. SELECTION GUIDE
In order to select adequately the protection system required, the following data must be considered:
•
System frequency
•
Auxiliary infeed voltage
•
Bus disposition
•
Transformer relation and characteristics (including burdens and cable lengths) of the current
transformers for each position
•
Optional functions required:
•
Position overcurrent supervision
•
Breaker failure logic
•
Tests system
•
Housing in separate 19-inch racks or in complete cabinets.
4.2. CALCULATION OF SETTINGS
For a correct application of the BUS1000 protection system and selection of its adjustments, the following
points must be considered:
4.2.1. MAIN CURRENT TRANSFORMERS
The BUS1000 system
does not require the use of dedicated current transformers
for bus differential
protection. Current transformers with positions associated to busses may be of different types and ratios.
Check that the relation between the highest and lowest transformation ratios of the current
transformers associated with the protected bus is not greater than 10.
Check that the saturation voltage in every current transformer is at least equal to the quotient between 500 V
and the transformation ratio of the auxiliary transformer connected to it. For example, for a position with an
auxiliary transformer of a 5/1 ratio, the saturation voltage of the main current transformer must be equal or
greater than 100 Volts.
4.2.2. INTERMEDIATE AUXILIARY CURRENT TRANSFORMERS
The transformation ratio of the auxiliary transformers provided for every position must be selected in such a
way that the global transformation ratio (resulting from the relation of the main transformers multiplied by the
auxiliary transformers) for every position associated to the busses to be protected is the same.
The first step to be taken is to start with the position whose main transformer has the greatest ratio, selecting
the lowest possible ratio for its auxiliary transformer, but without overloading the input to the bus protection
relay (2 I
N
maximum).
As an example, for a bus whose positions are provided with current transformers with 1000/5, 600/5 and
300/5 ratios, 5/1.67, 5/1 and 5/0.5 ratios will be selected respectively. This selection will provide a 600/1
global ratio for bus protection and will result in a full load current of 1.67 amps for inputs corresponding to
the circuits with CT ratio of 1000/5 A (full load primary current of 1000 A).
Check that the total of the currents of all the positions applied to the differential protection in maximum
current conditions going through the busses is not above 20 I
N
.